Pulling the 289 2V out of my 67 and dropping in a 390 out of a 73 F100. (Going with aftermarket heads and headers so it will fit.) My rear end is a stock 8" 2.73:1, I am looking at a 8.8" 3.27:1 out of a 69 F100 at a steal. New seals, brakes and less than 500 miles for $75. Will this swap over to my car. I don’t know the exact width and if the shocks will line up. Everything I am finding on swaps is for 9" rear ends out of trucks into mustangs and mustangs to 70+ cougars. Anyone ever done a truck to cat swap?
I haven’t done it. But I’ll venture a guess that the width will be too wide to fit correctly.
67 Cougar is 60", 69 F100 is 61.25". Too wide. Here’s the info I finally found.
http://www.roadkillcustoms.com/hot-rods-rat-rods/Rear-End-Widths.asp
Total noob question but how can a difference of 1.25" over 5 feet be a problem? It’s an extra 0.625" on each side, right? So barely more than a half inch?
Would affect spring-perch location(which could be fixed), and wheel/backspace issues(which could also be fixed)…may also affect pinion/yoke location…?? Just depends on how much you want to change, I suppose.
The 8.8 axle wasn’t introduced until the mid-eighties, so it would be unusual, to say the least, to find one under a '69 model truck. Are you sure its an 8.8 rather than the factory 9"?
Assuming its the original truck axle, aside from width issues, the leaf spring pads on a truck axle are on top of the housing, for a Cougar, they’re below, so that will have to be addressed. Also, the factory wheel stud spacing is different for trucks, so if you want your wheels to match front and back, you’ll need new axles with the proper bolt pattern. The truck brake drums won’t fit the new stud pattern, so unless they can be drilled out or otherwise modified to fit, you’ll need different brakes. There is a possibility that the drums from the 8" rear will bolt on, but trucks typically use a larger outer axle bearing than cars, and brake components are not interchangeable between large and small bearing axle housings. You’ll have to do some measuring to determine what you’ve got.
Speaking of measuring, truck driveshaft yokes, aside from having a wider bearing spacing than most small-block car housings (hybrid U-joints are available to mate these up) are typically shorter than car yokes. That can cause driveshaft length issues. But a 9" housing is a little deeper overall than an 8" housing, which makes up some of the difference. You’ll need to do some careful measuring and test fitting to determine if your current driveshaft can be safely used. (That’s assuming that the transmission output will be in the same spot after the 390 swap, which obviously isn’t a given.)
Shock mounting is totally different between trucks and Mustang/Cougar applications. Truck shocks have an eyelet on the bottom that fits into “U” brackets welded to the axle housing. Cougar shocks use studs that fit into the leaf spring clamping plates. The critical thing to note here is the diameter of the outer axle tubes where the U-bolts sit. If the truck axle housing diameter is larger, as most are, you’ll need new U-bolts to match the larger housing. That means the clamping plates, which the U-bolts pass through, won’t fit. I don’t know of anyone making Mustang/Cougar plates to fit the wider U-bolts, so unless you can find some, you’ll have to modify the old ones somehow, or have new ones fabricated.
Those are the major issues I can think of offhand. Otherwise, its a simple swap.
Of course, if its not the factory '69 truck rear axle, and is actually an 8.8 out of who-knows-what, all bets are off, since there are even more varieties of 8.8 housings than 9" ones.
All of you hit the nail on the head. In my experience swapping rear ends 1/4" on each side was max allowed. And it doesn’t matter what engine/transmission set up you have, you can’t move the rear end forward or backwards so the drive shaft has to be switched. It’s an 8.8" the guy used it as a temporary replacement on his 69 while rebuilding his 9" 4.11. So I don’t know the original vehicle. I think I will stay with the 8" and just swap out the guts to a lower gear. He’s 2 hours from me and I would waste a trip if it can’t be used. The 8" is a pretty tough rear contrary to what mustang folks say. Thanks for the help though.
An 8.8 will fit right in. but it needs to be from a 87-93 mustang. cut off all shock mounts coil spring perches. weld on new spring perches in the right place. use one axle from ford ranger, one from an areostar, that will give you 5 lug axles. disc brakes are easy, use explorer brakes. the 8.8 uses a flange instead of a pinion yoke, use a driveshaft from a 2wd explorer with a different universal, bolts right in.
just put a 9 inch in it and make life easy on yourself.