Removing a Hummer Differential

Read this Before You Start

Differential Rebuild Article

I got into this project when I decided to install a Detroit locker in the rear of my 98 Hummer wagon. The project ballooned when I discovered that I had to replace my parking brake cables. Since the rear would be apart I also did a rear brake job. This is also a good time to check your whole drive train because you will have a large portion of it apart.

 

The following tools will be needed:

• 9/16" (preferable T-handle - Snap-on RTB-18 about 32.00)
• 15mm open end (ratcheting preferable)
• 1 1/8" socket
• 15/16" socket
• 5/16" socket
• ½" socket
• Air impact wrench
• Air chisel
• ½" Ratcheting drive
• ¼" Ratcheting Drive
• ½" Torque Wrench capable of reaching 150 ft-lbs
• 3/8" Allen
• ½" Breaker Bar
• Thread Locker Red
• Thread Locker Blue
• Gear Lube
• Teflon Tape
• Drain Bucket
• Permatex Gasket sealant
• Floor Jack
• Jack stands
• Hammer
• Screwdriver
• HMMWV Torque List

Removal:

First thing to do when attempting to drop a differential is to remove the undercarriage protection. Then drain the gear fluid. If you're doing the rear remove the parking brake cables from the calipers.

I Stripped my Rear Differential hex head fill plug and tried a GM plug with a square socket as a replacement which is an exact fit (1/2" x 14). And the square end is harder to strip.
GM Part # 25522466

The Half shafts must be removed from the brake caliper and do not need to be removed from the truck. Chock the front wheels, put the transfer case in N and jack up one wheel under the A-arm. I use a 15mm socket in an impact gun and undo the bolts one at a time rotating the tire to align the next bolt. Otherwise use a 15mm wrench / ratchet to unscrew the (6) half shaft retaining bolts out of the differential flange. The half shafts will drop down and rest on the lower control arm. (how to replace the parking brake cables)

The brake calipers on both sides need to come off. Take the 9/16" / 15mm T-handle and remove the upper bolts holding the caliper on. Use any 9/16" for the easy to get to lowers. Carefully lift the calipers out of the caliper bracket while pulling the old brake pads out. Be Careful that the now loose rotor doesn't fall on you. Put the caliper aside and use a zip-tie or a hanger wire to hold the caliper suspended so you don't strain or damage the brake lines. Remove the rotor and brake pads. Inspect them for wear and replace if needed. At a minimum I'd replace the pads because the labor it takes to get this whole thing apart. See my brake article for details on doing this.

Next, grab your impact and your 1 1/8" socket and remove the output flanges where the half shaft / rotor was mounted. One easy way to keep the flanges from rotating is to screw one of the half shaft bolts all the way through the flange so it protrudes out the back side. Rotate the flange so the protruding bolt contacts the caliper bracket bolt. This will keep the flange from rotating while you remove the big bolt. .Slide the flanges out of the diff.

Move to the input side of the differential and remove the drive shaft caps with your 5/16" ratchet. Be careful that you don't let the U-joint caps fall off. They are filled with a bunch of needle bearings. If they do get loose (ask me how I know) then you have to retrieve all the bearings or get a new U-joint. Since a new U-joint is only 16.00 bucks I opted to replace it. (how to replace a U-Joint) The other end of the drive shaft is attached to a yoke that is just inserted into the transfercase. The drive shaft should be able to be pushed a bit towards the front of the truck and then drop down away from the diff input yoke. On my 98 the shaft pushed foreword and dropped down to rest between the muffler and fuel tank heat shield. If the shaft won't move out of the way then wait until the differential is loosened up.

Input side of the differential

There are now 6 bolts left to drop the differential out of the truck. Take the impact or a breaker bar and your 15/16" socket and start to loosen the 4 bolts on the side of the differential (there are 4 bolts on either side, 2 for the caliper bracket and 2 for the diff mounting bracket). Loosen the 2 bolts on the input side which are above the input yoke. Grab your floor jack and a flat piece of wood and raise it up until it is touching the differential. Remove the 6 bolts. Make sure that the brake calipers are tied away from the diff. Lower the jack and the diff should come down. If it doesn't jack it up a bit and then lower it. You may need to use a pry bar to get it to move. Lower the diff a couple of inches and reach over the top of the and remove the vent line. On my truck it was a 3/8" brass fitting. Lower the differential all the way down with the floor jack. As it comes down the diff will tilt with the input side raised. There is no reason to remove the input yoke to remove the diff. You do not want to remove the input yoke unless you have to because it's assembly is critical to the pinion gear's alignment within the diff.

Once out of the truck, remove the caliper mounting brackets with a 15/16" socket. After the caliper mounting brackets are removed, remove the differential cover bolts with a ½" socket.

Installation:

Install the caliper mounting brackets to the differential using locktite red and torque to 125 to 150 ft lbs. I've worked on a couple of trucks where these bolts loosened up and started to back out. If they back out far enough they can run into moving parts and destroy the brakes. In order to tighten these bolts you have to remove a half shaft, the brake caliper and rotor which is a major pain.

With the aid of the floor jack raise the differential into position making sure that it is located between the mounting brackets on either side of the differential.

Raise the differential halfway up and reconnect the vent line. Then raise it to the final location and finger start as many bolts as possible. Get all 6 started before you tighten any of them. I had a problem lining up the 2 bolts above the input yoke. I almost stripped out the threads on one. I used a jack and chain to pull the diff down and line up the last 2 bolts. You can see how to do this in my article about straightening your bent undercarriage protection. Using thread locker red, torque all of the bolts down to 125-150 ft-lbs.

Install the output flanges and the blue or orange oil-retaining seals. When installing the retaining nut apply a bead of Permatex around the lip of it and then use the impact to torque it down.

Re-install the brake rotors and half-shafts. Install the half shaft bolts with new nordlock washers. Using thread locker red, torque the bolts down to 57 ft-lbs. New bolts come with thread locker already on them.

Once again you don't want the half shaft bolts to back out and mangle the brakes. The picture on the left shows the beginning stages.

Assemble the brakes. Insert pads and calipers. Using thread locker blue and torque the 9/16" bolts to 40 ft-lbs. Be sure to seat the calipers in the proper orientation on the bracket or the bolt holes will not line up. If you removed the parking brake cables connect them up. Reach up and make sure that the steel brake lines are not touching the frame. If they are bend them away or they will rub a hole in the line.

Reconnect the rear drive shaft to the differential. Line up the U joint and place the bearing caps over the ends of the U-joint. Guide the assembly into the differential yoke. Place the drive shaft retaining caps over the bearings and tighten them into place.

Make sure the drain plug is tight and sealed. Fill the differential up with 2 quarts of gear fluid until the fluid is level at the bottom of the fill hole.