Technical 9" Bronco Diff Swap

Found a 9" early Bronco diff to swap into my '63 1/2 Comet. An old friend has it and I'm trying to wrap my head around a fair price to pay (how much new stuff I'm going to have to purchase). The late '50s Ford swap is 3/4" narrower but old threads here state the '64 Falcon is same width as the Bronco. Will the 8" axles fit the Bronco housing if it is small bearing? Will this allow a brake upgrade?

I don't have the 8" out of the Comet yet. It's my second vehicle and always ready for service if the DD has problems. Worked on my brother's '72 Bronco many years ago but never got into the diff, so I'm clueless. Thanks guys.

Joe

 

The early Bronco is 58" wheel mounting surface to wheel mounting surface. The 57-59 ford rear end is 57.25 WMS to WMS . The Bronco has 5 on 5 1/2 BC , You need 5 on 4 1/2" BC The axles from your 8" are the wrong length as the Bronco housing is centered. I would try to find a 57-59 Ford rear end to maintain your width and wheel bolt pattern.

 

The '66-'77 Bronco rear axles are ideal for hot rods, I just sold one of my extras to a good friend and I paid 500 bucks for it. I have one under my '32 and I have a extra for what ever comes down the pike. HRP

 

I run bronco rears in 3 cars, the 8 inch axles won't work, there's some cheap stock axles available on the 4x4 sites or you can order a new set in any bolt pattern you want for around $500 bucks.
There are a couple different bearings available and you will need to check that, if you know the year of the housing it'll be of great help to getting the correct ones.
The last one I redid was the oddball years "medium duty" and I never did find a gasket for between backing plate and housing, it has a weird big bearing but with small bearing bolt spacing.

 

My question is why do you feel you need the 9"? The 8" doesn't like high torque loads, but behind most 289/302s will live forever with street tires and no clutch sidestepping. Any small-bearing brake upgrade will fit the 8" (at least any that will fit inside a 15" wheel). I will note that the early 8" pumpkins like yours were known for pinion bearing failure, but a rebuild kit with the later upgraded bearings will fix that, or just get a newer pumpkin.

I used to have a '64 Comet with a built 302/4speed/8", I beat the snot out of it for almost 100K miles and never broke it...

 

Aware of the bolt pattern, why I asked about the axle swap. Okay, looking @ new axles, if Bronco. What perplexes me is the '64 Falcon info. The '63 1/2 cars have 2" springs, like the late '50s cars. '64 have 2 1/2". Maybe that's the kicker?

More good info

Hoping the tag is still attached to the carrier. Oddball Ford stuff? Nah hahaha

Thanks guys

Joe

 

Stroker crank, mucho torque. If I drive like Grandma, I load the plugs

Joe

 

by the time you buy the bronco 9, and the associated parts to make it work in your application, you would have as much into it as buying a new 9 with axles and less brakes. I Would look at Quick Performance.... $875 gets you a new housing with no mounting brackets and axles in the bolt pattern you need. $925 will get you one for a 64 to 66 mustang. Spec the housing for small bearing ends and you can put all you 8 inch brakes right on it. Now all you need a is a 3rd member, with the new axles get what ever spline you want, but 31 spline is what is in most 70's f100 trucks. Go fnd a third member from a 70's f100 2 wheel drive is typically 3.23 to 1 gear and 4x4 is typically 3.50 to one stock. if those gears work for you throw an bearing kit in it for $200 bucks and your set with new 9 inch. for right around $1200 bucks. Believe me, reworking an old one is not necessarily the most cost effective way to do the 9 inch.

https://www.quickperformance.com/QP-Bare-9-Inch-Housing-Axle-Package_p_15999.html

 

$476.00/pair.
https://www.moserengineering.com/custom-alloy-31-spline-axles.item

 

There's a lot of those in hot rods with bigger motors. The weak point is the spider gears, a switch to an aftermarket posi unit will cure that. How about $505 for new gears, clutch-style posi and the bearing kit? Or $865 for the same but with an Eaton TrueTrac (a much better gear style posi, no clutches to wear out or need for 'special' lube)?
Ford 8 Inch (8" Ford) (quickperformance.com)
I used to think the same way, gotta have a 9" like the big boys run. Its larger, heavier and less efficient. I had a 9" for my Comet, figuring I'd put it in when the 8" broke... it never did.

A 347 stroker still has a shorter 'arm' compared to a 351 or 350, so unless you're running a big power adder (NOX or blower/turbo) the 8" will take it with the upgrades. If you stay away from slicks, it may even take that. You may want to ask about high-strength axles, but remember that both the 8" and 9" use the same 28 spline axles. I broke a ton of those behind a FE...

 

The big bearing small pattern might be what they call "Big Bearing Torino" or just Torino which is a real popular gig.

 

And switch to a MSD box ignition, that will help with the loading up...

 

Foxbody 8.8" can be had for real cheap, like under $200 all day. They're 28-spline, but can handle 500hp 3000lb cars easy. Cut the brackets off the tubes in favor of some $20 leaf spring perches. They are 59-11/44" wide WMS to WMS, so lop an inch off each axle tube, throw some Currie Cut-To-Fit 5-lug axles in it for $275/pr.

You can also use an Explorer 8.8" with factory 31-spline axles, shorten the drivers side axle tube to narrow the width and center the pinion, then use another passenger side shaft on the shortened drivers side($10 junkyard or $75 new). They're already 31-spline and have small ford bolt pattern and disc brakes

8.8's are stronger and lighter than a 9" in stock form.

 

OK, heres my version of what to do............

IF the housing is close enough to work without any narrowing, Buy it.
Let me quantify that statement. The housing should come with a third member, and the brake backing plates and hardware and drums.

The stuff hanging on each end of the housing starts driving up expenses if its not there........and the same goes for trying to find a pumpkin.
You can clean and rebuild those parts usually and maybe turn the drums for reuse. Simply redrill the axles and drums for the correct pattern.

Most likely the pumpkin won't have the ratio you want and you will need to buy bearings and the needed gears. If you are lucky, theres a rebuildable posi in it. If not its about $500 for a good Eaton that has gears instead of clutches. Clutches wear out. So if its got one with clutches, then use it. If not.............


But........on the other hand, if you can find an 8.8 thats near enough to the right width and already contains a factory posi, and good brake hardware as well as an emergency brake cable for $2/300.....then you will be way ahead of the $$$ curve.
Best starting point is this book available from Amazon. It will educate you on which rearends to look for and how to tell what you are getting. Bout $25 and will save you way more than that!

an example:

 

I've got a couple vehicles that run an early 9 inch (1957 to 1959) cut down with Maverick 8 inch axles so that's an option. I suspect that the 1960 thru 1964 nine inch could be cut down as well.

 

This was my first consideration but a brake upgrade would be icing on the cake. The '63 1/2 drums are pathetically small for a fast car.

NASCAR approved

My current state of mind. If it is complete, 3.50 or 3.89 w/ posi and fits.

Joe

 

Already there.

Already there.

Joe

 

My preference would be late '50s housing. Thought I may be able to find one but unobtainium, it seems. I'm kicking the weeds. The '63 1/2 Falcon rally cars had cut down Galaxie diffs.

Joe

 

I agree with those who say that with the early Bronco rear the attraction is that it is the right width and has THE 5 on 5-1/2 lug bolt pattern that works great with early Ford hot rods making the only added expenses brakes if needed and maybe a third member swap to get the right gears.
When you start buying axles to change the bolt pattern, changing this that and another to get it where you want it, all the sudden you have way more time, money and effort tied up in it than if you just started from scratch.

 

Getting as rare as chicken lips but this is a 57 1/2 ton housing, you never know, you might stumble onto one if you know what you're looking at, the braketry and ends have been changed and it has been narrowed.
Edit
Now that I think about it, I had to add 2 inches to one side due to my wheel backspacing.

 

The bronco only had 2 gear sets available, 4.11 for 6 cyl models and 3.50 for the V8, the axles have the access hole so you may need to weld that up to redrill it to 5x4.5 pattern, 5x4.75 pattern definitely lands in the hole.

 

Yes, was looking @ the access holes thinking about drilling for the smaller lug spacing. That way can use the wider, bigger drums for brake upgrade. The 3.50 is my preference w/ the T-10 & no OD. Muchas gracias, amigos!

Have a plan- pull the rear wheels, plumb bob the drums, mark the floor & measure. Then measure the Bronco.
Transition cars are a trip

Joe

 

Are the 57 pickup rear-ends different than the cars? I've got several and I always thought the 57 was completely smooth and the 58 and 59 had dimples like the one in your picture.
P.S. don't ever let your wife overhear you saying that you're looking for a nice one with a narrow rearend and no dimples on it.. It may be misconstrued.

 

If you know what a 57 passenger car housing looks like all thats needed is to look at the truck housing and the difference is pretty clear, no welded-on tubes on the truck housings, also somewhat thicker material, the housings are formed with integral tubes and a much beefier web at the third member.

 

I did the 57 housing in my 64 Comet years ago , $25.00 complete axle , 4.10 gears . It was bolt in swap . Those days are gone , do the Ranger 8.8 shorten one side and add spring pads , never look back . The 8in would of held up just fine for a street driven car , but for $25.00 my Mom , didn’t raise a fool .

 

I cast my vote for the 8.8. Stronger & cheaper than the 9".
Maybe you're gonna drag race it...?? I don't know but.....unless you tub those rear wheel wells....you can't put a big enough tire under it to break a decent 8" !
Narrow rear tires are your "fuse" for saving a shelled-out rear end!
I'll shut-up about it.....
6sally6

 

You are the second cat to confirm this one. Trying to run down old lead on a '58 I passed on years ago. Bronco has to wait a few weeks while my friend is on vacation, so no rush. Will post back what I find out after I measure this 8" diff. I have a hunch the '64 Falcon dimensions stated in older threads may not be correct or this may be one of those oddball 6 month run things.

Nah, very valid points. 35 lbs. of air in 8" tire is my friend. Also no clutch popping or lead footing in 1st or 2nd gear. Having my fun on the top end for now. Read my handle, it's a quote from a very old late friend. A chain-smoking wino crop duster pilot, mechanic extraordinaire & dirt track racer

Joe

 

If there's any dirt track racing around you, there's probably a 9" guru nearby. I had one right around the corner from me, years ago. The car I had at the time was a perfect fit for a Maverick 8" and I ran with it for a while without any issues, other than it was an open carrier. My guru neighbor built me a 9", small bearing housing that the Maverick axles and brakes would fit and rebuilt a posi carrier with my choice of gears for me for about the same money as a new posi carrier and the and gears for the 8". And I got the 9" bragging rights.

Gary

 

Picked up a rear end out of '57 Skyliner. Big bearing axle housing, 3.56 gears. Bolts right up.

Anyone have the scoop on best source for brake parts? Lines, wheel cylinders, drums, etc.
I know there are a few vendors that specialize in '50s Ford but haven't dealt with them.

Thanks

Joe

 

I go with 70s F150 axles easiest to find and cheapest cut the housing down and use somethin like this https://tomsoffroad.com/parts/66-75-ford-bronco-31-spline-big-bearing-rear-axles