1966 12 bolt needs some help - Chevelle Tech
Transmission & Driveline Transmissions and Differentials

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post #1 of 69 (permalink) Old May 13th, 20, 8:51 AM Thread Starter
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1966 12 bolt needs some help

The 12 bolt in my '66 is in need of some parts.

It has been a bit growly/noisey and the pinion seal started leaking pretty bad.

Went under the car and it turns out the yoke was a little loose with the nut I thought had loosened a bit.

Decided to pull the cover and found a fair bit of metal in oil and decided to pull axles and carrier/crown to inspect.

The carrier had no side shim preload and pretty much fell out with caps removed.

The left side shim has had the race spinning on it and is missing material, the race bearing face surface has rough spots and missing material and the 80% of the roller surfaces are rough with missing material.

I think the gear set looks okay (can still see machine marks on the load side) and was changed by the previous owner and that's what started this mess, the car came with 4.10 and the gearset is 3.73.

I am leaning towards getting a local shop the rebuild it just for peace of mind and a warranty, what ever that's worth if there's a problem after.

The car is now 396 with m20 the 12 bolt is a posi and may swap to 454 of some configuration and probably end up with 550-600hp.

Is there any "should do" upgrades that should be done while its apart??

Thanks,
D
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post #2 of 69 (permalink) Old May 13th, 20, 9:58 AM
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Freddie
 
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Re: 1966 12 bolt needs some help

The '65 and '66 12 bolt rear ends are a little more difficult to rebuild due to the thin shims used for the differential. These shims are no longer available, so you have to make due with the after market shims and try to get them in place without damaging them. It's very hard to get any bearing preload with these shims.

Use quality parts when rebuilding. The USA Standard kits are pretty good if you want an economy kit. The Yukon kits are better. If you can get a kit from Tom's Differentials it's going to be the best. You might get by with using the gears again, but sometimes when you get a lot of movement in the gears like you had with the pinion nut and shims not being tight, it will cause abnormal wear on the gears and you might get some noise. Inspect the axles where the bearings run on them and if they have any wear or pits then replace them with quality parts. Be sure that the person who rebuild it knows how to set the pinion depth, bearing preload and backlash. Most shops don't have any idea how to do this.


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post #3 of 69 (permalink) Old May 13th, 20, 12:45 PM
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Greg.
 
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Re: 1966 12 bolt needs some help

Listen to Freddie if you are only going to do a Rebuild

What are you using your car for ?
Street/Hwy Cruzin only ?
Street/Strip occasionally ?

I drive my 67 on the Street/Hwy and go to the Track every Spring/Summer/Fall weekend that it does not Rain

So I had a Shop with 35 Years Experience in Racing & in the Business
Rebuild my Eaton Posi Spring Dif 12 Bolt and a year later it was back to one legging it at the Track etc.
this cost me 1/2 the Price of a New Rearend

So I bought a S60 from Strange for my 67 Chevelle with options that would make it last for the way I use my car ;
- Helical Gear Dif/Posi Unit https://www.strangeengineering.net/p...-s60-n-5.html/
- 1/2" Studs for a Chevy Wheel Pattern
- 11" Drum Brakes with Ford Ends
- Chrome Moly Yoke https://www.strangeengineering.net/p...ge-s60-n.html/
- LPW Alum Cover with Main Cap Bolts
https://www.strangeengineering.net/p...or-brace.html/
- Gearing choice
- 35 Spline Axles
https://www.strangeengineering.net/p...g-mounts.html/

https://www.strangeengineering.net/
RAIDER SS and 64tempestwagon like this.

67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/09/08
60' = 1.547
1/8 = 7.311 et / 91.76 mph
1/4 = 11.595 et / 114.28 mph


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post #4 of 69 (permalink) Old May 14th, 20, 2:08 AM Thread Starter
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Re: 1966 12 bolt needs some help

That's always the problem, unless you really know the place all you can do is go by gut, google, or word of mouth.

I was by the place I may take it to if I go that route and the had a look at everything and said case is good, gears are reusable and one axle is bad enough where bearing runs to replace.

So depending on axle cost, which he said would be $250 at the highest new Timken bearings, seals and assembly they could have it done for $1000-$1100 with one year warranty.

They have been there as long as I can remember and I'm half a century old now.....
Also claimed that all the dealerships in town use them when needed for Diff repairs.

Greg,
How much was your Strange diff delivered to your door?
how much difference is the price now then when you bought?

Thx,
D
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post #5 of 69 (permalink) Old May 14th, 20, 2:32 AM
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Re: 1966 12 bolt needs some help

HI
Diff crown wheel and pinion pattern , backlash and bearing preload takes time . Actual assembly time is only half the job .
Having a wide shim selection/ availability is critical for good setup which many shop donot have .

I have had 9 inch centre,, pinion preload to much [bearings notchy ] ,, carrier bearings etch corrosion ,, metal filings in housing ,, pinion depth to shallow by .007 thou
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post #6 of 69 (permalink) Old May 14th, 20, 7:59 AM
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Re: 1966 12 bolt needs some help

Quote:
Originally Posted by big gear head View Post
The '65 and '66 12 bolt rear ends are a little more difficult to rebuild due to the thin shims used for the differential. These shims are no longer available, so you have to make due with the after market shims and try to get them in place without damaging them. It's very hard to get any bearing preload with these shims.

Use quality parts when rebuilding. The USA Standard kits are pretty good if you want an economy kit. The Yukon kits are better. If you can get a kit from Tom's Differentials it's going to be the best. You might get by with using the gears again, but sometimes when you get a lot of movement in the gears like you had with the pinion nut and shims not being tight, it will cause abnormal wear on the gears and you might get some noise. Inspect the axles where the bearings run on them and if they have any wear or pits then replace them with quality parts. Be sure that the person who rebuild it knows how to set the pinion depth, bearing preload and backlash. Most shops don't have any idea how to do this.
All of this is spot on. I would venture a guess that the gears will be nearly impossible to set up properly without the proper shims, for a shop not familiar with the early Chevelle 12-bolts and also depending on how long you ran them this loose. Shims are difficult to come by for sure and my supply is slowly getting smaller though I do have several in the original GM packaging. Shim pack part numbers were 3907088, 3907089, 3851480/81/82/83/84 and 3876174 all of which contained three or four different thickness shims. I've attached a couple of photos of the shims.
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post #7 of 69 (permalink) Old May 14th, 20, 9:09 AM
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Freddie
 
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Re: 1966 12 bolt needs some help

I've got a stack of those shims too, but they are hard to find now. I bought several packs when they were discontinued just so I would have them. It's easy to damage them when driving them in.

Is that a Wavetrac sitting there? Someone spent some money!


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post #8 of 69 (permalink) Old May 14th, 20, 6:18 PM Thread Starter
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Re: 1966 12 bolt needs some help

Yes the shims as they are now, left shim is scarred/worn a bit from movement measure .080 each side and the pinion preload probably went away the same time the seal started spewing/failed which was maybe 400 miles of driving but who knows for sure how long the yoke has been loosening.

Possible scenarios I see maybe:

1 At best everything goes together and patterns out for them with no noise.

2 Would be patterns out with noise and I am ok with noise.

3 too noisy and out apart and change gear set.

4 seems good then gets worse starts eating itself and we're back here again.


Dave are you offering access to your shim stash?
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post #9 of 69 (permalink) Old May 14th, 20, 6:19 PM Thread Starter
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Re: 1966 12 bolt needs some help

Greg,
How much was your Strange diff delivered to your door?
how much difference is the price now then when you bought?

Thx,
D
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post #10 of 69 (permalink) Old May 14th, 20, 7:50 PM
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Greg.
 
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Re: 1966 12 bolt needs some help

Quote:
Originally Posted by Darren Trudeau View Post
That's always the problem, unless you really know the place all you can do is go by gut, google, or word of mouth.

I was by the place I may take it to if I go that route and the had a look at everything and said case is good, gears are reusable and one axle is bad enough where bearing runs to replace.

So depending on axle cost, which he said would be $250 at the highest new Timken bearings, seals and assembly they could have it done for $1000-$1100 with one year warranty.

They have been there as long as I can remember and I'm half a century old now.....
Also claimed that all the dealerships in town use them when needed for Diff repairs.

Greg,
How much was your Strange diff delivered to your door?
how much difference is the price now then when you bought?

Thx,
D
The S60 came ready/delivered to install with the Brake Lines on it and the Options I wanted
just insert Upper Bushings and Hook up Rear Brake Lines put in the Breakin Gear Oil of 4 +1 Pints
NO ADDITIVE NEEDED
Already set Up, so drive easy for 500 Miles and change Gear Oil again after

Cost me $ 3,500.Cdn which is about $ 2,450.us in late 2013

The Basic # PRSA05 I bought starts now at $ 2,450.us and then if any Options to be added to that

I do not think you could get a better deal IMHO

67 Chevelle Malibu SS Cdn
Born 283 / PG / A51
468/TH400 2,500 stall/ S60 3.70 Gs
Prev Best on M/T ET S/S #3454 street Tires/Dress 2018/05/20
60' = 1.664
1/8 = 7.532 et / 91 mph
1/4 = 11.814 et / 115 mph
NEW Best with 3,500+ Stall TC 2019/09/08
60' = 1.547
1/8 = 7.311 et / 91.76 mph
1/4 = 11.595 et / 114.28 mph


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post #11 of 69 (permalink) Old May 14th, 20, 8:32 PM Thread Starter
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Re: 1966 12 bolt needs some help

Thanks Greg, perhaps this is the time to envoke "buy once cry once" and then done.
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post #12 of 69 (permalink) Old May 14th, 20, 9:09 PM
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Re: 1966 12 bolt needs some help

Quote:
Originally Posted by big gear head View Post
I've got a stack of those shims too, but they are hard to find now. I bought several packs when they were discontinued just so I would have them. It's easy to damage them when driving them in.

Is that a Wavetrac sitting there? Someone spent some money!
Yes, it is but setting it up in an early Chevelle 12-bolt has a particlar challenge. The carrier bearings Moser sells to install it are a 32010X *** metric bearing which have cups (outer races) with an 80 mm (3.1496") o.d. that they (or Autotech/Wavetrac) centerless grind down to the nominal o.d. of the standard LM603012 3.0625" to fit in the 12-bolt carrier bearing saddles. The problem is that this metric bearing's roller cage extends approximately 0.035" beyond the end of the cup making it impossible to install the standard GM selective shim to set the preload and adjust gear back lash. Moser offers an Install kit but the special 0.102" thick shims they provide may not work in the early housing. I was able to locate a metric bearing that uses the same cone but has a 1.5 mm wider (17 mm total) and 82 mm diameter cone which could be centerless ground down to the required 3.0625" o.d. and would allow the use of standard GM shims. Problem is, and this is a big problem, the Timken bearing (XAB-32010X - YKB-32010X) is an OEM only part and is not available for resale and I don't even know what the application is. However, I was able to locate two original KOYO bearings of Japanese manufacture which I will have within 8-10 days and I'll go from there. Picture below illustrates the problem and sorry for cluttering up your thread Darren.


Quote:
Originally Posted by Darren Trudeau View Post
Yes the shims as they are now, left shim is scarred/worn a bit from movement measure .080 each side and the pinion preload probably went away the same time the seal started spewing/failed which was maybe 400 miles of driving but who knows for sure how long the yoke has been loosening.

Possible scenarios I see maybe:

1 At best everything goes together and patterns out for them with no noise.

2 Would be patterns out with noise and I am ok with noise.

3 too noisy and out apart and change gear set.

4 seems good then gets worse starts eating itself and we're back here again.


Dave are you offering access to your shim stash?
Yes, if you know what you need I will gladly send them to you.
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post #13 of 69 (permalink) Old May 14th, 20, 9:32 PM
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Freddie
 
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Re: 1966 12 bolt needs some help

Wow, what a pain. You could use a housing spreader and put the shims in with the differential.


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post #14 of 69 (permalink) Old May 15th, 20, 11:20 AM Thread Starter
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Re: 1966 12 bolt needs some help

Dave, thread cluttering is good it offers up potential useful info for anyone looking for it.

So Dave it seems like you are likely to know the answers to my concerns of rebuild and the likelyhood of degradation vs 4k outlay for new strange diff.

1) Do you think the pinion crush loss was because someone changed the gearset form 4.1 to 3.73 and didn't get new crush sleeve or new nut??

2) Chicken or egg first question here, do you think the left carrier race was moving on the shim because the bearing/race started failing or did it move because there was a lack of crush/press in cap/saddle area to hold the race in place.

3) If you could send me the same .086 shims (I think I read the notches right they measure at .087 with vernier caliper) is it likely to have the proper 0.010 press fit as someone above mentioned and likely the gears will pattern proper, be somewhat quiet because I really don't know if the set of 3.73 were setup properly or just stuffed in using what they had from 4.1 setup.

4) Also the 3.73 diff may be a whole different diff that was from another car would have been many to grab back in late 60's

How likely are the above situation to occur again?

Does anyone know if the diff housing was identified to the car from factory with serial numbers like the engines were?

Maybe I should get some pattern paint and assemble it to see where its at?

Sorry for the 20 questions. I got cold feet as I had a diff in a truck failed, rebuilt and had to be rebuilt again when a side shim broke

Thanks,
D
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post #15 of 69 (permalink) Old May 15th, 20, 11:35 AM
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Freddie
 
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Re: 1966 12 bolt needs some help

The pinion nut backing off is not unusual, It happens all the time. I use a new nut when I can and I always use red Locktite on the threads. Even with this I have still had a few back off.

The VIN was not stamped into the rear end like it was with the engine and transmission. I don't know why, but it wasn't. Checking the casting date and build date will help you determine if it is original to your car or not.

Most of these rear ends do not have what I consider the correct crush on the bearing race. Most of the time I find that the bearing bore is about .003 larger than the bearing race. You can tighten up the bore by carefully removing material from the mating surface of the cap. Be VERY careful if you do this.


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