8.5 ALTERNATIVE

ssn696

Living in the Past
Supporting Member
Jul 19, 2009
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Permanent Temporary
Brake plates on the axle ends should make an LS1 disc brake conversion a bolt-on.
 

melloelky

Comic Book Super Hero
Oct 22, 2017
2,957
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mass
Do you need stronger, cheaper or what is wrong with an 8.5?
I can't speak for the OP but the 8.5 is a sound diff but for a 30+ year old part with how many miles folks are asking a lot(in my opinion anyways) compared to the cost of a 9"
or 12 bolt made to order with 0 miles on it..
 
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L92 OLDS

Royal Smart Person
Mar 30, 2012
2,487
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West Michigan
I can't speak for the OP but the 8.5 is a sound diff but for a 30+ year old part with how many miles folks are asking a lot(in my opinion anyways) compared to the cost of a 9"
or 12 bolt made to order with 0 miles on it..
An 8.5” factory G body rear end will still be cheaper but I understand your point. And then there is the issue of putting a Ford part under a GM car 😳. Complete and utter sacrilege! I wonder what the differences in unsprung weight are. 9” housings have to be heavy....
 

gnvair

G-Body Guru
Sep 1, 2018
865
93
Southern New Jersey near Philly
The problem with the 8.5 is that they are not getting any easier to find as the years go by and when you do, people want a lot of money for a rear that might need a rebuild. The biggest issue with the factory GN/442 8.5 is the small axle tubes. They use the same small sized tubes as the 7.5 rears. As such, many of them if from a car that was raced on slicks could have a warped housing.
I used a 1995 Crown Vic 8.8 in my Malibu. I paid $150 for it from the local U Pull it yard. Upper ears are in the correct spot. I narrowed it and installed the Ford 9" style ends with the GM pattern so I could use the Blazer rear discs. I also made a cover adapter so that it looks like a Chevrolet 12 bolt. People think its a 12 bolt and don't realize unless I tell them :cool:
 

64nailhead

Goat Herder
Supporting Member
Dec 1, 2014
2,888
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Upstate NY
I can't speak for the OP but the 8.5 is a sound diff but for a 30+ year old part with how many miles folks are asking a lot(in my opinion anyways) compared to the cost of a 9"
or 12 bolt made to order with 0 miles on it..

An 8.5 is still cheaper than an aftermarket 9" - and it ain't a FORD!

If you can find a factory 8.5 from a Hurst or GN for $1200 or less, then it will be a big savings compared to a bare aftermarket 9". I guess we were fortunate to find one for $600. $6-800 of diff, bearings and axles and it will take 800+HP all day every day.
 

81cutlass

Comic Book Super Hero
Feb 16, 2009
3,251
113
Western MN
I went through arguably illogical levels of work to replace the axle tubes from a stock 7.5 and mate them into an 8.5 housing with a custom UCA plate. It was cost effective for me since the 7.5 was free, the 30 spline moser axles are $270, and the disk brakes and 3.73 gears came in the $75 zr2 s10 rear I got from the junk yard. The only painful part was a truetrac but that was after I grenaded a Yukon clutch posi.

As dumb as it is a GN 8.5 is still a cost effective method most of the time if you can find one.

A nodular case 9" with a good locker and a disk brake setup isn't cheap. I have built a 9" for a G body and you basically fork over $2grand+ up front or hunt (and usually fail) for a decent 31 spline posi and 3.23-4.11 gears. All the used 9" cases I find used are cheese grade ductile, 2.73 28 spline stuff, or spools with 6.83 gears for dirt racing. I spend an unhealthy level of time on classifieds pages and have essentially never seen street rated 31 spline lockers for 9" come up for sale with gear ratios that are useable. It's basically impossible to price out a posi 9" carrier for under $1000 new.

I wish the hotrod industry would spend more time looking into AAM 8.5" 10 bolt or 9.5" 14 bolt semi float stuff since they are actively going into the junk yard today with 30/33 spline carriers and have much superior gear patterns and way more efficient (the 9" is like a 2/10 on the efficiency rating, it's inadvertently strong because the pinion is jammed way off center)

Just my ramblings....

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gnvair

G-Body Guru
Sep 1, 2018
865
93
Southern New Jersey near Philly
Ask yourself how much will it cost to properly rebuild a given 8.5 on top of the purchase price.
Good 30 or 33 spline axles?
Aftermarket 30 or 33 spline carrier?
Bearings?
9" style ends or c clip eliminators?
Billet or chromoly yoke?
Girdle cover?
You could have $2 grand into it by the time you are done.
 
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melloelky

Comic Book Super Hero
Oct 22, 2017
2,957
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mass
Ask yourself how much will it cost to properly rebuild a given 8.5 on top of the purchase price.
Good 30 or 33 spline axles?
Aftermarket 30 or 33 spline carrier?
Bearings?
9" style ends or c clip eliminators?
Billet or chromoly yoke?
Girdle cover?
You could have $2 grand into it by the time you are done.
I don't know if co$t is@the forefront of the reasoning here :sneaky: sure deep down but putting a proven aftermarket ford style part in their GM's is just to hard on some people.no one clears their throat when someone posts a picture of installing a set of c-clip eliminators in their (insert any 10 bolt here)another proven aftermarket ford style part.ill do you one better,show of hands how many of you have run a jeep shaft in your life? chrysler?the horror,that's cross breeding rite there.those of you paying attention my hands up also.im also running a 99 f series upper radiator hose in place of my lower because I needed one with the 1-3/4 end and while I'm @ it my brake vac pump is out of an audi and it's quieter and more efficient than those rebranded airbrush compressors they push as brake assist operations.:p:coffee:
don't be scared kids..it's all the same they're parts
 
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