Is the 8 3/4 rear bulletproof?

[BBodiesRule]

This is for all of you drag racers that have a 8 3/4 bolted under a leaf-spring car.

I recently upgraded my engine, transmission and torque converter. My Cuda now cranks out 645 hp at 6300 rpm and 647 lb. ft. of torque at 4800 rpm. I am sending this power back to a 8 3/4 rear that has been outfitted with a back-brace, moser 35 spline (if my memory is correct) axles, a spool, and "green" bearings. My center section is a 742 unit. I change my rear lube once each race season. I have a TQ727 transmission set up with a Griner reverse manual valve body and a Torque Converter Techniques (a division of Dynamic Racing Transmissions) 9" 5300 rpm stall converter. The car has always run with a 727 and for most of its life, never saw more than 550 hp and 500 lb. ft. of torque.

My question is this: how often do you guys change your ring and pinion gears? I know that the weak link in the 8 3/4 is the ring and pinion gears, but I am getting confliciting advice on what to do about it. One school of thought is change them routinely, around every 100 passes. Another school of thought says, why throw away good parts needlessly; run the gears until you start to have a problem (the trick of course, is determining a "problem" before it causes damage). What do you say? What do your driveline experts tell you?

I don't want to go to the added weight (or cost!) of a Dana 60. Shoot me a response...I want to hear from the Mopar guys that use the 8 3/4 rear.

Thanks!

[rumblefish360]

NO, it's not bullet proof, The DANA is. The added weight is peanuts and requires near nil in terms of power compared to the 8-3/4 to turn. The wise choice is to get a DANA for high HP/Torque engines.
Fellas around my way are breaking them with there street 451 engines. There cars are '73 Duster and '73 Cuda. (Not mine)
My 8-3/4 has stood up to near 500 HP levels without sweating it. But, thats not exactly your power level now is it.
Don't waste your time, money and rebuilding efforts on sub pare parts. If the rear goes, you better have a rev limiter in the car to protect the engine.
When the time comes, go to Drive Train Specialists whom sell, custom fab DANA's for your car. Stock mounts or custom. Brand new DANA's built for cars. Not the truck versions.
I think I have seen these advertised @ around $1100 bucks. Bolt in, brand new.

[perfmachst]

hello, the 8 3/4 rear end has it limits. however, you can heat treat the ring gear (soften) which will extend the life of it.
for a dana?? try locating a dana 60 from a 67 to 72 1/2 ton ford pickup. this is the lighest one. there is only 32 lbs difference in weight. the dana came in four sizes. 1/2 ton ford, mopar, 3/4 ton and 1 ton. sizes. information taken from off road magazine. I have done this in my 340 duster. car ran the same. the only thing, I did was weld mopar ends on, added spring mounts. you can still use your axles and brakes.

[Eats4dz64]

On NOS Im getting a little under 600hp & Tq. I have a 8 3/4 with 391, stock axels and a 1968 never been rebuilt suregrip. I now have 2 years of bi-weekly thrashings on this rear and has been trouble free. Now im not saying this is safe or smart im just relating strength to the 8 3/4. Oh and the car with driver weighs 3380.

I use to go to this little garage in slumville to get my Toyota rear rebuilt (CHEAP), had to do it semi often beacuse it was on 44s with a stock rear. Well after breaking it twice in 2 years I decided to go to 4wheel parts and spend the BIG bucks to get good stuff and have a "PRO" assemble it for me. From there on out the damn thing broke every 2 to 3 months. Moral to the story is its not how much you spend its how you put it all together.

[creative1]

i have seen cars running 2000 hp through a dana 60... that would be from TWO all iron 392 hemis mounted inline. dunno what kind of torque, but it has to be GOBS!

there will always be someone running 700 horses through an 8 3/4... but the question is "for how long?" i think there is a reason mopar put dana 60's under all the 426 hemis... as for me, i have to be able to drive home from the track... i will keep my dana 60!

[70Barracuda]

The Dana is king!

Pefr, what is the weight diff between the Mopar car Dana and the 8 3/4?

[Beeracuda]

You didn't say what gears you have in it or what the car weighs. We have gotten as few as 65-70 passes on a set of the street gears or as many as 356 on a set of the 4.86 pro gears. All of these are transbrake launches at 5500+ at 2750-2775 lbs.

[MoparMarcIdaho]

Power than that,once spat the cross shaft right out the back and into the gas tank on a 69 runner with a warmed up 440 4 speed,but it was tired and I knew it too.I have never had any trouble with a DANA except for running my crew cab low enough on oil to starve the wheel bearings and it was so bad that I had to chip the inner race off the housing in pieces but after replacing just the bearings it is still doing just fine.Ford 1/2 ton pickup would be my choice for replacement if you do it.

[BBodiesRule]

Originally posted by Beeracuda
You didn't say what gears you have in it or what the car weighs. We have gotten as few as 65-70 passes on a set of the street gears or as many as 356 on a set of the 4.86 pro gears. All of these are transbrake launches at 5500+ at 2750-2775 lbs.

Beeracuda - See my new post "Is the 8 3/4 bulletproof - Part II"

Thanks.