Friday and today I was over at Mike's rebuilding the diff out of my '71. It's a pretty untouched, 120K mile, unit with 3.08 gears.

It's an interesting process to see what goes into doing one off these rebuilds properly. So many vendors offer "rebuilt diffs" that don't really deserve to be called "rebuilt".

I got to do much of the work with Mike directing (he enjoys the role of Yoda) and doing the tricky stuff. What we did is all part of Mike's standard rebuild so if you send your diff in, this is what you'll get done.

First step is a tear down and evaluation of what's going on. My diff wasn't giving me any problems, it was quiet. The primary reason for the rebuild was to install a set of 3.73 gears.

Tear down showed a ring & pinion that was completely worn out. This is shown by running a pattern with gear paste. My pattern was across the entire teeth.

The bearings were also worn out as shown by the rollers and the races having a rough surface.

After tear down all the parts went in a chemical bath to get paint and oil off. After that they are hosed off with water and blown dry.

Parts are then sand blasted and cleaned again. And gain. And again. And finally with lacquer thinner. Cleanliness is taken seriously.

The carrier gets the ring gear flange cut as they are always uneven. mine was 0.003" out which Mike says is expected. Back of ring gear of honed with a stone to remove high spots.

Carrier openings are ground and polished to avoid stress fractures.

Bearing caps are checked for stretch (mine were OK) and ends honed with a stone.

Posi clutches are shimmed to remove slop.

External surfaces are painted. Here's the case looking all nice.



Side yokes are checked for wear, mine were good as I replaced them a few years ago. With the way Mike sets up the posi there's no end play on the yokes at all.

New ring & pinion setup was done with setup (slip) bearings. The pattern came out great with the first pinion shim we tried. It helps to have Mike's experience!





New bearings are pressed on, parts are re-assembled and pattern is checked again. Housing and cover mating surfaces are honed with a stone to help prevent leaks.

Finally the diff is filled with fluid and run on the lathe for initial break-in.



The whole process from start to finish took 14 hours. A lot of work goes into these diffs!

 

Wish I lived close enough to Mike to work with him... great post, needs more pics.

 

Looks like a fun time!

Mike definitely knows these things and does great work.

So 3.73's huh????? Hmnnn........what are we planning???

JIM

 

I wish you guys had called me so I could have come over and got in the way. Great work as always. mike...

 

The 3.73's have been on my list for years, just never seemed to get around to it. With the 3.08's and the TKO I kept finding myself in between 3rd and 4th gear on city streets. Now I can keep it in 4th most of the time. I'll also be able to use 5th more.

Do you have yours running yet?

 

Great pics and write up Zwede. Really makes me wish I had known about Tracdogg when I had mine rebuilt so many years ago. I am sure mine is one of those that got thrown together as quick as possible. It makes no gear noise but it leaks at every yoke seal. Grrr.

 

Mike rebuilt my trailing arms and my '81 differential. He is very precise in his builds and offers very fair prices. He's a pretty good guy too.

Nice write up zwede.

 

Yoda???
It must be the hair
I have to admit, Markus being a computer guy, he is a damn good mechanic.
Even though the diff was quiet and working fine it was flat worn out. He did stub axles and a clutch pack quite a few years ago but other than that everything else was original. Time had caught up with it.
After the diff was fully set up I had him strip it down and scrub everything one more time. Except for the machining Markus did all the work, including polishing the carrier. He can paint good also!
One point I need to make. Since we set up the clutches without springs the stub axles have nearly 0 endplay. This is because the spider gears are always in constant mesh. If the springs were used then .005-.008 end play is required.
Mike

 

Mike, I need your number again. I found that if you drop your cell phone in a tub of laquer thinner.....it melts.
Mike

 

Steve,
Your spindles showed up Friday. I'll have your arms this week.
Mike

 

Mike did a bunch of parts on my two cars and so far I haven't been able to tear anything up. I'm still close to the last in the group I race with but Mike says if I can afford it he can fix that too.

Bill

 

Thanks for posting this zwede. Mike does excellent work and is a stand up guy.

I have a Mike's steel cap rebuilt '82 diff in my '73.

 

We actually toyed with the idea of putting one of my caps on Markus's diff. But workload and lack of time prevailed.

 

I enjoy my field trips to Tracdogg2's. I get visit his shops often, and get sound advice.
Zwede, did you transport your diffy in your spaceship/car-Tesla...

 

Yep, hauled the diff in warp drive (that's what I named the car in the mobile app). Diff fit in the little cubby in the trunk. The massive trunk still amazes me. I had a 55" TV in it and it made the TV look small.

 

Maybe I should add TX to my list of places to move to when I finally get sick enough of CA...

 

Oh yeah...running good. Hope to hit chassis dyno next week....couldn't make it last week. Need to see if it's actually making any power! Feels good. Had a good "slip and slide" ride in the 145-150 mph range the other day. Couldn't put my foot in it even at those speeds without spinning on a very mild 91 octane tune!

JIM

 

Tracdogg2 is the man! He set-up my diff a few years ago. He built it with some abusive auto-x action in mind. He is watching to see how the diff handles the abuse. So far no issues. In fact, I dropped it out and he checked it out about 1-year ago - virtually no wear! I also had him rebuild my M-22. That thing was totally worn out. We'll see how both handle the new power plant - a Dart 415 is on its way soon!
Gary

 

Update: Ran into a snag where my fairly new front diff mount came out in crumbles. Go repro-parts!

Got a NOS GM bushing off ebay but it delayed me a few days.

This morning I bolted the wheels back on and took it for the first drive. Notes I made to myself:

• EFI rocks. After sitting 2 weeks it fired right away and ran perfectly.
  
• Gears setup correctly (thanks Mike) will not make any noise, even during break-in. I never heard a peep out of them.
  
• I didn't add any posi additive as this is break-in fluid that will be changed in 100 miles. Even without the additive I didn't notice any chattering.
  
• 3.73 gears made all the parts of the car work together. Now the engine is in its happy place, the Tremec TKO gear spacing is right and the whole car feels happier.
  
• 5th is perfectly doable from 60 mph and up. Nice.
  
• I can now navigate my back allay and driveway in 1st without slipping the clutch.
  
• 4th is good for most city driving, 37-50 mph.
  
• The old rule-of-thumb of 1 st having to be a 10:1 overall ratio is bunkus. I was at 10:1 with the 3.08s. I'm now 12:1 with the 3.73s. I much prefer 12:1. It's better in every way. Driveways, parking lots, taking off from a light.

 

Sounds good....and yes....more first gear just makes everything nicer. Mine could use more first gear...but can only go so far with my trans.

JIM