8LikesCRC Battle Axe, GenXPro 10, 1/10th pan, Brushless, Lipo,4c, Road, Oval,TipsandTricks
04-17-2010, 03:46 PM
#1426
Joe-I have a team oval car coming back maybe in a month. I will keep you in mind.
Brakes
I use about 25-32% brakes on the wide pan car lately. There are 4-5 places on the track where I apply brakes. One is at the end of the straight when the car is going 65 mph. A very quick stab of the brakes makes the car dive into the sweeper and stay on the white line while most the local guys are 4-5 foot out running a longer line. This is the most strenuous place to apply brakes for the gear train. If you hear any unusual noise (teeth skipping) it is time to bring the car in for a checkup. 64 pitch gears will strip here immediately on first use of brakes. On 48 pitch gears there is usually something worn or loose that has caused the problem. I had a problem this Friday.
First check the gear lash and motor screws. That upper motor screw on a Gen X 10 is a bit of a problem. It is not backed up by aluminum on top, but by graphite. You need to use a little larger than normal washer up there and you need to tighten the crap out of that upper screw to get the proper clamping load. Otherwise the motor will rock forward and back increasing your gear lash on brakes. Just grab the back end of the motor and try to push it back. If that screw is loose the motor will move more and create enough gap at the gears to strip the gear on brakes.
Second a worn axle bearing or rear pod height spacer can cause a problem. I replaced both of these.
Third, any pod screw that gets loose and allows the motor plate to move with respect to the axle must be secured. This was my problem. High temperature Loctite is the best to use on the motor plate itself as it gets quite hot from a 3.5 motor. Also use a steel screw. To get the screw out later heat it 20 seconds with a good soldering iron or until "first smoke". Then it will back out easily with the normal tool.
I failed to do this and after a year of hard use and several attempts to lactate just the head the screw, the screw stripped the aluminum threads.
Now you need a new, customized in my case, motor plate for a repair, or you need to do a field repair.
This is what I did. First I tried a 3 mm Dubbro tap. The hole was too big. I had remembered that on an old used oval car the guy had used several #8 x 32 flat head screws on the pod bottom. There is just enough material in the motor plate. I drilled .136 diameter by maybe 1/4 inch deep. I sanded the point off an #8 x 32 Dubbro tap to make it more like a bottom tap. I tapped the hole. I sanded two more threads out of this starting tap to again make it more like a bottom tap and finished the hole with threads almost 1/4 inch deep. If you have been running pan cars for a while you will have some Aluminum #8 x 32 TPI flat head screws that they use on old Associated cars to secure on the front suspension. I had one that was 1/4 inch long. You can easily cut one to length with the cutoff wheel on the Dremmel. I used my Dremmel and a stone that is shaped to 82 degrees using the little rectangular stone the Dremmels come with. I enlarged the countersink just a little and got a good repair. Put on a new gear and all was well.
The moral here is to secure that screw to start with so you don't have this trouble. The screw head overhangs the motor, but there is no contact due to a bevel on the motor. It would be easy to sand this overhang away.
The other screw to use this high temperature red Loctite is the Panhard Bar mount screw that goes into the motor plate. The high temp Loctite is available at auto parts stores and can be used anywhere you would use normal temperature red Loctite.
Stainless Steel Screw strength
I had a report of a failure of a stainless steel screw being used in place of the supplied Alloy steel screw that sets the droop on JS cars. It torqued itself right in two. Stainless screws, that are available to us, are about half the strength of the alloy steel screws I supply. Just use the ugly grade 10.5 black screw.
The other tip is that on first install you are cutting threads. Back the screw out every once in while as you first pass through the graphite to ease the operation. An untapped hole is required for a friction fit.
Brakes
I use about 25-32% brakes on the wide pan car lately. There are 4-5 places on the track where I apply brakes. One is at the end of the straight when the car is going 65 mph. A very quick stab of the brakes makes the car dive into the sweeper and stay on the white line while most the local guys are 4-5 foot out running a longer line. This is the most strenuous place to apply brakes for the gear train. If you hear any unusual noise (teeth skipping) it is time to bring the car in for a checkup. 64 pitch gears will strip here immediately on first use of brakes. On 48 pitch gears there is usually something worn or loose that has caused the problem. I had a problem this Friday.
First check the gear lash and motor screws. That upper motor screw on a Gen X 10 is a bit of a problem. It is not backed up by aluminum on top, but by graphite. You need to use a little larger than normal washer up there and you need to tighten the crap out of that upper screw to get the proper clamping load. Otherwise the motor will rock forward and back increasing your gear lash on brakes. Just grab the back end of the motor and try to push it back. If that screw is loose the motor will move more and create enough gap at the gears to strip the gear on brakes.
Second a worn axle bearing or rear pod height spacer can cause a problem. I replaced both of these.
Third, any pod screw that gets loose and allows the motor plate to move with respect to the axle must be secured. This was my problem. High temperature Loctite is the best to use on the motor plate itself as it gets quite hot from a 3.5 motor. Also use a steel screw. To get the screw out later heat it 20 seconds with a good soldering iron or until "first smoke". Then it will back out easily with the normal tool.
I failed to do this and after a year of hard use and several attempts to lactate just the head the screw, the screw stripped the aluminum threads.
Now you need a new, customized in my case, motor plate for a repair, or you need to do a field repair.
This is what I did. First I tried a 3 mm Dubbro tap. The hole was too big. I had remembered that on an old used oval car the guy had used several #8 x 32 flat head screws on the pod bottom. There is just enough material in the motor plate. I drilled .136 diameter by maybe 1/4 inch deep. I sanded the point off an #8 x 32 Dubbro tap to make it more like a bottom tap. I tapped the hole. I sanded two more threads out of this starting tap to again make it more like a bottom tap and finished the hole with threads almost 1/4 inch deep. If you have been running pan cars for a while you will have some Aluminum #8 x 32 TPI flat head screws that they use on old Associated cars to secure on the front suspension. I had one that was 1/4 inch long. You can easily cut one to length with the cutoff wheel on the Dremmel. I used my Dremmel and a stone that is shaped to 82 degrees using the little rectangular stone the Dremmels come with. I enlarged the countersink just a little and got a good repair. Put on a new gear and all was well.
The moral here is to secure that screw to start with so you don't have this trouble. The screw head overhangs the motor, but there is no contact due to a bevel on the motor. It would be easy to sand this overhang away.
The other screw to use this high temperature red Loctite is the Panhard Bar mount screw that goes into the motor plate. The high temp Loctite is available at auto parts stores and can be used anywhere you would use normal temperature red Loctite.
Stainless Steel Screw strength
I had a report of a failure of a stainless steel screw being used in place of the supplied Alloy steel screw that sets the droop on JS cars. It torqued itself right in two. Stainless screws, that are available to us, are about half the strength of the alloy steel screws I supply. Just use the ugly grade 10.5 black screw.
The other tip is that on first install you are cutting threads. Back the screw out every once in while as you first pass through the graphite to ease the operation. An untapped hole is required for a friction fit.
Last edited by John Stranahan; 04-19-2010 at 04:12 PM.
04-18-2010, 02:40 PM
#1427
Tech Adept
John, what pinion gears do you use? I have settled with Kimbrough for my spurs but their carbon fibre pinions are a waste of time. They chip and wear very quickly using anything over an 8.5 motor. I have also used the Kawada pinions but they seem too thin. Should I try RW racing?
04-18-2010, 02:44 PM
#1428
Jim1-The best pinions for the wide pan are old stock Titanium Gold Pinions from Robinson Racing at Stormer. They are the proper width for the Kimbrough spurs and the Titanium Nitride coating makes the pinion last 10 times longer than a hardened steel pinion especially if you need the 12 tooth. My 12 tooth steel pinions were gone in a couple of runs. I get about 20 runs on the gold pinion.
http://www.stormerhobbies.com/cgi-bi...umb=on&smode=0
http://www.stormerhobbies.com/cgi-bi...umb=on&smode=0
Last edited by John Stranahan; 04-20-2010 at 08:43 AM.
04-18-2010, 09:42 PM
#1429
I post this note with permission. This is a JS pro owner who has been running it indoors. This is the first session outdoors but on very high grip asphalt. I will post my advice later, but if you have some of your own please add it in a post. Sounds like fun to me.
Hi John, here’s the lowdown.
JS Pro 10 @ 200mm with a Protoform Sophia body. Original setup was Associated green springs out back, coppers up front running 35wt oil all around. Links at stock angles, Jaco green rears and BSR double purple front (same as Jaco purple). Speedo is a Hobbywing 120A, same as the Speed Passion GT 2.0, mounted on the left nerf wing with ¾ oz of lead on the other wing to balance it. Weight at 1250 grams, slightly heavy but nothing to worry too much about.
Our track is smallish and set up in a parking lot (www.irocc.ca), fast pan cars and nitro sedans pull low eleven second fast laps. Traction is very high, as it’s heavily treated with sugar water. Some different surfaces due to asphalt patching, but fairly smooth.
The pod was sprung too soft at the outset. The car was tricycling (picking up the inside front), so I swapped the green springs for Associated gold (VCS, not RC18). On a freshly sugared surface during practice, it was really good and I was into the low 12 second range. I was really impressed with myself as I haven’t driven outside in a year and haven’t driven a pan car ever. Forward drive is unreal – the conventional pans were snaking all down the front straight and guys have to be really careful applying power, but I can hammer it and have no problem. (my bold (John)) Cranked the punch and timing on the speedo and was able to cope fine.
Once the heats started, though, traction was even higher and the traction rolling started. It was worst at the transition coming out of the back chute, when the car wasn’t even going that fast. As the day went on, it started rolling into the sweeper, obviously causing some spectacular flights that entertained the crowd. I think I went about trying to fix it the wrong way, by really stiffening up the rear end. I should’ve put your silver springs on instead of preloading the back and taking all the droop out of the front. I also put lilac rears on – I was going to put them all around but the Sophia body has very little tire clearance, and the full size fronts would not fit. The rear was so hard it was starting to skip across in corners. It actually worked pretty well despite the weird tire combo. What did really help was lowering the side links as far as possible, which mostly alleviated the traction rolling for the main. Well, except for one last big roll off the sweeper that broke a motor wire off and caused a DNF...
The only snag was that there is very, very little (to none) shock-to-tire clearance if using untrued rears. No issue at 235mm, but the narrow car suffers. As a pleasant surprise, the panhard did not come loose at all, and the front end was very durable. I see tons of potential despite the problems today, all of my own making.
Anyway, my “Outlaw WGT” idea is probably not going to work. I really do need the aero of a GTP body, plus the tire clearance, so I’m going back to 235mm. Would you be able to invoice me a wide top plate and send it along with the shock links?
R.
My advice was to go with short tires. Lower ride height as much as possible. Reduce droop. And I really like a front diffuser even on the 200 mm cars. It sucks the whole body down especially entering the sweeper. The efficient suspension lets the car get going a little faster than other cars on the straight.
Stock Front Roll Center Setting
I will note the front roll center stack on the kingpin for the stock roll center. E-ring, one plastic spacer, lower arm, one plastic spacer, Aluminum sleeve, steering arm, 3 black spacers, upper arm, one black spacer, E-ring. This puts the roll center at about chassis level so it is not developing too much grip. Raise the upper outer arm to raise the roll center.
Hi John, here’s the lowdown.
JS Pro 10 @ 200mm with a Protoform Sophia body. Original setup was Associated green springs out back, coppers up front running 35wt oil all around. Links at stock angles, Jaco green rears and BSR double purple front (same as Jaco purple). Speedo is a Hobbywing 120A, same as the Speed Passion GT 2.0, mounted on the left nerf wing with ¾ oz of lead on the other wing to balance it. Weight at 1250 grams, slightly heavy but nothing to worry too much about.
Our track is smallish and set up in a parking lot (www.irocc.ca), fast pan cars and nitro sedans pull low eleven second fast laps. Traction is very high, as it’s heavily treated with sugar water. Some different surfaces due to asphalt patching, but fairly smooth.
The pod was sprung too soft at the outset. The car was tricycling (picking up the inside front), so I swapped the green springs for Associated gold (VCS, not RC18). On a freshly sugared surface during practice, it was really good and I was into the low 12 second range. I was really impressed with myself as I haven’t driven outside in a year and haven’t driven a pan car ever. Forward drive is unreal – the conventional pans were snaking all down the front straight and guys have to be really careful applying power, but I can hammer it and have no problem. (my bold (John)) Cranked the punch and timing on the speedo and was able to cope fine.
Once the heats started, though, traction was even higher and the traction rolling started. It was worst at the transition coming out of the back chute, when the car wasn’t even going that fast. As the day went on, it started rolling into the sweeper, obviously causing some spectacular flights that entertained the crowd. I think I went about trying to fix it the wrong way, by really stiffening up the rear end. I should’ve put your silver springs on instead of preloading the back and taking all the droop out of the front. I also put lilac rears on – I was going to put them all around but the Sophia body has very little tire clearance, and the full size fronts would not fit. The rear was so hard it was starting to skip across in corners. It actually worked pretty well despite the weird tire combo. What did really help was lowering the side links as far as possible, which mostly alleviated the traction rolling for the main. Well, except for one last big roll off the sweeper that broke a motor wire off and caused a DNF...
The only snag was that there is very, very little (to none) shock-to-tire clearance if using untrued rears. No issue at 235mm, but the narrow car suffers. As a pleasant surprise, the panhard did not come loose at all, and the front end was very durable. I see tons of potential despite the problems today, all of my own making.
Anyway, my “Outlaw WGT” idea is probably not going to work. I really do need the aero of a GTP body, plus the tire clearance, so I’m going back to 235mm. Would you be able to invoice me a wide top plate and send it along with the shock links?
R.
My advice was to go with short tires. Lower ride height as much as possible. Reduce droop. And I really like a front diffuser even on the 200 mm cars. It sucks the whole body down especially entering the sweeper. The efficient suspension lets the car get going a little faster than other cars on the straight.
Stock Front Roll Center Setting
I will note the front roll center stack on the kingpin for the stock roll center. E-ring, one plastic spacer, lower arm, one plastic spacer, Aluminum sleeve, steering arm, 3 black spacers, upper arm, one black spacer, E-ring. This puts the roll center at about chassis level so it is not developing too much grip. Raise the upper outer arm to raise the roll center.
04-19-2010, 09:40 AM
#1430
Side link Angle
The elevated front of the side link does a couple of things. First if you look at the diagram you see that it affects the height of the instant center of the back end. You get a diagram very similar to roll center but this time it is aligned along the length of the car. As the instant center goes up, you get more antisquat. You raise the line from the tire to the intant center. Antisquat loads the tire on forward acceleration by lifting the front of the chassis. Standard pan cars have a much reduced effect as what happens there is that the center shock elongates and dampens the effect. That is responsible for the rocket like acceleration of the JS Pro cars.
A second factor is that the taller side links add roll steer. This can also be added to the CRC cars in less generous ammounts by raising the front of the side links a little. You then readjust the center pivot to remove any binding. You will get roll steer out. The Florida oval guys are fond of using roll steer out to free up the back end and gain more corner speed on the oval. It works the same on the JS pro cars. Instead of an overly planted rear end the car is easy to rotate. As the car rolls fully in a corner the rear end steers to the outside a full degree.
The height of the side link has little effect on rear roll stiffness. I don't think you can prevent traction roll by lowering it in the front.
I would lower the side links if the front of the car was lifting too much on power and causing loss of steering traction.
200 mm rear wing
We found that when running a 200 mm World GT variant car on our long track with a 10.5 that we were reaching speeds of 49 mph or so. This is just under the blowover speed for a standard World GT car. We found that a taller wing than the standard tiny World GT wing was needed to negotiate the high speed sweeper. We just broke the World Gt rules, which are intended for indoor tracks, in this area and used this wing.
http://www3.towerhobbies.com/cgi-bin...?&I=LXRAD9&P=7
This would help prevent traction rolls entering the sweeper as would a diffuser.
Latest lightweight Diffuser
I had a strong headwind one practice day with the sliding kingpin strut front suspension on a 200 mm pan, above, running only a 10.5. The car was happily going airborne on the straight which is now relatively smooth compared to our previous surface. As insurance for such conditions I added a front diffuser.
This straight wing makes a great diffuser for the Peugeot 905 B body. Just a little trimming is required.
https://www.ssl-stormerhobbies.com/c...=ns&pn=HPI7120
The picture shows a lightweight LEXAN diffuser on a Peugeot 905 B body made from a touring car wing.
The elevated front of the side link does a couple of things. First if you look at the diagram you see that it affects the height of the instant center of the back end. You get a diagram very similar to roll center but this time it is aligned along the length of the car. As the instant center goes up, you get more antisquat. You raise the line from the tire to the intant center. Antisquat loads the tire on forward acceleration by lifting the front of the chassis. Standard pan cars have a much reduced effect as what happens there is that the center shock elongates and dampens the effect. That is responsible for the rocket like acceleration of the JS Pro cars.
A second factor is that the taller side links add roll steer. This can also be added to the CRC cars in less generous ammounts by raising the front of the side links a little. You then readjust the center pivot to remove any binding. You will get roll steer out. The Florida oval guys are fond of using roll steer out to free up the back end and gain more corner speed on the oval. It works the same on the JS pro cars. Instead of an overly planted rear end the car is easy to rotate. As the car rolls fully in a corner the rear end steers to the outside a full degree.
The height of the side link has little effect on rear roll stiffness. I don't think you can prevent traction roll by lowering it in the front.
I would lower the side links if the front of the car was lifting too much on power and causing loss of steering traction.
200 mm rear wing
We found that when running a 200 mm World GT variant car on our long track with a 10.5 that we were reaching speeds of 49 mph or so. This is just under the blowover speed for a standard World GT car. We found that a taller wing than the standard tiny World GT wing was needed to negotiate the high speed sweeper. We just broke the World Gt rules, which are intended for indoor tracks, in this area and used this wing.
http://www3.towerhobbies.com/cgi-bin...?&I=LXRAD9&P=7
This would help prevent traction rolls entering the sweeper as would a diffuser.
Latest lightweight Diffuser
I had a strong headwind one practice day with the sliding kingpin strut front suspension on a 200 mm pan, above, running only a 10.5. The car was happily going airborne on the straight which is now relatively smooth compared to our previous surface. As insurance for such conditions I added a front diffuser.
This straight wing makes a great diffuser for the Peugeot 905 B body. Just a little trimming is required.
https://www.ssl-stormerhobbies.com/c...=ns&pn=HPI7120
The picture shows a lightweight LEXAN diffuser on a Peugeot 905 B body made from a touring car wing.
Last edited by John Stranahan; 04-20-2010 at 08:39 AM.
04-19-2010, 02:25 PM
#1431
john or anyone else, What is the shock angle when mounted on the gen x 10? I mounted my shock on my pantoura but it is too horizontal it seems. When compressed the shock goes more horizontal wich induces degressive behaviour of the shock (goes effective softer when compressed more).
My chassis is also hitting the asfalt when on full speed. The height is 6 to 6.5mm but still it hits the asfalt on speed (58+ miles per hour) could that have something to do with the degressive behaviour of the shock?
My chassis is also hitting the asfalt when on full speed. The height is 6 to 6.5mm but still it hits the asfalt on speed (58+ miles per hour) could that have something to do with the degressive behaviour of the shock?
04-19-2010, 03:06 PM
#1432
I think the stock angle is a little lower in the front. This will give you the straightest stroke. The rear shock pivot does go forward and down on bump. I have mentioned previously the stroke is just going to have to be crooked because of the geometry of the standard pan car. Just don't worry about it. Rebuild the shock as needed. As far as keeping off the ground, you are just going to have to go stiffer with that center shock spring. In my test this has almost no effect on steering so just keep going stiffer (and maybe 1 mm higher) until your chassis and pod are protected. Slight wear can be accomodated on the worst bumps by changing the rearmost chassis screws once in a while. You could also sneak in some downstop limiters. It can be cushioned with an O-ring. These would be between the spring seat and the O-ring end of the shock body. I have never needed to do that.
John
John
04-19-2010, 11:18 PM
#1433
It has already been advised to me to use some nitro fuel line as a downstop but wanted to see if there was another way.
Sparks were flying when the chassis hit the asfalt everytime at speed so bye bye to my new chassis. At the moment the front is a little lower then the back. I will try to raise the shock at the back (on the top plate) a little more and lower the spoiler extention a little. I already have put in one of my stiffest spring and still it hit the asphalt (albeit a little later on the straight). It is not what i was expecting when driving with a 10.5t with a 2s lipo. With my rc10l2 i never had this problem even with a 4.5t or 6.5t in it (the pod does travel a little different on the L2 cause of the t-plate). Some more tests will follow.
Sparks were flying when the chassis hit the asfalt everytime at speed so bye bye to my new chassis. At the moment the front is a little lower then the back. I will try to raise the shock at the back (on the top plate) a little more and lower the spoiler extention a little. I already have put in one of my stiffest spring and still it hit the asphalt (albeit a little later on the straight). It is not what i was expecting when driving with a 10.5t with a 2s lipo. With my rc10l2 i never had this problem even with a 4.5t or 6.5t in it (the pod does travel a little different on the L2 cause of the t-plate). Some more tests will follow.
04-20-2010, 10:16 AM
#1435
@mathijs, yeah the springs are more or less wich i used on the L2. The shock being more horizontale doesn't help either as it feels more soft that way then placing it more at an angle. I already used some washers to move the ballcup up and just now i put a fuel tubing on the piston as a bumpstop and that worked out great. I didn't drive it yet but it doesn't hit the ground anymore(see other forum)
I used a soft springs and oil (35wt and 3 hole ) with 0.020 front springs cause on the MACH the conditions at this moment er very slippery , specially in the evening. I guess it was way too soft at the back together with the horizontal placing of the shock and the speed it was going. Either way, it didn't help to get rid of the oversteer completly. Pink back and purple front is the way to go (or maybe lilac as well)
(sorry for the people that are on muliple forums. I posted help messages eveywhere to get more change of help quike as i have a race this weekend
)
I used a soft springs and oil (35wt and 3 hole ) with 0.020 front springs cause on the MACH the conditions at this moment er very slippery , specially in the evening. I guess it was way too soft at the back together with the horizontal placing of the shock and the speed it was going. Either way, it didn't help to get rid of the oversteer completly. Pink back and purple front is the way to go (or maybe lilac as well)
(sorry for the people that are on muliple forums. I posted help messages eveywhere to get more change of help quike as i have a race this weekend
)
04-20-2010, 10:01 PM
#1437
Springing to avoid oversteer. Go stiffer on front springs. Go softer on rear side springs. At high speed you can be too soft on roll stiffness and drag the outside rear corner of the chassis on the sweeper. You will lose gobs of traction. Go stiffer in front and rear sides to prevent this. Grip may return.
04-20-2010, 11:22 PM
#1438
. Going from complete oversteer (i could not even go on the throttle) with pink back and purple front to quite severe understeer with only changing those fronts to ufra 
. I will try them next week after i tried the lilacs and might come back to you on that 
. i probably would have to use magenta back tires to get some steering back.I might also go a little stiffer on the side springs. I used white crc springs. They didn't touch the pod so the pod could move freely. I will first give it some pre load and see if that helps.
Last edited by 2wdrive; 04-20-2010 at 11:53 PM.
04-21-2010, 09:27 AM
#1439
Here is a link to a suspension tuning reference that I just completed putting on the Web. It consist of a chapter in a book that I wrote titled RC Electric Car Reference. It is updated here to the third edition now. There are some excerpts from my threads. Now if you see a picture of a touring car there, don't think it does not apply to a pan car. Most things do. Some things are specifict to a 2-wheel drive. Those are discussed. The title of the chapter is "Cornering at the Limit". It is good to have a high speed connection. For the first time in glorious color.
http://www.stranahan-rc.com/corneringatthelimit.html
http://www.stranahan-rc.com/corneringatthelimit.html
04-21-2010, 11:11 PM
#1440
Putting on the big pinions
Most pan cars need a little hand work to put on the big pinions which require the motor to move farther than normal forward. The CRC pod is no different. First look at the forward bottom motor plate securing screw. Top left in the motor opening in the photo. Sand the little reinforcing bump off. Put some Red high temp Loctite on the screw and seat it well. Now the motor will hit the front of the motor opening in the pod plate. You need to bevel the plate to a knife edge to gain some more clearance. Look and see where the motor hits the pod plate and remove some material there. The limit on forward movement on Gen X 10 and Battle Axe is then, after work, when the motor touches the center post. If you have the old graphite foot ball and Pivot ball plastics, they may need some beveling as well. On JS Pro ten cars there is no center post on the pod anymore for performance reasons. The limit will be when the motor touches the Panhard bar at full droop of the pod.
Building and Breaking in the Ball Diff
I had been running RC cars about 3-4 years before I picked up my first pan car. Much to my surprise there were a bunch of odd things that pan car guys liked to do to their diffs that we touring car guys using the same basic mechanism did not do.
So here is a good method to build the diff: skipping all the unnecessary things.
First do not sand your diff rings. What you need for smooth operation is a uniformly thick diff ring. Not a flat diff ring. Sanding will likely make them non uniformly thick unless you take great pains and measure the thickness often as you sand. We use enough pressure on the diff to flatten diff rings. In addition I tested the lightweight diff rings I like to use on the surface plate. They are flat. Thickness is also very uniform to .0001 inch. The graphite balls cut through any surface texture, so that is a waste of time as well.
Use carbide diff balls. There is a world of difference. This is what insures a smooth diff. Same on the touring cars. I use 1/8 carbide balls from Track Attack for the pan car. JS Pro cars come with carbide installed.
No Separate Thrust Bearing Needed
Thrust bearings are added by the misconception that a caged radial ball bearing is not designed to carry a side load. This is not true. In fact the side thrust that they can carry is about a high as the radial load they can carry. I believe Boca bearings has these specs and notes. I tested a diff with an extra new thrust bearing. It was actually rough because of the thrust bearing. I took it off and things smoothed right out. There are people that argue with me on the above two points but they have not read the literature on bearings and they have not tested the flatness and thought through what the sanding does to uniformity of thickness.
So assemble the diff like the instructions. Put on some diff lube. Don’t be worried about how much. Any excess will spin out on that first 65 mph run down the straight.
Grip the left tire and spur with left hand. Try to spin the right tire. It should be hard. You are slipping the diff. If it slips easy tighten that #8 x 32 TPI nut. If you use the plastic nut, you will need to tighten it every session as well as during the session as the threads stretch away from the pressure. Instead use a Nylock Aluminum nut Like the Associated TC3 wheel nut or the nice red nuts from Hyperdrive. Then you will tighten the diff, break it in, retighten it then leave it alone until it needs service. The aluminum threads will not flow. The nylon insert will keep it in place. JS pro cars come with the Hyperdrive Nylock nut.
Now grab a tire and run the motor for 30 seconds. This breaks in the diff rings. The carbide balls cut a nice smooth groove .002 inch deep or so. Retighten the diff. Now you are ready for weeks of running with no attention.
Pic
That's Jim's brand new JS Pro 10 heading to the UK. Came out nice.
Most pan cars need a little hand work to put on the big pinions which require the motor to move farther than normal forward. The CRC pod is no different. First look at the forward bottom motor plate securing screw. Top left in the motor opening in the photo. Sand the little reinforcing bump off. Put some Red high temp Loctite on the screw and seat it well. Now the motor will hit the front of the motor opening in the pod plate. You need to bevel the plate to a knife edge to gain some more clearance. Look and see where the motor hits the pod plate and remove some material there. The limit on forward movement on Gen X 10 and Battle Axe is then, after work, when the motor touches the center post. If you have the old graphite foot ball and Pivot ball plastics, they may need some beveling as well. On JS Pro ten cars there is no center post on the pod anymore for performance reasons. The limit will be when the motor touches the Panhard bar at full droop of the pod.
Building and Breaking in the Ball Diff
I had been running RC cars about 3-4 years before I picked up my first pan car. Much to my surprise there were a bunch of odd things that pan car guys liked to do to their diffs that we touring car guys using the same basic mechanism did not do.
So here is a good method to build the diff: skipping all the unnecessary things.
First do not sand your diff rings. What you need for smooth operation is a uniformly thick diff ring. Not a flat diff ring. Sanding will likely make them non uniformly thick unless you take great pains and measure the thickness often as you sand. We use enough pressure on the diff to flatten diff rings. In addition I tested the lightweight diff rings I like to use on the surface plate. They are flat. Thickness is also very uniform to .0001 inch. The graphite balls cut through any surface texture, so that is a waste of time as well.
Use carbide diff balls. There is a world of difference. This is what insures a smooth diff. Same on the touring cars. I use 1/8 carbide balls from Track Attack for the pan car. JS Pro cars come with carbide installed.
No Separate Thrust Bearing Needed
Thrust bearings are added by the misconception that a caged radial ball bearing is not designed to carry a side load. This is not true. In fact the side thrust that they can carry is about a high as the radial load they can carry. I believe Boca bearings has these specs and notes. I tested a diff with an extra new thrust bearing. It was actually rough because of the thrust bearing. I took it off and things smoothed right out. There are people that argue with me on the above two points but they have not read the literature on bearings and they have not tested the flatness and thought through what the sanding does to uniformity of thickness.
So assemble the diff like the instructions. Put on some diff lube. Don’t be worried about how much. Any excess will spin out on that first 65 mph run down the straight.
Grip the left tire and spur with left hand. Try to spin the right tire. It should be hard. You are slipping the diff. If it slips easy tighten that #8 x 32 TPI nut. If you use the plastic nut, you will need to tighten it every session as well as during the session as the threads stretch away from the pressure. Instead use a Nylock Aluminum nut Like the Associated TC3 wheel nut or the nice red nuts from Hyperdrive. Then you will tighten the diff, break it in, retighten it then leave it alone until it needs service. The aluminum threads will not flow. The nylon insert will keep it in place. JS pro cars come with the Hyperdrive Nylock nut.
Now grab a tire and run the motor for 30 seconds. This breaks in the diff rings. The carbide balls cut a nice smooth groove .002 inch deep or so. Retighten the diff. Now you are ready for weeks of running with no attention.
Pic
That's Jim's brand new JS Pro 10 heading to the UK. Came out nice.