Diff Too Tight?

[vaz9764 0]

On my TA01 Escort, fully ballraced and greased, when I spin one of the front wheels by hand, the opposite wheel spins in the opposite direction beautifully - for 2-3 seconds. It appears friction free.

However when I spin one of the rear wheels, the opposite one spins in the opposite direction but both rear wheels stop instantly when I let go.

Should the rear diff spin as freely as the front one when not engaging the motor?

[vaz9764 0]

It must have been, I rebuilt and re-greased it but didn't screw it back together as tight. Much better now.

[Spetz83 0]

Generally they shouldn't be that easy to spin, otherwise it's just an open diff.

And, most people prefer the front being tighter than the rear, as it makes driving easier

[terry.sc 16]

The front end has a gear diff in it, the rear end has a ball diff in it, like every TA01/02 tourer.

The gear diff will turn freely, there's no drag in the system. This setup is better in the front end as spinning freely it means you have as much steering as possible as the wheels aren't fighting with the steering, but if a wheel lifts off the ground all power goes to the wheel with no traction and you lose acceleration.

The ball diff is held together by friction, there's lots of drag to stop the wheels spinning free. This means if a wheel slips power is still transferred to the other wheel to give you better traction. This limited slip action will reduce steering if in the front, but the limited slip also gives you more traction for better acceleration. This is why there's a ball diff in the rear.

If you ever adjusted the ball diff to spin as freely as a gear diff you will find there is no drive as the ball diff would be slipping under power.

[94eg! 834]

It must have been, I rebuilt and re-greased it but didn't screw it back together as tight. Much better now.

This is how you destroy a ball-diff. The ball diff should be tight as you first described. If not, it will allow the balls to slip and wear flat spots. The rear ball-diff MUST be adjusted as described in the manual. You should not be able to spin the main ring-gear (or pulley) by hand when locking either out-drive.

[TA-Mark 195]

If you leave the nut loose on the TA-01 (Manta-Ray) ball diff or the TA-03 ball diff, the assembly will come undone while driving. To adjust the 'tightness' of these diffs you need to shim them and the nut must always be done up tight.

The newer diffs have a spring loaded adjustment for the 'tightness' of the ball diff action, not so in the older Tamiya ball diffs.

I highly recommend bonding the outdrives into the diff plates with Loctite on the Manta-Ray and TA-03 ball diffs. The spline is very short and sometimes the outdrive 'walks' out of the diff plate just enough to start it stripping the splines. Bonding them in when new solves this. Just make sure you put the bearing on before you bond.

[vaz9764 0]

I've tightened it back up now. Thanks everyone.