RC10 WC Stealth diff got loose

[Chemical]

The diff thrust bolt got loose on my RC10 WC Stealth transmission at the VONATS. Also the bolt was getting stripped.

• Yes... it was on the correct side.

• I was using dogbones and not CVAs.

• I didn't put the plastic "cap" over the bolt after adjusting it.

As someone suggested, I think the dogbone was up against the bolt to rub it and unscrew it.

Sound like a reasonable explanation?
Anybody else with such an issue?

[RC10th]

Was it a fresh diff rebuild ?

[Lonestar]

The diff thrust bolt got loose on my RC10 WC Stealth transmission at the VONATS. Also the bolt was getting stripped.

• Yes... it was on the correct side.

• I was using dogbones and not CVAs.

• I didn't put the plastic "cap" over the bolt after adjusting it.

As someone suggested, I think the dogbone was up against the bolt to rub it and unscrew it.

Sound like a reasonable explanation?
Anybody else with such an issue?

Fresh T-nut with a TINY drop of threadlock?

[Chemical]

It was / is a brand new transmission.
I assembled it by purchasing all-new parts à la carte.

[RC10th]

My guess is with all new parts the diff wasn't broken in, so as the parts bedded in it loosened up. Also if you didn't pre compress the thrust spring a few times it could have lost some of its tension and loosened up as well.

[jwscab]

too many little things it could be to pinpoint exactly without looking at it. Off the cuff I'd say the primary failure would be the lock T nut or perhaps some dirt in the thrust causing friction enough to unwind the bolt. if the dog bone is fairly loose in the drives, I doubt it would be that unless you are seeing any binding through the travel range.

[Chemical]

Come to think of it. The dog bone got out of whack once. That may have gotten one side spinning a lot more than the other.
I agree, too many little variables.

[Chemical]

Thanks all! I appreciate the input.

[jbmeyer13]

too many little things it could be to pinpoint exactly without looking at it. Off the cuff I'd say the primary failure would be the lock T nut or perhaps some dirt in the thrust causing friction enough to unwind the bolt. if the dog bone is fairly loose in the drives, I doubt it would be that unless you are seeing any binding through the travel range.

For my '91 Worlds replica I rebuilt my diff (with original version slipper clutch) with fresh parts about 8-10 track sessions ago after the diff started barking. At that time, after talking to a long time racer at my local club we had come to the consensus that the screw likely backed out because it had been sitting compressed for 30-yrs. I've been getting some track time over the last 2-weeks in preparation of a potential trip up for the VONATS. This is the series of events across last 4-days:

Thursday: After a practice session I took apart my CVA's, repacked with grease and put everything back together. My M4 primes were completely shot so installed a brand new set all the way around. I did not break the tires in artificially and decided to simply run them in.
Friday: During practice I had the left CVA fall out a couple of times so I placed limiters on both rear shocks that evening.
Saturday: I tightened up the slipper clutch which really improved traction and low end punch. Even with new tires that weren't broken in the lap times improved substantially. However, I had the same problem with the left CVA as it fell out 4-5 times during the session so on Saturday evening I doubled up on the limiters.
Sunday: The limiters took care of the CVA issue and was able to get in the thick of it during a session with all modern car's mainly B6 & B74's. After a fellow racers truggy landed on me after a triple jump the Spur screws backed out of the assembly and it came off. I then took apart the tranny to examine it for any additional damage and found that the diff was very loose and of course the rings were slightly notched. The spur gear needs to be replaced but all of the other gears are fine.

The questions here are:

1) Are these events likely connected or coincidental?

2) Is it possible that the tightening of the slipper caused enough force from the truggy impact to be transmitted through the drivetrain to back out the diff screw? This seems unlikely; especially given that the gears are all unblemished and I'd expect that the torsional force required to unscrew the shaft would likely rip up the gears.

3) Can diff rings get notched without hearing the tranny barking? My understanding is there is no subtle degradation; more like once the diff is loose and slips the rings are compromised and you have to start over with all new carbide balls, diff screw, spring, etc.

4) After initial break-in how often should the diff require tightening? After 8-days having a diff loosen with all new parts was not on my radar. I've built (and rebuilt) stealth tranny's in the past with no issues so this is quite a surprise.

[jwscab]

Yeah I'd bet the combination of tightening the slipper, the crossup on the track and it sounds like a decent amount of miles on the diff rebuild finally got it to the point where it needs some attention. I usually build the diff, take a few laps, and then check tightness.

The last rebuild on my woin had a totally fragged set of diff rings, melted diff gear and balls, but still felt ok. Truly weird.

After pulling the car off the track anytime, I always spin the diff as part of the maintenance on the car, if it feels funny I'll investigate. I also carry a spare stealth to swap out rather than rebuild.

[jbmeyer13]

Yeah I'd bet the combination of tightening the slipper, the crossup on the track and it sounds like a decent amount of miles on the diff rebuild finally got it to the point where it needs some attention. I usually build the diff, take a few laps, and then check tightness.

The last rebuild on my woin had a totally fragged set of diff rings, melted diff gear and balls, but still felt ok. Truly weird.

After pulling the car off the track anytime, I always spin the diff as part of the maintenance on the car, if it feels funny I'll investigate. I also carry a spare stealth to swap out rather than rebuild.

I just ordered 15 diff rings so hoping that will last a while. Having prebuilt spare Stealth’s is ideal but at this point hard to achieve as the re-re cases are crap. Basically need to buy second hand team cars and cannibalize parts.

My outdrives are toast so replaced those and also did the outdrive bearings as premptive maintenance. I’m trying to pice together a V2 slipper now (oh that lovely B4 top shaft...)and hoping the robustness of that design will help. The modern high bite track surfaces result in a lot more wear and tear than the old loomy tracks.

[Chemical]

It has been a while... I haven't run the "new" car since it dropped out of the 2019 Vintage Off Road Nationals. Afterwards I took out the electronics and put them in my B6.1. Therefore I haven't been able to tell if my re-assembled diff are going to hold up.
My original 6 gear has been out a few times in the yard and on the street. Ironically, the 30 year-old car was the one with the fortitude to last through two mains D & C of the VONATS.