Axle Offset

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punkin
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Axle Offset

Post by punkin » Sun Apr 14, 2019 11:03 am

Hello all,

My first post here and thank you to the administrator for allowing me to post here.

I have a 1968 firebird with a 10 bolt BOP 8.2 differential. I'm preparing for a 4-wheel disc brake conversion. I plan to use Wilwood products. According to Wilwood, a critical measurement would be what they're calling axle offset. This is the distance between the axle housing end flange to the face of the axle when fully seated. They indicate that for the 8.2 BOP this should be 2.75".

When I measure my set up I actually measure 3.1".

When axle fully engaged, the bearing extends from the axle housing approx .1"
Measuring the axle face to the bearing face is 3.0"
The inner race spacer is .6" thick
The bearing is .66 " thick
The axle is 29.75" long

When the axle is fully engaged, it is not bottoming out at the spline end and the bearing/spacer does appear to be fully seated. All the measurements seem to add up. How is it my total off-set is .25" too far extended?

Any thoughts?
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monzaz
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Re: Axle Offset

Post by monzaz » Mon Apr 15, 2019 6:01 am

2.75 all gm ARE 2.75... CARS 1964-2002 WITH ORIGINAL drum BRAKES 9.5 X2 BRAKE SYSTEM. Which is what you have.
It is the distance from the base of your housing flange to the / backing plate base to your axle flange surface where the drum mates your axles.
You have it measured as 3"
The axle DOES extend about 1/8 inch out of the tune end, (the same thickness as the backing plate) as the backing plate is part of the system and usually most econo disc brakes systems supply a small spacer plate (shaped the same as the housing flange pattern) to replace the backing plate thickness.

How Wilwood does it I am unsure.
Make sure you tell them you have BOP bolt in axle rear and ask them if it is compatible with this type of bolt in axle rear.

The offset is 2.75 that is the info you need.

J D Race
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punkin
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Re: Axle Offset

Post by punkin » Mon Apr 15, 2019 8:30 am

I thank you very much for your reply. I've been pulling my hair out over this for a couple weeks now. Wilwood tells me that I should measure per this diagram and that it should be 2.75". When I measure as such, I get a hair over 3".
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monzaz
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Re: Axle Offset

Post by monzaz » Mon Apr 15, 2019 11:06 am

Do not know... I DO know I deal with GM rears EVERYDAY... and pontiac, buick, olds, chevy all interchange the drum brake systems A body 1964-1977 F body 1967- 1981
Even 1982 - 2004 S-10 drum brake system and most all the f-body from 1982-2002 drum brakes.
1978-1988 G-body s-10 F-body vehicles again will use the same offset but do not have the same backing plate flange bolt pattern as the early models .

Jim
JD Race
J D Race

punkin
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Re: Axle Offset

Post by punkin » Mon Apr 15, 2019 7:51 pm

Good to talk to you again today and I really think you've solved my problem. Here's a close up of that bearing surface at the end of the axle. As you suspected, there's an extra machined surface as you move closer to the axle flange. There's another shoulder. I'll get some additional measurements from Wilwood and I'll be ordering those Yukon axles from you tomorrow.

THANKS!!!
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monzaz
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Re: Axle Offset

Post by monzaz » Thu Apr 18, 2019 8:44 am

There is always and answer...Just takes some time to figure it out. Glad we can help ot. Jim Mitschke JD Race

So for everyone reading this.
Jim - has a Oiled bearing BOLT in axle in a sealed bearing rear application.
The offset from the bearing land is 3" on the oiled bearing where the seal is also installed on the axle shaft outboard the bearing keeping the oil in the rear.
What he needs is a sealed bearing axle with the 2.75 offset and the seal is pressed into the housing tube end and no oil gets to the bearing at all.

1964-1969 early are sealed bearings from BOP GM like.
1969 late through 1976 are all oiled bearing axles BOP GM that bolt into the housing....

Good luck out there - Make a good difference in life!
J D Race
Jim
J D Race

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