8 inch limited slip questions (3 Viewers)

[Gubbtratt1]

I'm soon at the point in my LJ70 build where I'll be working on the axles. All the normal maintenance and repairs should be in the manual, but I've got a few questions regarding the stock limited slip diff I've got in the rear axle:

1. How will using normal 75w90 oil affect performance, compared to the proper LSD 75w90 oil? I'm not too sure the previous owner knew he had an LSD.

2. I remember reading how to tune it by adding spacers to the spring, but I can't find anything about that now. Does anyone have experience or knowledge about this?

3. If I take it apart to inspect and/or tune the spring, do I have to check wear pattern and backlash if I put it back exactly as I removed it? What problems do I get if it's bad?

4. Does the rear diff bolt straight into the front axle in case I at some point get one locker and decide to install it in the rear axle?

5. In the same scenario as question 4, is it better to run locker rear, LSD front or LSD rear, locker front?

 

[JuanJ]

Hello,

Normal gear oil can damage the discs/thrust washers of the limited slip mechanism.

There is a thrust washer that is used to adjust the pinion gear backslash. However, it is not available as a part or tool. There is a procedure on the FSM to adjust it using replacement thrust washers.

If you can see bare metal in a thrust washer, it must be replaced. The reference thickness is 1.74 mm or 0.0685 in. If the clutch plates show wear, replace them as necessary.

The spring free length should be 31.3 mm or 1.232 in.

As far as I know, 70 Series trucks had LSD differentials on the rear axle only.

A good setup would be an LSD in the rear axle and a locker in the front axle.





Juan

 

[Felde]

If you are unsure of the condition of your LSD:
Jack up the rear axle both sides and turn one wheel. Both wheels should rotate the same direction (so no 'open diff' behavior).
If you put one wheel on the ground, you shouldn't be able to rotate the other wheel by hand.
That's how my rear axle (with a working LSD) behaves.
Cheers Ralf

 

[Gubbtratt1]

If you are unsure of the condition of your LSD:
Jack up the rear axle both sides and turn one wheel. Both wheels should rotate the same direction (so no 'open diff' behavior).
If you put one wheel on the ground, you shouldn't be able to rotate the other wheel by hand.
That's how my rear axle (with a working LSD) behaves.
Cheers Ralf

With one wheel in the air and one on the ground the wheel in the air is fairly easy to spin by hand, so there's definitely something wrong.

 

[Felde]

Uh. Sorry to hear that.
Well, probably it's about your usecase:
If you are anyways about to dig into the diff, just go ahead. But those LSD parts are $$$.
If you just occasionally need 4x4 and have some time, you might want to just put proper LSD oil and change it often. The clogged discs might free up.
If you are about serious offroading (which I assume, as you are also discussing front locker options), you might want to go for a different solution anyways. The LSD helps offroad, but it's no match to a full locking axle. The LSD is rather designed for acting a few seconds in slippery conditions.
A proper locker would probably not be more expensive than replacing those LSD discs.
A LSD in the rear and something else in the front doesn't make any sense to me at all. If fully locked, then in the rear first.
Good Luck Ralf

 

[Gubbtratt1]

Uh. Sorry to hear that.
Well, probably it's about your usecase:
If you are anyways about to dig into the diff, just go ahead. But those LSD parts are $$$.
If you just occasionally need 4x4 and have some time, you might want to just put proper LSD oil and change it often. The clogged discs might free up.
If you are about serious offroading (which I assume, as you are also discussing front locker options), you might want to go for a different solution anyways. The LSD helps offroad, but it's no match to a full locking axle. The LSD is rather designed for acting a few seconds in slippery conditions.
A proper locker would probably not be more expensive than replacing those LSD discs.
A LSD in the rear and something else in the front doesn't make any sense to me at all. If fully locked, then in the rear first.
Good Luck Ralf

After reading your last reply I checked what a rebuild kit would cost. About 500€. I can get an air locker for 750€, so if the discs needs replacing I'll just get a proper locker instead.

 

[Eurasiaoverland]

Are the friction discs so expensive?

I rebuilt my BJ60 rear diff (9.5") with an LSD from a late model 80 Series, genuine friction discs are about 5 euros each (in Japan). The clutch discs are a little more expensive, maybe 15 euros.

If you strip the diff, it should be properly rebuilt, setting the backlash, bearing pre-load, and running a pattern on the ring gear teeth. Probably the pre-load was too low on an old, worn diff. Running the bearings with too little pre-load will eventually wear out expensive parts.

 

[Gubbtratt1]

Are the friction discs so expensive?

I rebuilt my BJ60 rear diff (9.5") with an LSD from a late model 80 Series, genuine friction discs are about 5 euros each (in Japan). The clutch discs are a little more expensive, maybe 15 euros.

If you strip the diff, it should be properly rebuilt, setting the backlash, bearing pre-load, and running a pattern on the ring gear teeth. Probably the pre-load was too low on an old, worn diff. Running the bearings with too little pre-load will eventually wear out expensive parts.

The only rebuild kit I could find in Europe was just over 500€. I found just the clutch and friction discs for a Supra (should be the same axle) on ebay for 250€ for all of them. Even when you do the math on your japanese prices it ends up at 170€ for the lot, plus shipping from Japan.

I was wondering if I could leave backlash and pattern alone because I thought it had to be adjusted with shims like on Dana axles, and I really don't like working with shims. Turns out it's just two nuts though, so that makes it a lot easier.

 

[Eurasiaoverland]

To be honest, everything I read about Toyota LSDs is that they are pretty poor from new, and of course wear out (especially if non LSD oil or no friction modifier is in the diff). If maintained, they seem to be a reasonable 'road' LSD for a part-time 4WD. But no use for off-roading I think. But on the 9.5' diff, the open diff has two spider gears, and the LSD four, so if nothing else, it should be a stronger diff.

I don't think a front LSD is a good idea. Really you want an open diff in the front to allow the car to steer. For off road, a proper diff lock may be useful, but it should be something you can control.

 

[Gubbtratt1]

I've read similar reviews of the stock LSD, except for one thread where someone had tuned it to the point that tyres slipped in corners on tarmac. I can't find that thread now though.

I believe 8 inch open diffs were available with both two and four spider gears. LSD has four, and air lockers, both ARB, slightly cheaper versions and absolute chinesium ones seems to all have four.

 

[Gubbtratt1]

The clutch plates doesn't look too bad to me.

Measuring the whole stack makes them look very bad though. According to the manual I'd need over 2mm of shims. My options are:

1. Add 2-3mm of shims per side. Cheap, hopefully.

2. Get new clutch discs. 250€.

3. Get a chinesium air locker. 400€.

 

[Eurasiaoverland]

That friction disc looks very bad, it is scored (oil contamination) and looks glazed. They should have a dark grey coating, any signs of bare metal mean worn out to me. I think the minimum Toyota spec of 1.76 mm or whatever it is in the FSM is nonsense, as it would leave a huge thickness well beyond the thickest factory shim disc.

What do the clutch discs look like?

What's the wear like on the diff siide gears and spider gears? With that much wear on the discs, the spider gear backlash must have been way out.

 

[Gubbtratt1]

The metal discs are more scored than the friction discs. The gears are unevenly worn, but doesn't seem worn out to me.

 

[Eurasiaoverland]

I think all your friction discs and clutch discs are for the scrap bin unfortunately. I've never seen them that bad.

Spider gears look worn but OK. Check the back side of the side gears (the ones which engage with the half-dhaft splines) as that is also a friction surface.

 

[Gubbtratt1]

Side gears (or at least one of them) looks a lot better, but is still a bit scored.

Would rebuilding this or getting a chinese air locker be a better investment?