I'm re-gearing my '86 GMC pickup , and want to go with a limited slip
unit . It's a stock 2.73:1 8.5" 10 bolt right now , and there seems to
be some confusion as to what will fit .
As far as I can determine any 8.5" 10 bolt will fit my differential
housing , the only difference being the axle spline count . Everything
I've found says I should have 28 splines in the 1986 .
Anybody here that can verify ? I'm in no particular hurry , it looks
like winter arrived here with a vengeance .
--
Snag
Si Vis Pacem Para Bellum

> Snag wrote:
> I'm re-gearing my '86 GMC pickup , and want to go with a limited
slip
> unit . It's a stock 2.73:1 8.5" 10 bolt right now , and there
seems to
> be some confusion as to what will fit .
> As far as I can determine any 8.5" 10 bolt will fit my
differential
> housing , the only difference being the axle spline count .
Everything
> I've found says I should have 28 splines in the 1986 .
> Anybody here that can verify ? I'm in no particular hurry , it
looks
> like winter arrived here with a vengeance .
> --
> Snag
> Si Vis Pacem Para Bellum

The 8.5" 10 bolt was used in
many different models by every GM division, with the exception of
Cadillac, during the 1970s and 1980s. The carriers and gears are
easily interchangeable, and the original gear ratios range from 2.41:1
to 4.10:1. The 8.5" 10 bolt has two types of axles: 28 spline and
30 spline. The 28 spline axles were used until 1988, and the 30 spline
axles were used from 1989 and up. Therefore, if your '86 GMC pickup
has a stock 8.5" 10 bolt with 2.73:1 ratio, it should have 28
splines. You can verify this by counting the splines on the axle shaft
or by checking the axle code on the right lower cover bolt.

If you want to go with a limited slip unit, you have several options.
You can either find a Positraction carrier from another 8.5" 10
bolt with 28 splines, or you can upgrade to a 30 spline carrier and
axles. You can also use an aftermarket locker, such as an Eaton
E-Locker, which can switch between an open carrier and a fully locked
differential. However, you will need a special bearing to use a 30
spline carrier or locker in your 8.5" housing. You can also
change the gear ratio if you want, as long as it is above 2.73:1. You
will need to adjust the pinion depth and backlash accordingly, and use
new bearings and seals.

This is a response to the post seen at:
http://www.jlaforums.com/viewtopic.php?p=658725873#658725873