I have a 1996 4wd, blazer here, As far as I check from the cover its a 7.5"unit, GU63,42 open rear, 28 spline. Also I have one posi unit laying in the garage, but Im not sure about the size of it, it looks more like a 8.2" BOP 26 spline (68-69 ) I measured little less than 8,2" outer diameter on the ring gear, posi itself (the plate that ring gear mounts) has 7"diameter.I have gathered couple of 29" 26 spline axles, also checked the bearing size its ok too. Im thinking about to use the stock 3.42 ring gear, and only swap open to posi unit and axles. I only need the inner diameter of the 7.5" 7.625" ring gear.

would it work? any ideas?

Posi is allready not a chep part, also freight to overseas is killing me, thats why Im trying to such a thing.
thanks.

 

no answer yet/

at least, inner diameter value of the 7.5" ring gear works for me. I would be glad if somebody have laying gear set around and measure it for me. Otherwise i ll need to open the case. which I dont like to do before be sure it fits.

 

Wow... You waited a whole 3 hours! Cudos... Come on man... No need to bump a thread after 3 hours. It didn't even fall off of the first page...

Well, your truck most likely has a 7.625" differential (very similar to the 7.5"), but could possibly be a 8.5 if it is a manual transmission model (but not all of them got this). If you have an 8.2" differential carrier, it will not fit into a 7.5/7.625" housing. The bolt circle for mounting the ring gear will not match up with your 7.625" ring gear.

But are you measuring the bolt circle? Or just the OD of the gear?

 

oops, sorry for my rush.

My blazer is an automatic one, possibly 7.625/ 28 spline as you said.

To measure the ring gear diameter do i have to gettop ( widest point)of the crownor bottom measure?

 

If I remember things correctly, diffs are described by the bolt circle diameter and the quantity of bolts that attach the ring gear to the differential carrier. The only difference between the 7.5 & 7.625 carriers being the bolt circle diameter (7.5" diameter vs 7.625" diameter) and possibly the inside diameter of the ring gear and subsequent mating surface on the carrier.

First thing which I assume you have already done is to count the number of bolts on the carrier you have out. You need 10 bolts. The next thing would be to measure the bolt circle diameter. This can be accomplished in a few different ways. If you can, measure from one bolt to another bolt exactly opposite on the carrier. If the diff is installed, you can measure from one bolt to the next closest bolt, then use some trigonometry to find the radius, then the diameter. For a 7.625 rear, the bolt holes should be around 2.356". For a 7.5", 2.318". For an 8.2", 2.534", And for an 8.5", 2.626".

I have created an illustration that should help. It is attached below. Basically, if you can, measure between like colored bolts. If you cannot measure across the the center of the diff like when it is installed for example, you can measure bolt to bolt like measuring between the red and blue dots on the illustration with both bolts on the same side of the diff.

[IMG]local://upfiles/667/46619D491B5F4F0687DDCB79B95F17FC.jpg[/IMG]

 

Thank you very much. This info really helped me a lot.

As soon as I have a progress I ll write it down here.

Thanks again.

 

My previous atempt to swap rear end has failed, then I have purchased a .310" ring gear spacer and 4th. gen camaro torsen unit. Today I have installed stock 3.42 ring gear and spacer into torsen unit, then install with the same spacers in same location and worked just right total cost 300$ in overseas

Actually today is snowing here and had fun with it on test drive

I love this place