Ok, I've seen this question posted a few times but can't find an answer. I've been confused ever since a replaced my first bearing seal.

I have a 99 F150 with a 9.75 rear end. I wasnt sure about that before but I have verified it. Its a 12 bolt case, tag said 9.75 and I measured the ring gear. When I got the repar bearing/seal for the 9.75, it was too big. The 8.8 fit perfectly. I assumed that the parts store made a mistake, until I had to do the other said and had the same problem.

I know that ford changed the rear end setup in mid 99 but I don't know the details. My driver side axle is shot and I need to order a new one. Do they make 2 axles for the 9.75?? I found only 1 site out of about 30 that sells 2 but I dont want to order unless I'm sure. Why don't they all sell 2 styles for the 9.75? (no, i'm not talking about driver/passenger side when I say 2 styles) The site has the axles listed as 9.75/34 spline/33.37(small bearing) and 9.75/34 spline/33.37(large bearing).

Do you think its only the bearing and axle tube that are different or did they change the axle diameter as well? My axle measures approx 1.375" dia. (the bearing surface is approx 1.55") Does anyone know what there 9.75 axles measures?

I noticed the other posts usually just say that the guy must have got the wrong parts. Thats not the case here. I have triple checked everything. I hope someone can shed some light.

Thanks
Brian

 

Looks like you have the same issue as this guy:

https://www.f150online.com/forums/ot...-rear-end.html

 

It may be the same issue. I can't tell. I know for sure that there hasnt been any swapping of rear ends or engines. I wash I had the tag from the rear end but I was convinced that it was wrong last time i had it apart so I tossed it.

I tried to talk to parts at Ford but they won't give out much info. They always assume you are just probing for info so you can go shop elsewhere, which is pretty much what I was doing. $240 for an axle @ ford and $120 online.

The tech at for did say that there was a mid year change in 99. She thought it had something to do with the studs changed to or from 10mm to or from 12mm. I dont know if thats even related.

I do know that I have a 99, 5.4, 4WD, 9.75 with 3.73 gears. In my post above I said that I found 1 site that has 2 axles for the 9.75. One with a small and one with a large bearing. I know mine uses a smaller bearing but I just want to find someone here that has dealt with this issue before so that I can be 100% sure before I order. It seems like there were very few trucks that use this axle/bearing setup.

I could really use any input. I'm desperate to get this thing back on the road so I can get

 

OK, I think I solved it. Axle cost me $240 from ford cuz they were the only ones that had an answer. All of the other parts stores offer 1 axle for the 9.75 and for the 8.8.

The ford tech used my VIN and told me that the tag on the rear end (had i not tossed it) indicated 3.73 gear and 9.75 locking. Also, it said 923A which I guess is the code that says that I have one of the few trucks with a different axle and bearing setup. My trucks takes (driver side) a F75Z4234MB axle. This is identical to the 8.8 axle except it has a 34 tooth spline instead of 31. 99% of F150's with the 9.75 use a F75Z4234LB.

So, I hope this helps anyone with this problem in the future. If you have a 9.75" rear end and the replacment bearings are way too big and for some odd reason the 8.8 bearings fit.......you have the above axle. You didnt get the wrong parts, nobody swapped the motor or rear end when you weren't looking and my personal favorite.....Ford didn't throw in some old parts that they had laying around. For one reason or another ford used a smaller diameter axle on some 9.75 rears from 97-mid99. They switch to the other axle in mid 99.