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Old 04-21-2005, 09:07 PM
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GM 10 bolt Diff ID numbers?

I have a 10 bolt limited slip diff that is in a 87 Chev p/u. I may have crossed the drums over from another diff. I had out of another truck. same year, both 1/2 ton but the other was not a limited slip. The drum rubs on the backing plate as it is too deep. Does anyone know if there was different size brakes available for these trucks? I know nothing about past history of this truck, except it had a BBC in it. I suppose the diff may not be original either... Can I ID the diff by casting numbers?

Thanks,


Gear

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Old 04-22-2005, 11:42 AM
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11x2 and 11x2 1/2 brakes were available for 2wds from 73-87

The code is stamped in the front or top of the right side axle tube and will be a 3 letter code.
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Old 04-22-2005, 04:43 PM
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Thanks....any Idea if these axles will withstand a little abuse? 3:08 now, maybe 3:73's (?) later....(or what ever mid to high 3 something gears are available....)

Cheers

Gear,
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Old 04-25-2005, 03:08 PM
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Sounds like a good reason to convert to disc brakes

8.5's can be strong axles if they are in a lite vehicle (like the one in my S10).

Weak points are:
Housing flex (good diff cover helps this)
Only 28 spline axles (you can swap in later 30 spline axles/carrier)
Pinion deflection (solid spacer helps)
Many trucks came with a 'Gov-Lock' diff. It is junk and should be swapped out for something stronger ASAP (good time to go to 30 spline)

How much power will you be putting thru it and what is it going under?
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Old 04-25-2005, 09:02 PM
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Its in an 87 SWB 1/2ton. Likely start with 300 - 350 hp or so...what is the Gov-loc diff?
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Old 04-25-2005, 10:30 PM
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The gov-lock is what GM put (and still might) in all their trucks. It isn't like any normal diff (not a limited slip, open diff, or normal true locker). It locks up based on differential wheel speed. When you get one wheel going about 100rpm faster then the other it will lock solid. Other then that is is just like an open diff. Because it lets the spinning wheel gain speed before it engages it often goes bang and blows its self up taking out the entire rear end with it. They were VERY common in 4x4's but found their way into many 2wd's too. You say it is a limited slip so most likely it is a gov-lock.

This is what they look like (sorry it was hard to find a pic of one still in 1 piece )


You can get the 30-spline axles from any 2wd blazer or sub from 88-91 (the old body style...the new body style would be too wide) and an aftermarket carrier wouldn't be a bad idea either. You will need somewhat special carrier bearings to get the aftermarket 30-spline carrier to fit. The 88-91 carrier (maybe longer ) used the same carrier bearings as the earlier axles which made that section of the carrier thin and proun to failure. Just make sure that you tell whoever you order the parts from what you are doing and they will set you up with what you need.
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Old 04-26-2005, 06:12 PM
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Thanks.....mine does not look like that one....YET. I think I'll baby mine untill I'm ready for a new one.
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Old 04-27-2005, 06:41 AM
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Quote:
Originally Posted by Triaged
This is what they look like (sorry it was hard to find a pic of one still in 1 piece )
Here you go.

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Old 04-27-2005, 09:45 AM
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Quote:
Originally Posted by M&M CUSTOM
Here you go.
Thanks for the pics. Do you know what year truck that diff is out of?

I have a gov-lock in the 8.5" axle (that came out of a 2000 blazer w/ 20kmi) in my truck and as soon as I get some more power in front of it (stock 2.8L for now ) I will be swapping in a better diff (and some other parts).


This is some of the info I have found so far. I don't have sources for most of it...I've just been saving it as I find it.

Quote:
Check your bearing sizes ... make certain the '94 rear end will fit your truck. GM changed the rear end bearing sizes on at least the 1/2 ton trucks, maybe the heavy duty trucks also, beginning in '99 ... I think.
Here is what I ran into when I installed a '99 ... I think ... GM 1/2 ton truck posi (complete carrier) into my '91 Chevy Z71 1/2 ton 8.5 inch 10 bolt rear end:
To make a '99 (I think) or newer Eaton Posi work in an older truck (like my '91 Z71) use the following bearings:
Timken Part Number: LM102949 - Cone
Timken Part Number: LM102911 - Race
Check out:
http://www.ibuyautoparts.com/PosiTractions.html
http://www.timken.com
Call Shep at Drivetrain Specialists - 702-876-3100 or Todd Bennett at Eaton 616-789-3360.
Timken F.Y.I.:
LM501349 Cone - 1.6250 Bore
LM501314 Cup - 2.8910 OD
Bearing Width - 0.8437
LM603049 Cone - 1.7812 Bore
LM603012 Cup - 3.0625 OD
Bearing Width - 0.8437
LM102949 Cone - 1.7812 Bore
LM102911 Cup - 2.8910 OD
Bearing Width - 0.8437
I needed LM102949 & LM102911 to make a later model Eaton Posi (10-bolt - 8.5 inch - 30-spline) work in my '91 Chevy Z71.
I paid $12.30 each for the LM102949 Cone & 11.67 each for the LM102911 cup.
I think at the same point that they changed to the carrier bearings they also started calling it a 8.625" axle. I don't think they changed anything else (i.e. it still uses all the other parts including R&P that the 8.5" uses).

Some parts I'm looking at:

Diff Cover
http://www.jegs.com/cgi-bin/ncommerc...46&prmenbr=361

These guys sell the solid pinion spacers (you can get them from summit but I don't think they are on the website...call them)
http://www.store.yahoo.com/ratech/88gmaxpa.html

This is the diff I'd like. I haven't heard much about it but it looks good for the price
http://www.jegs.com/cgi-bin/ncommerc...75&prmenbr=361

This is my next on my list
http://store.summitracing.com/defaul...3&autoview=sku

If you are looking for just a normal clutch pack limited slip this is it (and this one really is a "Posi")
http://www.jegs.com/cgi-bin/ncommerc...42&prmenbr=361

Last edited by Triaged; 04-27-2005 at 10:16 AM.
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