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Old 05-23-2021, 10:32 AM   #1
jleslein
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Non stock rear end

1975 Grand Am; purchased in February, now tackling rear drum brakes. The parts in kit purchased for this yr/make/model doesn’t match parts in rear end! In addition I found that differential gasket I bought earlier was 10 bolt like I have, but different pattern. My brother says a previous owner likely swapped in a different rear end. Now the $64 question; how to proceed? Maybe convert to disc to bypass whole issue? Not sure how to I.D. exactly what rear end I have? Thanks for any info!
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Old 05-23-2021, 01:17 PM   #2
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Re: Non stock rear end

hey jl,
welcome to Automotive Forums..
your brother is likely right. so, most GM rear ends
either had a tag near rear diff, or stamped with a 7-digit
alpha/numeric on the back side of the tube/housing..
first 2 are ratio, second set is month/yr, third is day, last single is a/b/c shift
since chevy was cranking out more than buick/olds/pontiac,
it is probably from a caprice, monte, or impala..
another possible way to figure it out (if no tag; usually removed, and
if you cannot find stamping), is to take pic of the 10-bolt rear end and post..
pics:
https://imgur.com/a/RN2XIBJ
hope this helps..
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Old 05-24-2021, 03:49 PM   #3
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Re: Non stock rear end

ctesla thanks for info- no luck with tag, will look closer for tube stamp. Drums on rear are huge- 12” ID on drums, the drums I bought for this car fit inside them!
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Old 05-24-2021, 04:09 PM   #4
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Smile Re: Non stock rear end

my photo won’t load “413 entity too large” but differential cover looks like far left from images in your link, with fill plug at about 3 o’clock and 10 bolts. Wish I could post pic, prolly my state of the fart I phone 6... and thanks again very much for taking the time to reply!
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Old 05-24-2021, 06:25 PM   #5
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Re: Non stock rear end

Upload your images to imgur and post them that way.
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Old 05-25-2021, 09:24 AM   #6
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Re: Non stock rear end

Stealthee is right..
go to imgur 's website, drag your pic in, they'll give you link to post here..
odd's are rear end was swapped, so this might help:

https://www.chevydiy.com/history-and...differentials/

but, back in the day, many vehicles were custom ordered for police/taxi or heavy service use cars.. your Grand Am might have RPOs (maybe?) posted in glove box;
if so, here are some rear end codes to look for:

https://www.differentials.com/gm-axl...ication-codes/

but my old Laguna S3 chevelle did not have placard in glove box..
i found the build sheet stuffed in the coil springs under the back seat
when i pulled it once to retrieve a dang snap on wrench that fell behind
and under the cushion..

good luck.. and waiting for pics..
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Old 11-05-2021, 07:06 PM   #7
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Re: Non stock rear end

depending on when the car was made, you could have a previous or the next year rear end installed from the factory. GM was good about getting rid of crap they had laying around at the end of a year...or month or week.
Without seeing the yours its hard to guess exactly why its not correct per make model and year.
But this site might help you identify yours.

https://www.chevyhardcore.com/tech-s...10-bolt-chevy/
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