My current axle is slightly bent on the passenger side and I plan on swapping it out with a new-ish axle.

The truck I have currently has an H9 axle code:
99 F150 5.4 4R70W w/ 8.8RG 3:55 (drum brakes / 5 bolt)

I plan to swap it with an B6 axle taken from the below vehicle:
01 F150 7700 5.4 4R100 ???RG 3:73 (disc brakes / 7 bolt)

I'm not entirely sure if the donor has a 9.75 or 10.5 Ring gear. Any way to determine prior to opening diff cover? Most of what I read says it's a 9.75 but I've read some conflicting information saying there's a heavy haul package and that the 4R100 is sometimes paired with a 10.5.

Secondly, will I need to swap the front axle as well? I'm assuming both front and rear axle need to be geared the same.

Not sure about driveshaft fitament either. Pretty sure I'll need to keep the driveshaft and diff paired when I swap, but I wasn't sure if there will be spline count differences where the axle goes into the T-case.

As for the rear brakes, going from drum to disc will be an upgrade. I plant to swap parking brake cables as well. Has anyone else done a similar swap? Do you think I'm missing anything? I've got new bigger leaf springs currently on the 99', so won't swap the springs since they have more leafs than the 7700.

 

The 7 lug 7700 uses a 10.25" rear. You will have to regear the front axle to match, and get a programmer and tunes to correct the speedometer/odometer.

If this were my truck, I'd simply replace the rear axle with the same thing. Costs a lot less in the long run, and a lot easier to do.

 

Thanks!
good to know it is a 10.25, was having a lot of trouble finding that info. Checked all the tags on the diff but couldn't make much of them.

Also I did not consider the speedo / odometer factor. Thanks for the heads up on that as well.

I was kind of on the fence with this - but weighed the pros and cons.

The whole swap will only cost me my time, the donor vehicle was free and I have a brand new set of duratrac tires and rims on the 7 bolt wheels already so it saves me un-mounting them off rims and re balancing them to the 5 bolts. Cost wise I think the only thing I'll need to pay for is U-bolts for the axle where it bolts to the springs.

I just built my dream shop so can do this in the comfort of a heated garage with all the tools to do it on my days off (8 on 6 off shift)

If I get a scrapyard axle I run the risk of opening a can of worms (ie; find it's also bent / shot axle shafts, bad internals, etc) at least this way I know the axle is good and have it just sitting here. Plus I figure the added payload capacity on the axle can't hurt.

 

I seem to remember that axles for the 7 lug rear are not available new any more. So, if the axle bearing went bad requiring a new bearing and axle, you may have difficulty finding another axle. My 2 cents.