Thread: Ford 9" rear end questions

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I've been looking for a rear end for my fully fendered Model A coupe build. I have found a few 9" Ford rear ends but none the size I need. ~58". So here are my questions.

1. Can any 9" ford rear end be cut down?
2. Does it matter if it's a 28 or 31 spline?
3. If I want to change the ratio, is it really as easy as changing out the chunk? (Is that the right term?)
4.Since I need to have it cut down. What would be the perfect width for a Model A coupe, wms to wms? 56"? 57"? 58"?

1) Yes, any 9" ford diff can be narrowed. You might want to check with someone like John's Rear Ends for the price of a new one, built to your width.
2) 31 spline axles are significantly stronger.
3) Yes, you can change out the pumpkin, but all you need is a new ring & pinion, a crush sleeve and a set of shims.
4) I have no idea.

The Ford 9" have two different ends. One is what they call a big end rear, the other a small. This you need to know from the start to get the correct brake parts, either drum or disc.
One other thing when buying a used rear..........make sure it is straight!!. it can be out a small amount and you will never see it. But if you take it to someone who knows what they are doing, they can tell you if it's straight or not.

And to keep adding...........typical tube size for the two side tubes is 3" the length of each. However, there are some '70s vintage housings, mostly from Torinos, that have a neck down toward the brake end (this is the tube, not the bearing Tom mentioned). It's not much of a problem, but could make for an odd deal depending on shortening process. Speaking of which, a qualified guy will have a fixture which consists mostly of a large, straight bar and some bearing sized end adapters to hold the housing straight when rewelding the ends on after cutting. I've known one guy who had the experience to heat the right places to re-tweak after welding to straighten a housing, but that kind of experience is not very common.

There is no "perfect" width, though any of the three you mentioned will work well enough. There are lots of choices of e.g.; fendered of hiboy? Size of tire, and even more important wheel offset; mounting method of rear end and it's components. I would probably go for the 56" myself, but I like a deep set face on a wheel, and understand how to account for wheel back space and tire bulge.

I would look for a 9" in the 50's through 60's years that has either of the wheel bearing sizes. The best bet is to find one with a driver's side axle in the 25" to 26+" range. This will allow you to shorten the passenger side only. The passenger side axle should be in the 29" + or - range. You will need to look at the drum register diameter on the axle flange and try to match these up, but register rings are available to correct for this. Also bearing offset that determines drum/shoe width must match from axle to axle. Just measure through the hole in flange from outer face to the bearing and match these up. An example: 26 1/16" driver axle plus 1 1/16" gap for spider gear shaft plus 29 5/8" passenger axle gives you a 56 3/4" flange to flange width. Great for 7" wheel and 3 3/4 wheel offset. The pinion offset is influenced by the axle length difference from side to side. Small bearing axles come in shorter lengths.

I'm pretty sure that all the early Ford cars used a 56 1/2" track, same as the width of two horse's butts pulling a Roman chariot and the same gauge as a railroad track. "Track" would be center to center of the tires on the same axle. Since you're probably not going to run the skinny litte stock tires or use the same wheel offset as Henry did, anything from 56 1/2" to 59 1/2" (1 1/2" difference per side) should work fine, depending on wheel backset and width.

From a rodder with a Model A fenderless roadster....
"I have an early Bronco 9" rear end ( 66-77). It measures 58" wheel mounting surface to wheel mounting surface.This is in a fenderless '30 model A roadster with 10" tires on 8" rims with 5 1/4" back space. This works well IMHO as I don't like the tires sticking out too far nor in too far. If you're going to run reversed wheels you may want to go with 56". 56-58" is a good range for this type of car."

From a rodder who used an 8.8" in a '40.
"I bought some new ones from a ford supplier from 2002 explorers that had disc brakes and 3.55 gears, 31 spline axles , they measure 59 1/2 face to face . we put one in the 40 sedan and it was perfect. also fit 55 chevy very good." (remember, all early Fords up through '48 were built on a 56 1/2" track, so anything that will fit a '40 will fit an A. Also, 2002 Explorer and probably other year Explorers with an 8.8" would have 5-lug wheels from the factory).

80's V8 Mustangs with drum brakes will have the narrowest 8.8" differentials and could have Traction Lock differentials.

If you get anywhere close, you can finish the width with wheels having a different backset measurement.

Here's a good article on the 8.8" unit, telling how to convert 4-lug to 5-lug.....
The Ford 8.8 Mustang Rear End - Car Craft Magazine

And another good article on the Explorer 8.8"....
http://www.therangerstation.com/tech...lorer8_8.shtml

Oh, and the correct nomenclature for the "chunk" is "third member" or "pig".

Personally, I'd be thinkin' Jaguar or Thunderbird IRS, but hey, whatever blows your skirt up.

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As luck would have it. I just ran across a Ford 8"-5 lug from a 1977 Maverick. 56.5" wms to wms. 2.79 gears but I should be able to change it if I don't like it.

I just went and checked the original rear end. It's 54.5" wms to wms. Rim mounting surface is centered on the rim. It's 60.5" outside of tire to outside of tire(not that it means much). Since I'm pushing 60 and this will be a daily driver, I think the 8" will work. Any opinions on 8" ford rear ends. (Yes I know I just took my own thread off the original topic.)

For a daily driver with 250 - 300 hp, I'd say that should work fine. Currie Enterprises, Tom's Differentials and Moser Engineering will have axles, gears and other parts for them. Detroit Locker, Detroit Tru-Trac and Auburn Posi's are available for them, as well as gears from 2.80:1 to 4.62:1. 3.55:1 is a nice all-around street gear that will work great with a 700R4 or standard 3-speed auto or 4 or 5-speed manual.

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That 56.5" Maverick 8" will be perfect for the full fendered model A. They use the same small bearing 28 spline axle as the early 9" uses. A great find! Look for original Ford 8" gears on Ebay. They are the best. What engine/ trans will you have? And rear tire size?

My understanding was pretty much all Fords before '48 can use a 56" width (flange to flange) for pretty much the same reasons stated (wagon width) I would say it could vary a bit as it could be made up in wheel offset. If you are going to narrow the axles, try to grab the widest possible, the reason is after the spline the axle reduces in width for about 3" so cutting off a axle by 3" will put you in the reduced diameter resulting in some expensive work, this only apply's if you are resplining your axles, if buying new no big deal. I used a large Harbor Freight pipe cutter to make sure the tubes where cut square (only thing I ever used it for)
Next thing I would say (my opinion only), just short of drag racing with slicks or circle track how many have ever really torn up a good rear end, has anybody?? Just curious. You should be fine with a 8", I recently saw a Top Fuel slingshot built in the 60's and they ran a 50's olds rearend, with something like 9 splines, true it never hooked up but this thing had 1500+ hp, I put a maverick 8" in my new rod and I haven't ever lost any sleep about whether its stout enough or not, true the 9" is stouter but still haven't ever heard of a 8" ever being torn up, and most non rodders swear its a 9", but the biggest benifit is the drop out 3rd member just like the 9" and the ability to get bolt on disc brakes etc. have fun Matthyj

Originally Posted by Deuce4dad

That 56.5" Maverick 8" will be perfect for the full fendered model A. They use the same small bearing 28 spline axle as the early 9" uses. A great find! Look for original Ford 8" gears on Ebay. They are the best. What engine/ trans will you have? And rear tire size?

What do you mean "...original Ford gears"? Surely not a used ring & pinion? Just my opinion, but I'd never, ever take a set of used gears over new, regardless the price. New gears are not that expensive, and even a touch of surface rust on the mating surfaces creates micro pits that lead to stress cracks that lead to catastrophic failure.

Thanks for all of the replies. If this needs replacement parts. They will be new, not used. I'm already looking into what it will take to convert to disc brakes.

Deuce4dad...engine will be a mild built sbc. Transmission is a B-W T5 from a V8 Camaro. Tire size I'm still working on.

techinspector1...I did look at Jag, Vet, and T-Bird irs. Getting one mounted in this tiny frame looked beyond my capabilities. Third member or pig. Got it.

chopt50wgn...There is a rear end place down the road from me. I will be taking it to him to have it checked.

Originally Posted by GeorgiaDad

Thanks for all of the replies.. Third member or pig. Got it..

It must be a regional thing.. I've heard the "chunk" called a pig maybe twice... both times on here. third member seems to be the most common here in the nor'east.

Originally Posted by GeorgiaDad

I'm already looking into what it will take to convert to disc brakes..

For info on disk brake conversion, take a look at Speedway Motors Catalog.

You may or may not want a Speedway kit, but there is good info on the catalog page. There is a kit with e-brake, and one without. There is also a link to axle flange identification and a good illustrated instruction on installation.

These conversions are not cheap compared to just freshening up your drum brakes.

If you don't have the rear end already lood for a 9er from a Lincoln Versice or Ford Granada--they have disc brakes with parking brake--------