So I was looking at the race car tire wear yesterday and noticed that 3 of the tires were barely worn, but the inside edge of the passenger side rear diff was worn down to the cords and the outside edge and middle of the tire were the same as the other 3.

I expect that it was burning the inside rear coming out of Turns 5, 10 and 3. This means that I need to either find a crutch of super aggressive rear diff gear lube or rebuilding the rear diff and making it a lot tighter. It never showed this with the Toyo's only since I have gone to the Conti's.

I am looking at the Redline 75-140 NS as a gearlube, however if I need to rebuild the diff, how tough is it to do? I assume it is easy for you Mazda Techs, but I haven't rebuilt a diff for about 30 years, so I am a bit tentative about doing it and is it cost effective to do?

Ideas, comments?

Eric

 

No ideas, but I'm interested too - I have an S4 clutch-type diff I got from a salvage 7, and if it's reasonable for me to rebuild myself, I will. I know it's not hard to take it apart and replace the clutch disks and reassemble it (I've found a how-to on rx7club before); however, setting the pinion up correctly with the ring gear is the part I have at best a tenuous grasp of - I understand doing it wrong will lead to a noisy diff and possibly accelerated and uneven wear of the ring and pinion teeth. For that reason, I'm reluctant to take the diff apart to check the wear of the clutches, since I don't want to have to pay someone to set up the pinion (unless its cheap, like me!), but by the same token, it's a lot of work to take the diff back out if I find after the fact the clutches are worn.

 

Maybe consider a Kaaz or similiar instead. A lot more bite!

thewird

 

The KAAZ 1.5 way would be a great solution, I just don't want to drop $1500 in to the just the diff right now. Thats a couple of race weekends! I am also trying to be a bit frugal as I want to get the Cougar back on the track again next year and my racing budget only stretches so far.

I believe that Mazda sold a racing/tighter clutch pack kit for the S4 clutch diff previously and it was reasonable at under $150 bucks, but I don't know if it is still available.

Eric

 

Well, I just did some research and the cheap Chumpcar or $2013 Challenge guys use an added shim made from a (and I kid you not) beer can added to each side and lightly sand the disks and plates to put a new cross hatching on them. They also change the orientation of the discs and plates so that they are setup on each side alternating rather than side by side. In almost all cases this addition of the shim and new posi fluid has resulted in a boost of release point torque to 150 ft/lbs. What is mentioned as the diff killing factor, is the heat build up. anything over 200 F sustained, basically kills the unit.

That is great for racing and aggressive street. Seems that I have my solution and anything that involves RX7's and beer can't be all bad.

Eric

 

Read about this, let us know how it goes. Document the process if you can !

 

did you end up doing this? mine doesnt seem to lock as hard anymore

 

Not yet. My life is pretty busy and I just haven't got the time for a bit. I will be doing this before the next race season as I wore out my passenger side slicks inner edge from tire spin at CTMP in my last race.

My diff is jelly and needs some firming up.

Eric

 

same here planning on doing something with mine this winter , it gets pretty expensive replacing all new parts