I have a 28 spline 9" rear end that fits my 66 but does not have the gear ratio I want, I have a 31 spline 9" rear end from a 76 with the correct ratio and it was recently rebuilt but the housing is to wide, I assume the 31 spline center section will fit into the 28 spline housing and I will have to get new shorter 31 spline axles, but what about the brake components? will the big bearing backing plates fit the 28 spline housing? what about the axle bearings? are they the same? didn't ford f100's switch to 31 spline rear end in 1970 to 72 axles, would I be better off looking for an early 31 spline housing and just change the center section? any help would be appreciated.

 

I wonder if you could put the 28 spline side gears in the third member you want to use?
And just keep on trucking with your housing and axles?

These guys Currie Enterprises Racing Rear End Categories have lots of stuff if you have some coin to toss...I'm sure a quick phone call to them they could at least answer all you questions..They are the 9 inch pros..

Greg

 

Housings are all big bearing. 29 and 31 spline third members fit in the housings. New axles need to be made to use your 66 backing plates or upgrade to the later big brakes.

Garbz

 

Yes, you can put 28 spline side gears in a 31 spline case and run it in the older axle. That's what I'm running in my '61.
You cannot, however go the other way. The 31 spline side gears will go into the 28 spline case, *but* the 31 spline axles will not fit through the hole in the case where the bearing rides. This is why the axles in my donor truck are only held in by the outer bearing retainer :-)

 

what else would hold them in.

 

This gets complicated. I put '76 rear brakes on my '66, so I can give you the precise details. All of the directions below apply only to the Ford 9" rear.

Putting '70s rear brakes on a '67 or earlier axle is a great idea - it gives you more stopping in the rear. Doing it the way I describe below will allow you to use all 70's brake parts. You can use your '66 axle housing, as long as you do the the following:
1. Use the '66 axle housing and parking brake cables (removed from the '66 backing plates)
2. Use '68 - '72 axle shafts - you cannot use the '67 or earlier, see below
3. Use a later master cylinder with a larger bore, or double pump the brakes.
The '70s backing plates have offset to the inside to allow for wider shoes, but the axle shafts themselves also have about 1/4 inch extension outwards.
This means you cannot use '67 or earlier axle shafts with the later brakes, but must use '68 - '72. You cannot use the '73 and later in the '66 housing because the axle shafts are longer, unless you cut and re-spline them - not an inexpensive operation.
The '70s wheel cylinders have a larger bore, so they require more fluid to actuate them. The '66 master cylinder just doesn't have a large enough bore to fill them and the fronts too, without going almost to the floor. If you can get the shoes on all 4 wheels very close to the drums, you will be OK, but a hard stop may require a double pump to get enough pressure up to hit the brakes hard.

Hope this helps.

 

Basically the inner ends of the axle are just flopping in the air. It's ok for moving it around the yard or putting it up on a trailer, but no way I'd way to try and move it on the street. That's all I was trying to say.

 

Overland, Crow, Banjopicker

Not trying to redirect this thread, but, I heard it said the '76 housing is too wide to fit a '66?

Not having tried this, I guess I don't understand the problem. Does this mean you are unable to swap the entire rear end assy the to get improved ratio/braking (maybe stronger axles) of the later year model? I guess this would be due to wider spring perch?, wheelbase? some other reason?

I ask because it just is sounding like everything is being upgraded EXCEPT the housing, and I am wondering why it has to be retained?

 

OH, the rear axle housing was lengthened in '73 by about 4 inches overall. '72 and earlier trucks have a rear axle narrower than the front stance. Stand back behind a Slick (or up to '72) and the things look kinda bowlegged because the rear wheels don't track in line with the fronts.
Ford corrected this in '73 by widening the rear frame and moving the axles out a bit. (I think they widened the body too, but I am not sure of that.)
To use a '73 - up axles on a '72 or earlier truck, the spring perches and shock mounts have to be moved inboard, and wheels with appropriate offset (backset?? not sure of the right term here) have to be used.
Stock wheels will interfere with the fenders, is why offset ones must be used.

 

This came from a site called "Ultrastang" there is a bunch more info and pictures there to help out your search. Here is some of the info.

1. 1965-1966 Mustang 8 & 9-inch housing width: 52¼".

2. 1967-1970 Mustang 8 & 9-inch housing width: 54¼".

3. 1971-1973 Mustang 8 & 9-inch housing width: 56".

4. 1957-1959 Ford big-cars 9-inch housing width: 52¼".

5. 1960 model T-Bird 9-inch housing width: 52¾".

6. 1975-1980 Granada/Monarch 8 & 9-inch housing width: 52¼"

7. 1977-1980 Lincoln Versailles 9-inch housing width: 52¼"

8. *1957-1972 Ford pickup 9-inch housing width: 56"

9. 1973-1979 Ford pickup 9-inch housing width: 59¾"

10. 1980-1985 Ford pickup 9-inch housing width:??

11. 1966-1977 Ford Bronco housing width: 52¼"

12. 1978-1985 Ford Bronco housing width:??

 

I measured across the 76 axle housing and it measures 60 1/2 inches, the stock 66 housing measures 56 1/2 so a difference of 4"... what year did ford F100 trucks switch to a 31 spline axle? if they did it in the 70, 71 or 72 years I could just find a 31 spline housing and put all the new parts in it and it would be a direct bolt up. anyone know when ford trucks went to 31 spline?

 

Unfortunately, there is no switch year. Ford used 28 splined axles all the way up into the early '80s, mostly for F-100s and light duty vans. I don't know about the cars.
F-150s will usually have 31 splines, but I disassembled a mid-70s one with 28, so there really is no way to know.
The only way I know to confirm is to pull the axle.

 

Some 1970/72's / Some 1973/79's / 1980/83 F100's; 1980/86 F150's are all 31 spline.

Y'all are speaking of 1968/72 F100 9" rear axles like there is only one, but...You are either forgetting something, or are unaware that...

Ford offered THREE different 1968/72 F100 9 inch rear axles!

Ford offered a H/D 9" rear axle in 1968/72 F100's. 1970/72's with this rear axle have 31 spline axleshafts (which are obsolete-no one has any, hard to find used).

Even though classified as a 9" this rear axle has a 9 3/8" ring gear.

ONLY five parts are the same as used in a 9 inch: 1 pinon bearing, 1 pinion race, pinon seal, housing gasket and the pilot bearing's retainer.

EVERYTHING else is 9 3/8" ONLY including the axle seals.

1973/79: Some F100/150's have 31 spline axleshafts, some have 28 spline axleshafts as it depends on the application.
------------------------------------------------------------------------------------------------------------------
Ford widened the rear frame rails (behind the cab) beginning in 1973 on F100/150's, most F250/350's.

1961/72 F100/350's have rear frame rails that are 33 1/2" inches apart.

1973/79 F100's, 1975/79 F150's have rear frame rails that are 37 1/2" apart.

1973/77 F250 4WD's (High Boys) & 1973/79 F350's on the 140" wheelbase have 33 1/2" rear frame rails.

All other 1973/79 F250/350's have 37 1/2" rear frame rails.

 

usually the 31 spline were used in post tract hd app

the standard carrier were the same on the ford 9" so the axle gears inside the ring gear carrier could be interchanged.