Center diff issue?

[Fallguy]

Car will not roll by hand on the ground. Front will roll, rear will roll, all 4 together will not. Disconnected the pinion from the spur gear, same symptoms. Front and rear wheels spin in opposite direction when turning one wheel by hand so that is good.

Took center diff out and apart, everything looks fine. Before opening, I can spin the center diff cups in opposite direction. If I hold the cups with one hand between my forefinger and thumb and try to spin the spur gear in either direction, it won't move. Is that normal?

Not sure how else to diagnose my problem.

 

[Sargent_Horse]

Car will not roll by hand on the ground. Front will roll, rear will roll, all 4 together will not. Disconnected the pinion from the spur gear, same symptoms. Front and rear wheels spin in opposite direction when turning one wheel by hand so that is good.

Took center diff out and apart, everything looks fine. Before opening, I can spin the center diff cups in opposite direction. If I hold the cups with one hand between my forefinger and thumb and try to spin the spur gear in either direction, it won't move. Is that normal?

Not sure how else to diagnose my problem.

You should be able to spin the cups in opposite directions just like the front and rears. However, even with the center diff locked all 4 wheels should spin together. Make sure that you don't have your front/rear diffs aren't opposite from each other (Make sure that your ring gears are both on the left or right when looking at the open bulkhead).

If you hold both cups and try to spin the spur, it won't spin cause they'd be going in the same direction.

 

[Fallguy]

You should be able to spin the cups in opposite directions just like the front and rears. However, even with the center diff locked all 4 wheels should spin together. Make sure that you don't have your front/rear diffs aren't opposite from each other (Make sure that your ring gears are both on the left or right when looking at the open bulkhead).

If you hold both cups and try to spin the spur, it won't spin cause they'd be going in the same direction.

Thank you, I'll check the ring gears next

 

[Fallguy]

Front and rear diffs in same and correct direction.

 

[SrC]

Car will not roll by hand on the ground. Front will roll, rear will roll, all 4 together will not. Disconnected the pinion from the spur gear, same symptoms. Front and rear wheels spin in opposite direction when turning one wheel by hand so that is good.

Took center diff out and apart, everything looks fine. Before opening, I can spin the center diff cups in opposite direction. If I hold the cups with one hand between my forefinger and thumb and try to spin the spur gear in either direction, it won't move. Is that normal?

Not sure how else to diagnose my problem.

The diff is fine if holding both cups and the gear wont turn. That is fine.
Now that the motor and center is out of the driveline equation, it should be apparent why it wont roll. It just has to roll now.
Is it actually locked at this point still???

 

[Fallguy]

The diff is fine if holding both cups and the gear wont turn. That is fine.
Now that the motor and center is out of the driveline equation, it should be apparent why it wont roll. It just has to roll now.
Is it actually locked at this point still???

I need to fill the center diff back up and reinstall. However I didn't do anything except inspect so not sure it will change. Will get everything back together tonight. It was still doing it with the motor removed so I'm at a loss at this point.

 

[SrC]

Im confused on this one. We covered all the bases.
The only time I had a fully locked up drivetrain is when the armature in the motor exploded due to a BB failure and also one time when the spring washer shims inside split apart and shredded the armature. Armature can shred apart and lock up all.
What I thought you had originally. But this is not the case here.

 

[Fallguy]

Im confused on this one. We covered all the bases.
The only time I had a fully locked up drivetrain is when the armature in the motor exploded due to a BB failure and also one time when the spring washer shims inside split apart and shredded the armature. Armature can shred apart and lock up all.
What I thought you had originally. But this is not the case here.

Thank you, I'll keep you posted.

 

[Sargent_Horse]

With the center diff out, can you spin the two front wheels or two rear wheels in the same direction? I'm thinking completely seized input cup bearing perhaps.

 

[Fallguy]

With the center diff out, can you spin the two front wheels or two rear wheels in the same direction? I'm thinking completely seized input cup bearing perhaps.

Correct. I'll take the cups off and inspect the bearings before reassembly. Thank you for the suggestion.

 

[Fallguy]

Got it figured out. The car is actually a TA rc8.2e. It's a rtr car. For some reason, the motor mount was sitting too low on the chassis which was throwing the angle off, causing the rear center diff cuff to rub on the aluminum motor mount hole for the diff. I put a couple of washers under the motor mount which corrected the geometry and everything is smooth now.

So the motor mount is a TA hop up mount. This is my 2nd rc8.2e. I put the same mount in my first one without issue. I don't remember there being any sort of spacer that goes underneath.

This second rc8.2e was purchased pre-owned and came like this, not working with the same aluminum mount. Weird.

In any event, everything works now and thank you all for the help and suggestions!