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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend> please help id this 10 bolt posi
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Topic Review (Newest First)
03-11-2011 11:36 AM
cutthroatkid I found the code,went&really hit it hard with a wire brush&anyhow looks like 4yp g4142 I can't seem to find any info on it.Any ideas?
03-11-2011 02:06 AM
ericnova72 Just having both axles turning in the same direction does not gaurantee a posi, a burnt up open differential that has friction welded the spider gears to the pin will behave the same way. Best to remove the cover and see exactly what you have.

Widtn measurement needs to be from where the wheel bolts on to get the true width. Nobody lists them by backside of the drum measurements.
03-11-2011 01:35 AM
Originally Posted by cutthroatkid
This is the date code. It says the casting was made in a year ending in "4". The stamped axle tube numbers are what's really needed.
03-10-2011 11:55 PM
cutthroatkid Ok I can get some more pix in the morning.I know its a posi,I sat it up on aome blocks&both trums spin the same way.How should I measure it?I just dis from inner hib to hub it was 58 inches.It looks pretty much identical to my monte carlo rear.I took some degreasser&wd40&a wire brush to it&can't find anymore codes Thanks for the help.
03-10-2011 11:38 PM
ericnova72 It is definately an 8.5" 10-bolt, identified by the cast corner "blocks" at 5 o'clock and 7 o'clock just below the cover face. I don't see a posi tag(it would have been an stamped aluminum tag about 1-1/2" long x 5/8" wide saying "use positraction differential lube only", attached to a cover bolt, but they frequently corrode and rot off) so you'll have to remove the cover to know for sure what is inside.

Width measurement needed is wheel mounting surface to wheel mounting surface. Just off hand based off the width you have given and the suspension brackets is that it is 73-77 A-body, but that is just a guess at this point.

A picture of the end of the housing where it meets the brake backing plate would help, as a look at the bolt pattern and size could narrow ID down further. There is the possibility it is a Type O(Oldsmobile) 8.5" and the housing end is different.

Could also be an 8.5" from a full size GM(Caprice/Impala) depending on total width.

The #'s you have posted won't help.
03-10-2011 11:05 PM
03-10-2011 10:34 PM
cutthroatkid Ok it'll take me a bit to get all of these piz uploaded can't find any other codes me& 2 othee guys looked. Also if it helps from the back of the drums one to another meaure about 58 inches.
03-10-2011 10:22 PM
cutthroatkid Let me see if this works.
03-10-2011 09:24 PM
ericnova72 Only code that will mean anything will be stamped into the forward side of an axle tube. Casting #'s won't ID it. a picture would make this real easy.

There is an ID chart at for ID'ing the different 10-bolts. Click on "site map", then on "axle codes" and it will take you to the ID page.
03-10-2011 09:13 PM
please help id this 10 bolt posi

I have a rear end that was in my grandfather's shop after he passed.Its a 10 bolt looks to be an 8.5 &it is a posi.The only codes I can find are one that says gm 49 another that says 12515002 &one more that has what looks like a o with a horizontal line in it thene 154 and another o with the horizontal line like oe 154 o. PLEASE help Ive looked&looked&can't seem to find no info.

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