HOW TO: Rebuild the MK3 Rear Differential.

[Asterix]

I wanted to make sure I could get a rear pinion bearing off intact, in case I had to do so while setting up the rebuild. There's a chance I'll need to change that spacer that goes on under it. I paid about $140 for a new bearing, and it was somewhat hard to get, so I really don't want to mess it up. The new bearing on a new pinion should come off more easily, though it still took quite a bit of force to put on.

The next fun is the companion flange is a really tight fit on my new pinion. I can't just tap it on with a plastic hammer, even after a thorough cleaning. After a little searching I found someone describing their Toyota truck diff rebuild, where they pressed it on and off a couple of times to loosen it up. That's my plan, too.

 

[Asterix]

Argh! It looks like my new ring and pinion doesn't fit. I tried the thinnest side gear plate washer (spacer between the case and carrier) and the thinnest pinion spacer under the rear bearing and I get only about 2 mils of backlash on the ring gear. Time to ask Weir for advice, as he sold me the ring and pinion. I need to get 8-10 mils of backlash according to the paper that came with the ring & pinion.

 

[TurboStreetCar]

What brand R&P is it?

 

[Asterix]

Weir won't tell me who made the R&P. It's European - that's all I can tell. I could find no other source for a 4.3 set.

The part that confuses me is when I did some quick dimension checks between new and old R&P, they measure very close to the same (ring gear height, pinion gear height & diameter). Maybe I'll check more carefully. Then again, we're talking about only a few mils here. I'd rather not take the ring gear back off the diff case as I already bent over all the little tabs on the retainer plates.

Maybe I'll try swapping the two case side bearings and see if that helps.

I just tried removing the rear pinion bearing outer race from the carrier, cleaning everything carefully, then reassembling. Since I got the same measurements, that's not it.

Just swapped the side case bearings, cleaning the surfaces carefully and making sure they are pressed on all the way. I get the same measurements again, so that's not it either. It's looking like the ring & pinion aren't quite right.

Update: Weir is confident the R&P will fit. First, I put the spacer under the pinion gear back to the one that was there, as it doesn't really affect backlash. I ordered the thinnest side washer (90201-52001) and a "matching" one (90201-52023) so I can get preload on the side bearings. My cobbled-together washer probably isn't good enough. He also said to install the side bearing caps, torqued to spec, before measuring backlash. Once I get the parts, I'll check again. Backlash changes just about 1:1 for side washer thickness, so it's pretty easy to then order the one I need if the backlash is too much.

(The 2 side washers my diff came with measured 5.82mm and give good preload, which I checked. If I buy a thinnest one at 2.58mm, a 3.24mm one one the other side should give me good preload again.)

 

[Asterix]

Update: I received my two new side washers, -52001 and -52023. Together they gave me good preload. However, my backlash is still 0.002".

Weir has offered to make me a side washer that's 0.096" thick, which would give 0.008" of backlash. What I may do is grind down one side bearing face so it will press 0.006" further onto the case, moving the ring gear 0.006" away from the pinion. Then I would shim the other side bearing up 0.006" so I can use the two new washers. I have a granite lapping stone and fine sandpaper; it should not take long to remove 0.006". The flatness isn't super important on that face of the bearing. I also have shims from McMaster that fit perfectly under the side bearings.

Toyota says the minimum backlash is 0.005", so I may go with that. It depends on how quickly my grinding goes. Bearing steel is very hard.

Weir said this is the first time he's had a ring & pinion not fit with the standard washers from Toyota. Lucky me.

Update: I ground down one side bearing, and after numerous tries with different shims, I found 6-8mils of backlash and the proper preload. Turns out I only needed to take 4 mils off that one side bearing, but I needed to add another mil of shim on the other side to get enough preload. This R&P has about 2 mils of variation for backlash.

 

[Asterix]

Next, I went to check the pattern, which looks funny to me. It's not bad for one tooth, for each drive and coast sides, but they don't match. That is, where the drive side is fine, the coast is to the inside.

I need to check in more places around the ring gear and see what it's like there. Since this R&P has a variation of about 2 mils for backlash, I suspect the pattern varies as well. I just hope I can find a place where the pattern is good enough everywhere.

Update: After painting more teeth (total of 8), the pattern looks pretty good to me. I've sent photos to Weir for his opinion.

 

[Asterix]

Update: After painting again with prussian blue and then some almond Rustoleum oil paint, I got better photos of the pattern, which I can post if anyone wants to see them. Clamping the carrier down to my workbench probably also helped, as I could get more force on the gears.

Weir has declared my pattern to be good. Yay!

I need to add another thou of shim under the tooth-side side bearing to get a bit more preload, but other than that it's set up. I should be able to get it complete and back on the car this weekend.

 

[Asterix]

All done! It's back in the car and seems to be running well. Between the exhaust and worn-out transmission noise, it's hard to tell... The hardest part is now not romping on it for 500 miles.

 

[TurboStreetCar]

Glad to see you got it sorted. How do you like the 4.30? What do you use the car for?

I feel like I hurt my cars performance going to the 3.91 from the 3.73. It spins so easy, feel like less gear is better for street play over 500hp.

 

[Grandavi]

I thought a 3.73 was better for high speed, therefore would be harder to spin. Maybe in thinking backwards?

 

[TurboStreetCar]

Exactly right, witch is why I feel like I hurt my cars performance going to the higher numeric (shorter ratio) 3.91 from the lower numeric (taller ratio) 3.73. I'd be able to launch with less wheelspin if I kept the 3.73.

Can't imagine a 4.30, I don't think id have traction in third. I'd love to try a 3.55.

 

[Grandavi]

Good, because I am putting in a 3.73 this summer (I believe the 1988 MA70 in Canada with a 7MGTE came with the 3.91 diff which is what I believe is in mine now). Mine is a tiny bit clunky and I found a 3.73 with very low mileage (about 30k miles) for 1200 CDN.

I'm not sure if that's a good price, but the guy I am buying from will stand behind it so if there is any issue he will do the R&R. (in the end, that can chew up any savings on an "unknown" cheaper one)

I'm at 400 whp currently so I think the 3.73 will be a good match. Most of my driving is done between 50-85 mph, and the bulk of my mileage is on longer highway drives.

Looking at rebuilding and this is way out of my league. Don't have the time/skill/equipment... lol. I envy you guys. My precision is limited to 1/16" ... lol

 

[Asterix]

Glad to see you got it sorted. How do you like the 4.30? What do you use the car for?

I feel like I hurt my cars performance going to the 3.91 from the 3.73. It spins so easy, feel like less gear is better for street play over 500hp.

I have an NA... 4.3 is necessary. It's my daily driver, mainly in the winter. Finding another used 4.3 LSD in my neighborhood proved to be impossible.

 

[Asterix]

After a few weeks, I finished driving the 500 miles recommended for break-in. I used Valvoline as break-in oil. After draining that, I refilled with Redline 75W90NS, and added 20ml of the slip additive. It took very little time to start gripping like crazy, like backing out of my garage and going the 100' to the street. So, I added 20ml more. Then 10ml more, etc, until I had added the whole bottle (120ml). It's still gripping hard, but it's drivable. I drove it a couple of miles around the neighborhood, and it settled a bit, but it's still too much. The slightest deviation from straight, and I can feel it. So, Monday I'll stop by the store and get some more additive. OG Racing is near my office.

The Valvoline must have a huge amount of slip additive in it. It didn't make any noise whatsoever with that oil. Of course, it didn't grip very well either.

 

[3p141592654]

If that doesn't work, I'd try a refill with Mobil 1. My experience with it was that it resulted in too little LSD action on my stock diff.

 

[TurboStreetCar]

I have a similar experience. The "Carquest" oil i used initially with no additive was butter smooth. The Redline NS i put in after made the rear VERY loud and i thought something had come apart inside the diff. I added like 20ML of redline slip additive and its better but still makes noise.

I was going to add more but the more you add the more you counter act the extra grip from the MAX-Grip spring. Whats the point of adding the MAX-Grip spring to just add extra additive to make it slip and be smooth?

Im just gonna live with the noise/chatter. I know its locked up and thats what i wanted when i built it.

 

[Asterix]

I hear ya, Nosechunks. I want good grip too, but where it is now, the car hops around tight corners under power. That's not good. I can live with the groaning and such, but not with hopping.

After sitting overnight, it's slightly less grippy, but is still too much. I'd like it to be smoother than it is. Not Valvoline/Mobil 1 kind of smooth, as they pretty much neuter the LSD. I'll find a happy medium, I'm sure, once I get another bottle of Redline's slip juice.

3p, I gave up on Mobil 1 a very long time ago for exactly that reason. I've been mixing Redline's regular and NS for years. With this new rebuild and Weir's spring, I just need to find my mix again.

 

[3p141592654]

NP. Just giving you options in case you hadn't been down that path.

 

[Asterix]

(Thanks for the suggestion, 3p.)

Today I drained my NS + 120ml of additive and replaced it with "regular" Red Line 75W90 I had on my shelf. I think it's closer to what I want, but on the slip side. I'll know fer sure after driving the car to work tomorrow, as I just tooled around the neighborhood a little bit today. On some tight corners, there was a little groan, but no popping like before.

Maybe next weekend I'll try 1qt of regular and top off with NS. That may be the recipe for me. Or, I'll just add more slip juice. Not sure yet...

Maybe I'll bug Red Line and see if they'll tell me how much slip juice their regular 75W90 has in it.

 

[TurboStreetCar]

Oh wow. I don't have any hopping around corners even before I put and additive in the Redline NS.

What tires do you have on the rear of the car. I have 275 drag radials so maybe that's why I didn't have and hopping.

When I looked into it IIRC redline recommended 10% mixture of additive.