Shimming Stock LSD

[roostmeyer]

Has anyone over shimmed the factory cone type differential or is the carrier not easily split-able?

My LSD is shot, one wheel peel in the rain is out of control with TCS turned off. Car has 144k, so it's not a huge surprise that the stock LSD is worn out. I've just been living with it, since it's just a fun daily driver that I occasionally autocross.

In the last week or so my clutch has started to slip. I'd like to address the diff while the transmission is out. If I had $1450 sitting around it would be going to a lift and transmission jack to make the clutch job easier, not to a quaife or OSG for a ten year old car.

I've shimmed the diff 3 or 4 times on my trans am with a borg warner 9-bolt:
https://www.youtube.com/watch?v=8B4EoeU0l38
Not exactly rocket science, just add shims until all free play is gone on the spider gears. Of course access is a lot easier on a solid axle.

[roostmeyer]

So bad news, the cones and the sun gear are single piece, so there's nothing to shim. On the borg warner 9 bolt that I'm familiar the cone/friction surface is separate from the sun gear, so you can place shims in between to tighten up the limited slip. I'm guessing there was ~.030" of slop between the 2 spider gears. Without a preload spring, the diff is essentially going to freewill in no or low load conditions. That's been my experience in the rain and with junk tires.

There is some good news though, a traction lock S-spring from an 8.8 fits nicely and should put a nice amount of preload on the diff. I think it may be too much preload for a daily driver, but I'll find out later this weekend once I've got the car back together with a fidanza flywheel and new luk clutch. I used YSPSPR-004 from yukon gear since it was available with prime shipping and I didn't want to have to wait long to get the car back together. The clearance around our 30 spline axles are close, but I think it will work. There is a 31 spline version YSPSPR-005 for 31 spline axles, but it's quite a bit more.

Supposedly the F150 springs are stiffer than mustang ones if you want to go to a junkyard, but I didn't have the time this time around.

[Fstrnyou]

Interested to see how this works out. I don't have a 3, but I have several friends that do. Might be worthwhile to have a few spring's on hand for future repairs...if it works.

[roostmeyer]

Finally got this thing back together. There's only maybe 5-10ftlbs of preload in the diff, not nearly as much I expected. I guess it's better than locking up with 100+ftlbs of break away preload and acting like a spool in a parking lot. I'm still breaking in the clutch, so I haven't really pushed the diff around corners yet. And I've yet to drive it in the rain, but hopefully I'll have a better idea if it's helped wheel spin in a few days of driving it.

The fidanza FW definitely makes things harder to modulate, but I'm getting the hang of it. Rev matching on down shifts is definitely easier and motor seems to get up in revs faster in low gears.

Bad news is I managed to somehow lose fifth gear. I swore all the shifter forks moved prior sealing up the case. I'll pull the shifter later this week and make sure it's not a shifter issue. Of all the gears to lose, 5th isn't too bad. I'll probably live without it for a bit before I tear it all apart again if it's not a shifter issue.

If/when I take it apart to fix whatever I messed up in the transmission I may put a couple washers between the spring and spider gears to increase the amount of preload on the springs. I may shoot an email to GKN and mazda motorsports and ask if the conical washers are available at all. If they're not I'm tempted to take some low grit sand paper and rough up the surfaces between the spider gears and conical washers while in there.

[Fstrnyou]

Does the shifter go up into 5th but no engagement or is the shifter locked out?

I would say if you lost 5th AND 6th, then the solution "could" be a simple shifter cable adjustment. But if 6th works, but not 5th, then I'd say it's internal to the trans.

[roostmeyer]

Way overdue for an update. I took the case apart again and fixed fifth gear. It was a dropped checkball, just like Tomas described in his LSD swap out thread. Just a PSA, if that happens to you, pull the damn car apart ASAP. I drove it that way for a month, and there was a lot of brass dust in my tranny fluid. My guess is that checkball was pushing the fifth gear syncro into something and causing a bunch of wear. Tranny still shifts the same so I think I got lucky.

While I had it out, I took the diff apart again. I chucked the LSD cones up in my mini lathe and roughed them up with a 60 grit grinder wheel. In hindsight, I should've shimmed the traction lok spring with a washer or two to increase preload. I saw basically no difference between the roughed up cones and before when they were polished smooth from 140k miles of wear. Oh well, hopefully I don't have to open it up again anytime soon.

I've now have driven it in rain, snow etc. and done an autocross. I'd say it's improvement, but only a small one. If somebody else tries this I'd say go for a traction lok spring from an F150, toss a few washers behind the standard traction lok spring, or maybe try the spring pack from a miata super LSD.

I'll try to edit this and add photos later.

[MSMS3]

What diff fluid did you use and did you add any friction modifier? When mine was starting to act up going around corners I drained diff fluid, replaced with new OEM fluid but added a few ounces of Redline friction modifier and the diff acted like new. Mileage was about the same as yours.

[roostmeyer]

Right now it's got the cheapest gl4 75/90 from autozone. I wanted to flush out any of the brass before putting back in redline MTL. I've ran redline NS in the diff on my trans am to try to tighten that diff up, but I think that is a true gear oil and not a tranny oil. My experience has been friction modifier tends to loosen up the diff, but I could try adding it to the cheap crap that's in there now and see if it makes a difference.