12 bolt swap
 

I don't know if anyone's ever done this before. I know people swap 12 bolt (C) rears into their 3rd gens all the time but can you just as easily put a 12 bolt truck rear in as well? I got one sitting in my dads garage and it has no purpose. I'll have to cut it down 3 inches and swap mounting hardware but what do i do about the tourque arm? Where would it mount up to? Forgive me if this is a stupid question but i just bought my 87 Firebird last month and i never dealt with F bodies before. Does anyone have any tips?

if you made some kind of adjustable ladder bar setup or 4 link you might be able to.. Currie Industries might make a bolt on/weld on torque arm mount for that too.

Not worth it because you would have to do some cobbling.

1.) It won't have the mounting stuff you need. I believe the torque arm mount is cast into the center section of the 3rd and 4th gen rears so it's not easily added. You would have to preheat the center section before welding and take the proper steps in welding steel to cast iron (assuming your TQ arm mount would be steel). Going to a 4 link or ladder bar setup is doable but costly.

2.) Narrowing the axle tubes would also require you to narrow the axle shafts, which pretty much means you'd have to buy new ones. Narrowing axle tubes is also risky to do without a jig to keep everything square.

3.) Gearsets are not the same. The truck pinion stem diameter is only 1.437 vs. 1.625 on the car unit so you could not use passenger car gears. The passenger 12 bolt is stronger for this reason.

IMO, not worth it. The crappy part is that no 3rd or 4th gen came with a 12 bolt stock (I think the Dana 44 is the best they got, and that's good but really rare) so your best bet would be to search online for a used 12 bolt or pony up for a new rear (12 bolt, 9", or S60). I'd find out what gears and differential are in it and see if you can sell it to get money towards a new rear or other modificiations. You might be able to re-use the posi but if I were you I'd only re-use it if it's an Eaton.

ron has a 12 bolt for sale... already set up for a 4th gen but will bolt into a 3rd

You would need new shafts anyway to retain 5lug in the rear. As stated truck 12bolts are turds. While they are techincally a little stronger than a 10b all the offroading guys steer clear from them.

Thanks. I won't bother with it. I was on the Strange web site and the S60 they make for third gen F bodies would be nice to have. I don't think i'll ever have to worry about breaking it no matter what kind of motor is in front of it. Does anybody have one?

I got a 3.23 open diff. I don't think i'll get much for that.

I'm pretty sure that ELChiefWS6 has one in his car, but he hasn't been around much lately.

- Justin

Go with a STRANGE rear. I got one 4 my 94 Camaro but when I ordered it got it for a 92 or earlier because of the 3 inches narrower 2 fit wider slicks. The torque arm mount IS cast into the rear housing. Also I am using a JEGSTER adj touque arm. they have their own mount but it is a little bit of a project but definetly worth it. Set the pinion angle between 2 1/2 degrees and 3 degrees. Any other questions don't hesitate 2 ask.

Thanks alot guys.

You can also try to get a Borg Warner 9 bolt from some of the later 3rd Gen's, assuming your power levels aren't going to be too crazy. Alot less money then a 12 bolt and easier to find then the Dana

I decided to stay with the 10 bolt for now and befor i put the full race motor in i'm getting the Strange S60. Thank for the help.

FYI you need to shorten your driveshaft with the s60
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BDSM BRUTAL

1.625" to be exact.

if your power level will be high, a custom driveshaft might do you some good, strange can sell you a driveshaft thats the right length.

I didn't know you had to have a custom drive shaft with the S60 but along with the new rear I will also have a TH 400 which will require a custom drive shaft and cross member anyway. But in either case i did see the custom crome-moly tubular drive shafts that Strange makes. I got the new catalog. The prices aren't bad either.

IIRC, the S60 uses 1350 U-Joints anyway, so a stocker wouldn't work that way either.