SV Pro diff rebuild ?

[sunbeam]

Hi,

I've had my Cougar SV Pro for about 4 months and race it every week @ 4 races per race day @ 5 minutes per race plus practise. The diff has not been touched since I first built the car from new.

So that's about 64 races = about 6 hours racing plus maybe 30% practise ? Maybe 8 hours in total running time. I never 'play' with her outside the club, so every time she is run, it's in full racing anger !!

I have a 6.5 in her, 82% throttle, slipper adjusted for smoothness (no stepping out, wheelies or wheel spin) and normally finish in the 'A', at club level (caldicot 60% carpet 40% wood)

Last week I felt my diff getting a little tighter than I had set it up from new, so adjusted it to be more free. It was to free and the next race was interesting ! I still finished just one lap under FTD and equalled my last race time. The diff did not screech, just slipped quite a bit and made a noise that was not right.

After that race I tried to adjust it, but found that nothing short of the bolt being fully tight was good enough to stop it slipping. At fully tight the diff felt fine. The next race went well, the diff was perfect.

When I got home I stripped the diff down and found that all the cone washers were flat and there was a very SLIGHT groove in the thrust plates where the balls run (Ceramic Nitride Diff Balls). I can't understand why the diff got tighter, but I assume the race with the diff lose caused the balls to wear down and the diff washers to 'grove'. This I assume is why I needed to to fully tighten the diff bolt to stop it slipping for the next race and in doing so crushed all the cone washers? The pulley is still perfect.

I've now ordered :-
U3019 Ceramic Nitride Diff Balls
U2573 pro diff screw set
U3740 Diff washers

So my questions are :-

1, Is 8 full hours of flat out racing a good life for the Cougar SV Pro diff before a rebuild ?
2, On a rebuild, do you need to replace all the parts I have bought ?
3, How long are the Ceramic Nitride balls expected to last under race condition while slipping badly ?

Thanks

Rob.

[sunbeam]

Anybody?

[hazeandfizz]

Best thing to do is inspect the diff every couple of months, then if you have slight wear on the diff plates you can give them a quick rub on some wet or dry to get rid of the groove.

A clean, re-grease and a quick rub of the plates every 2 months will extend the life of the balls (never replaced mine in over a year). The I would fit a new pro diff kit every 2nd build. The reason for fitting the kit is the plates go flat and the diff bolts can snap if they have been in for a while.

Not sure why the diff went tight on you!

Hope that helps,
James.

[sunbeam]

Hi,

Thanks for that, can the balls damage if the diff slips badly for one race?

[bigred5765]

if the diff slips it will cut a groove in the diff rings this makes the diff loosen its self,it must be rebuilt once that happens,

[sunbeam]

Hi,

When you say rebuild, do I buy new rings or just polish the groove out or turn the rings over?

Will the balls be damaged and need replacing?

As I've said above, I've ordered all these parts anyway, but it's good to know what to do properly.

Thanks.

[bigred5765]

if there ceramic balls they should be ok, just replace diff rings youll only need to replace thrust race and washers when a rebuild doest feel smooth or washers are flat

[sunbeam]

OK, thanks.