HOW TO: Rebuild the MK3 Rear Differential.

[Asterix]

I have stock sawblades with 225/50 Continental DWS tires. Nothing fancy. I can see how much grippier tires probably would reduce the hopping.

The "regular" Red Line 75W90 has too much slip now. But, this just means I need to find something in between. The bottle of friction modifier says on it 4% is for broken-in units, and up to 8% for break-in. If we can believe the TSRM, the diff takes 1.3 liters of oil, so 8% is 104ml.

I won't have a chance to try another mix until the weekend, so I have all week to decide.

 

[TurboStreetCar]

Yea thats prolly why. Seems you went threw all the effort for maximum "limited" in limited slip but now your tires cant keep up hahahaha.

Im going to change the fluid in the spring in my car and ill prolly put in the same 25ml.

 

[Asterix]

Yeah, well... I rebuilt my diff because there was way too much play in the R&P, I thought the bearings were making noise, and I wanted more grip. And, I figured while I was in there, I'd make sure I had more grip than I needed, because it's so much easier to add slip than grip.

Plus, this is my toy/project car, and it was fun to do.

 

[gp-7mgte]

Glad I found this my thread, my LSD doesn't seem to be doing its job any more. Have been get stuck in snow with only one wheel spinning. Looks like it's time for a rebuild. Is there any additives I could try using to help in the meantime to a rebuild?

 

[Asterix]

To add grip, you need to drain the oil and refill with oil that has less slip additive. There's nothing you can add to reduce the slip. Start with Redline's 75W90NS and add the friction modifier (also from Redline) until it's as quiet as you like. If you add too much slip, you get to start over again. With a stock 89+ unit, it probably won't take much friction modifier to be quiet. I'd experiment with that first.

Most GL5 oils with the friction modifier already in have too much, so you end up with not enough LSD action.

 

[TurboStreetCar]

Correct, Friction modifier makes the clutches slip more. IF you really want it to lock up, drain and refill with Redline NS. There is ZERO modifier in that fluid so you would have the most grip possible.

Keep in mind though, its a "LIMITED slip" for a reason. It isnt a locker, if one tire has traction and the other is on ice, you still may be stuck.

 

[3p141592654]

Also, after a drain and refill it takes a while for the new oil to work its way between the clutch plates.

 

[gp-7mgte]

Thanks for the info, I will try it out soon.

 

[Bru]

Why does the diagram in the 1987 Toyota service manual differ from what I am finding in 2 LSD differentials that I have opened and even yours from the pictures? In the service manual they have you putting the square pinned retainer in the right hand side of the case and the round one in the ring gear side of the case. The two differentials that I have opened are the other way around from the factory. Maybe it's interchangeable?

 

[TurboStreetCar]

Yea, looking back I see they are opposite. I don't believe it matters as long as the square plate with the holes is on the same side as the pinion support that has the two posts to key them together.

This prevents the spider gears from twisting the spring.

 

[black89t]

So I'm in the middle of swapping over to 3.73 from 3.91 because I broke the ring gear on my 3.91 and had a spare 3.73. Also wanted the extra mph in 4th and just see how I like it since I've had 3.91 ever since I did my swap. I tore it down to put in a newer set of clutch packs I had and to add shims/ the extra spring from the weir kit. Got that done checked backlash and it was good at 6-7 thousands but the contact pattern isn't ideal. It's on the toe of the drive side pretty bad. The coast side looks better but still on the heel a little much. It's looking like the pinion depth is the issue. I really didn't want to mess with doing the bearings. especially adjusting pinion depth because that will require pressing the bearing on and off that everyone seems to have a nightmare doing. Looking at turbo street cars pattern his is sorta similar. thoughts??

drive side



coast side

 

[TurboStreetCar]

It does look low on the tooth. Mine was low, but centered higher. Yours seems to be centered right at the bottom of the tooth. Maybe contact weir And see what he thinks?

We're those used gears?

 

[black89t]

It does look low on the tooth. Mine was low, but centered higher. Yours seems to be centered right at the bottom of the tooth. Maybe contact weir And see what he thinks?

We're those used gears?

yeah its the diff that was originally in my car. it's never seen much abuse though. i found this thread on sf where his pattern looked close to mine and he got a really nice pattern after moving the pinion away from the ring gear. if i recall this diff wined some and that was part of the reason i went to a 3.91 i had plus for autox at the time.


http://www.supraforums.com/forum/sh...-Experts-Need-Opinion-on-Ring-Contact-Pattern


i plan on launching pretty hard with slicks and know getting the gears to mesh right has a lot to do with their strength. was curious if others had this problem with their mk3.

 

[TurboStreetCar]

When I did my rebuild I reused the same gears. So all I needed to do was match the pattern that was already there. If you don't get the pattern and backlash set up how it was, you'll be riding them on a different portion then was already worn and could result in noise.

 

[black89t]

yeah this diff i took apart to just do the clutch pack/shim/spring. put it all back how it was and this is the pattern i got. i do recall this diff whining. i'm curious what will happen if i adjust the pinion if it will run quieter and get a good pattern so decided to tear into it. got the pinion bearing off pretty easily actually. just heated with a mapp gas torch and pressed it out. i have the same press as you too. it made some noise but nothing out of the ordinary when pressing stuff. the shim in there was .076-.077 i'm guessing its the .0764. thinking i'm going to order the bearings get the .0669 or .0681 not positive which one yet then throw it together and see how it looks. those are the two thinnest on the chart.

 

[Asterix]

When checking the pattern, it's important to get the side bearing cap bolts torqued a bit. The diff case must be solidly in its place before you measure anything. I will also suggest making sure the outer races and the carrier are perfectly clean so they sit together properly.

The TSRM doesn't say to install the side bearing caps before checking backlash, but it's a good practice anyway.

Are you installing a solid spacer to replace the crush sleeve?

 

[black89t]

finally got to messing with this. ended up getting a .0717" shim to play it safe and put it together. the dam pattern isn't really looking as good as id like it still. you can see the prussian blue isn't as thick at the top but i'm still not happy with it. the .0669" is the thinnest looking like that might be more where it needs to be.

and i have the caps torqued when checking the pattern and all. it lays pretty consistent patterns with the prussian blue. also doing the crush sleeve eliminator have had one for a while now. pretty sure its a yukon its high quality and fits perfect though! was sorta a pita getting the preload right but happy I'm doing it.

the hardest or more so annoying part for me was i installed the larger race and looked to see if it was seated. there was a small space on one half and was flush on the other side. so i knocked it back out (brass drift work best doesn't bounce around and won't damage anything) to find that side of the case had a slight chamfered edge making it look like it wasn't seated. knock it back it with the old race agian and was good to go :biglaugh:

 

[Piratetip]

Fun process isn't it?

 

[black89t]

Fun process isn't it?

its a little tedious but i don't mind. also like to know its being done right.

ended up going to a local off road shop that does lots of lockers and gears. they had some shims they gave me. rockys off road ftw. i got a .050, .010, and .015. tried .060 first and it put it on the opposite side too much. then went with .065 which got me a pattern im happy with. its a little on the toe side but with used gears apparently you want it more so there if it has to be one or the other. the new bearing presses on and off easy too nothing like the old one thats been on there forever so thats not anything to worry about. another thing i did was the shims on the diff i swapped to get the backlash a little tighter. was .119 on the ring side .121 on the other. went from .007-.008 to .006-.007 and made the pattern a little deeper in the ring gear. think this is going to have a lot to do with it holding up to launches better. i'll let you guys know how it runs when i get it in the car!

this was with the .060



the .065



this was after the backlash adjustment and the pattern im going to run.



the aftermarket shim. it actually has more surface area for the bearing to seat on which is nice.



and cause i know we all like pics heres my broken ring gear. looks like it wasn't meshing good either how it just broke the heal off. also you can see the 3.73 has larger teeth than the 3.90 which is a plus.

 

[Piratetip]

Also step up the thickness on the carrier bearing shims for the preload?