I have a 1990 F-150 with a 351 in it and a non-limited slip diff. It is an auto 4x4, i was wondering what it would take to convert it to a posi rear end?

 

The difference between a posi and a good limited slip isn't a lot, and you can have vastly better performance from the factory LS with a simple clutch restack which is guaranteed to be a lot cheaper than swapping in an Detroit Trutrac or something similar.

 

So whats the biggest difference? The better the durability, the better because this truck is a snow pusher. How hard would it be to drop in a Posi/LS rear end, and re-stack the clutch gears?

 

You can buy an 8.8 trak-Loc rebuild kit for $100 and all you have to do is re-arrange the disks so they alternate fricktion disk/pressure plate instead of the stock arrangement with pressure plates back to back. That puts more friction material in the diff and brings the diff preload up into the usefull range, and the end result is you now have a diff that only allows about 20% slip versus the stock calibration that allows about 80% slip. You can do this work yourself in your driveway in about and hour.

A true posi like the Detroit Trutrac will cost about $500 for the diff alone and you could easily spend another $500 getting it installed since the diff carrier has to be removed from the housing, the ring gear transfered and new bearings pressed on, and then the whole diff has to be setup again.

 

So how much can i expect to pay at a junk yard for a used LS diff or posi rear end? Cause i want to swap out the axle, diff etc b/c its an open rear end. Do you think i could find a posi at a junk yard even?

 

You won't find a Posi they were never offered but you should have no problem finding a factory LS diff with the 3.55 ratio being the most popular, look for axle code H9 on the drivers door calibration decal.

 

Ok thanks for your help man, much appreciated. Also, can i find the kit at oreillys or do i need to find one online? And could you possibly provide a source of detailed instructions or pictures on how to convert the clutch gears?

 

The cluch kits are widely available so I suspect you will find them at your local parts store. Doing the job isn't that hard especially if you are working on a junkyard axle that you have already removed from under a vehicle. Start by removing the diff cover and draining the fluid. Remove the pinion shaft lock bolt and slide out the pinion shaft, that's the large shaft that goes throught he center of the diff. With that out of the way you can remove the S spring, then push the axles in a little and remove the C-clips, you can then pull the axles back out a little. The next step is to remove the spider gears, start with the top one and spin it slightly while you pull on it and it will come out of the housing. Same for the bottom one and then the side gears will just pull out. Behind the side gears are the clutch packs, pull these out and replace with the new kit but restack them with alternating friction and pressure plates, this will require the use of one of the old friction plates and will leave you with an extra pressure plate. Now put it all back together and install a new pinion lock bolt, fill the diff with fluid and add a bottle of friction modifier... which you can buy at the local dealer.

 

Great info Conanski. It won't let me rep you again but I tried. I have the same deal on my truck, non-ls 3:55 and need a better setup. I'm saving this thread for sure.

 

Hi all, I have a 1950 Ford f-1 with just a regular old rear differential. I would like to convert it to a possi track but I am not sure how to go about this. I have seen possi track rear ends avalible on Speedway motors but I am looking to do it for less money. Would swapping an old ford ranger rear end work, maybe a toyota pickup, they have simmilar wheel bases...

All suggestions welcome, thank you,

Finn

 

This is an 11 year old post. You'd be better served by just starting a new thread, and asking your question.

And if you're talking about the Factory rear end in a 1950 F-1, you'd be better off asking in the appropriate forum:
https://www.ford-trucks.com/forums/forum41/