9" rear end swap pre-questions

Alright, so I found a decently priced 9 inch from a '58 Edsel to handle the 429 swap motor. The guy selling it told me its 60" and has the 43" spring perch length that the mustang uses. It's got 3.56 gears with the old 5x5 bolt pattern.

My question is this: is there anything I'm not considering before I pull the trigger and buy this 9 inch? I know it's 1 inch shorter overall but it doesn't look like it would interfere with anything being only a half inch shorter on each side. It seems like the leaf springs would be a bolt on unless there's different spring perch styles I'm not aware of. And are the 3.56 gears any good behind a C6?

Any insight would help greatly!

The width should not be a problem and may even give you a bit easier time getting wider tires tucked underneath. Replacing the axles will get you wheel bolt pattern corrected.

3.56 would be about the extreme end of the gear range that would allow street driving and you are still going to be operating in the 3000+ rpm range for anything on the highway. I would say it is a better match for an OD transmission. Also early 9" rear ends are more commonly open rear ends and coming out of an Edsel I'd bet against it being positrac (though it might be a 31 spline unit)

Overall, I'd say you could make it work if it was all you could find or afford but that it isn't optimal

What have you got in the car right now?

Strongly agree with Jeff's inference as there are better options, especially since you will probably be changing axles to get the 5 X 4.5 bolt pattern. You could probably found a 9" pumpkin (with Posi) out of a pickup or even some passenger cars pretty cheap.

For my 472 (429 block, 460 crank, bored .060), I pulled a 28 spline 3.50 with traction Lok pumpkin out of a 1970 Galaxie XL. I think I spent 50$. Those 28 spline axles should be fine unless you are going with some insane torque. For my 545 which dynoed in excess of 700 foot pounds of torque, I am going with 35 splines after market rear.

To me it depends upon how much torque you plan on putting in that BBF.

When looking around, you might want to look at late '60s and early '70 broncos which also usually had a posi.

...just a thought.

BT

If your doing an axle swap don't forget about a good 8.8 out of an explorer. With a few mods its an easy swap and they are cheap and plentiful in the boneyards. You get disc brakes, 373 gears, posi, 5x4.5 bolt pattern and 31 spline axles all in one shot. I have been running my 8.8 for several years now with 0 problems! And I'm pushing 550-600hp. Just another option for ya.

Turtle's suggestion is a good one. I would rather have the 9" for those power levels, but it is more because of my familiarity than any actual superiority of the parts. Cost wise the 8.8 is a bargain. Rebuilding them is much less fun than a 9" though

You won't be happy with a 429 and an open rear end. Not to mention the bolt pattern issue. I'd wait to find something that makes more sense as others have said. Just my opinion. You might try searching on "Ad Hunt'r" or "Racing Junk". Good luck. Chuck

I think I remember from years back that the pre 60's Ford big car rears fit 65-66 Mustangs. Knowing they are a few inches narrower than our cars-I'd recheck the fit. The leaf springs back then were narrower than the mustangs had-so you might have to do some widening on the perch mounts.

Thanks guys. I think I gathered a census that this rear end might not be best after all. Definitely some good points I didn't consider there. I also found a Lincoln Versailles 9" with posi like yall mentioned and disc brakes but the guy wants $600! This is apparently a first gen mustang guys dream. I'm gonna have to consider pulling an 8.8 out of an explorer though too cuz there's plenty in the yards here.

So if mines not a 9 is it just an 8" and not an 8.8? I don't know the difference here but the original motor in the car was a 302.

So is it a big deal if its 31 or 28 spline or did the 9's only come with one option?

Thanks guys. I think I gathered a census that this rear end might not be best after all. Definitely some good points I didn't consider there. I also found a Lincoln Versailles 9" with posi like yall mentioned and disc brakes but the guy wants $600! This is apparently a first gen mustang guys dream. I'm gonna have to consider pulling an 8.8 out of an explorer though too cuz there's plenty in the yards here.

So if mines not a 9 is it just an 8" and not an 8.8? I don't know the difference here but the original motor in the car was a 302.

So is it a big deal if its 31 or 28 spline or did the 9's only come with one option?

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Your mustang is either an 8 or 9 inch. They didn't come with 8.8". Easy way to tell the 8" from 9" is to look at the back of the housing where the pumpkin goes in. If its all smooth and round its probably the 8". If it has a vertical bulge on one side its a 9". the bulge is from the larger 9" ring gear. My car was originally a 302 car and it had the 8" The 8.8 is very easy to tell from the 8 and 9" because it has a cover on the back. Mosy of the early 9" came with 28 spline axles even the 66-76 bronco axles came with both 28 and 31 spline. One is called big bearing 9" and the other is a small bearing 9", refer to the axle bearing at the end of the tubes.

Many of the 8.8 came with 28 spline axles, mostly in the rangers. I cant remember all the years explorer axles were drum but most late model rear were disc.

The 9" from the Lincoln is a good rear but it came with 28 spline axles also. I had one in my Bronco II and loved it.

28 spline axles in a 9" will take a hell of a pounding, 31 are better. If your getting crazy you can buy 33 and 35 spline axles, but for most street applications its overkill.

For the 8.8 I would definitely recommend the late model rears with the 31 spline axles for strength. 28 would be fine for a mild motor but 31 is way better and just as easy to find with the disc brakes. Since the 8.8 is a c-clip type axle, it is more prone than the 9" to break in that area, but like I said before I have beat the snot out of mine for several years with 0 trouble.

Ok im done rambling. Heres a link to some info on the 8.8 http://www.therangerstation.com/tech_library/Explorer8_8.shtml

Ok. Yea most 9" I'm finding are 28 splines. Still better than my 8" though apparently. I think it'd be fine handling a stock 429 (Hi compression) for most everyday use but if I ever get the urge to punch it, I don't want to break my rear end .

So I've asked a lot of questions but I forgot one. Wouldn't a gear ratio of 2.98 or something like that be better for street/highway use compared to 3.56 and others? The driveshaft is spinning less to turn the wheels meaning lower rpm's all around right? Reason I ask is, I found a '72 Ford LTD 9" for $200 and from what i found the gears are guesstimated at 2.98 online.

You'll be fine with the 28 spline ,unless you put slicks on and start doing holeshots. I would start look for a 9" that will bolt in,the ltd rear end you mentioned is a coil sring and you would have a lot of grinding and welding to do. A 3:25 ratio would be good to find and you could always add some type of posi and 31 spline axle later.

Ok. Yea most 9" I'm finding are 28 splines. Still better than my 8" though apparently. I think it'd be fine handling a stock 429 (Hi compression) for most everyday use but if I ever get the urge to punch it, I don't want to break my rear end .

So I've asked a lot of questions but I forgot one. Wouldn't a gear ratio of 2.98 or something like that be better for street/highway use compared to 3.56 and others? The driveshaft is spinning less to turn the wheels meaning lower rpm's all around right? Reason I ask is, I found a '72 Ford LTD 9" for $200 and from what i found the gears are guesstimated at 2.98 online.

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I have 373 gears and love them around town. On the highway they can be a bit steep. I can run 60mph and turn around 2800-3000. I want to get an OD tranny, just haven't got to it yet. I had 3.05 gear before and it seemed gutless. 3.50 gears seems to be a very good all around gear ratio.

You wont have to worry too much about snapping an axle on a 28 spline 9 inch . They are plenty tough. With slicks on at the track, maybe??? but on street tires and 2.98 gears you aren't going to break anything! I am running 550+hp and cannot hook up at all. That's probably why my 8.8 has lasted so long. Im sure if I go to the track and get tires really sticky, something is going to let loose and break. But for now I can stomp it at 45mph and blow the rear tires up in smoke.

Perhaps I can add something

the 8" rear end is not some anemic POS the 28 spline axles are interchangeable with the 9", and IIRC even the axle and carrier bearings are the same.

You can get a posi unit in the 8" center section.

If your engine is at stock power levels and you don't run on the drag strip it will probably last many years.

Perhaps I can add something

the 8" rear end is not some anemic POS the 28 spline axles are interchangeable with the 9", and IIRC even the axle and carrier bearings are the same.

You can get a posi unit in the 8" center section.

If your engine is at stock power levels and you don't run on the drag strip it will probably last many years.

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Jeff is right. You can get gears and a posi for the 8 inch and probably be pretty happy with it for street use.

the two weak points I am aware of are bearing cap failures and the factory posi units. I understand that a posi unit is available and that there is a mod for the bearing caps

Dang. That sucks to hear that 3.05 feels gutless to you. I was about to update that the LTD guy actually has a '72 torino 9" with 3.00 gears that he failed to mention when I spoke to him on the phone! I got pretty excited and was thinking about picking it up. Not nodular and still don't know if its 31 or 28 spline. Couldn't find a tag on it but somehow he was confident about the 3.00 gears. Should be exact width as the mustangs we have. Thoughts?

The con here is its set up for coil springs so I'd have to cut and weld the 8" spring perches on the 9". I'll be looking on the forum for that job.

If not I'm running with the 8 inch since y'all seem fairly confident it'd be fine for street use! And possibly get some posi gears for it later on.

Wow lots of opinions. I bought a 73 Mach 1 Q new. I broke 3 yokes on the rear between May and July. The bearing caps would explode and then the yoke went. They fixed them under warranty with no questions because they knew how I drove, lol. I went to the shop manager and told him something had to be wrong a 9" with a stock 73 351 should never break. He got the Ford factory rep to drop by and as soon as he got under her car he knew what was wrong. They had put the wrong size 9" U joints on. Car was made late in model run and they called from factory and didn't want to give me 4 speed but I insisted they find one. They ordered a new driveshaft and different yoke and never broke another. I was only running F-70 X 14 tires so they did not stick. At that time it was the driveshaft that the NASCAR Ford drivers used so must have been pretty good. Tire size is what breaks things not H.P or Torque.

You should also look for staggered shocks and the sway bar if you are going to upgrade. I was told that the comp. suspension with automatic did not have staggered shocks but my 72 Q vert, C-6 auto has staggered and sway bar. You never know what you will find under there.

David