10 bolt confusion

[oldiron]

Ok, I'm confused. I thought I knew a little about diffs but I'm getting confused about the GM 10 bolt. I have a 83 Chev truck but I'm not sure if the rearend has been changed out or not. It's been through many owners and now its resting place is with me. The rear is a ratio of 3.08. I pulled a 3.73 ring and pinion and axles out of a newer model Chev 1/2 ton truck (90's something: not sure what year). The newer axles have a larger diameter shaft and are longer than the 10 bolt that is in it now. I'm thinking that the 10 bolt I have is what they call a 8.2 10 bolt and what I pulled is a 8.5 10 bolt ring and pinion?. My question is: Can anybody tell me what the difference is between a 8.2 and a 8.5 GM 10 bolt is. I'm suspecting that it is the diameter of the ring??? How come the axle shafts are bigger diameter and longer than my 10 bolt?

 

[6.2Blazer]

The fullsize trucks never used the 8.2 10-bolt (yes, that is referring to the ring gear diameter).

The 10-bolts originally used 28-spline 1.28" diameter axle shafts. Around '89 they switched to 30-spline 1.31" shafts, which explains the slightly larger shafts.

The next generation Chevy/GM trucks with the new body style and IFS ('88 for pickups, '92 for Blazers and Suburbans) did use a slightly wider rear 10-bolt, so thus it would have the longer and larger shafts.

 

[imiceman44]

The fullsize trucks never used the 8.2 10-bolt (yes, that is referring to the ring gear diameter).

The 10-bolts originally used 28-spline 1.28" diameter axle shafts. Around '89 they switched to 30-spline 1.31" shafts, which explains the slightly larger shafts.

The next generation Chevy/GM trucks with the new body style and IFS ('88 for pickups, '92 for Blazers and Suburbans) did use a slightly wider rear 10-bolt, so thus it would have the longer and larger shafts.

ANd that was when they started to call them 8.6, even though they still are 8.5".

 

[6.2Blazer]

ANd that was when they started to call them 8.6, even though they still are 8.5".

Pretty sure it was later (late 90's , early 2000's maybe?) when they went to the 8.6".

Just thinking, I know that some vans had wider rear axles so that could explain the difference also.

 

[oldiron]

I really appreciate you answering my questions. Even though I’ve joined this forum a while ago, I am not a knowledgeable computer user when it comes to this forum. I hope I replied back to the right address or person to give thanks for the information on 10 bolts.

(Just a FYI) I did go back to the salvage yard today to check the year of the Chevy truck I pulled the 3.73’s ring, pinion and axle’s out of. It was a 93 ½ ton full size pickup with IFS front suspension. I then search around and notice that the older Blazers in the bone yard had the “smaller” 10 bolts under them. The lugs in the axles are even smaller diameter than the newer truck’s 10 bolt rear end. I measured the distance of each rear end 10 bolt from brake backing plate to backing plate: the smaller 10 bolt on the Blazers measured just less than 56 inches and the Chevy trucks measured just over 59 inches.

Anyway, I think I’m back on track to replacing my ring and pinion from 3.08’s to 3.73’s thanks to you. The reason I’m doing this is because my 83 truck had a welded spider gears (Lincoln Lock) in the front 3.08 diff case and I got a great deal on a different front diff with 3.73’s to replace it with (Free). I didn’t like the welded spider gears on the front. It was really hard to turn, even though I trailer this truck to my favorite wheeling sites. Anyway, I need the back pinion to match the front and that is why I am on this quest. Not to mention, I get a better ratio for crawling around on the rocks. I have taken the bed off this truck and shorten the frame and cut of the leaf springs off and replaced the rear with my home made 3 link suspension. It works great. The truck was going to the salvage yard so I thought I would experiment with it. It is a fun toy to play with. It has many donor parts on it from several different years of trucks.
I also own a 72 Blazer that I’ve put a FF 14 bolt in the rear and a matching gear ration (4.56’s) Danna 44 on the front. I’ve had this Blazer a long time and have enjoyed wheeling it as well. The 14 bolt with the 4.56’s sure do get down a crawl up Moab’s 4X4 trails. I make that trip every year and sometimes twice a year.

Thanks again.