How fast on a 8.5 10 bolt rear?

[BABY BOEING]

Hello all, I had a disapointing outting at the track this past Sunday when I broke 7 teeth off my ring gear. The rear end is all factory stock GM and the pass before it let go neted a 1.54 60 ft. time (allthough I did try to leave with more boost when it let go). I'm considering rebuilding with new Richmond gears, Mosier axles,T/A cover, and c-clip eliminators or should I go with a 9 inch. Can you please help by posting your 60 ft. times with an 8.5 rear and the mods you have done. Thanks in advance, Jon

 

[Intercooler]

Sounds freaky. You aren't going to hurt a good 8.5 unit with the times you are running. A 9" is over-kill and will eat HP.

 

[azgn]

1.48......figure its good to the 1.3's

30 spline Moser's, TA Girdle, Ford type bolt in axles (no c-clips), Eaton posi


my chassis guy says the GM 8.5 is as good as the 9" (unless you like to change gears often)

 

[NastyGn]

I know there are very many combinations with different experiences. My car had no problem with the 8.5 with after market axles, gears and rear cover and held up good with 1.40
60' times running 10.74's. The problem came with the new motor and going with a tranny brake. With a weight of 3650 and power to run some 1.33 60' times the rear end lasted 3 passes and I tore out all the teeth in the ring gear. it was doing some nice wheelies hehehe

So with your set up I would not think you should have a problem.

Take Care

 

[TurboDave]

Originally posted by BABY BOEING
Hello all, I had a disapointing outting at the track this past Sunday when I broke 7 teeth off my ring gear. The rear end is all factory stock GM and the pass before it let go neted a 1.54 60 ft. time (allthough I did try to leave with more boost when it let go). I'm considering rebuilding with new Richmond gears, Mosier axles,T/A cover, and c-clip eliminators or should I go with a 9 inch. Can you please help by posting your 60 ft. times with an 8.5 rear and the mods you have done. Thanks in advance, Jon

One additional thought though. If you absolutely must spend the money for a better rear end (I.E. Ford 9") Why not look into the new GM 12 Bolt? It's not as lunky as the 9" and significantly stronger.

 

[GNVAIR]

If I might add my $.02
I would try to stay with OEM GM gears as they are usuallu lapped a heck of a lot better than the Richmonds. US Gear makes a good set as well. The Richmonds tend to be very brittle. If you want a very stout combo for your 8.5, try adding either a spool or a good 30 spline Eaton, as well as some decent axles. If you drive the car a lot on the street, then you might want to steer clear of the c clip eliminators as they are almost guaranteed to leak. The best set up is the Ford style flanges available through Moser or Tom's Differentials. It converts the GM axle housing to "bolt in" style axles. From what I understand, there is now a GM style flange that allows this same set up so you can use 64-72 A body rear drums instead of having to use the Ford drums.
Final touches would be a good set of carrier studs and an LPW girdle with the housing braces.
All of which I mentioned is the set up I will be using on the Malibu in my sig. Yes, that car has a GN 8.5 rear. The 8.5 is every bit as durable as the 12 bolt when you use the correct pieces. Good luck!

 

[Scott231]

Let's not forget that Cal Hartline just went 8.92 at 147 with an 8.5" GM differential. And you think a 9" Ford is necessary?

 

[86brick]

Scott, I thought Cal went 8.92 @152mph?? I didn't know he did it with a 8.5" GM rearend though!!!

 

[laz]

The ten bolt rear is every bit as strong as a 12 bolt. I know Dave Henninger from Wheel to wheel has run one for ever and he run as fast as 8.40s@160 at 3200lbs. I know a local that riped 7 teeth off ring gear we put another used 3.42 production gear and it`s still going strong. The reason that this rear broke is it had alot of backlash the carrier bearings were shot and it hummed for atleast 1 year! LAZ

 

[Scott231]

Originally posted by 86brick
Scott, I thought Cal went 8.92 @152mph?? I didn't know he did it with a 8.5" GM rearend though!!!

147...152...whatever. The point is that the 8.5" can withstand much, much more than people give it credit. It is the force of the initial launch that can break a differential...not a top end charge.

 

[Joe 1320]

Ditto on the correct backlash...... I suspect that either the gears were replacement gears or the wear pattern/backlash were not up to snuff. These rears can take a huge amount of torque. It is also possible that the housing may have been a little "tweaked" and the axle tubes were not exactly straight. If eveything is tight and within spec, you should have no problems. Axles, now that is a different story.....

 

[GNSCOTT]

.02 time. I think an 8.5 rear works really well in a light car, but put it in a 3700# car w/ driver and try a 1.3 60ft and pray.

 

[BABY BOEING]

Thanks for all the input guys, I believe I'll stick with the 8.5 10 bolt. I wasn't aware that GM gears were better than Richmonds. Can you please tell me more about the bolt in axles that won't leak. (how much are they and where are they available from? Thanks Jon

 

[Scott231]

Originally posted by BABY BOEING
Thanks for all the input guys, I believe I'll stick with the 8.5 10 bolt. I wasn't aware that GM gears were better than Richmonds. Can you please tell me more about the bolt in axles that won't leak. (how much are they and where are they available from? Thanks Jon

Someone doesn't know what they are talking about....

You can buy street gear or race gears from most of the gear manufacturers. The street gears are harder and longer lasting...but the hardness makes them more susceptable to explosive breakage. The race gear are softer. They will more easily absorb the shock of a hardcore launch and last thorugh many such launches. On the street however, they get chewed up pretty easily from the daily wear and tear.

 

[GNVAIR]

Stay with stock GM gears if it will be street and strip. Trust me on that one. If it is race only, then you might want to go with a race gear. But IMHO, they aren't necessary.

 

[EightSecV6]

We ran 9.30's at 151 with an 8.5 at 3680#, treading on thin ice! The lighter the car, the less likely you are to break it. As far as i know there is not a "Pro" gear made for the 8.5, we are kind of stuck with the street gear, USUALLY a ratio numerically lower than a 4.10 is not availabe for any rear.
Bill

 

[SubZero350]

The GM 8.5 is a very good unit. Like many have said on here, with good aftermarket (or in most cases good stock) parts it will give you years of trouble free service.

The Ford 9 inch unit has a few issues that many don't like to admit. The ford unit is designed with the pinion riding lower on the ring gear centerline than most other diffs including the GM 8.5. This results in an additional 4% power loss over the GM units because of increased internal friction. Another important shortfall of the ford is without a stout center section, it is actually weaker than the 8.5 and not much stronger than the 7.5; so beware what you are buying before you pay for it if you must use a ford! Ford Center Sections are available in grey cast iron, nodular cast iron, billet aluminum, and others.

Those two reasons should be enough reason to stay away from the 9". If you must have more strength, look into the 14 bolt GM rear out of the "newer" trucks (if it would fit).

 

[TurboDave]

Originally posted by SubZero350
The GM 8.5 is a very good unit. Like many have said on here, with good aftermarket (or in most cases good stock) parts it will give you years of trouble free service.

The Ford 9 inch unit has a few issues that many don't like to admit. The ford unit is designed with the pinion riding lower on the ring gear centerline than most other diffs including the GM 8.5. This results in an additional 4% power loss over the GM units because of increased internal friction. Another important shortfall of the ford is without a stout center section, it is actually weaker than the 8.5 and not much stronger than the 7.5; so beware what you are buying before you pay for it if you must use a ford! Ford Center Sections are available in grey cast iron, nodular cast iron, billet aluminum, and others.

Those two reasons should be enough reason to stay away from the 9". If you must have more strength, look into the 14 bolt GM rear out of the "newer" trucks (if it would fit).

Good points indeed!! But as I tried to say earlier. The GM 8.5 is a very capable unit deeeep into the 11's with no modifications.

BUT, once you need to go quicker, by the time you sunk the money into the parts needed to strengthen it (if you're going to go FAST), you'd be money ahead with the new GM 12bolt. It should easilly take a car into the 9's with virtually no mods, is stronger, and doesn't have the aformentioned shortcomings of the Ford 9"

 

[REDS HOT AIR]

from my personel experiences i have seen more failures from 12 bolts than 8.5's in same weight / hp cars

dont know why ... i build plenty of both rears and the 8.5 is a nice unit.

Btw: the rear in my car is factory stock with 197,000 miles on it ....
humms a lil but still gettin it...will be freshining it up over the winter.

 

[TurboDave]

Originally posted by REDS HOT AIR
from my personel experiences i have seen more failures from 12 bolts than 8.5's in same weight / hp cars

dont know why ... i build plenty of both rears and the 8.5 is a nice unit.

Btw: the rear in my car is factory stock with 197,000 miles on it ....
humms a lil but still gettin it...will be freshining it up over the winter.

Are we talking about the New 12 bolts or the old ones(60's and 70's vintage)? I was refering to the new ones just released in the last 12 months.

I've seen a few of the new ones under some pretty "nasty" 8 & 9 second cars