Technical Rearend question

I am starting my roadster pickup build ( starting with a t bucket project that was running and driving at one point). The question I have is it came with an 8” ford rearend in it , I would like to keep it if possible, I am curious if it will withstand a 300-400 hp small block Chevrolet with automatic transmission? I plan on building a nice driver out, which we all know my have a hard launch ( lead foot) from time to time but not planning a full race car. I am open to suggestions, I know a 9” is more bulletproof but would like to use what I have if it will hold up, even if I have to upgrade it a bit.


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Not likely to get enough tire bite in the lightweight rods we build here. Sure, you could break it with posi, slicks and the right rear setup.. but A/T and just stuffing it won't or shouldn't hurt it. One good thing is that there are lots of ratios you can get for $140 shipped on ebay...and it's lighter than a 9" so it helps a tiny bit on "unsprung weight" which helps the ride.

 

Use it! It will be fine.

Pat

 

Keep it. Run it.

Unless you have a set up chassis, on slicks, on a sticky track, and the axle is already beat-up, it will stand up just fine.

Even then, it still will probably be fine.

 

People discount the strength of the 8". It will hold a lot more than you will be throwing at it.

 

It will hold up fine.

You might just as well have the pleasure of pounding the crap out of it and breaking it before you pull it out and throw it away. Then you will know the limits of that particular rear axle assembly, but the next one might be different. At least that is my perspective. Gene

 

Mine is out of an early fairlane. It has the skinniest axles I have ever seen. I was running 235/75s at 19 PSI on my A with a 327/PG and a 3.55 gear when I was driving it. All it ever did was spin the tires if I hit it hard. Never hurt the axles. The gears came out of a Pinto/Bobcat 6 cyl. MT wagon. All strengthening a component does is move the weak spot.

 

As long as you're traction-limited, it'll hold up. And it's not HP that kills them, it's torque. Ford limited these to use behind 302s and smaller motors, once they hit 351" the 9" was used.

 

I'll agree with that most of the time, but Ford is known for some goofy things. I've seen 8" rears in Granada's with 351W's from the factory, as well as Granada's with 9" rears and a 250 I6. The 8" in my car came out from under a 66 Fairlane that was a factory 390 automatic car. These might have been Friday or Monday cars, there might have been a mixup, or it could just simply be they used what was in the parts bin that day.

 

Use it enjoy it and never look back , lots of facts are from benchracers ! It will be fine , I have beat an 8 in for years no issues , sold to a buddy still bangin on it today no issues

 

Yeah, Ford got sloppy in the late '70s and used the 8" behind some 351Ws. But at this point, they were smogged so badly that power was less than what the earlier 289/302s could put out, so they would live behind them.

If four wheel discs were ordered on the Grenada/Monarch, you got the 9", regardless of engine. And I strongly suspect that the '66 Fairlane had a rear axle replacement before you got to it.

Too much torque in the 'average' car would kill the 8" pinion bearings if you didn't break it....

I'd go with a 8.8 these days; if they're good enough for full-size trucks, they'll hold up in a car.

 

I don't know if you have pick and pull in your area,we bought a 8.8 with posi and choice of drum or disc brakes for less than 150 complete on there deal on 3 day weekends

 

Friend of mine replaced the clutch on a customer car. When he took it out on the main drag for "testing" the enormous torque of a stock 302/manual three speed ripped the 8" pumpkin clean out of the housing. You've already admitted you're going to thrash on the car, do you really want to spend time cleaning 90 weight gear oil off of a public street?

 

Pics, or it didn't happen.

 

Which reminds me, I need to get another one.

 

I think I've broken at least one of just about every rear axle a car company has installed in a car or light truck. My motto used to be "If you haven't broken it yet, your not trying hard enough."
The odds are the 8" will be fine, and its already in the car. If it isn't, after he brakes it, he can choose something tougher that will move the weak point to somewhere else.
Oh, and for the record, I never had to clean up a public street after something broke. Gene

 

Broke two 8.8's, a 9", an 8.25 , a 7.5 and whatever that POS was in my 62 Comet with the 170 6cyl. Oddly enough, I haven't broke any since I passed my 40th birthday about 20 yrs ago. I guess they're building them better now...

 

You're traveling through another dimension, a dimension not only of sight and sound but of mind. A journey into a wondrous land whose boundaries are that of imagination. That's the signpost up ahead—your next stop, the Twilight Zone!

 

Exactly.

 

I used a maverick 8" [3:00-1 open differential] in my 49 ford coupe with a 300 HP 355/350 turbo with a shift improver kit. Car was about 3100 LBS and had fairly skinny tires. Never had a problem.

 

My '65 Mustang had a 289 4 speed, and 8" rear end.
When the car was about a year old, I was giving a couple friends a ride. One was in the front and the
other guy in the back seat. Wound it up in 1st, speed shifted into 2nd gear, and all hell broke loose.

We coasted to a stop, walked back down the road, and there, close to the ditch, laid my twisted up drive
shaft, pinion gear, all still attached to the pinion housing that had busted out of the 3rd member housing.

It happened to me, so I Know it can happen. Maybe that is what happened to junkman8888's friend.

 

8" in my 40 behind 330HP and after 30,000 miles of fun driving, no problems whatsoever.

 

ran a few but with basically stock 302's, no problems... the mavericks were about 49.5" between backing plates... good fit in a model A...

 

Now this is possible . I've seen plenty of 9" pinion flanges break. I'm sure you could break an 8 " with a stick shift car.. I know I could.
Lots of folks on these forums don't quite understand what breaks rears, driveshafts , transmissions, and what doesn't.

 

Run it, unless you got slicks and a 4spd it will work just fine.

 

plenty strong , use it , break it , then go to a 9 inch !!

 

The 8" will be more than enough.
9" Fords are huge and will look too big.
Something to think about.

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He’ll be a man step up to a Rockwell , I have broken them . Maybe you can break on in a Rod

 

Some people have no mechanical sense!
8" is plenty strong enough for a hot rod with a mild 400hp motor and
the type of tires we use on real hot rods. AND it will have less parasitic drag/friction than a 9".
A drag car /slicks etc or something with stupid looking 20inch wide tires, that is another story.

 

I just had built a nice little 9" posi 3:70 gear . 31 spline. Centered pinion, out of a Maverick. 57" mounting surface to mounting surface. Hemi coming aboard. Salute!