GMC Western States

 Tech Center Number 21 - May 1998

Removing a Front Wheel Knuckle

by Egon H. Elssner


After several cycles of knuckle removal and installation I have settled into the detailed procedure that follows. The procedure does not require the use of a high power impact wrench which makes it useful "on the road."
The procedure and data given here are based on the X7525A GMC Motorhome Maintenance Manual and presentations given originally by Darrel Winterfelt, Ken Thoma and others. As with all non-GMC approved procedure, what you do to your coach, you do it at your own risk.

Knuckle Removal
In the process of removing the knuckle, a lot of torque is usually needed to loosen up the drive axle nut. First, the transmission should be taken out of Park because the parking pawl inside the transmission may break during axle nut loosening.
I have found that the necessary torque to loosen the axle nut may be applied if the wheel is left on the vehicle and the tire is on the ground with the normal weight on it. The rear wheel parking brake will usually not be sufficient to hold the vehicle during this loosening
procedure. I have found that an easy and safe way to hold the coach is to
simply drop the two rear support bogies onto suitable wood blocks by letting the air out of the air bags.
Loosening the drive axle nut will require a high torque wrench setup. A very satisfactory arrangement can be made up by using a long handle wrench. For some stubborn axle nuts it may be necessary to apply torque of up to 1000 ft. lbs. This is equivalent to a 160 lb. man standing on the end of a 6 foot long wrench! To make up a long wrench, I start with a 3/4 inch drive breaker bar (about 20" long) and make extensions out of pipe.
Pry the grease cap from the front wheel. Remove the drive axle nut cotter pin and place a 1 1/2 "socket with a 7" extension over the nut. The extension is necessary to get the handle of the "breaker bar wrench assembly' away from the side of the coach. With the extension it is necessary to support the breaker bar
end of the extension to be able to use the breaker bar. For this support I use a
piece of 3/4 inch plywood, standing on edge, with a suitable hole (1 1/2" dia. for the head end of the extension) drilled at the correct height. Loosen the drive axle nut but do not remove.
Loosen the wheel lug nuts but don't remove. Place a 4 ton bottle jack under the frame to the front frame extension junction and raise until a 12" high jack stand fits under the frame alongside the bottle jack. Remove the bottle jack and place it under the lower control arm just outboard of the sway bar. A small iron plate or bar can be used between the jack and the control arm to distribute the load to both sides of the control arm. Raise the wheel off the ground just enough to remove the wheel. Remove the wheel.
With a suitable two-jaw puller remove the steering tie rod after removing the cotter pin and nut. Removing the steering tie rod at this time allows the knuckle to be moved from side to side, useful in removing the brake caliper. Move the tie rod out of the way.
Using a 3/4" box end wrench with a long handle, remove the upper ball joint nut after removing the cotter pin. No need to worry about the upper ball joint stud coming loose, it will stay put until removed from its tapered socket at a later time. After removing the nut remove the brake line clamp from the ball joint stud.
Obtain a piece of wire to support the caliper when removed. With a 3/8" hex wrench (Allen), back out the brake caliper bolts. Remove the brake caliper assembly and support it from the upper end of the shock absorber with the wire, being careful not to kink the brake line or to drop the brake pads out of the calipers.
Make sure that the drive axle nut can be easily removed at this point, but leave the nut on until ready to remove the knuckle.
The GMC Maintenance manual shows the lower ball joint being removed with a large two jaw puller. Some mechanics loosen the lower ball joint by supporting the end of the lower ball joint stud (on the backed off nut) on a small jack to apply a pop out force and, with a pair of hammers, beat on the flange until the cone of the ball joint pops out. A far easier solution is to use a two jaw puller made of a modified Pitman arm puller. A few turns with a long handle wrench separates the ball joint from the knuckle.
The next step is to loosen the upper ball joint. The classic way is to apply pressure with a crow bar between the knuckle and the upper control arm and, using a hammer backed up by another hammer on the opposite side, rapping the flange holding the ball joint stud until it yields. A much easier and less damaging procedure is to push the stud up using a 'pusher'. The pusher is inserted behind the joint (over the CV joint). The upper part of the pusher fits over the knuckle flange (around the grease boot) and the ball joint stud fits into the slot of the lower bar of the pusher. After taking up the slack and aligning the pusher into position, a few twists of a short handle open-end wrench pops out the stud. It's a good idea to put the stud nut back onto the loosen ball joint until the knuckle is ready to be removed.
Everything is now loose, ready for knuckle removal. Remove the nut on the lower control arm. Remove the axle drive nut and washer and push the drive axle back as far as it can go (into the inner CV joint). While holding the knuckle to stabilize it, remove the upper ball joint nut and swing the upper control arm up and out of the way. An important procedure follows: Tilt the knuckle top outward and turn the knuckle (to the fight or left) to gain sufficient clearance for the drive axle to come out of the hub and the lower ball joint stud to come free of the knuckle simultaneously. The knuckle is moderately heavy (about 50 lbs.) and with the drive line still attached, even slightly heavier, so caution is advised in handling. Lower the knuckle to the ground.

Replace or repack wheel bearings and replace upper and/or lower ball joints as needed. Clean the ball joint cones and cone bores of the knuckle. Only a slight trace of grease is permitted for assembly (See the X7525A manual, Page 3A-22 (Note)). Lightly grease the seal area of the CV Joint.
Pre-position the drive axle end and lower ball joint to maximize working space when lifting knuckle into position (see Disassembly). A rubber band wrapped in a figure 8 around the lower ball joint grease boot and the lower control arm will help hold the boot in place during assembly.
Lift and position knuckle to engage drive axle and lower ball joint stud. Start lower ball joint nut on stud. Having an assistant handy helps while lifting the knuckle into position and starting the lower ball joint nut. An alternative is to balance the knuckle on a block of wood or small jack. Fully engage drive axle into hub, place axle nut washer and start drive axle nut. Run up the nut on the lower ball joint nut but do not torque. Pull down upper control arm to engage ball joint stud and start nut (without brake line clamp at this time).
Lightly tighten the drive axle nut. Visually make sure that the outer CV Joint mates with the drive axle seal. Any gap between the joint and seal will result in grease leakage, bearing contamination with dirt and water with possible bearing failure and brake pad and rotor contamination by grease.
Torque the lower ball joint nut to 100 ft. lbs. Check alignment of cotter pin hole and tighten nut to insert the cotter pin. If the torque seems excessive, try a different nut. Fit the cotter pin.
Torque upper ball joint nut {without the brake line clamp). Without a special adapter which I haven't been able to find, it is impossible to accurately torque this nut to the specified 40 to 60 ft. lbs. Use a long handle box end wrench to set the cone of the ball joint stud into the knuckle, estimating the applied torque as best you can.
Clean and grease (with a silicon grease) the bushings upon which the caliper slides as the pads wear. See the X7525 manual, Page 5-20 Figure 12.
Check the lay of the brake hose and slip the brake caliper into the knuckle. Very likely you will need more pad to pad clearance to do this easily. Push the brake cylinder into the caliper with either a tool made for it or a C clamp and suitable metal plate. It may be necessary to drain some brake fluid from the master brake cylinder to avoid overflow when pressing the cylinder into the caliper. See the X7525 manual, Page 5-19.
Insert the caliper bolts and torque to 35 ft. lbs. It is important to torque these bolts because they can work loose and cause catastrophic braking/drivability problems if they fall out (a personal experience) With the brake pads relatively loose, check that the caliper assembly slides freely on the bushings.
Loosen and remove the upper control arm stud nut. Place the brake line clamp over the stud and replace the nut. Check the brake line for freedom of movement when the knuckle is moved from side to side. Tighten the nut to insert the cotter pin. Fit the pin. At this time, it's a good idea to degrease the brake rotor with a spray brake cleaner and clean paper towels.
From inside the coach, step on the brake pedal to set the brake caliper. Check brake fluid level. Most likely, the brake pads will drag after this operation. The pads are normally pushed apart by the slight typical side to side wobble of the brake rotor. It is, however, a good idea to check for brake drag and heating .after a few miles of driving.
Fit the steering tie rod and torque the nut to 40 ft. lbs. Tighten nut to allow cotter pin insertion. Fit the pin.
Before you install the wheel, tighten the drive axle nut as much as you easily can (up to about 140 ft. lbs.).
Install the wheel and tighten the lug nuts as much as you easily can. Block the wheel with a 2x4 and torque the drive axle nut to 140 ft. lbs. Torque the wheel lug nuts to your favorite torque (I use 200 ft. lbs. on my steel rims, the owner's manual says 250 ft. lbs.). Lower the wheel and remove the bottle jack. Place it under the frame and remove the frame block.
Check the fit for a cotter pin on the drive axle. Tighten (but never loosen) the nut to the next pin insertion point. If the torque would appear to greatly exceed 280 ft. lbs. (the upper end of the 140 to 280 ft. lbs. specified in X7525) it might be a good idea to try a different axle nut or washer. Fit the pin. A slightly curved pin goes in quite easily. With a screwdriver, bend up the longer end of the pin leaving the shorter end straight.

Tools and Props in approximate order of usage

2 wood blocks 12" long 6 x 10 (for rear axle support)
Small chisel or screwdriver (for cap removal)
3/4" drive breaker bar
7" long 3/4" drive extension
1 1/2" socket, 3/4" drive (for drive axle nut)
6 foot extension for breaker bar
Piece of 3/4" plywood with hole (for breaker bar support)
Bottle jack, 4 ton
12" high Jack Stand or wood block equivalent
Small metal plate or bar {for lower control arm jack support)
heavy duty wire cutter for cotter pins {8" handle is nice)
pliers or long nose pliers (for cotter pins)
3/4" socket, 1/2" drive (for steering tie rod nut)
3/4" box end wrench, long handle {for upper ball joint nut)
3/8" hex (Allen) wrench with 3/8" drive (for caliper bolts)
6" long 3/8" drive extension
1/2" drive to 3/8" drive adapter (to adapt torque wrench for caliper bolts)
12" piece of 1/2" or 3/4" pipe to extend ratchet wrenches (for convenience) Upper ball joint pusher
15/16" socket, 1/2" drive (for lower ball joint nut)
Lower ball joint pusher
3/8" drive ratchet wrench
1/2" drive ratchet wrench
1/2" drive torque wrench, to 150 ft. lbs. (for steering tie rod, lower ball joint nut and brake caliper bolts)
3/4" drive torque wrench, to 300 ft. lbs. (for drive axle nut and wheel lug nuts)
Socket for wheel lug nuts
Cotter pins: 5/32" x 1" (for axle drive nut}, 1/8" x 1 1/2" (all others).

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