Friday, September 20, 2019

Wltoys 12428b (part 23: RWD with locked rear diff)

So the rear wheel drive conversion has been very interesting.  Not only has it allowed me to isolate and then optimise the rear end, it's unlocked an entirely different vehicle from the AWD one.

However, one thing was immediately obvious, rear wheel traction was sorely lacking.  Hence, locking the rear diff with BlueTac :)

I kept another diff open, hence labeling.

I did this rather hastily and didn't bother taking any in-progress pictures.  However the process is pretty straight forward:
  1. Remove the wheels and rear differential cover etc.
  2. Remove the differential and axle assembly.
  3. Carefully open the differential by removing the 4 screws.
  4. Carefully note the arrangement of the spider gears.
  5. Carefully remove the spider gears onto a sheet of white paper.
  6. De-grease and clean the spider gears and inside their housing.
  7. Take a wad of BlueTac and shove it into the housing..
  8. Reinstall the spider gears, embedding them in the BlueTac.
  9. Shove more BlueTac on top of the spider gears.  Aim to fill it with only the smallest amount coming out of the screw holes upon re-assembly.
  10. Reassemble the differential, carefully tightening screws.  Don't force it.  If you have not enough then the spider gears will still move.  Too much and it won't go back together properly.  
  11. ..fettle until it works ;)
  12. Reinstall in the reverse order of disassembly.

Road Test:

OMFG.  The thing is a beast. Totally different animal..
  1. It feels more agile, nimble, responsive.  And powerful.
  2. Will readily lift a front wheel under acceleration.
  3. Brake application causes rear wheel lock, done carelessly induces spinout.
  4. Turning circle doesn't seem to be badly impacted.
  5. Can now easily do doughnuts.. ;)

Offroad Test:

Hmmmm... something isn't quite right.  It's nearly uncontrollable on full throttle.. I think it's torque steer?

  1. Whenever the car is at full throttle it will steer to the right (clockwise).
  2. From a standing start it will just do a doughnut, always the same direction.
  3. Trim the steering to the left, under full throttle it will travel straight, and then off throttle will travel to the left.  So i don't think a steering or even a toe issue.
  4. It only appeared to happen when the diff was locked.  RWD with open diff didn't have this issue.
Some interesting information.  Fixes? I'll try adjusting the front toe, that needs doing already.  Failing that I don't mind going back to AWD.  I feel like the rear is solid now which is how this all started in the first place.. ;)

UPDATE 1: Fixed the issues with toe out and steering play, but even on tarmac it still very readily wants to steer to the right.  

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