Differential / drive question
 

Hi all,

Just wanted to clarify something - when your 4WD truck is off the ground, and you put power to the wheels, and one wheel doesn't spin, that's correct isn't it? As that shows the differential is doing its job and the wheel with the most resistance does not turn but it's not a fault - shows the diff is doing its job, right? This is the case of my Revo with CVDs.

My old e-maxx - I've noticed all 4 wheels turn, with a good deal of vibration too, when power is applied off the ground. But that is an old, and fairly worn, drivetrain.

Just want to check there's no problem with the revo - I can live with maxx not being at its best!

Thanks

RE: Differential / drive question
 

Your diffs maybe running dry.Thus little resistance.
But yes its normal that one wheel will spin up faster than the other.

The tyres could have dirt in them and be unbalanced vibrating the truck as it drives.

RE: Differential / drive question
 

Hmm... if I lift the rear wheels off the ground then try a bit of throttle they spin fine, but if I lift just the front wheels off and try a bit of throttle - the rears bite and want to drive, the fronts don't spin.

Is that right? I know there are probably different weight oils in front/rear, but I would've thought the fronts would've spun freely in that situation with the rears not able to move... I need a lesson in diff logic before I take the whole thing apart, perhaps unnecessarily!

Thanks

RE: Differential / drive question
 

When you hold the truck off the ground, all 4 tires should spin freely when you give it throttle. It sounds to me like you are missing a wheel pin, or more likely a CVD pin has backed out and you have no drive at the one front wheel.

Try this. Sit the truck on a block so the wheels are suspended. Give it steady throttle and then grab one wheel on the back of the truck, either side is fine. Now the wheel opposite of it should be spinning twice as fast as it was if the differential and driveline are all working correctly. Now, do the same to the front and make sure it does the same. If so, everything should be working correctly.

Also, when the one wheel isnt spinning, look to see if the CVD running to it is turning or not.

Eric

RE: Differential / drive question
 

Thanks Eric

Seems the CVDs are running to both front wheels - i.e. they're turning up into the diff if I physically turn the wheels. With the truck upside down and just trimming the throttle to just make it run, the centre CVD going into the front diff is turning, and the front left is being turned, but the front right CVD just sits idle, slightly wobbling. The rear wheels I think behave as you suggested. Also if I try to hold both rear wheels, nothing transfers to the front wheels, they just stop and I feel resistance. If I stop the front wheels (bearing in mind the front right isn't turning anyway) it has no effect - the rears just keep truning the same.

What do you think?

RE: Differential / drive question
 

Something is wrong on the front right. If the wheel isnt getting power. Its either a CVD problem, or something in the differential itself most likely. Id say just pull that one side aparty and if nothing is visibly wrong, pull the front diff and inspect it, but your problem should be right there somewhere.

Eric

RE: Differential / drive question
 

Thanks Eric - problem solved. The hex pin screw - I dunno the technical name, has dropped out the front right CVD at the diff end, so it was just spinning loosely, but I couldn't see the cvd was just spinning round the yoke(?) at that end until I got in real close with a pen torch.

I haven't got the right screw to replace, but sticking a small screw in there at least confirms the drivetrain is acting normally when I turn the wheels manually, so good that the diff appears to be ok.

Just need to find where to get that one little screw now! Lol

Thanks for the help.