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Post Info TOPIC: Removal and rebuild of the 8.875" 12 bolt.


Poncho Master!

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RE: Removal and rebuild of the 8.875" 12 bolt.


Always a pleasure reading your posts Mark, keep up the good (great) work and thanks for taking the time.

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Barry -

2 x 68 Beaumonts, 1post, 1 hardtop (projects)

2x 65 Chevelle 300 deluxe (projects)

69 SS396 300 deluxe post

 

 

 

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Canadian Poncho Superstar!

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Thanks Barry,

It's always fun to take pictures and review what you've done later. And perhaps someone else might see such a project as just a little less "Black art".



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


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good idea with the coffee can mark wink

most 10/12 bolt rears i've done, a .028 shim is usually dead on.



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Canadian Poncho Superstar!

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Dave, now when you say the .028 shim, do you mean the solid spacer or the depth shim?

 



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


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oops, depth shim wink



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Canadian Poncho Superstar!

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I've got a .031 in place for the depth to start. 

Do you think I should start at .028? Really not a big deal to change, since I have a removable inner test bearing in place!



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


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try the .031, good place to start...



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Canadian Poncho Superstar!

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Back at it after a vacation;

Made a set of locating pins that screw into the ring gear and help locate it correctly on the carrier. Cut some bolts down and slotted the ends for removal.

pins.jpg

Made sure the mating surfaces were completely burr free. Ran a stone over the ring and carrier flanges, wiped them completely clean. Again, gently heated the gear and it went on like butter. Also heated the carrier bearings and they drove on with little drama.

Hint; If working on a posi, use a axle bolted to a tire and rim for a stand. Excellent when tightening in place and final torquing the ring gear. Will not work with a open carrier.

axlestand_edited-1.jpg

Degreased the ring bolts, used blue Loctite and torqued them to 45 Ft/Lbs.

A picture below of the godsend "super shims". They capture the smaller shims in two robust, interlocking outer halves. This allows even the thinnest shims to be driven in. I start with a deadblow hammer, then drive them in all the way with a small brass drift. Make sure the housing face has no burrs that would be "shaved off" when driving the pack in. To start I went with a .031 + .010 shim in each pack. I'm now at .028/.010 in one and .031/.010 in the other. The super shim empty measures about .205.

I make it tight enough that the carrier needs to be pried out. If you can pull it out by hand, it's far too loose.

supershims.jpg 

After 5 tries starting with a .031 pinion shim and ending with a .038 I'm now here. Backlash .007. No good yet. The coast seems fair, but I can't seem to get the drive down into the flank of the gear. Will just keep trying. Might try more backlash at .038, or maybe even go down to .029 and see what happens. All fun. Thank god for the "Test" pinion bearing! I'll get her eventually.

Drive,

drive5vclose_edited-1.jpg

Coast,

coast5forweb.jpg



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


Poncho Master!

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Axle tubes seem solid in the center section but are press fit with just a couple of spot welds. Many folks weld the tubes solidly starting with 4 evenly spaced welds around the joint. I have seen a few loosen up there, even on low H.P. cars, and it can cause problems. You probably know this and find it unnecessary, but it can be inexpensive insurance. Honed pinion bearing is sure a time and money saver!! Notice the unique 12 bolt cover design to route lube splash to the side bearings. 12 bolts still are my favorite and I would be running one if Shawn and I were still buds!! Darn.

Thanks
Randy



-- Edited by GLHS60 on Saturday 26th of July 2014 12:46:46 AM

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Canadian Poncho Superstar!

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Well, I did consider having the tubes welded, but decided against it since it's no DIY job. In fact, I bet there is very few people that can or are willing to even nickel weld steel to cast iron properly in my town. 

But you're right on, with it probably being inexpensive insurance, cheaper than having a failed tube! We'll keep our fingers crossed.

The honed out pinion bearing is definitely a good idea, problem is, with my setup, it put me at a .040 shim to even get anything resembling a good pattern. And that is apparently unusual. So, not trusting it, I decided on going with a .035 shim behind the final press on bearing. Wrong...

I should have trusted the test bearing .040. The pattern is the same between the test and real bearing at .035!!!

So now I have to find a shop with a quality press and clam-shell to press it off (hopefully not destroy it). Then I'll probably go with a .042 shim. 

Trust the honed out test bearing. Some gear sets can be fickle.

 

Cheers,



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


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All buttoned up. Need to just make up some new axle brake lines, and I'll try to get it in today!

Final pattern, could have gone just a little deeper with the pinion, but I'm told this will be fine. .040 pinion shim, carrier, .037 left, .040 right. .008 backlash. 22 inch pounds pinion preload.

Capture.JPG

Before,

forwebpost2.jpg

After,

A little cart I made up using a furniture dolly to bring it round from the shed.

forwebpost1.jpg



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


Guru

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Nice!

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65 Catalina 2+2 421 4bbl,  Auto, White, w/red interior, Buckets w/column shift.

66 Grande Parisienne, 2dr HT, 327 4bbl, Auto.

Had the 66 since about 83 and the 65 since 88.
Both still require a lot of work.


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In!

Brakes tomorrow and then a long awaited road test.

forweb4.jpg

rorweb5.jpg

 



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


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Nice job Mark. That diff looks way to nice to be hidden under the car smile



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What a great tutorial. I will be coming back to this thread when I start my 12 bolt rebuild.

 

Ian



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Canadian Poncho Superstar!

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She's finally back on the road! Road tested at 5pm today

The new drive seems very smooth so far. But I'm getting a random slow (brake drum speed) Shish, shish, shish, from what I hope is just a brake issue. It goes mostly away on braking or light turns. Sometimes gone altogether. The E brake cables are totally hanging down slack. Could that cause it? Lets hope its brakes, really sounds like it's brake drum timed and not the posi which I would assume to be quicker in time. I turned tight fast figure eights in the high school parking lot, no clutch clicking. Using Quaker State 80/90 non synth Posi gearlube with 3/4 bottle of GM positrack supplement.

Going real easy on the gear break in, so no booting er' yet, but I can tell you, I'll likely need another gear at some point! 2.73's to a 3.55's will do that, lol! It really revs now, but feels ready to run. She is definitely more lively on the get go. But I'm ok until the dream 4L80 shows up at my door.

Suspension wise...it's totally tight. I Love the feel compared to the old wasted elastomeric bushings. But obviously anything would be an improvement over 47 year old rubber .

I was a little concerned about the Delsphere joints up front on the new control arms being too solid...wrong. They impart no perceivable harshness into the chassis. Just make it feel tight and connected, even over sharp bumps, and overall much more compliant over uneven pavement! Rips into fast tight corners no sweat, smoother lean in and out and more predictable. Safer. The Hotchkis bar is certainly an improvement. Get the bar off the arms, makes sense to me. It all tells me it's time for new or better rubber on the back!

I haven't even dialed any rebound into the Ridetech shocks yet but we'll start at the bottom and work up. Looking forward to a gentle easy gear break in.

Can you tell I'm happy?

Thanks for watching!

Cheers, Mark


DSC_3267[1].jpg



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


Canadian Poncho Superstar!

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As a 2019 update to the 12 bolt build, I have to say that after many miles, all has been 100% trouble free. No noise at all, still lays two even black patches. Building these things is always a wait and see, but if you're careful, use quality parts and don't cut corners you'll be fine handling it yourself...in fact, you can do a better job than paying to have it done!

The one thing I did do was change the lube after about 400 miles. And added the GM positraction additive again on the fill. Cheers.



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


A Poncho Legend!

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Removal and rebuild of the 8.875


Old thread but I can't find what I'm looking for pertaining to this. Did you at one time post information on pinion seals and how the seals available for 12 bolts were the wrong depth? I have an NOS GM seal for my posi that I plan to put in my car. Not rebuilding the diff but I want to do pinion and axle seals. I think I saw where you posted the measurement for it and mentioned if you the wrong seal is installed it will hit bottom before the flange bottoms on the housing.

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1966 Strato Chief 2 door, 427 4 speed, 44,000 original miles "FAKE_66"



Canadian Poncho Superstar!

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Removal and rebuild of the 8.875" 12 bolt.


Not sure I ever covered that aspect. But I was just reviewing stuff in prep for doing a 12 bolt, and came across some important info on the seal height.

One of the few available, still correct to GM spec seals is the Rateck 6109. In this excellent image below, taken from the web, you can see this "correct" seal to the left, and a generic one that usually comes with a install kit.

If you do get one with your kit, and it looks like the red one, be sure to install it about 3/16" proud of the housing flange. Do not drive it down all the way flush. Otherwise the lip will be driven into the bearing inner race, and will not seal. I don't know why they still include this incorrect seal. Maybe that has changed since 2014.

50835639763_e7d01f4852_z.jpg

 

 

 

 



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


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4SPEED427 wrote:

Old thread but I can't find what I'm looking for pertaining to this. Did you at one time post information on pinion seals and how the seals available for 12 bolts were the wrong depth? I have an NOS GM seal for my posi that I plan to put in my car. Not rebuilding the diff but I want to do pinion and axle seals. I think I saw where you posted the measurement for it and mentioned if you the wrong seal is installed it will hit bottom before the flange bottoms on the housing.


 There's a YouTube video that pertains to what you're talking about Carl.  Go to the 37:45 minute mark.

 



-- Edited by seventy2plus2 on Saturday 16th of January 2021 07:21:10 PM

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A Poncho Legend!

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Removal and rebuild of the 8.875


I checked that out, great info but one key piece of info missing still. I needed to know the correct depth, the maximum amount of depth the correct seal could have. After much digging online I finally found a post where someone posted that the seal can't be more than approx .532". I measured my NOS GM seal, pretty much .530".

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1966 Strato Chief 2 door, 427 4 speed, 44,000 original miles "FAKE_66"



Addicted!

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Removal and rebuild of the 8.875" 12 bolt.


cdnpont wrote:

Not sure I ever covered that aspect. But I was just reviewing stuff in prep for doing a 12 bolt, and came across some important info on the seal height.

One of the few available, still correct to GM spec seals is the Rateck 6109. In this excellent image below, taken from the web, you can see this "correct" seal to the left, and a generic one that usually comes with a install kit.

If you do get one with your kit, and it looks like the red one, be sure to install it about 3/16" proud of the housing flange. Do not drive it down all the way flush. Otherwise the lip will be driven into the bearing inner race, and will not seal. I don't know why they still include this incorrect seal. Maybe that has changed since 2014.

50835639763_e7d01f4852_z.jpg

 

 


 Wow  - this is REALLY good to know!!!

I also liked this hint:

Hint; If working on a posi, use a axle bolted to a tire and rim for a stand. Excellent when tightening in place and final torquing the ring gear. Will not work with a open carrier.

I would have never thought of that - I will definitely do this now!!



-- Edited by unruhjonny on Sunday 17th of January 2021 01:09:42 PM



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A Poncho Legend!

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I found a source for the Ratech in Canada, cheaper than Summit unless you are ordering other stuff from Summit.

https://www.amazon.ca/Ratech-6109-Pinion-Seal/dp/B001P2D3LK



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1966 Strato Chief 2 door, 427 4 speed, 44,000 original miles "FAKE_66"



Canadian Poncho Superstar!

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Remember to put a light bead of ultra black around the seal shell before driving it in. And never forget some on the pinion splines as well.



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65 Laurentian post, 67 Grande Parisienne 4 door HT. 
 


A Poncho Legend!

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Removal and rebuild of the 8.875


Yes, I've been reading that. I've never done that before but I guess just been lucky!

One place I read where a guy said the Ratech seal is not as good a quality rubber as the GM. If I can find a little shim for my GM seal I'm going to use it. I have a couple of ideas for a shim that may work, and barring that I'll make something.

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1966 Strato Chief 2 door, 427 4 speed, 44,000 original miles "FAKE_66"

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