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RC10th wrote:The easiest way to tell is pull the gear cover off, hold the spur gear with your fingers and while holding the spur gear push the car forward.

Under no/low power everything moves and acts as it should. It's when the motor's power is applied that it all goes down hill.

RC10th wrote:Also about the dogbone depending on what model (pictures help)

If it has true "dogbones" check that the springs are in the axles, they tension the dogbones into the diff cups and if they are missing can allow the dogbones to eject the vehicle. They look like a ballpoint pen spring.

Yeap the springs are both there (one in each receiver at the wheel). Could be that they just need to be replaced though as they have probably lost some/all their tension after 10+ years.

gnat wrote:

RC10th wrote:The easiest way to tell is pull the gear cover off, hold the spur gear with your fingers and while holding the spur gear push the car forward.

Under no/low power everything moves and acts as it should. It's when the motor's power is applied that it all goes down hill.

This is precisely why you hold the gear and push the car forward, it puts the car under the same stress as normal operation and allows you to see where the slipping is coming from. If your finding it hard to get enough "traction" while holding the spur gear pushing the car try this.

Hold the spur gear with your right hand to prevent it from turning while using your wrist to press down and hold the right rear wheel stationary. With your left hand grab the left rear wheel and turn it.

Top shaft spins = slipper problem
Top shaft doesn't spin = diff or broken axle roll pin.

Following your directions, nothing moves as long as as the spur is held in place.

As I suspected the spur is missing all it's teeth on about a quarter of it. When I rebuilt the transmission I found that I apparently didn't follow the instructions when I originally assembled it as I had both the spur and pinion installed backwards and tight up against each other. Following the directions when I rebuilt it only has the gears overlapping half of each other so I'm not surprised that the spur is dead now...

As far as the dogbone, it looks like one of the times it popped out the spring made a break for it and is now gone. Gonna guess that it had just lost tension which was letting the DB pop out a bit from time to time until it must have let the wheel end out enough to let the spring escape at which point it became almost un-driveable due to the DB constantly popping out.

Swung by my local shop to get some help figuring out what my next car (truck) will be and a new spur and some fuel line (what they recommended over springs for the dogbones) was only $8 (I'd forgotten how these things nip you to death...).

So now it's back to running on pavement again, but it's still useless in the grass.

Turns out the "missing" spring was actually still there, it was just stuck in a completely compressed state and looks like a piece had been torn off.