Rearend Swap info - FAQ

sinisterstang65 · Apr 6, 2010

I have a 1965 Mustang with a 351W, and im trying to decide on what rearend to install. It currently has 3.55 Gears, but its not posi. We are thinking about getting a 9" with 4:11 gears with posi. We want good hook up, but want somthing streetable, bc its a daily driven car. Any suggestions?

D.Hearne · Apr 6, 2010

4.11's are never going to be "street freindly" without an overdrive transmission. With no overdrive, don't go any higher than 3.50's. 3.70's being the absolute limit here, depending on the tire diameter. The taller the tire, the higher the ratio you can live with.

sinisterstang65 · Apr 7, 2010

RE

Alright, well right now it has really small tires on it, and hopefully soon we r going to upgrade. Do you think that it would be cheaper to rebuilt the 3.55 gears and make it posi, or buy a 373 with posi, price is somewhat an issue, but also want somthing that will hook up good and drive well also, bc it only has a FMX tranny, and we are putting in a TCI breakaway. Any info is needed thanks

jlangholzj · Jun 16, 2010

I've been searching around for a 9" lately, and I noticed that the early bronco's have a 9" thats about 58"-58.5" flange to flange. I can't find anything on ofset though...these should work shouldn't they?

Georgia Snake · Aug 15, 2010

9" rearend

One fact that has been over looked here. I used a 1957 Fairlane Stationwagon in my 1965 Mustang. It is true it is the narrowest which allows for the use of wider wheels and tires. If the rear is robbed from a stationwagon as mine was you also get much bigger drum brakes than stock as mine has. On a street driven car or even an SCCA Solo 2 car as mine is, you would not need to upgrade to rear disc brakes unless you just have to. Lets face it, the car isn't on a full blown road course where brake fade is an issue. I have a running debate on this issue with a friend that upgraded his Boss 302 to rear discs and I brake as well if not better in my 65 as he does in his Boss. By the way, this is the same set up that Shelby used in the racing GT 350's in 65.

HDTony · Dec 11, 2010

Anyone have a pic of exactly where to measure from? Which flange are we always talking about? Are we measuring from inside, outside, center or some other portioon of the flange?

Also could someone eplain exactly whatbthe pinion angles should be. For a 65? I have to weld my spring perches on.

HDTony · Dec 11, 2010

Check out ultrastang's site: Ultrastang - Steve Ainsworth

this site is great lots of info here

The Ford 9-inch Rear End

Georgia Snake · Dec 12, 2010

9" rearend

I always measured from drum face to drum face and the rearend I was refering to had the spring mounts in the same place as the Mustang and all the angles were the same as well. The only thing I had to change was the parking brake cables as the 1957 Fairlane Stationwagon i robbed my rear from is a much longer car. I this set up if you can still find a doner car to rob one from. I got lucky.

eldercaddy · Dec 23, 2010

Nice information on Ford 9" rearends. Really like it blascrw. Good job!

HDTony · Jan 10, 2011

I'm still looking for reliable driveshaft offset info as well. my local shop says 3 degrees down from the transmission. but I've seen conflicting numbers.

anyone know for sure, so I can tack these perches in place?

HDTony · Jan 16, 2011

echo echo, is this thing on? lol

Blaker1983 · Feb 23, 2011

I just wanted to add in case it wasn't in here that on a 67-68 mustang and any possible mustangs with the same dimensions that a newer 8.8" rear end will fit and work on your mustang. I have a 8.8" in my 1967 coupe with disc brakes that I picked up for 150.00 + 3.73's for 50.00 extra and it went in with no problem. The only modification is to remove the old spring perches and weld new ones on (paid 20.00 for a pair from Summit) - Line everything up and you're good to go. Just make sure if you use the old style yoke on your driveshaft you will need to change it out. Hope this information helps anyone, and if you have any questions about it let me know, thanks.

Blaker1983 · Feb 23, 2011

HDTony said:
I'm still looking for reliable driveshaft offset info as well. my local shop says 3 degrees down from the transmission. but I've seen conflicting numbers.

anyone know for sure, so I can tack these perches in place?

on my 67 i did 4 degrees pinion angle.

HDTony · Apr 3, 2011

Blaker1983 said:
on my 67 i did 4 degrees pinion angle.

Gotcha... Thanks!

HDTony · Apr 3, 2011

Length question.

The 9" i have is going to need to be shortened, its 59.5 axle flange to axle flange. My question is do I have it brought down to 57.25 or should I go slightly narrower. I am mounting 15x8 magnum 500's.

Is 57.25 the Ideal length?

Jerimiah1977 · May 1, 2011

I have an 81 Capri RS with the L6 motor. I am having alot of trouble finding the rear differential cover I need. Mine has only 8 bolts where the usual is 10. can you help me figure out what rear end my car has? I only bought it 3 months ago, and have not been able to find what I need. All I can find is the gasket for it.

96 DOHC Cobra · May 1, 2011

Jerimiah1977 said:
I have an 81 Capri RS with the L6 motor. I am having alot of trouble finding the rear differential cover I need. Mine has only 8 bolts where the usual is 10. can you help me figure out what rear end my car has? I only bought it 3 months ago, and have not been able to find what I need. All I can find is the gasket for it.

I think it's a 6.75" rear. If you found the correct gasket for it, you should be able to tell what cover you need. Don't expect to find any aftermarket cover for it.

HDTony · May 14, 2011

My rear end is off at strange engineering getting shortened and new axles made up, going half an inch short on each side from stock.

HDTony · Aug 14, 2011

Narrowed 9" installed. Shortened half inch over stock on each side with custom axles from strange engineering. 245/60/15's on 15x8 magnum 500's. Springs and shackles are from summit racing. Bottom plates are from a 67 mustang, to fit the 3" ubolt. Shocks are basic motorcraft from NPD.

2jzpony · Nov 1, 2011

I like to know what length the axles are in the 57.25" rear end. And can i use the 28 spline axles from the 8 inch rear in a 9 inch as long as the 3rd member is 28 spline?

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