HZJ75 LSD rear diff rebuild options

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Eurasiaoverland said:
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.
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It's 1996.

I wish it was pre 1990. Then it wouldn't be LSD and I wouldn't be having this trouble. It would be finished by now.


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The backlash needs to be checked with the spider pressed firmly into the case half. I've seen people doing it on a press but don't have one myself.
 
Thanks for the pictures - looks just the same as mine, except I have the later spider/cross shaft which is thicker but has a smaller diameter spring.

I echo your feelings of wishing it was a simple open diff. It took me hours to get a backlash value I was happy with, and then hours again trying all the different solid spacer shim thicknesses. It had better not make a single noise when I finally get my 60 running!

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I'm a bit hazy on how it worked in the end, but I think I had about 0.65 mm of shims (I only have the standard 2.00 mm friction plates as I did not re-use the worn calibrated shims that came with the original diff I bought) on each side when I checked the pre-load in each half. Then after assembling it without the spring, I figured the halves were more tightly clamped together than I could achieve on the bench, so I thinned the shim pack back to about 0.4 or 0.5 mm. As you say, you can't get the DTI in through the assembled case, but by that point I'd spent so long fondling the spider gears that I was confident that I could tell when the backlash was in range.
 
Also maybe worth considering how many of these there are around the place, how many are high mileage by now and therefore getting rebuilt, and not many stories about failures from bad setting up? Therefore they maybe aren't as finicky as they seem?
 
Could be. I wouldn't know how to tell if there was too little backlash in the spider gears, I guess maybe a noise on cornering?

From the lack of online information, I don't think these get rebuilt very often. Probably most out there are worn out and functioning as open diffs and when the ring gear or pinions finally wear out they get replaced. Pretty much every thread I looked at on (almost all AUS/NZ) just gave the recommendation to replace the factory LSD with a Lokka or air locker.
 
Eurasiaoverland said:
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.
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I understand what you mean here. But is it really necessary to assemble the pinion shaft then pull it apart again? Even though it says to in the book.

Considering that:
Firstly, the book has a spec for the turning force preload measurement that includes the seal drag and has an additional figure to add for the carrier bearing load.
Secondly, I'm re-using all components apart from the bearings, and I'm pretty sure I'm the first one who has ever been inside it since the factory, so I'm not going to have to pull it apart again and change the pinion spacer or anything.
 
I think you could get a drag value for the oil seal, then add on your pinion bearing pre-load by crushing the sleeve in small increments. Then add the diff carrier, set your backlash and add the carrier bearing pre-load. Only issue is you'll need a new sleeve if you over-crush it, or if you can't get a good pattern and need to change the pinion shim.
 
I managed to do it in one go, just small increments. I had a spare collapsible spacer in case I overdid it, but didn't need to use it. I can see pulling it apart again would be more likely to be needed if setting up a solid spacer shim set, or if replacing the crown and pinion and not knowing what pinion spacer washer would be correct.

Interesting to note, I didn't get up to the initial nut tightening torque recommended by the service manual before the turning torque came up to where it should be.

Now in the vehicle and seems to be running okay.
 
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This bit. Don't go full steam with this, even though the book tells you to.
I was probably more than 3/4 of the way, but it never clicked off.
Hopefully this helps future rebuilders who may read this.
 
Eurasiaoverland said:
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.
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I've just rebuilt another rear LSD diff. This time I had less confidence that nobody had been into it previously, so I tried your trick of making the old bearings a sliding fit.

I'm wondering though, what did you file your bearings with? I used a carbide burr in a die grinder and got there eventually, but it probably wore as much off the carbide burr as it did from the bearing races. You must have had something super hard.

Also worth noting, I had a few spare pinion spacers so I had several goes at it until I got a pattern that I was okay with. Not overjoyed with, but okay with. So then I fitted the new bearings and got an even better pattern. So the old bearings (which weren't trashed) to the new bearings makes a difference, therefore the sliding fit bearings trick isn't actually foolproof.

To do it properly, you probably need to file out brand new bearings, and nobody wants to do that. Another interesting thing is that the different pinion spacer washers didn't make as much difference as I expected. So it's all a bit of a hazy practice to me. Maybe I'm trying to get too precious with it.
 
HZJ75 FARMER said:
I've just rebuilt another rear LSD diff. This time I had less confidence that nobody had been into it previously, so I tried your trick of making the old bearings a sliding fit.

I'm wondering though, what did you file your bearings with? I used a carbide burr in a die grinder and got there eventually, but it probably wore as much off the carbide burr as it did from the bearing races. You must have had something super hard.

Also worth noting, I had a few spare pinion spacers so I had several goes at it until I got a pattern that I was okay with. Not overjoyed with, but okay with. So then I fitted the new bearings and got an even better pattern. So the old bearings (which weren't trashed) to the new bearings makes a difference, therefore the sliding fit bearings trick isn't actually foolproof.

To do it properly, you probably need to file out brand new bearings, and nobody wants to do that. Another interesting thing is that the different pinion spacer washers didn't make as much difference as I expected. So it's all a bit of a hazy practice to me. Maybe I'm trying to get too precious with it.
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On the 567k km rear diff that came with my BJ60, sloppy maintenance and our local bodger mechanics had ensured that the outer pinion bearing was a loose fit on the pinion. In fact, the pinion was so sloppy that the shaft itself was worn, and the splines were almost gone too. Even on a brand new OEM pinion the old bearing was a loose fit. I didn't re-run a pattern after the final torquing on my front diff (with a crush spacer) but I was using the old bearing on a new race when I set the diff up.

I bought a new bearing to file out to fit my rear diff (which has a 33 mm pinion vs. the 30 mm pinion of the original). I'm not sure about Australia but where I am I can get a new genuine bearing sent from Japan for maybe AU$40 , shipped in a larger parts order. That's a lot less than the Toyota tool to pull the bearing out, which is the correct way to do it. In the end, I went solid spacer and now have an untouched spare pinion bearing.
 
flo17 said:
I see you have the same setup as my differential (see page 4 here: https://toyotamanuals.gitlab.io/RM0...0584e/repair2/html/frame_rm00000318p000x.html).
Have you found the part numbers for new clutch plates?


On my side, the parts are below spec:


  • Clutch plates: 1.97 to 2.03 mm
  • Thrust washers: 1.97 to 2.06 mm

Most setups I’ve seen have more clutch plates or thrust washers, which is why I’m asking.
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I didn't replace any clutch plates.

How far out of spec are yours? Mine were on the thin side of the spec, and a couple were just slightly below spec.

But I had no interest in the LSD itself, only the backlash of the spider gears. So all I concentrated on was using shims to get the backlash correct.

In my experience, and in my application, the LSD is a waste of time. Maybe I'm wrong. I'm welcome to hear from anyone who thinks they are any good.

If you want part numbers, have you tried looking up Amayama parts? You can either buy from them if you are prepared to wait a fair while for shipping, or you can just use them as an online parts book.
 
flo17 said:
I see you have the same setup as my differential (see page 4 here: https://toyotamanuals.gitlab.io/RM0...0584e/repair2/html/frame_rm00000318p000x.html).
Have you found the part numbers for new clutch plates?


On my side, the parts are below spec:


  • Clutch plates: 1.97 to 2.03 mm
  • Thrust washers: 1.97 to 2.06 mm

Most setups I’ve seen have more clutch plates or thrust washers, which is why I’m asking.
Click to expand...
Why not tell us your model and year.

70/80 Series LSDs went from 8 friction discs to 6 friction discs in around 1995/6.
 
Exact, I have a HZJ70 from 1999.

Regarding the thrust washer thicknesses, I have measured these :

  • 1.95 mm
  • 1.94 mm
  • 2.25 mm
  • 1.96 mm
  • 1.97 mm
  • 2.37 mm

The free length of the preload spring measures 33.18 mm.

A friend told me that he wound up the spring with a 1mm shim to give it more force and trigger the LSD more quickly.

I also checked on Amayama however width are not specified so I'm an not sure to order the correct one.
 
flo17 said:
Exact, I have a HZJ70 from 1999.

Regarding the thrust washer thicknesses, I have measured these :

  • 1.95 mm
  • 1.94 mm
  • 2.25 mm
  • 1.96 mm
  • 1.97 mm
  • 2.37 mm

The free length of the preload spring measures 33.18 mm.

A friend told me that he wound up the spring with a 1mm shim to give it more force and trigger the LSD more quickly.

I also checked on Amayama however width are not specified so I'm an not sure to order the correct one
Click to expand...
Thrust washers (the friction discs) are 41361-60340
Clutch discs (the steel discs) are 41385-60011

If you read back in this thread, I have explained that from factory there were thrust washers of varying thickness, to achieve the proper spider gear backlash fron factory. However, to the end user there are only standard sized thrust washers (2.00 mm) and the backlash is set by shims. These I have shown in this thread, with part numbers displayed.
 
Thank you for your reply and for the detailed information.
I will order the parts and try to adjust the backlash using shims as described.
 
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