How Strong Is The 8.5 With 30 Spline Axles

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Boost231

What's An Intercooler
Staff member
Joined
May 26, 2001
As the title says, how strong is the 8.5 on 30 spline stuff. Guessing it should live a long time in the high 1.3 range. Weak point being the ring gear?

Also at what point do 1/2 studs become a weak area?

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Ive seen a bone stock rearend go 1.45 60 ft and 10.40s in the 1/4. Car weighed in at 3400#s off a transbrake. The rear has over 50 1/4 mile passes, no issues at all. I would think a 30 spline setup should be ok in the high 1.3 range depending on weight. My buddy has a 7 second car with 1/2 in studs and he’s about 3200#s.
 
They can go a long way no doubt. A Ford 9" is bolt in on G-bodys and it SUPER easy to work on. Just my $.02.
 
Depends what you plan on doing with it, I guess.

Mine has got a TA rear cover/girdle, 30 spline axles, Eaton posi, and has held up nicely for well over 15 years now. This work was done before the twin turbo conversion. However, I must admit we have never launched the car very hard. A few 60's in the high 1.4's back in the day. But mostly softer 1.5's and 6's.

Still, it's driven more often than most less modified TR's and gets a good workout all summer and every summer.
 
If you plan on racing your 8.5 , weld your axle tubes. If you plan on selling it and going to a different rear end, the demand for a GN rear end is high in the GBody world. You can easily sell it for near 1/2 the price of what you intend to install. I bought a used 8.5 that had a lot of bracing and mods done and the only thing that I changed was a 3.73 back to a 3.42.
 
Tubes welded, brace kit, highest spline count you can and it helps, the low 60's slowly kill it
 
I wouldn't try to make it live with consistent 1.30's ... I've seen stock ones let go with 1.50's

Weight of the car has a strong impact on longevity .. if your talking a handful of launches over a few years .. no big deal

Word of caution .. if your going to gamble .. check the axles often for twist ... broken axles can make a mess
 
Boost231 said:
As the title says, how strong is the 8.5 on 30 spline stuff. Guessing it should live a long time in the high 1.3 range. Weak point being the ring gear?

Also at what point do 1/2 studs become a weak area?

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Click to expand...

With hundreds of 9 sec. passes with 30 spline axles and 1.40 leaves and better, the weak point is the ring and pinion.

The ring and pinion was changed at least every other race season.
 
I started killing ring and pinions at 9.30's and 1.30 60 foot times at 3600 lbs with transbrake. It twisted the axles at the splines after about 5 years of it. Would knock a tooth or two off the ring gear every year and actually bent the axle tubes several times. If you are going to beat the crap out of it put a 9 inch in it. The axles where 30 spline Mosers , axle tubes welded, and TA rear cover. I have not hurt the 9 inch since i put it in.
 
it WILL fail at some point, trans brake, big slicks, quest for good 60 ft times,
just call quick performance , and be done with it, ( consider 35 spline axles in the 9in , over kill? yup, )
why tempt fate?
 
What about running a spool on a strip/street car? I’m on borrowed time with my stock rear and axles. 1.3-1.4 60’s 3650#.


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wb_7354 said:
What about running a spool on a strip/street car? I’m on borrowed time with my stock rear and axles. 1.3-1.4 60’s 3650#.


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Click to expand...

It sucks !
The spool is a pita in the street
 
Nick Micale said:
With hundreds of 9 sec. passes with 30 spline axles and 1.40 leaves and better, the weak point is the ring and pinion.

The ring and pinion was changed at least every other race season.
Click to expand...

I'm going to add another data point to this.
I don't drag race, and I still chipped a tooth off the ring gear. Best I could tell is an outer bearing locked up, then spun and that knocked the tooth off. Lucky for me it ended up stuck to the magnet on the back cover.

Inspect and record.
 
wb_7354 said:
What about running a spool on a strip/street car? I’m on borrowed time with my stock rear and axles. 1.3-1.4 60’s 3650#.


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Click to expand...


ran a spool with 33 spline axles in my 8.5 for a very long time. no issues at all except backing up in reverse which sucks but its not all that bad. i sold that rearend and went with 31 spline and disk brakes. next will be a 9" of sorts
 
Boost231 said:
ran a spool with 33 spline axles in my 8.5 for a very long time. no issues at all except backing up in reverse which sucks but its not all that bad. i sold that rearend and went with 31 spline and disk brakes. next will be a 9" of sorts
Click to expand...

That's what I have now, doesn't bother me...with 18 psi in the MT DR Pros it's a little jerky, but throw more in them for driving around and it smooths out on the slow turns a whole lot.
 
It will take a damn lot for a long time if no tire shake occurs.


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Boost231 said:
Guessing it should live a long time in the high 1.3 range.
Click to expand...
dont bet on it.the main factor is weight of the car,take a 3800/3900 tr loaded up dead hook it on a track or street and it becomes an issue.ring and pinion,bending axle tubes,will usually break before the axles.most guys roll the dice on the rear it just depends on how bad you shock it and weight your trying to move.
 
Mr.Spool said:
their fine
Click to expand...

Yup.

The studs provide clamp force. The friction between the wheel and the hub face is what keeps the hub from spinning free of the wheel.

As long as the clamp load is enough to make that interface solid, you're good. Even the stock 12mm wheel studs should be able to be torqued enough to provide enough clamp that you're not going to have a problem.

If you shear the studs off, then you didn't have the wheels properly torqued or the studs were fatigued to the point they weren't clamping properly anymore.

If you want to be sure, you can treat them like rod bolts. Measure the stud lengths with a caliper, record it, and check them periodically. If you see them starting to stretch, replace them.
 
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