2004 F-150 Lariat - 4WD, New Body Style
Rear diff is a 9.75 with posi-traction.

I've had a rear end roar since I've had the truck. I decided to re-gear, and in the process perform a rebuild.
I've Purchased -
ZG F9.75-456-11 USA Standard Ring & Pinion gear set for '11 & up Ford 9.75" in a 4.56 ratio
YK F9.75-CNV-J Yukon Master Overhaul Kit, Ford 9.75" diff, '00-'07 w/'11 & up ring & pinion
AK 1561FD Yukon Rear Axle Bearing and Seal Kit
YPKF9.75-PC 9.75" TracLoc Clutch Set, 16 Pieces

So far I've got everything removed & cleaned, and the new pinion has been reinstalled (I removed and re-used the original spacer between pinion gear and inner bearing)

While I wait for the clutch set to arrive, I'm curious if blindly re-using the original pinion gear spacer is smart, or should I attempt to select a new shim? I don't have any of the custom tools for this.

The Factory Service Manual calls for Synthetic 75W90 + friction modifier, what's the consensus on gear oil these days? I'm a Red Line fan, should I attempt to use that instead?

 

Unless Yukon recommends otherwise, use 75W140 full synthetic lube and Ford XL-3 friction modifier. I know the Redline gear lube has friction modifiers, but put one 4oz bottle of the Ford additive in with it. Get that from the dealer, it's cheaper than having a bottle shipped.

You DO know that you also have to regear the front, right? If you don't, pull the front driveshaft.

 

I think 75W140 synthetic is the recommended fluid with Ford FM for the rear and 75W90 is recommended for the front diff in 4x4s.
You need to use a new crush sleeve to get the proper preload on the pinion bearings. The shim behind the rear pinion bearing is probably okay using the original but the proper way is to measure the pinion depth. You definitely need to check the gear pattern.

 

Odd, the service manual says otherwise. Was there some discovery made that I"m unaware of?

That's what I did last fluid change. I wasnt sure if the Red Line fluids already had the additive. If I need to add separately, it will be the OEM Ford stuff from the dealer!

Good advice, the front is already scheduled after the rear is done. I made extra sure that my gear ratio would be available for both the front 8.8 and the rear 9.75.

I pasted a screenshot of my factory service manual above.

Measuring the pinion depth requires the special Rotunda tools, right? Unless i take it to a local differential shop that's off the table. Yukon included two crush sleeves. If the gear pattern is horribly Toe or Heel, I'll suck it up and take it down there - then I can reassemble properly with the second sleeve.

 

I'm also a little more than concerned about my spider gear thrust washers. Both are similar. Where they spin on the inside of the case is scored in a circular pattern.

The spiders themselves appear to be pristine.

 

75W140 has been the recommendation for over 20 years. I don't know why your manual says otherwise. Here's what Amsoil says:

https://www.amsoil.com/garage/intern...150%20PICKUP+5

 

Perhaps Ford tried that high efficiency 75W90 temporarily. Before I used any 75W90 I would make sure it met the Ford specification for that year. Actually, I would use 75W140.

I highly recommend you get a pro to do the gear changes. It isn't amateur work. If you are determined to do it yourself watch all the videos you can find on how to do it before you attempt it. I don't know about today, but quite a few years ago, Richmond Gear would tell you that their gears with a higher numerical ratio than 4.10 would be noisy.

That said, I have changed gears in a 69 Chevelle 12 bolt rear and rebuilt a 74 Ford rear (back in the 70's) but I didn't really know what I was doing. I did not use new gears and they did sing a little afterwards but otherwise seemed okay. I was lucky I didn't really screw them up.

 

I called the Ford dealership and he said they use Alldata - the Ford FSM's have been too difficult to maintain. Alldata says 75W140 as well. That being said, the 140 vs 90 is the "winter" spec - so we're only concerning ourselves with a cold viscosity, and the running temp viscosity is the same.

The dealership also shows XL-3 friction modifier instead of XL-7.

I'll go with 75W140, and the Ford XL-3 Friction modifier.

 

Thrust washers on spider gears were trashed. Ended up buying a new differential case.

Replaced all bearings and races, new clutches, 4.56 ring & pinion installed. Torqued pinion nut until spin resistance was 25-in-lbs without backing the nut off. Re-used pinion shim, and case shims. Both case shims measured 0.267 inches. Ring gear backlash measured 0.007 inches.

Here's the mesh patterns:
Coast pattern

Coast pattern

Drive pattern

Drive pattern

 

Should be good to go!

 

Sweet. Thank you, I was waiting for feedback to threadlock the cap nuts and bolt on the cover!

 

Looks pretty good. You double check back lash between the pinion and the ring?

 

Not to hijack your thread here, but about to do a rear diff service to my vehicle as well. Same truck - 04 F-150 Lariat 4x4 with LSD. Used to work parts for a Ford dealer, but that was years ago so I don't remember all the numbers. I no longer have access to the Ford manuals, but I have a Chilton manual that states 75W90 for the '04, but 75W140 for '05 and newer models, which should have the same rear differential. Dealership sold me 75W140, and the friction modifier. Based on the other comments on this thread, I think it's safe to use the 75W140 as well.

I do have a question about the RTV though. If I remember correctly, we used TA-30 for the gasket maker. They gave me TA-357 instead, saying it superseded the TA-30. Is that what I should use?

 

I don't use RTV, I use a real gasket. With that said, TA-357 looks to be a better product than TA-30.

 

I purchased a cast aluminum diff cover, so I ended up using Ultra Grey with no gasket material.

From my research, the 9.75 rears used the same bearings and gearsets from 2004 all the way to 2011. After 2011, the pinion was changed and requires a bearing with a different inside diameter. I'm sure the different lube viscosity for the 2004 was just a typo or at least was quickly superceded. The friction modifier is only necessary if you are running a "wet clutch" limited slip. If you have an open diff, the friction modifier is not necessary.

Oh, and I have the Ford FSM CD files from 1996 up to 2008. They don't like newer versions of Windows, but a virtual machine running WinXP displays them nicely.