Hello, I recently burnt out the gears in the rear end of my 87 F-150,I am hoping to take the whole rear end of an 84 150 I have whith a bad engine. This is somthing I have never attempted before. I was kind of hoping someone could give me some advice on the easiest way to go about this. Anything I need to whatch out for any special tools I'll need?
Thanks for any help you can provide, Todd R.

 

87 will have a 8.8" rear with ABS sensor. 84 can be 8.8" or 9" and won't have sensor so the ABS light will stay on. If 9" driveshaft mods will be required.

 

Thanks for the reply, I could not read the numbers on the tag of either truck. How can I tell if the 84 is 8.8 or 9? Also how do I figure out the gear ratio to tell if they are compatable? I know the 87 is a 3.55.
Thanks again Todd R.

 

8.8" has a bolt on rear cover. 9" the entire differential can be removed from the front.

 

Thanks again, both have bolt on rear covers. That just leaves the gear ratio, and of course how to do it.
Thanks again for your help, Todd R.

 

I just did it. ...again. It's not difficult.

 

What is the axle code from the sticker on drivers door pillar? Or you can count the teeth on ring and pinion gears then divide ring by pinion.

 

The axle code on the door says 18.

 

You could also look for the tag bolted to the diff cover. If you're lucky, no one has removed it. The gear ratio will be stamped on the tag.

 

I just pulled the tag of and cleaned it up, if i am reading this right it is a 3.08. I also counted the revolutons: the drve shaft turns 1.5 turns for one wheel turn. Does this make sense? If this is a 3.08, is it a suitable replacement for my 3.55?
Thanks again for everyones help, Todd R.

 

Yup, 1.5 turns sounds about right for an open diff with 3.08s.

The suitability of the 3.08s vs. the 3.55s is purely a matter of personal taste and the way you use your truck. With the 3.08s, you will be turning fewer RPMs then with 3.55s at the same given MPH. The 3.08s will be a little more sluggish off the line and they won't get a load moving as well but you MAY notice a slight increase in mileage.

Don't forget that you speedo will read a little slow with the 3.08s unless you swap in the correct speedo gears.

 

Thanks mudder, but will the gears be close enough to match with my front end? My other option would be to trade both the front and rear,but that seams like more work than it's worth. I may just rebuild th 3.55.

 

Oh, I didn't realize you were talking about a 4wd. In that case, no the 3.08s will definetly not work.

Depending on what all is wrong with your current diff, you may be better off rebuilding it. If it's just the gears that are fried then I'd say get some new gears in the one you have.

 

to my knowlege It's everything, I figure as long as I'm in there I may as well do it right. I have really bad luck whith things. I am the only person I know who has blown three straight six 300's. Unstopable my ****. Any way thanks for your help I think I will start another thread looking for advice on brands of after market and LSD's.
Thanks, Todd R.

 

You can drive off-road (in slick stuff) with wildly different ratios, but it's better to have the hi-speed (low number) in the front. I've driven with both arrangements recently when I pulled each axle & had it rebuilt while driving on spare parts. My truck has 3.07F/3.08R and my spares were 3.54F/3.55R.