durtbag

I have a CK25 on its way. I am needing to know which bodies will have adequate clearance when running 0 reactive caster and roll center shims?

DesertRat

iTrader: (2)

CRC's lola and toyota both fit, at least they fit with 5 degree blocks and room to spare.

RussF

iTrader: (22)

Still having trouble getting my car to go straight both on and off power. Recap of problem is that on power it pulls left and off power it pulls right.

I've tried everything I can think of such as a diff rebuild, new bearings and front end parts everywhere. The one thing I didn't do before trying it last time out was center the servo, which has since been done but not tested. One thing that made me crazy was that looking at the car it appeared the right side had much less caster than the left. With two shims back and one front the right was practically vertical. The left was slanted back noticeably further. The car was still very difficult to drive that way and we put all three shims in the back and added about 2mm more rear pod droop. This helped alot to make the car more derivable. but did not eliminate the pulling left/right problem. Funny thing... everybody broke during the mains so it was just me running all by myself with all eyes on my line. The general comment was that I could not hold a straight line, which is accurate, the car is a handful.

So I went back to disassembling the front end to correct or find the source of the unequal caster and install the servo centered. Each and every part to me seems perfectly matched the same left to right. but when assembled the right definately has less caster than the left.

This is the view from above. See how the right knuckle appears more vertical than the left?


This is the side view of the right. It has about 3.5 - 4 degrees of castor based on my rough comparission to the camber gauge in the pic. I show about 5 degrees but its pretty clear that its not actually that much.



This is the left side compared to the same 5 degree gauge. Its pretty clear that it is at least 5 degrees maybe 6 or 7. At any rate its more than the right side.


This is my knucles in as straigt of a line as I can get.


This is my caster blocks (the least angled ones) and they look same.


This is the caster blocks with pins sitting on camber gain shims and they look the same.


This is my upper arms. They seem the same size.


So the big question.... What the (expletive) have I done wrong here??!! Is it me or is there something wrong with the way my kit or parts manufactured?

Serzoni

iTrader: (13)

if you remove the roll center shims, does everything line up?

chad508

iTrader: (6)

If caster is off on one side Adjust your shims. It most likely will never be the same side to side.

DesertRat

iTrader: (2)

RussF, if this is all thats wrong with your front end, you are looking at the wrong end of the car. Put it on a balance and see if one of your rear tires has more weight on it than the other.

RussF

iTrader: (22)

Dont know. Will try it.

RussF

iTrader: (22)

I have that same thought. Just gives me the creeps to have to "rig" it. I even measured the little shims and made sure to get equal stacks on each side. I plan to move one of the left forward and leave all 3 back on the right.

RussF

iTrader: (22)

Are you saying that uneven Caster angles could not cause the left/right pull symptoms? Maybe not. Might be more of a cornering issue with that. I had spent the most time working on the rear of the car to make sure its free, untweaked, and built as good as possible. It is possible that there is just something wrong with the kit since its ALWAYS done it since day one. I always assumed it was something I did wrong. I still think that because everybody else has good luck with thier CRC Xti-WC. Maybe I should get the new kit and start over.

I could certainly balance it all together with the pod attached, thats easy. To balance the chassis and the pod separately probably wont happen.

chad508

iTrader: (6)

It’s not going to work right balancing the pod and chassis together.

Johnny Carey

iTrader: (10)

Makes it sounds like center pivot issue, or a servo that is garbage.

vafactor

iTrader: (6)

It’s not that unusual (although not ideal or desirable) to need different caster shims side to side in order to achieve the same caster angle on both sides. Sounds to me as if your rear pod isn’t right. Most of the erratic cars that I see have their rear pods bound up. A few things to check: first, make sure that the pivot balls are nice and free at both ends of both side links. Often the links are too tight on the pivot balls even with no clamping from the pinch bolts. If so, that can be easily fixed by putting tiny o rings in the little gap where the pinch bolts go in order to spread the link ends so that they doesn’t grab the pivot balls too snugly. Then you use the pinch bolts to adjust the link ends to achieve the desired free movement with minimal slop. Speedmerchant sells tiny o rings for this specific purpose. I cut my own little rubber spacers from a length of tiny silicone fuel tubing. They work a treat. Next thing to check is that the center pivot ball is nice and free in its nylon socket. Often they are not. Use the two little 2-56 screws to adjust the center pivot to achieve free movement of the center pivot ball. It is often necessary to leave those little screw a little loose in order to make the pivot ball swivel freely. Last thing...make sure that the center pivot is adjusted so that the pod’s side to side rocking action is nice and free. If the adjustment is out in one direction, the motion will just feel tight. And if the adjustment is out in the other direction, the side to side will feel clicky or notchy. When it’s just right, the pod will swivel completely free side to side, front to back, and both side links will also swivel freely on their pivot balls. Any pod binding whatsoever is the kiss of death for the handling of any 1/12th scale car, not just the CRC. Sounds to me as if you’ve been looking mostly for a front end problem while the real problem sounds as if it is more likely a bound up or misaligned rear pod.

vafactor

iTrader: (6)

Once you are sure that your rear pod’s action is completely free (as described above) then here’s a few things to check up front:
On a completely assembled front end, the simple test is to remove the e-clip and spring from each side and lift up on the steering block. See if the suspension assembly will drop freely under just its own weight. If so, good. If not, then there is at least one bind (and probably more) that needs to be corrected. First, the CRC upper arms usually fit too tight on the upper hinge pin. An .080” drill bit works good to ream the little holes in the upper arms so that the arms will pivot freely on the hinge pins. It is critical that they do. Then, the 3 nylon caster shims often “add up” to be slightly too thick and, if so, they will also cause a bind if they are simply pushed onto position. Often it is helpful to “skinny up” one of the caster shims by rubbing it on some fine sandpaper until the group of shims will slide into place just nice - with minimal play but more importantly without ANY bind. Of course the upper arm’s outer pivot balls must be adjusted to that they swivel nice and free in the steering blocks. And the lower arm’s pivot ball must swivel freely in the lower arm. Last thing - the kingpins must glide easily thru the lower pivot balls. Sometimes there's a little ridge or burr on the edges of the nylon lower pivot balls that can be easily cleaned up with a sharp hobby knife. Bottom line is that the front suspension on both sides needs to drop freely and easily just by its own weight when the springs are removed. If either side doesn’t do so, then there is still a bind that needs to be located and corrected. I can’t even tell you how many ill handling cars I’ve looked at for guys who are struggling and almost without exception the cars are all bound up on both ends. Until the suspension components move freely and without any binding, it is virtually impossible to tune the car’s handling. When in doubt, a little bit of slop is a whole lot better than any bind whatsoever.

JimmyMac

iTrader: (2)

Is the rear axle centered to center pivot point and does the center pivot point line up with the front center point? Outer edge of front tires should be equal distance from left to center vs center to right. Same with the rear. Then check wheelbase using unmounted wheels (foamless). Left and right wheelbase should be the same. If not, something is off (duh, hehe).

RussF

iTrader: (22)

Thanks so much for the detailed response. Below are my answers in red.