6 replies to this topic

[Justin Baltrucki]

So i have been suspicious that my mazdacomp diff may not be working very well.
I have some inside wheelspin in the tight corners at limerock dry and wet conditions.

I jacked up the rear end, put it in gear, and rotated one side by hand.
There was no resistance and the other side spun the opposite direction. It's acting just like an open diff.

Am i correct in assuming that the clutch packs are shot/worn/no preload?
What should the torque spec be on the diff for resistance to rotate?

I know torsens cant be checked without load on the gears, but I though the maxdacomp would provide some drag with the above procedure. Does the diff need some speed difference to provide the necessary loading/resistance?

Time for a rebuild? - I purchased a clutch pack kit, but I want to make sure I am testing this correctly.

PS - redline 75/90 for limited slip - changed every race - Always comes out with very fine debris on the magnet.

Thanks

[LarryKing]

Both tires are in the air?

Put the car in neutral, lift one rear tire off the ground, leave one rear tire on the ground. Use a torque wrench on the axel nut and see how many ft/lbs it takes to turn the wheel. Start with your torque wrench set low - like 10 ft/lbs.

[pat slattery]

Anyone have any acceptable torque number that would indicate all is well?

[LarryKing]

Saul Speedwell is the one to ask. If my memory serves it isn't a big number, something less than 20 ft/lbs.

[Justin Baltrucki]

Both tires are in the air?

Put the car in neutral, lift one rear tire off the ground, leave one rear tire on the ground. Use a torque wrench on the axel nut and see how many ft/lbs it takes to turn the wheel. Start with your torque wrench set low - like 10 ft/lbs.

Yeah I had both in the air. Car in gear, so the gears/diff body/trans shaft wont turn.
Then rotated one wheel and the other freewheeled in the opposite direction like an open diff.
The spider gears were both turning within the diff body, so not much if any resistance to the clutches.

WIth 1 wheel on the ground and the car in neutral you will get some resistance because you are spinning the diff body, pinion, driveshaft, and transmission over around one fixed spider gear on the grounded wheel, so you feel some resistance, but you can't tell what,s from the clutches/spider gears and whats just from all the drag from the other parts. WIth both wheels in the air and the diff body stationary you just feel the resistance from the spider gears turning in the diff and the clutch packs. And I didn't feel anything other than the drag an open diff would provide. - I am just not sure if you need some speed to get this thing to bite in and provide some torque.

It appears there are some conical belleville washers in the clutch pack, But I am not sure how much preload/drag these should be providing, and when it's time for a rebuild. I know some BMW diffs can be super shimmed for massive lock up at the expense of low clutch life. Are people adjusting the mazdacomp diffs? Is there a service manual for the overhaul procedure? Ideally you should be able to three wheel through a corner and still put the measly 100 lb ft down through 1 outside wheel.

.

[SaulSpeedwell]

Yeah I had both in the air. Car in gear, so the gears/diff body/trans shaft wont turn.
Then rotated one wheel and the other freewheeled in the opposite direction like an open diff.
The spider gears were both turning within the diff body, so not much if any resistance to the clutches.

WIth 1 wheel on the ground and the car in neutral you will get some resistance because you are spinning the diff body, pinion, driveshaft, and transmission over around one fixed spider gear on the grounded wheel, so you feel some resistance, but you can't tell what,s from the clutches/spider gears and whats just from all the drag from the other parts. WIth both wheels in the air and the diff body stationary you just feel the resistance from the spider gears turning in the diff and the clutch packs. And I didn't feel anything other than the drag an open diff would provide. - I am just not sure if you need some speed to get this thing to bite in and provide some torque.

It appears there are some conical belleville washers in the clutch pack, But I am not sure how much preload/drag these should be providing, and when it's time for a rebuild. I know some BMW diffs can be super shimmed for massive lock up at the expense of low clutch life. Are people adjusting the mazdacomp diffs? Is there a service manual for the overhaul procedure? Ideally you should be able to three wheel through a corner and still put the measly 100 lb ft down through 1 outside wheel.

.

Answered several times years ago, but maybe never got ported over from SpecMiata.Com.

You will likely never need that clutch kit, even after the pinion shatters because it was set to the too-loose FSM side bearing preload specs After 50 weekends, the clutches measured within 0.001" of the rebuild kit. IIRC, the kit does not include "springs"/Belleville washers.

Fresh install: ~15 ft-lbs.
After "break-in" with 75W-90 NS (no LSD additive): 9 +/- 2 ft-lbs
With LSD additive: <7 ft-lbs.
When hot: subtract 2 ft-lbs

If you are getting wheelspin and below 7 ft-lbs:
A. Change to 75W-90NS.
OR
B. Drain and "wash" diff out with brake cleaner or similar, then do A.
OR
C. Disassemble, clean everything, prove to yourself the clutches are completely unworn compared to your rebuild kit, and then do A.

"Ideally" you don't want any more breakaway torque than is necessary to prevent wheelspin because the measly 100 ft-lb is being asked to overcome that torque any time you aren't going straight. An open-diff 100 ft-lb car will outrun a welded axle 100 ft-lb car down the Mid O backstraight, because the Mid O backstraight isn't straight and the tires have stagger.

[Justin Baltrucki]

Thanks for the tech info - I will give it a try with a lower range torque wrench