Strength of 8" versus 9"

[gearheadbill]

Can anyone give me some knowlegable feedback as to the strength of a Ford 8" rearend. From what I can see and have heard, it's similar to a small bearing 9", cept it's got an 8" ring gear rather than 9". I have a very nice 56 1/2" wide 8" I want to use in a coupe I'm building, but don't want to shoot myself in the foot. Car has a mildly built 425 nailhead/th400 combo (500+ lbs/feet torque) but I'm usually very gentle with my cars. Thanks for any help.

[flyin'eye]

Breaking a rearend usually has more to do with traction than the power your engine is making. I've ran 8" rears in 2 cars, never had a problem. Unless you're using a big tire that's gonna hook real hard, you should be OK.

[Andy]

I've used a 8' from a Maverick under a 32 roadster for at least a 100k. No problems. The question should be how much weight (traction) do you have. No weight=no way to load the rear.I like them because the car will ride better with less unsprung weight. http://www.jalopyjournal.com/ubbthreads/images/graemlins/smile.gif

[old beet]

Main reason for running 9in in street cars= choice of ratios and easy to find posi units. Seldom see an 8in break......OLDBEET

[Levis Classic]

8 inch is good to about 375 hp - anything above that you might want to go with the 9"

[**DONOTDELETE**]

I run 8's in everything I build. Maverick rears work great, fit perfect in 32-34 Fords and the pumpkins are smaller. Huge hp might fuck one up but all my motors barely run anyways..... so there you go.

As a matter of fact, when my Quickchange blew up, I put an 8 back in it. I have never replaced one and i have never paid more than 100 bucks for one.

[Deuce Roadster]

[ QUOTE ]
8 inch is good to about 375 hp - anything above that you might want to go with the 9"

[/ QUOTE ]


http://www.jalopyjournal.com/ubbthreads/images/graemlins/smirk.gif

In the 60's when Ford built Mustangs ...they used the 8 incher for the 225HP and less models. When the HiPo ones came out (271 HP) ..Ford went to the 9 inch. http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif


Ford must think the 8 is good for LESS than 271 HP.

Lots more gear ratios for the 9.
Lots more of them made by Ford.... 1957 to the mid 80's



http://www.jalopyjournal.com/ubbthreads/images/graemlins/crazy.gif

[286merc]

Many popular street ratios are plentiful in the 8", its when you want 3.8 and steeper that the 9" takes over. I have several 3.25 lockers out of 65-6 Mtangs. The circle track guys are big into the regular 3.25 and 3.5 and they are plentiful around racing towns.

Also there are several versions of the 9", the 57-60 arent true 9", they have a 8 3/4 ring and a weak WAR casting ID housing.
The HD big bearing 31 spline 9" is the racing one. Those command big bucks now that the pickup truck roundy racers are allowed to use them in GM's!

Good comment about unsprung weight, there is certainly a noticable difference when lifting them. Anybody know the 2 weights?

[Lionheart]

Deuce, your right on. In 65 my new 225 hp Mustang 8 in. rearend literally exploded on a power shift to second gear. Busted the pinion housing out and drive shaft bent up like a pretzel. Found the parts in the ditch about a block back. Cleaned out my shorts,had her towed back to the Ford dealership i worked for and put a 9 inch in. It's still in there.....Lanny

[59BuickWagon]

I had an 8 3/4 Mopar and had a total of 300,000 on with no problems. Went to an 8" to get the tires under the fenders and lost 4 axle bearing due to too much weight. Never had any center section problems though. So what's this going in, anything heavy?

Dennis

PS Now have a Currie 9" with BIG bearings and no worries:)

[buzzard]

I have an 8" in my A coupe. It's open drive. I've broken 2 sets of rear wishbones, sheared the driveshaft, and broke the welds on my ladder bars. No probs with the 8". If I can find a posi unit for it, I'll keep it. Otherwise, I'm going 9".

[38Chevy454]

I have to agree with the general consensus that the 8-inch will hold up fine on the street with street tires. You will break the tires loose before the rearend breaks.

I had a friend that used to race a 8-inch 4.56 mini-spooled rearend with trans brake and slicks. Would hold up for a low-budget then it gave out when he switched from a 302 to a 351. Guess that little extra torque sent it over the edge......

Bottom line, a 8-inch should be fine for any small block on the street, or big block in a light car. Get a high torque engine and get it hooked up and you are in trouble. http://www.jalopyjournal.com/ubbthreads/images/graemlins/shocked.gif http://www.jalopyjournal.com/ubbthreads/images/graemlins/shocked.gif

[zibo]

the driving style makes a huge difference,
if your a cruiser or a burner.

rick bradley (ojai) with the 6pot hemi 30 sport coupe-\
has a later '42 banjo truck rearend in his ride.

the guy drives his shit so hard,
he actually broke an axle,
not the key,
the axle.
that was after 5-600 miles,
umpteen burnouts
and hard takeoffs and turns,
with slicks.

you would just figure,
that an 8" has to be stronger than those old banjos.

--------------------------------
I remember searching for rearends for my '53 suburban,
and all the pics had 12 bolts in the rear,
but I found a 10 bolt posi,
that was rare for the time,
but htat rear end is too strong for the puny motor.

-------------------------------------
the 8" looks good too,
nice and round and bowled,
and the gear ratios are usually
freeway ready.

-------------------
good luck!
tp

[roadstar]

A friend of mine has a 8" in his 40ford coupe and has a 375hp pontiac with a four speed. He beats on it constantly and has only broke the pinion flange. If you drive your shit easy like you say it will last as long as you have the car. And if you want to get on once in a while it should hold up fine.

[gearheadbill]

Thanks to all who replied. The 8" I have is almost completely brand new; rebuilt diff, new brakes, bearing etc. and since it's going into a fenerless 32 coupe running bias ply tires, I'm gonna go for it. Have always used 9" or 8 3/4" Mopar rearends in past: never an 8". I guess I'll find out. http://www.jalopyjournal.com/ubbthreads/images/graemlins/smirk.gif

[rickyracer1962]

FUCK 8" rear ends. blew 5 of those things up, finally found the right size 9" put it in and havent grenaded it yet. i dont think they will live long behind any car your going to be playing around with, unless you have a 75 horse small block chevy like low-n-loud. http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[Jake H.]

The only people I know that run eight-inch rearends with no breakage problems have relatively light cars with mild engines and/or drive like grannys. Super secret hamber boneyard tip: if you can find an old thunderbird from '58 thru '63, they have a nine-inch rear much narrower than other factory offerings.

[prime mover]

I have seen 8's take a shit ton of beating mostly in lighter cars, I have 3 cars with them and wont ever change.

[rickyracer1962]

maybe your cars dont hook up? of maybe your running 75 horsepower small block chevys. who knows.

[prime mover]

what are you running that broke 5 8 inch reareads? The only people I've heard downtalk them never owned one.

[rickyracer1962]

was running them in my ranchero. daily driver, mild 289 with a top loader four speed.

[SimonSez]

I have seen an 8" rear in a 12 second 3400 lb car without breaking, but it was an automatic on street tyres and not hooking all that hard.

Maybe they aren't up to the sort of punishment that a 4-speed can dish out ???

[old beet]

289 with a top loader, you'd be lucky to break WIND....OLDBEET

[rickyracer1962]

hahahaha.... yeah 289's are slow. anyone want to race? http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif

[prime mover]

what do you run in the 1/4? my 289 is slow for a reason.

[SamIyam]

I'll race you with my 283 and wax your ass by two seconds in the quarter mile... http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif
Sam.

[rickyracer1962]

when did you get a 283 sam? what did you do with the 350 that was in the roach rod? http://www.jalopyjournal.com/ubbthreads/images/graemlins/grin.gif