Hello all. I've been driving a 1978 Bronco(my first vehicle) for about 9 years and now that I have a newer truck, I find myself at a loss for knowledge with it. I have a 1999 F-150 4x4, 5.4L, auto. Was just wondering if anyone could tell me the type of rearend used in them. Is it an 8.8", 9.75, or does it depend on the "package" you bought from Ford????? From reading on this site, the rear vibration I'm feeling seems to be common and related to the clutch packs. Wish these rears were more like my 9" in my Bronco. The reason I'm wondering about which rear I have is I'd like some sort of locker for it, preferably a Detroit EZ locker. They have one for the 8.8" 31 spline. Any info would be greatly appreciated.

 

Given that its a 5.4L it SHOULD be a 9.75. The way to tell is look at the shape of the diff. If it looks like a square with rounded corners its an 8.8. If it looks somewhat reminicent of a D60 or sterling its a 9.75.


The shuddering is most likely the clutch packs getting work out. Thats a very common problem for that diff. I don't know if I'd go with a Sleazy Locker or not. Granted its cheap, but its road manners are not all that great. To be honest I'd rather drive my welded diff Ranger than one with an EZ locker as they can lock and unlock at unexpected times making things "interesting".

 

You could try adding some friction modifier to the rear end and see if it will help before doing any major repairs. Local dealer will have it in stock, less than 10 bucks.

Robbie

 

Thanks for the help. I'll check out the shape and I'll try the friction modifier.

 

There should be two tags on the rear telling you everything you want to know about the diff. Just crawl under and take a look.

 

5.4 = 9.75". Only the LS needs friction modifier. There are no 9.75" lockers on the market that I know of, but there are several clutch-type aftermarket options.