How fast with an 8.5 rear and what was done to make it hold up?

[GNVAIR]

I have a GN 8.5 rear for my Malibu and am in the process of building a stroker LT1 with a Tremec TKO 5 speed with nitrous. This would be more than enough power to put the car into the 10's.
What is the limit of the GN 8.5 rear when used with a good 30 spline after market axle and a 800 pound preload after market Eaton?
I spoke with a gentleman that runs A&D auto in New Jersey and he explained that even after I add those items and a girdle that the weak point becomes the axle tubes since they are only 2 3/4". He said the amount of flex a high horse power engine puts on the rear can still break an axle because of this flex.
He recommended that I go with a 12 bolt since it has 3" tubes that are actually have a thicker wall thickness than the 8.5.
He also recommended against using 33 spline axles at all since the inner diameter of the carrier where the axle goes in, makes the carrier bearing register paper thin thus creating a weak spot.
Lets hear what some of the mid 10 second and faster guys have to say.
2 things I have going against me are the stick and the nitrous, both of which hit the rear way harder.

 

[Two Lane]

Lee,

I'm a GM diehard, but if the upgrades you planned for the 8.5 are deemed insufficient, I'd skip the 12 bolt altogether, & go directly to the Ford 9".

Not much difference cost-wise, significant difference in strength.

HTH

 

[Lee Thompson]

8.5 rear

I have seen this personally.
OC Cantrell goes low 9 s @ 148 mph with a 8.5 rear. occasionally standing it up. He has Richmond 3.73 gears, spool and 33 spline axles. He also has the large aluminum cover with the braces. This rear has held up for 3 years. ---Trans brake
Dave Poppe goes 9.40 @ 141 with a 1.29 60 ft.----foot brake

If done correctly, IMO the 8.5 will handle lots of power.

 

[Mike_G]

Jack Cotton is running a 8.5 into the low 9s, He also launches off a transbrake ...
A properly Built 8.5 can go along way...The 8.5 he left on the track at BG was replaced with another equipped with a spool<was an eaton posi up til then>,axles, and C-clip eliminators

 

[STP]

I've seen plenty of 8 sec mustangs still running a 8.8 in..You've seen how some of those guys leave the line on the jug....8.5 will do the job

 

[GNVAIR]

I had considered the Ford 9", but there were some down sides to it. First off, the driver side axle is always the weak side on the Ford 9" since the axle shaft is shorter on that side plus because the carrier is so small, it is very hard to get a decent posi unit; and I dont consider a Detroit Locker a posi as most of them never unlock......its just a very heavy and expensive spool in my eyes.
I guess what I am actually looking for is someone that has broken an 8.5 housing or an after market 30 spline axle in one and what actually caused it.

 

[86brick]

Lee, how much does/will the car weigh with you in it?? Maybe Cal Hartline will chime in cause he seems to be going the fastest with the factory 8.5 rear (8.63 @159mph with low 1.3 60' times and his car weighs 3450lbs if I'm not mistaken).... I would think as long as you correct the weak points which seem to be the axle tubes and posi you should be fine unless the car is really heavy (3800-4000lbs or more) and if it is on the heavier side you might want to consider the 12-bolt....
HTH

 

[Chris Taylor]

With the combo you have listed you will have no problems with the 8.5 rear. That is if it is set up right.

I have a friend that uses a 8.5 in his 69 Nova. This is a 3000# class racing car turning 1.2 60's. Third season and no problems.

 

[matt87]

order a dana 60 and forget about it. i think strange makes them ready to bolt in for about 1700.00. a little heavy but it doesnt rob as much hp like a ford 9".

 

[GNVAIR]

Originally posted by ILBCNU6
I believe Jack broke off the pinion yoke at BG on his last run. The new "Moser" 12" might be a good choice too! Of course the Ford 9" will handle lots of abuse. The 8.5" rear would need the axle tubes welded to the carrier housing with aligning the bearings, add the new outer bearing retainers,( eliminating the C-clips) a girdle housing with the axel supports would make a strong set-up too! Why not buy a TR and drive it to the track, cruise nights, and run 10's all day? Sorry but I had to add that! Good Racing! Gene

I plan on running a Mark Williams billet yoke so I can run 1350 series u joints on mine, so that weak point is eliminated.
I have a guy here local that sets up rears. I was planning to have the tubes welded and straightened and get the bolt in style flanges that Mark Williams and Moser sell that allow the use of Ford 9" style bearings. I am also going to run an LPW cover. From what I was shown, it is the best on the market. Believe it or not, the TA cover does have the set screw/reinforcement bolts tapped all the way through and the can strip out. People I have talked to locally said the housing brace is just "window dressing" and really doesnt do much. Again, I am just going by the info I have accumulated from speaking to different people.
I already have a TR that is knocking on the 10's.
I wanted something that was V8/stick shift that was just as fast.
My Malibu is heavily optioned like my GN and with the stroker LT1 it will be just as driveable.

Originally posted by 86brick
Lee, how much does/will the car weigh with you in it?? Maybe Cal Hartline will chime in cause he seems to be going the fastest with the factory 8.5 rear (8.63 @159mph with low 1.3 60' times and his car weighs 3450lbs if I'm not mistaken).... I would think as long as you correct the weak points which seem to be the axle tubes and posi you should be fine unless the car is really heavy (3800-4000lbs or more) and if it is on the heavier side you might want to consider the 12-bolt....
HTH

The car honestly will probably be around 3500lbs when I am done
It will be a late model LT1 based engine with aluminum heads, Tremec TKO 2. It has almost every factory option on it (air, gauge package,power bucket seats, console, power windows and locks, tilt, F41 suspension, power trunk, etc.
I have upgraded the brakes and some pieces of the suspension.
I added 16x8 GTA wheels, aluminum radiator support and will have a steel Goodmark cowl on it soon before it is painted. I am trying to keep the body all steel. I am still trying to decide whether to go with fiberglass bumpers since the stockers weigh a ton. But the hood, fenders and trunk will remain. Along with all the sounded deadening since I like my cars somewhat quiet

 

[GNVAIR]

Originally posted by ILBCNU6
I run the TA housing cover, and I believe the LPW cover has the same style carrier cap tensioner bolts, no leaks from mine either. (you torque them to a inch lb setting only) You are on the right track in reinforcing the rear end and I'm going to do mine too! Another choice is a GM B body rear end which has the 3" tubes and bolt in axle retainers stock. I'm looking into doing that modification on my GN instead ruining my stock rear end. The Buick built rear ends don't even compare to any Chevy or Corporate one! (3" tubes and huge axles that are much bigger than any chevy 12 bolt) All Chevies make HP with ultra high rpms compared to any Buick engine. I like all flow with maximum blow engine, without a taste of NO2 or Geritol! I'll be building a 800 hp street combo soon! Good Racing! Gene

The LPW cover is tapped all the way through where the tension bolts thread in. The TA is only tapped about 1".
The B body rear end swapping would be very involved since the 77-96 b bodies were just the 73-77 A bodies with a different body on them. Putting a late model 8.5 from a b body into a g body would be just as involved as installing an early 12 bolt into one. The upper control arm ears are on a different angle, the coil spring pads and the lower shock mounts would have to be changed; besides narrowing the housing.
The main issue with the g body 8.5 is that GM cast a new 8.5 center section with the g body style ears and used the same small diameter tubes as they used in the 7.5's.
Yup, there is nothing as sweet sounding as a V8 spinning some R's and rowing the gears. Its a nice to be able to choose what I want to drive on a given day

 

[turbo buicks]

the guy who built my tranny, Rich Bracchia, who owns Victory Transmission has gone 9.50 w/a stock rear end and driveshaft. hes putting in a t88 this weekend and will be shooting for mid 8's.

 

[Louie L.]

Cal Hartline just went mid 8s at the Snowbird nats with the 8.5. Strange spool, Moser 33 spline axels, TA girdle, c clip eliminators ....thats It!

 

[NastyGn]

Originally posted by GNVAIR
I guess what I am actually looking for is someone that has broken an 8.5 housing or an after market 30 spline axle in one and what actually caused it.

My personal opinion is what will effect the 8.5 the most is the weight of the car. Mine is 3650 and I never broke the axles or the housing. What I did was the pinion gear sheared off all the teeth of the ring gear after running three 1.33 60's the 4th one it made a big BOOM. From what I seen and read like you all have.
(many people running faster than me) is that the 8.5 is a strong rear end but I think the weight of the car is what will kill them.

My 8.5 rear end had the 30 spline axles, welded tubes, Detroit Locker and aftermarket rear cover, c-clip eleminators with bigger bearings on the end. You can not get a set of pro gears for our 8.5 rear ends. No one makes them. So after spending a total of $1,700 to beef up the 8.5 and then to fix it after I broke it I went with a 9".

Have a Happy Holiday.

 

[REDS HOT AIR]

you'll have some bad luck..

my last malibu went bottom 10's with a 7.5 rear with all gm parts in it....406 sb with nos lasted a whole season then got rid of car

buddy's 84 camaro been 9.70's on 7.5 gm guts and moser axles ...468 bb with small shot of nos been going for 4 years now

another buddy in a 85 monte ss running 1.42 60 fts with 406 sb all motor high 10's with richmond gear gm auburn unit and c-clip moser's broke twice with stock axles but been going fine since mosers

but if you have any wheel hop any rear will break no matter what you put in it.

so gm gear eaton unit and mosers should be plenty for tens with a 8.5