Technical How much power will an 8 inch ford take?

Where is everyone getting this "8-3/4" as a Ford rearend?!?!? 8-3/4" is a MoPar rear.

Ford had the old **** rear before 1957. it should not be considered for anything but a restoration.

In 1957 they introduced the 9".

In the early 60's they introduced the 8" for lower powered cars that didn't need the 9".

Some Lincolns and big Mercs had a 9-1/4" ring gear but on the outside they look like a 9" and will take a 9" center section and gear in the housing. Be careful around these, some parts interchange, others don't.

The 8" rear was mostly found in 289/302 Mustangs, Mavericks and Granadas.

Ford NEVER made an 8-3/4" rear.

SPark

 

The rear end in your photos doesnt look like an 8 in. Ford to me . Maybe I’m not seeing it correctly , it looks Mopar to me


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I hear you Dave, problem seems to be that what I call an 8 inch Ford diff is different to the diff being discussed in this thread.
My diff is definitely a Ford diff but earlier that the ones in discussion.
I realise now the diff's we are discussing are the ones generally confused for 9 inch diff's by newbies.
The one I have, there is no way it can be confused as a 9 inch or anything similar as it is way too small and was run behind a Ford flathead engine in its original life.
Definitely not from a Mopar, but I had heard with some of these early diffs some parts were common to both.

 

Well explained and has cleared it for me.
Seems I was way out on a limb by myself.

 

The 8" first appeared under the new-for-'62 Fairlanes and Mercury Meteors. From then on at one time or another, it was used in pretty much every Ford/Mercury car with a 302 or smaller motor (except full size; to the best of my knowledge, Ford never used it in any full size) all the way into the early '80s. It was never used in trucks/vans/Broncos. It was Ford's 'medium duty' car axle, with a 7.5" 'light duty' axle used behind the smaller sixes in the lighter cars like the Mustang, Falcon, Comet, Maverick (almost always in 4-lug form); the 7.5" was never used in the intermediates like the Fairlane, late '60s Comets, Torinos or Montegos.

'49-56, Ford used two rear axles; the 'heavy duty' Dana 42 (similar to a Dana 44, but very little parts interchange) used in trucks, station wagons, taxis, police cars, T-birds and optional for 'performance' versions. The 'standard duty' was used in everything else. The easy identifier for both of these is the u-joint; rather than a conventional yoke with u-bolts, these used a flange arrangement with machined and threaded bearing cups on the u-joint that bolted to the flange. Major repair parts are getting hard to find for these, and gear ratios are limited; the 'tallest' ratio offered was 3.32 IIRC, with most being in the 3.7 to 4.1 range, although some were as low as 4.6.

 

Yes Steve you have nailed it, mine is the '49 - 56 non Dana diff with the bearing caps as you described at 3.7:1 ratio. Great little rear end for a light not too powerful drive line.

 

I have the stock 8" in my wife's comet running a 302 making 362hp to the tire on a ch***is Dyno with a tremic 5 spd. Never broke it yet. Had the 8" in my 65 falcon with a 615 hores 331 stroker that ran 10.30's with good axles and never broke a thing. With a 8" wide slick that car went a best of 1.41 60' on a foot brake hanging the wheels 9" off the ground. They live a long time in light cars with good power...

 

The 8" rear was also in many Fairlanes, Comets and in late 70's Mustang II's. I've never had a problem with any of them.


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The 4 lug version was used on 4 and 6 cylinder cars, and has smaller necked down axle tubes and smaller brakes than the 5 lug versions. When the 250 six came out, cars with it got the 5 lug axles with the larger brakes. Only 4 lug version that I know of that was used behind a V8 was in the Mustang II's. All were 28 spline as far as I know. Chunks are the same, only difference is the early rears had the fill plug on the rear of the housing, and the later ones had the fill plug on the chunk. Something to look for, if you use an early chunk in a late housing, you have no fill plug, and if you use a late chunk in a early housing you have two fill plugs. I'm using a late chunk in an early housing in my car.

 

currie makes an updated pinion carrier...that and drilling/tapping the holes deeper and using longer grade 8 bolts to attach it goes a long way in increasing durability......also use the '67 up reinforced case (currie even made an aluminum case) someone makes a 31 spline trac loc but that may be overkill on an 8......also stick with 3.55 or higher (lower numerically) gears.....more teeth on pinion...

 

Yeah, I had to do a quick swap at a shop where I worked. Forgot about that little "feature". I ended up having to fill it, slowly, through the vent tube.

 

Ford did make a 8-3/4 version of a 9" rear..Why for I have no clue but they take a smaller dia thread on the retaining bolts..Have to use a bolt with a 1/2" dia for a bit under the head then 7/16" threads for the ring gear..I have a 3.89 set out of a 62 station wagon...The 9-1/4 is actually a 9-3/8" and usually had a 4 pinion open diff, not sure if posi was available..

 

Yup. For the first few years of the 9", it was not 9".

 

I ran a 8"with 4:11;s, and 7" wrinkle walls at the drag strip in the 70's behind a pretty hot 289, never broke it. My friend however split the third member of his 8" in two, right behind the pinion bearing running a 260 two barrel. Wheel hopped twice and bang.
Would a 8.8 out of an early Explorer with the drum brakes be a reasonable compromise? The weight I think is somewhere between a 8" and a 9".

B

 

My first car was a 68 Cougar XR7, 302, 2bbl, C4 trans, I also broke 6 or 7 pumpkins. I would never use an 8 in under anything! Then I bought a 68 340 4 speed Dart GTS, Never bought another Ford! 3,4 and 5 thousand RPM clutch dumps, and the 8 3/4 took it all.

 

Anything can be broken, if you try hard enough.

 

I'm broke and I did not even try... hahaha!

 

The 8" would hold up best behind an automatic. Just avoid the 4-luggers and try to get something as late as possible.

Another weak link is the pinion flange size. With some regret I have a 1310 in my Ford with a 9" Trac Lok 3.89 ratio. I don't pull hole shots with it, I'll tromp on it from a roll. Trans is a 4-speed.