HZJ75 LSD rear diff rebuild options

[HZJ75 FARMER]

I've found my rear diff has a lot of metal flakes in the oil. It's not dismantled yet but as there's no clunking hopefully it will be just failing bearings and the gears may be okay.

The rebuild kits are cheap. But the LSD clutch plates are $80 each, and there are 6 of them. After 480,000km they will presumably be worn out. Buying new ones wouldn't be so bad if it was worthwhile. But it's a fair bit of money to put into something that isn't very good anyway. I actually wouldn't care if it had no LSD, just an open diff like the older models.

So, I don't really need to replace them if I place no value on the LSD. But, if they are worn, they will affect the backlash of the side gears? Do they generally wear to a point of affecting the side gear backlash, or do they just wear a bit until they are ineffective as a LSD and then stop wearing?

What do people normally do when they are rebuild a LSD? Seeing the rebuild kits don't come with and plates, makes me think maybe people just ignore them?

Obviously I'll be able to make better decisions once I pull it apart, but I'm just wanting to get some research done beforehand.

 

[Eurasiaoverland]

You can get late 70/80 series clutch plates (41361-60341) for far less than the earlier plate (41361-60051). They are identical to look at, but -60341 to me had a slightly coarser surface texture.

The 80 Series LSD had eight clutch plates and six discs until about 1995 or 96, then six/four after that. I think the 70 Series may be the same.

To answer your question, if the overall stack of clutch plates and discs has lost material, the procedure is to shim them up to restore the backlash of the spider gears to the side gears. The shims come in four thicknesses.

If your spider gears and side gears are worn (and I believe they are more susceptible to wear than in an open diff), then I've read on a Russian site that they are hard to set up.

There is a real dearth of information on these online as they were not supplied in the 80 Series in the US and Australian sites usually just moan about how they wear out. I only found useful information by one diff expert on the drive2.ru site.

That's my finished diff. The build got way out of hand and it took years to find a new LSD carrier (which I could only find in Russia, posted by a friend there to Kazakhstan from where a friend who was driving RTW in his 105 took it as far as India, to be brought out to SE Asia by yet another friend).

My original open diff was completely worn out to the point that the only re-used parts in the end were the diff housing and the adjuster nuts for the side gear pre-load.

 

[lacalvette]

Well, I did an experience which I did not try yet. I moved the rear LSD third member to the front. Took it appart and friction plate did not look worn. But had too much back lash in the small pinion gear. I realised that the thrust bearing on the LSD were thinner than those used on an open diff. So I took 4 thrust bearing from different open diff and installed them into the LSD diff, brought back lash to spec.
As I mentioned, did not try it (truck still in work in progress mode) but it is lock when I turn by hand, hope not too much ...

 

[HZJ75 FARMER]

I have found a failing carrier bearing and everything else looks reusable, including the LSD plates.

But, the spider/side gears will need the backlash adjusted as I have about 0.7mm.

Any tips about how much each size shim changes the backlash? Or just have to go the expensive way and buy a couple of each?

The dished thrust washers behind the spider gears will also affect the backlash, so it does look like it will be a bit difficult to set up.

 

[HZJ75 FARMER]

Also - opinions on rebuild with a solid pinion spacer, or a collapsible spacer?

 

[Eurasiaoverland]

The spider gear shims come only in a single size, I would not replace them unless they are very worn, in which case the gear (set) probably needs replacing.

If you want to buy as few shims as possible, maybe try 2x 0.20 mm and see what difference they make to the backlash.

I was persuaded to run a solid spacer. In theory it should eliminate the backing off of pre-load over time, but I have not started running my solid spacer LSD yet.

I bought the overpriced Terrain Tamer SS 'kit' with 3 shims. Those cowboys either don't know how to set up a diff, or just sell you any old crap and let you fix their problem.

The shims are far too coarse to be useful. The difference in running with their smallest shim, or no shim was between a pinion which was totally loose, to being locked up pretty much solid (far too much pre-load). The shims are 0.20, 0.30 and 0.50 mmm sizes IIRC. I needed 0.06 mm in the end, and had to cut these shims myself from stainless shim stock.

So the solid spacer is a lot more work to set up, but it does remove the need to pull off the pinion bearing after setting the ring gear backlash.

So I would recommend a solid spacer, but make sure you have your own shims, don't buy the garbage from Terrain Tamer.

 

[HZJ75 FARMER]

Great advice about the kit, thanks mate.

I've actually decided it won't hurt to have a few spare LSD shims on hand, I'm going to have to rebuild another one later on, so they might get used there anyway.

So considering that it's going to be very difficult for me to get custom pinion shims for a solid spacer, and considering it's done 480,000km with the original collapsible spacer maybe I'm better off just going with collapsible again? It wasn't even a pinion bearing that failed, it was a carrier bearing.

 

[Eurasiaoverland]

For normal use, I don't think the collapsible spacer can be that bad. I would go to the top end of the pre-load range to give it the best chance.

Take your old outer (smaller) pinion shaft bearing and file/hone out the centre bore so it is no longer an interference fit on the shaft. Then you can slide it on and off for the setup, and put a new bearing on in the final step of diff setup.

 

[lacalvette]

I have found a failing carrier bearing and everything else looks reusable, including the LSD plates.

I have found a failing carrier bearing and everything else looks reusable, including the LSD plates.

But, the spider/side gears will need the backlash adjusted as I have about 0.7mm.

Any tips about how much each size shim changes the backlash? Or just have to go the expensive way and buy a couple of each?

The dished thrust washers behind the spider gears will also affect the backlash, so it does look like it will be a bit difficult to set up.

View attachment 4047909

I'm using a 1994 FSM and it is different than your. In the 1994:
an open diff back lash is adjusted by selecting different pinion gear thrust washer thickness.
an LSD diff back lash is adjusted by selecting an adjusting washer of different thickness.

Not too sure about your manual if they use both method to adjust backlash?
But that was my understanding that either moving closer spider/ pinion gear or side gear would reduce back lash. I do have a couple open diff hanging around so when I figured out the thrust bearing thikness diffence, I went this route and brough the back lash to spec. I think either way work.

As for the solid spacer, finding the right shim to obtain the specified preload can take time. Crush sleeve can be tricky for the first time ahah

 

[lacalvette]

For normal use, I don't think the collapsible spacer can be that bad. I would go to the top end of the pre-load range to give it the best chance.

Take your old outer (smaller) pinion shaft bearing and file/hone out the centre bore so it is no longer an interference fit on the shaft. Then you can slide it on and off for the setup, and put a new bearing on in the final step of diff setup.

Just to mention that all the 60 and 70 third member that I played with, had the smaller bearing slide freely on the pinion. I did retrofit an 8 inch e-locker in an rear open diff 4runner axle. Both those third member had the smaller bearing interference fitment.

 

[Eurasiaoverland]

I'm using a 1994 FSM and it is different than your. In the 1994:
an open diff back lash is adjusted by selecting different pinion gear thrust washer thickness.
an LSD diff back lash is adjusted by selecting an adjusting washer of different thickness.

Not too sure about your manual if they use both method to adjust backlash?
But that was my understanding that either moving closer spider/ pinion gear or side gear would reduce back lash. I do have a couple open diff hanging around so when I figured out the thrust bearing thikness diffence, I went this route and brough the back lash to spec. I think either way work.

As for the solid spacer, finding the right shim to obtain the specified preload can take time. Crush sleeve can be tricky for the first time ahah

View attachment 4048063

View attachment 4048064

View attachment 4048072

From factory, the LSD was set up using different thicknesses of 'washer', which is what the FSM calls the friction discs. But these were never sold as individual parts; only the shims are available to the end user. Note that the shims for the LSD (which I show in a picture above) and not the same as the shims for the open diff (which I have for my front diff).

Just to mention that all the 60 and 70 third member that I played with, had the smaller bearing slide freely on the pinion. I did retrofit an 8 inch e-locker in an rear open diff 4runner axle. Both those third member had the smaller bearing interference fitment.

If the pinion bearing is not an interference fit, to me it is an indication that something is worn or a poorly made aftermarket part. With a new genuine pinion shaft and new genuine bearing, I get an interference fit. On my front diff with the original pinion shaft, a new genuine bearing is an interference fit.

It's common for pinion bearings to spin on the shaft if the pre-load is lost. This causes wear and then the interference fit is lost. Just like worn wheel bearing spindles, I would expect that once they are worn like this, there will problems with losing bearing pre-load in the near future.

 

[lacalvette]

I'm refering to the small pinion gear thrust washer, not the friction disc in the clutch pack.

In an open diff, the only way to adjust the back lash is to varying these thrust washer thickness.

I'm curious because the picture of the book HZJ75FARMER share is for an LSD and it's says to select a thrust washer to adjust backlash.

 

[Eurasiaoverland]

I'm refering to the small pinion gear thrust washer, not the friction disc in the clutch pack.

In an open diff, the only way to adjust the back lash is to varying these thrust washer thickness.

I'm curious because the picture of the book HZJ75FARMER share is for an LSD and it's says to select a thrust washer to adjust backlash.

View attachment 4048343

The manual is referring to adjusting the shims on the side gear (open diff) or changing the thickness of the outer friction disc in the LSD. In practice, both 2 pinion open diff and 4 pinion LSD are adjusted using side gear shims. The dished thrust washer for the small spider gear is not adjustable, on either diff type.

 

[lacalvette]

The manual is referring to adjusting the shims on the side gear (open diff) or changing the thickness of the outer friction disc in the LSD. In practice, both 2 pinion open diff and 4 pinion LSD are adjusted using side gear shims. The dished thrust washer for the small spider gear is not adjustable, on either diff type.

I see now maybe the dished thrust bearing on mine were just worn off? The different thickness on dished thrust washer from 4 and 2 pinion found on my diff lead me to think there was different size....
Thanks

Edit, was curious and went digging, all washer are made in steel, including side gear's one. So I don't think they really wear, some marks...
I measured the washer, on the 4 pinion are 0.83mm, the one on the 2 pinion are 1.72mm. They are identical exept thickness.
there is different part number but I can not confirm thickness vs number.

 

[Eurasiaoverland]

Great advice about the kit, thanks mate.

I've actually decided it won't hurt to have a few spare LSD shims on hand, I'm going to have to rebuild another one later on, so they might get used there anyway.

So considering that it's going to be very difficult for me to get custom pinion shims for a solid spacer, and considering it's done 480,000km with the original collapsible spacer maybe I'm better off just going with collapsible again? It wasn't even a pinion bearing that failed, it was a carrier bearing.

One issue you may face: From factory, the outer-most friction discs are thicker than the rest of the friction discs (which are 2.00 mm). Probably something like 2.20-2.30 mm. Adding a 0.20 mm shim either side will bring the side gears quite a bit closer together. You might find that they become too tight, in which case you may need to get two new standard (2.00 mm) friction plates. These are the only friction plates you can buy.

 

[HZJ75 FARMER]

I'm having trouble with the backlash, following the process described in the service manual. If done while the carrier is split apart it's pretty fiddly to hold the side gear to stop it moving, and rock the spider gear to measure the backlash.

Also difficult to get a point near the top of the geartooth that the dial indicator tip can sit nicely, due to the gear teeth being so short and rounded. When the dial indicator tip is placed near the top, as the gear moves it can give a false reading as it's shifting on the curve.

But after perseverance it is possible to get shims put in that give correct backlash. Then repeat on the other half.

However, when the two halves are bolted together, the backlash seems to disappear. It's not possible to get my dial indicator tip in through the hole when it's bolted together, but I can't feel any rocking with my fingers.

If I dismantle it and remove the shims, and reassemble, then I am able to feel what seems like nice backlash. But with no shims, the backlash is huge when the halves are apart.

So, are you supposed to set it up in halves as good as possible, and then ignore the no backlash when it's together? Or, ignore the service manual procedure and just feel for some backlash when it's bolted together?

Or, seeing there doesn't seem to be any YouTube videos about how to set it up, am I overthinking it and should just slap it back together like perhaps other people probably do?

 

[HZJ75 FARMER]

My feeling would be that I would rather feel some backlash when assembled. Even if it isn't properly measurable.

 

[Eurasiaoverland]

I went through the same process. My reasoning is that when the two halves are assembled, unless the two side gears are perfectly in phase, you will not get any backlash as the spider gears will be under tension, and there is no way you'll be able to move the side gears with your fingers. So I stuck with the FSM procedure. I think I assembled the diff halves with only one side gear (but with the spring and retainers) to check that my backlash value was steady when assembled.

 

[Eurasiaoverland]

Sorry, I think I assembled it with both side gears but no spring to check the backlash when assembled.

If you have any pictures of your diff internals, I'd be interested to see. I'm not sure I have ever seen a pre-1990 LSD carrier.

 

[HZJ75 FARMER]

Thanks.
I had the axle in on the top side, to try to turn it as I tightened the bolts to try to get the gears snugged in, with the same thought process that the gears may be binding. Obviously can't turn it when the bolts are tight.

Edit, I have tried with no spring, and still get no backlash when assembled if shimmed.