So in the next two months I will be having my transmission rebuilt by t56rebuilds.com but my question is, should it be neccesary with the mods in my sig (plus a new cam and heads this summer) to put a ford 9" in place of my stock 10 bolt with 3.42, my other question is that my friend has a 78 f150 with a 9" and 4.11 posi in great condition...could i directly replace my rear with his or what kind of modifications and what estimates on time and money would be for doing this project...ne advice will be greatly appreciated!
Vince

 

If your going to be doing 5K clutch dumps with sticky tires, you need a stronger rear. Whether you need a 9-inch is subject to debate.... weight more, more power losses, driveshaft geometry issues, tunnel clearance issues, etc compared to a 12-bolt. If you drive it more rationally, on street tires, your 10-bolt might survive.

The Ford truck rear will not have a place to bolt on your torque arm, so you would have to fabricate and weld up a torque arm mount. Good chance the width would not be correct, so you might need to change the width, widening it or narrowingf it, welding in new axle tubes and buying new axles. You will have to strip all the brackets and attachments off the truck rear, take all the brackets and attachments off a 10-bolt (spring seats, panhard rod mount, shock mounts, LCA mounts), and weld them to the truck rear. You will lose your ABS (although you might be able to put reluctors on the axles, behind the hubs if you have TCS). You will have to figure out how to change the disc brake mounting brackets on the end of the axle tubes.

 

Thanks for the informative write up! I wont be doing 5k clutch drops but I may be doin some 3k at the track when I go...I will have a built engine and tranny and a stage 3..and I already have a set of 275 Nitto 555r drags on my rear so we will just see. Rumor has it when I asked the guy i bought my car from he said the rear was "rebuilt" at 85k miles but who knows. Ne other opinions and advice would be greatly appreciated! thanks
Vince

 

I'd say in the long run, look for a Strange or Moser GP and pick one of those up. I grenaded my 10-bolt with just rough bolt-ons and Nitto DRs.

As for fitting the 9"; it could be done, but there's a lot of work involved; if you can do it or get it done cheap do it; otherwise, I'd look into buying one.

 

For some reason, 7.5 ten bolts hold up well for me. I ran a minispooled 7.5 with 3.73's in my old '85 Monte Carlo that ran 11.80's @ 115 with high 1.6/ low 1.7 60' times and it never broke with over 200 dragstrip passes on ET streets. I also drove this car as my daily driver. No teeth cracking, nothing. Slightly twisted axles was my only problem. That and the cross pin got a little S shaped. As they always say, results not typical. In a stick shift car, it's going to get destroyed.