Has My LSD Given Up the Ghost?

1982 Starlet. Solid rear axle. TRD LSD.

Recently I've noticed that when I try to ease into my driveway--which is steep--I get stuck. The car lifts the right front and left rear wheel. The rear wheel isn't making any contact with the ground. It simply spins freely. The other rear wheel that has all of the weight on it doesn't move. Now, it's always done this but the problem is much more pronounced now that I am running Toyo R888s. There is always a little slime running at the edge of the driveway and if I didn't barrel right in I'd often get stuck on that slime and have to reverse and back out and try again. However, now, I can't even get the car to move in reverse. I get out and roll it back.

Is this normal in a situation where one wheel has absolutely no grip? I would have thought that the weighted wheel would push me through. The car still still lays two stripes when I launch hard...

What type of LSD is it? Clutch type, viscous, torsen?

If it is Torsen it will act like an open diff with one wheel in the air.

Edit: From what I see from a quick search it should be clutch type.

Have someone sit on the lifted corner of the bumper. Lol.

If it's a clutch type, yes, it's moved on to greener pastures.

If it's a clutch type, it might be worn out, but it also might just be preloaded too lightly to move the car up a bit of a hill with 1 tire in the air (preload determines how much power it can transfer with 1 tire free-spinning).

Time for a ford 8.8 swap.

Time to shim it and get some more life out of the clutches.

EvanB wrote: Time to shim it and get some more life out of the clutches.

This too! It worked on my trac lok

If you still see funny colors and, like, beyond man, then it's still working.

Yeah, it's a clutch type. Do you really think I need to re-shim it? I can still do a mean two wheel burnout. I think parts are non-existent for this 1982 vintage LSD. I might be able to order some from TRD Japan...but you can imagine the pain that'll cause me.

I can kind of imagine that with all of the weight on one wheel and that wheel having a super sticky tire, the clutches for the weighted wheel just saying "Screw you buddy. You have 80bhp and a 5.6" LSD...and you want us to push your ass up this driveway by our self? Ha!"

With the one tire in the air I can actually rotate that tire by hand...is that supposed to be possible? Don't clutch type LSDs use centrifugal force to throw the clutches outward thus locking at higher wheel speeds but acting open at low wheel speeds?

I shimmed my worn RX-7 diff with beer cans cut into appropriate sized circles and brought the preload from practically nothing to 100+ lb ft.

Is it different than the AE86 diff? I know a friend got all the bits and pieces to rebuild his recently and it wasn't too bad. Beer can shims at clearly the way to go though.

Try a bit of e-brake? Supposed to help transfer a bit more torque if one wheel isn't making any contact, but I've never had a chance to test this. Be my guinea pig!

redvalkyrie wrote: With the one tire in the air I can actually rotate that tire by hand...is that supposed to be possible? Don't clutch type LSDs use centrifugal force to throw the clutches outward thus locking at higher wheel speeds but acting open at low wheel speeds?

Depends on the unit, the simplest clutch LSDs are preloaded with a spring and that's the only force on the clutches aside from the spider gears trying to push apart under load. Then you get into the more complex 1/1.5/2 way pressure ring LSDs that can behave as an open diff at rest/low power input (not as you describe though, that's a Eaton "gov lock" locker).

These videos explain. https://www.youtube.com/embed/WeLm7wHvdxQ

https://www.youtube.com/embed/PEdnH7_7_yc

Here's something important: If your diff is that worn out, then the axle gears have probably moved away from the spider gears to the point that the tip loading of the gear teeth will have them breaking soon, resulting in catastrophic diff failure. Rebuild or shim that bitch before nasty, nasty things happen. Friction diffs are not maintenance free.

if it's a stock LSD.. it might not have a lot of load to begin with. BMW used to have two types, the one for the M Cars and the one my 318ti had, the "winter package" LSD. It was lightly loaded and while it could allow the car to do a nice two wheeled burnout, if you got one into the air like you are doing, engine torque would overwhelm it and just spin one wheel

Would a friction modifier help the LSD until I can hung down parts? I was thinking that maybe the Redline friction additive would help.. They claim it increase pressure i the clutches

I don't know anything about the Redline stuff, but the Ford friction modifier does the opposite of what you want. It actually makes the clutch pack slipperier to make the diff not groan while driving around tight turns.

Also, I forgot to mention earlier, I agree that light parking brake application may help you out of the "wheel in the air" scenario.

I'd just pull it apart and see what's up, it's not that hard. If the carrier bearings are shimmed (rather than threaded adjusters) you just keep track of your bearing shims and slap it back together the same way it came apart, no reading gear contact patterns required. I think your tire change is coincidental and it's just worn out and needs to be shimmed up or rebuilt. Tear it down and post some pics, keep close track of the shims, no need to remove the pinion gear/shaft unless the bearings have play, just drop the carrier out and see whats going on in the differential itself.

The LSD does have the ability tighten down the main bearings but I think that only affects the ring and pinion engagement pattern...?

redvalkyrie wrote: The LSD does have the ability tighten down the main bearings but I think that only affects the ring and pinion engagement pattern...?

You are correct. Adding shims or clutches can work though.

Well, if I'm going to pull the LSD, I might as well rebuild it--I found the TRD PN for the rebuild kit--40107-KP611. However, it's discontinued. I'm sure there is a kit sitting on a shelf somewhere but finding it could be impossible.

I gather I can make my own shims out of thin steel cut to size. What about the actual clutches? Is there an American company that might have some that would fit or be able to make custom units? Can the clutches' friction material be replaced like you can do with a brake pad?

snailmont5oh wrote: Here's something important: If your diff is that worn out, then the axle gears have probably moved away from the spider gears to the point that the tip loading of the gear teeth will have them breaking soon, resulting in catastrophic diff failure.

That is mainly a problem with the crappy Trac-Loks and Positractions with direct side gear impingement, a necessary design compromise in order to make a limited slip work with C-clip axles.

Decently better diffs like the type Toyota and Mazda and others use a separate area for the clutches. The preload spring is a lot stiffer and shorter-traveled. The clutches themselves wear very minimally because they are much harder (it's more like steel on steel rather than fiber clutches). A .010 shim can be the difference between zero preload and 150ft-lb preload.

Plus these units almost always have four spider gears, not two.

redvalkyrie wrote: I gather I can make my own shims out of thin steel cut to size. What about the actual clutches? Is there an American company that might have some that would fit or be able to make custom units? Can the clutches' friction material be replaced like you can do with a brake pad?

For shims I just use diff bearing preload shims.

Friction material isn't going to be anything like a brake pad or clutch disk. Much much much thinner and harder. It's probably actually still fine, just glazed. Give the inners and outers a light scuffing with a Scotch-Brite pad, clean 'em up, and put it back together.