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Old 11-23-2011, 10:20 AM   #1
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Default Slowing Down the Front Diff

I have a JRXS-R that I intend to run rubber tire on carpet with, my problem is that I have tried a front spool but the feel of the car with a diff in the front is more in-tune with my style, but only when its tight instead of a more open diff. In running the diff as tight as it needed to be to limit the slip it wore out very quickly, becoming gritty in the course of a few runs and ruining the thrust bearing. I have tried using thick black grease in the diff but it was only marginally better than the standard white diff grease. Ideally I could replace this with a gear diff with thick fluid but no such thing exists for this older car, so what do you think my best course of action is to slow the diff down without destroying it? Any help is good help.
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Old 11-23-2011, 10:24 AM   #2
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I have a JRXS-R that I intend to run rubber tire on carpet with, my problem is that I have tried a front spool but the feel of the car with a diff in the front is more in-tune with my style, but only when its tight instead of a more open diff. In running the diff as tight as it needed to be to limit the slip it wore out very quickly, becoming gritty in the course of a few runs and ruining the thrust bearing. I have tried using thick black grease in the diff but it was only marginally better than the standard white diff grease. Ideally I could replace this with a gear diff with thick fluid but no such thing exists for this older car, so what do you think my best course of action is to slow the diff down without destroying it? Any help is good help.
That's a tough one, especially with the R's plastic outdrive, when you try and tighten the diff to the point it should be the threads will strip. We used to be able to run a oneway in that car and it wasn't terribly loose off power, might be worth trying. If not, keep working on the setup until a spool is comfortable, look at mike haynes old posts, I know he ended up with a setup on old JRX springs I think in the 8lb range in the rear.
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Old 11-23-2011, 10:32 AM   #3
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That's a tough one, especially with the R's plastic outdrive, when you try and tighten the diff to the point it should be the threads will strip. We used to be able to run a oneway in that car and it wasn't terribly loose off power, might be worth trying. If not, keep working on the setup until a spool is comfortable, look at mike haynes old posts, I know he ended up with a setup on old JRX springs I think in the 8lb range in the rear.
Thanks, the spool will probably be my final outcome anyway, but on a spur-of-the-moment deal I bought one of Stormer's last one-way bearings for the car, so I'll have to give that a try especially as I am a roll-through-the-corner and let-the-setup-scrub-speed racer as opposed to always being on the brakes. I am currently running the softest JRXS spring in the rear, i think its 10.5 pounds, and a 15 pound in the front, and it works well to get the dive and squat that the car seems to need in rubber tire, and the swaybars keep it from cornering like a short course truck. I'll give the one-way and spool option a go, its free so I might as well.
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Old 11-23-2011, 10:52 AM   #4
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Thanks, the spool will probably be my final outcome anyway, but on a spur-of-the-moment deal I bought one of Stormer's last one-way bearings for the car, so I'll have to give that a try especially as I am a roll-through-the-corner and let-the-setup-scrub-speed racer as opposed to always being on the brakes. I am currently running the softest JRXS spring in the rear, i think its 10.5 pounds, and a 15 pound in the front, and it works well to get the dive and squat that the car seems to need in rubber tire, and the swaybars keep it from cornering like a short course truck. I'll give the one-way and spool option a go, its free so I might as well.
For rubber tire on carpet IMO you will be at a major disadvantage running a front diff. Just too much lost drive off the corners. Perhaps try an automotive grease like a wheel bearing grease to try to slow down the action? Messy but may get your diff to where you need it.

I fought for a long time trying to make a diff work and once I went to a spool and got used to it I was really kicking myself. They are better.
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Old 11-23-2011, 11:10 AM   #5
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so what do you think my best course of action is to slow the diff down without destroying it?
i have had good success by sandwiching in an o-ring on one/both sides of the pulley. sounds goofy, but throwing one in just inside of the balls on each side will do the trick. you can play with the number (one side or two), durometer rating, and thickness (to a degree) in order to vary the resistance. as you build the diff, the orings will hit first. then, they'll compress until the diff rings finally hit the balls. it's actually pretty sweet.

looking at the losi pulleys, there's little space between the balls and the center bore. however, that should suffice as you're likely looking at 1mm thick o-rings on each side to start. i don't know what that center bore is, but you're looking at something like this:

ringers

ringers-2



if you really want to get scientific with the o-rings, go here: www.mcmaster.com
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Last edited by seaball; 11-23-2011 at 11:23 AM.
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Old 11-23-2011, 11:26 AM   #6
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Have you tried the "brown" diff grease that Losi sells? We used to use it in the front diff when running foam tires. It is way thicker than reg diff lube.
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Old 11-23-2011, 11:29 AM   #7
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i have had good success by sandwiching in an o-ring on one/both sides of the pulley. sounds goofy, but throwing one in just inside of the balls on each side will do the trick. you can play with the number (one side or two), durometer rating, and thickness (to a degree) in order to vary the resistance. as you build the diff, the orings will hit first. then, they'll compress until the diff rings finally hit the balls. it's actually pretty sweet.

looking at the losi pulleys, there's little space between the balls and the center bore. however, that should suffice as you're likely looking at 1mm thick o-rings on each side to start. i don't know what that center bore is, but you're looking at something like this:

ringers

ringers-2



if you really want to get scientific with the o-rings, go here: www.mcmaster.com
I never tried that, but the oring that holds the diff in the eccentric should be the right size to try that out.
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Old 11-23-2011, 11:33 AM   #8
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Originally Posted by seaball View Post
i have had good success by sandwiching in an o-ring on one/both sides of the pulley. sounds goofy, but throwing one in just inside of the balls on each side will do the trick. you can play with the number (one side or two), durometer rating, and thickness (to a degree) in order to vary the resistance. as you build the diff, the orings will hit first. then, they'll compress until the diff rings finally hit the balls. it's actually pretty sweet.

looking at the losi pulleys, there's little space between the balls and the center bore. however, that should suffice as you're likely looking at 1mm thick o-rings on each side to start. i don't know what that center bore is, but you're looking at something like this:

ringers

ringers-2



if you really want to get scientific with the o-rings, go here: www.mcmaster.com
I tried that, for some reason it felt kinda jerky for me, instead of being fluid it would hold on to a certain point and then let go, and that didn't feel like a viable diff action for touring car.

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Have you tried the "brown" diff grease that Losi sells? We used to use it in the front diff when running foam tires. It is way thicker than reg diff lube.
I have heard of brown Losi grease, never seen a tube of it in person. I doubt it would be much thicker than the black stuff I tried, but I will keep an eye out.

In summary, I'm going for the spool and then maybe trying the front one-way, keeping the diff fresh for the once in a blue moon we may run foamies or as a backup for the rear diff.
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Current rides: Diggity DC4 Chassis #10. Losi JRX-S Type R. Losi 22 4.0, CRC Xi (retired), CRC Altered Ego Aluminum Chassis. Associated B4 based dirt oval late model.
WTB: Carpet racing in Arizona.
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Old 11-23-2011, 11:51 AM   #9
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I tried that, for some reason it felt kinda jerky for me, instead of being fluid it would hold on to a certain point and then let go, and that didn't feel like a viable diff action for touring car.
yep, that's the drawback is that the force/torque curve peaks at the 'break' point and settles in to some dynamic constant (or close). friction, in short. you can minimize this by lubing up.

the above won't be as soft on center as a viscous gear diff, but if built correctly, will allow for some off-power diff action, if that's what you're after. plus, it's fairly easy on the drivetrain.
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Old 11-23-2011, 11:52 AM   #10
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If you are pretty good at fabricating things you can also try this:

Find some of the old Traxxas rulon pegs that they used to use in their slipper clutches. Take the diff pulley and drill out two (opposite each other) of the diff ball holes to the same dia as the rulon peg. Take two of the pegs and cut the length down to just a little thicker than the diff balls. Insert the pegs into the holes you drilled out and then build the rest of the diff like normal. The diff balls keep the pegs from getting totally smashed, but they provide much more friction against the rings and the diff is really difficult to turn over.....kind of like a g diff w/putty.
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Old 11-23-2011, 12:12 PM   #11
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hit the balls. it's actually pretty sweet.
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