8 inch strength?

[alcino]

My 8 inch rear has stood up to some abuse, but I wanted to know who has broken one, where did it break(casing, pinion suport, axl, ring, pinion, yoke), what hp/tq were you pushing, what trans(stick, auto), and what were you doing(side steping the clutch on slicks at 6000rpm).

Currie makes an aluminum casing(alumin8) for the 8 that is stronger and lighter than the stock, plus they make an alumim pinion suport that has a bigger bearing adding more strength. I was hoping most of the issues of breaking involved the case, pinion support, and or axles(since I upgraded to better ones).

thanks for any info

 

[Blue Thunder]

The 8" looks just like the 9", but slightly smaller. It's not that easy to blow one up. I would imagine that the axles would be the weak link. If you get a new chunk and carrier unit, I would suggest getting the higher spline number, so you could also get the matching larger axles. The aftermarket race axles are going to be a lot stronger than stock units, even at the same spline number, so I doubt you would ever break a larger one.

P.S. oops, I'm still half asleep, I missed the part were you mentioned that you already got new axles. Problem solved.

 

[alcino]

Ya, I got Dutchman 28spline axles. I don't think the 8 can accept anything more than 28 spline. Mustangs and fast Fords had a 68 mustang pulling 11sec 1/4 miles with an 8 and dutchman axles. seemed to take the abuse. I'm nowhere near that. So I think I'm ok for adding lots more power than I have.

Just want to ask around be for I invest money. Did you know the pinion is only 25 spline? How does it not break before the 28 spl axles? Is it the fact that the torque has not been multiplied by the diff? Interesting.

 

[1badII]

The axles aren't the weak link, it's the differential itself. They usually break the spider gears. Sometimes the ring and pinion itself. I have been told the breaking point is around 350 ft-lbs at the rear wheels, but it all depends on how you use the car. If you are making more than that and run a 4/5 speed or transbrake at the drag strip and the car hooks, then you are sitting on a time bomb. As far as street and road course/autocross, you should be fine.

 

[Mstng2]

I have heard that you can run 10 sec or lower on 8 inch. I believe that to be true. My II is running 400HP and has had no issues with the 8 rear end. (even with slicks)

 

[Blue Thunder]

Ya, I got Dutchman 28spline axles. I don't think the 8 can accept anything more than 28 spline. Mustangs and fast Fords had a 68 mustang pulling 11sec 1/4 miles with an 8 and dutchman axles. seemed to take the abuse. I'm nowhere near that. So I think I'm ok for adding lots more power than I have.

Just want to ask around be for I invest money. Did you know the pinion is only 25 spline? How does it not break before the 28 spl axles? Is it the fact that the torque has not been multiplied by the diff? Interesting.

I ran the stock 8" peg-leg rear in my 'Stang for a long time, and with 2 different engine combinations, including the 340hp 302. The car(rear was original) had well over 120k miles on it(odometer had broken) when I finally retired the 8" and installed the 9" housing. It never had any trouble at all, and I think I still have the chunk laying around somewhere, still in useable condition.

I didnt realize the axles in the 8 were 28 spline, I thought they were smaller. The 9" rear housing in my II still has its original 1959 thunderbird axles, which are also 28 spline. So far, even after 12 years, 7 of which with the 500+hp stroker motor in the car, no troubles with the 28 spline axles. If the 8" does indeed have similar size axles, I doubt they'll ever break unless you hook it to a high hp motor with slicks.
I doubt anything else will break on the chunk, either, again, other than with the severe duty mentioned above. Road racing isnt very hard on such equipment, so long as it doesnt get too hot. (thus, NASCAR runs those little oil coolers on the rear)

 

[alcino]

Good info. Thanks. I'm not super into drag racing anyway. Mostly autoX and road racing. I like trying to make the car as light as possible, so I want to keep the 8, and upgrading to the aluminum casing and pinion suport.

My plans for the future was to build a motor putting 400+ hp to the wheels and was hoping it would survive. Looks like it should since my car is light and I don't plan on "shocking" it regularly on a sticky dragstrip with big sticky slicks.

 

[alcino]

Did some research. A 28 spline 9 and 8 inch will have the same axles and spider gears. interesting.

 

[Blue Thunder]

Ever checked out the IRS setup on a vette or viper? Supposedly, it's a single transverse mounted fiberglass leaf spring with an all aluminum dana.. (60?)housing, alum. arms, some type of super tough shafts, and obviously, the viper version would be able to deal with some serious torque. A vette guy told me that the entire assembly weighs about 90 pounds. I bet the 9" complete suspension weighs over 200.
A II with a Viper IRS? Imagine that. It might even have the same 5-lug pattern. How convenient.