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hd78glide · Addicted!

68 Parisienne rear end gears

seventy2plus2 · Canadian Poncho Superstar!

There is a code on the passenger side axle tube extending from the main differential center unit over to the brakes. The code will be stamped on the front of the tube, a few inches away from the main diff unit. If you get me the code I'll see what I can figure out. Usually the easiest way to get the code is to take a wire brush to that area, and rub chalk into the stamping to get the digits.

427carl · A Poncho Legend!

General Motors

[edit]GM diff covers

GM diff covers

10 bolt 8.5 inch GM corporate rear end

Axle codes by year

[edit]10 bolt

[edit]10 bolt ID tips

If you don't have the codes on hand to identify if a 10 bolt rear end is an 8.5" or not, you can measure the distance between the very bottom bolt for the cover and the next adjacent bolt (either right of left), it will be 3-3/4" for a 8.5" and 3-1/4" for a 7.5".
Note: Some installation kits for the 8.5" and 7.5" use ring gear bolts with a 5/8" head, so if someone has rebuilt the rearend with one of these kits the bolts will have smaller heads than the original bolts.

Another tip is to check the size of the pinion nut. The 8.2" uses a 1-1/8 inch socket on the nut and the 7.5" and 8.5" use a 1-1/4 inch socket. That is as long as they have a OEM type nut on them.

There are usually two distinctive lugs cast into the bottom of the 10 bolt rear end housing. These lugs are arrowed in the image above.

The ring gear of the corporate 10 bolt is secured by 7/16-20 left hand thread bolts having a 3/4" hex head on them; there will be ten bolts holding the ring gear to the differential. The ring gear is (as mentioned) 8.5" diameter and the pinion shaft diameter is the same as the 12 bolt at 1.625". The 8.5" pinion has 30 splines.

The 8.2" diff will have 10 bolts holding the ring gear on the diff, the bolts will have a 9/16" hex head and be right hand threaded. The 8.2" uses ten 3/8-24 right hand thread bolts to hold the ring gear on the diff. The pinion diameter is 1.438", having 25 splines.

4SPEED427 · A Poncho Legend!

hd78glide wrote:

Hi, I have a 10 bolt rear end in my car, is there any way of knowing the size and how many splines without opening it up? I've been looking online, because I want to put a posi and change the ratio, but I don't know if it is 8.5", or 32 spline or what.

Thanks

If it's the original it would be an 8.2".

Does it have the protruding upside down "V" on the outside of the cover?

hd78glide · Addicted!

Thanks for all the responses. I can't look closely right now because my Pontiac is up on a lift, with my truck under. I am changing the coolant on my truck. When I am finished I will have a closer look, but the cover definately has the upside down V. on the cover.

67Poncho · Uber Guru

'68 Diff Codes.JPG

koolconvertible · Poncho Master!

whats the difference between a standard and positraction axle?

427carl · A Poncho Legend!

koolconvertible wrote:
whats the difference between a standard and positraction axle?

Standard rear will spin the right rear wheel, if theres a loss of traction

Positraction will spin both rear tires if there loss of traction (positive traction)

Heres my standard rear "suffering a loss of traction"

GOT A POSI FOR IT NOW copy.jpg

koolconvertible · Poncho Master!

Thanks, nice licorice whip!! Sorry, may not have been clear there....I know that difference! Just put a posi centre in mine....I thought it referred to the axles as being different in some way....odd thought ai know...

427carl · A Poncho Legend!

A posi trac requires a posi Carrier but I think/though the axles were the same

I smile when I see so many car guys spending tons on a posi trac

Around here, theres no place to go to spin the tires...

Locals call police if you honk your horn

Cops are like flies

Unless you drag race a posi is kinda useless (2 cents) Like ceramic headers on a car that never gets wet or cold lol

koolconvertible · Poncho Master!

Fortunately, they're not like flies here, I lole all available grunt to get to the road, we also have drag strips...had to reco my diff and found a good posi. very hard to come by here in Oz so has good poser value too....

hd78glide · Addicted!

Removed the cover on my diff, 15 41 so I have the factory ratio of 2:73. I want to lower the ratio and put a tranny with overdrive. Thinking of 3:73 with either a 700R4 or 4L60E, Would love to put a 5 or 6 spd manual, but putting another AT would be easier, but probably more $$, especially for the 4L60E.

I might do the gearing this winter, and maybe a posi unit, and tranny winter.

hd78glide · Addicted!

Ring Gear 1 GM 3910823 15 41 1 68
1 = Chevrolet
GM = General Motors
3910823 = part number
15 = pinion teeth
41 = ring gear teeth
1 68 = January 1968

Looks like original ring gear. My car was manufactured April of 68.

seventy2plus2 · Canadian Poncho Superstar!

Just curious, what's the stamping on the passenger side axle tube?

hd78glide · Addicted!

seventy2plus2 wrote:
Just curious, what's the stamping on the passenger side axle tube?

I haven't found them yet. I've scraped buildup off the tubes, but nothing yet. I haven's cleaned with solvent yet.

4SPEED427 · A Poncho Legend!

Passenger side tube near the inner end of the tube, front of the tube. Just keep digging, it's there!

67Poncho · Uber Guru

Carl Stevenson wrote:
Passenger side tube near the inner end of the tube, front of the tube. Just keep digging, it's there!

Disregard the year... All the same...

photo 3.JPG

4SPEED427 · A Poncho Legend!

I'm not sure why they say the bottom. Vince, haven't you found that most of them you can stare at the tube with the car on a hoist and the code is almost staring right back at you?

67Poncho · Uber Guru

Carl Stevenson wrote:
I'm not sure why they say the bottom. Vince, haven't you found that most of them you can stare at the tube with the car on a hoist and the code is almost staring right back at you?

I should have said disregard the location too.... Yea... Always on the front side facing the front of the car....

-- Edited by 67Poncho on Tuesday 13th of January 2015 11:41:54 AM

hd78glide · Addicted!

That helps, I will look tomorrow.

Thanks.

hd78glide · Addicted!

I will look at other areas, but the area identified doesn't have anything stamped on the axle tube, towards the front of the car on passenger side.

seventy2plus2 · Canadian Poncho Superstar!

Try going a little higher, the numbers on my 69 housing are towards the top. You've certainly cleaned a large area, I've always just been able to used a wire brush to clear away the surface rust.

67Poncho · Uber Guru

1662295?AWSAccessKeyId=1XXJBWHKN0QBQS6TGPG2&Expires=1421884800&Signature=44b%2BW0naOxOio8H%2F%2BkNgdTwZyrM%3D

That's the cleanest tube I've seen, EVER! (lol) I wonder if there are no stampings, would it be a warranty diff? It should be easy to see..

hd78glide · Addicted!

Hopefully tomorrow I will get it completely cleaned off. My health can only handle about an hour of physical work a day.

hd78glide · Addicted!

Found it. Maybe an inch higher than I previously cleaned. axle tube number.JPG