The classic 1973 - 1978 GMC Motorhome is a marvelous machine. However, as most GMC owners know, the front end is a weak point of the design. Around 2007, Bill Hubler developed a kit to retrofit GM heavy duty truck parts onto the GMC motorhome front end. In 2011, Manny Trovao figured out how to improve the kit and brought the cost down by buying new parts in large quantities. The result is the new Version II One-Ton Front End Kit.
This is a terrific upgrade that solves a lot of problems. Given how difficult and expensive it is to service the original bearings and how often it must be done, this is a cost effective solution for that problem alone. It provides much bigger sealed bearings good for 200K miles. In addition, it gives you heavy-duty knuckles, ball joints, and CV joints, bigger brake rotors, reinforced lower A-arms, and a spacer that moves the front wheels into line with the rear.
These instructions describe how I installed the Version II kit. Mostly. They also include tips from pros and things I learned that I wish I'd known in advance. Special thanks to the knowledgeable people who provided advice, encouragement, proofreading, ideas, and extra pictures, and THANK YOU Manny Trovao and Bill Hubler for this great upgrade!
These instructions are available on the web at http://www.machinesoflovinggrace.net/gmc/frontend. Email suggestions and comments to molggmc at sonic.net.
THIS IS A WORK IN PROGRESS. I will update it as I get feedback. Please use the most current version. This copy was published 3/18/2016.
IMPORTANT NOTE: Manny routinely upgrades his kits as he gets feedback. Some of the parts you receive may look different from the ones pictured here. I will try to keep these instructions updated if there are significant changes.
WARNING: USE AT YOUR OWN RISK! Working around and under a 6-ton vehicle is hazardous. The instructions are as correct as I can make them, but I OFFER NO GUARANTEES ABOUT ANYTHING. I have no monetary interest in the people or products mentioned in this document.
You'll need right and left front brake calipers for a 1996 GMC/Chevy Suburban Diesel 4x4 with 8600 lbs GVW (also referenced in parts catalogs as having 13" rear brake drums). Order "loaded" or "semi-loaded" calipers so you get all the hardware required. If you get "semi-loaded" calipers, you'll also have to order brake pads.
Note: These are NOT the same calipers as the 80mm upgrade to the OEM front brakes.
Some sample part numbers are listed below. Unless otherwise noted, these are loaded calipers (include pads):
If you haven't already upgraded these parts, you should also consider getting:
If you find the upper A-arm cam bolts are stripped, order Moog K5266. Specialty Products Company (SPC) 83160 will also work, but the cams are slightly smaller. One kit does both sides of one A-arm, so to replace all you'll need two kits.
The seals on the back of the knuckles have been inspected and determined to be in good condition. There are also dust shields on the new axles that fit over the seals for extra protection. If you prefer to replace the knuckle seals with new ones, the NAPA part number is NOS 31504.
Note: It is possible to do this work without the torsion bar unloader on most coaches, but the tool will certainly make it easier. You MUST use the tool if you need to adjust ride height after the installation. Given that you're installing a lot of new parts and moving things around, your old ride height settings may not be correct. As of this writing, Manny Trovao has a couple of these tools to lend for installing the kit.
The point here is to remove everything attached to the upper and lower A-arms (aka “Control Arms”). The specific order is not always important, but some ways are easier than others.
Remove the cotter pins from the tie rod end and upper and lower ball joints.
Place a jack under the lower A-arm and raise it to take pressure off the shock absorber. Remove the upper bolt and lower nut and remove the shock.
Note: Removing the shock first makes it easier to work on the brake line connection.
Leave the jack under the lower A-arm.
Position a container under the brake line to catch fluid. Use 3/8" and 5/8" flare wrenches to separate the flexible brake line from the hard brake line. It may be completely rusted in place and you may end up breaking the metal line if you flex it too much. If you don't use flare wrenches, you will almost certainly destroy the fittings. Even with flare wrenches, it can be very difficult.
Note: Vise grips may help keep the flare wrench ends from spreading as you try to remove brake fittings.
Pull the locking tab from the frame support to release the flexible line.
Remove the nut from the upper ball joint stud and pull off the bracket that supports the brake hose. Thread the castle nut back onto the end of the upper ball joint stud.
Disconnect the sway bar link from the lower A-arm.
With the tie rod and sway bar link disconnected, you can now turn the knuckle to more easily get at the caliper bolts. Remove the caliper bolts with a 3/8" hex wrench. Remove any other brackets or cable ties holding the flexible brake line. Slide the caliper off the rotor. If it's stuck, you may need to use a big C-clamp to retract the piston (see manual).
While holding onto the knuckle, remove the castle nut and pull the stud out of the top of the knuckle. Guide the knuckle down so it's hanging from the lower ball joint.
Back off the lower ball joint castle nut so it's partly off the end of the ball joint stud. This will keep the pitman puller tool from slipping off the stud. Position the tool arms over the knuckle eye and its threaded rod against the end of the ball joint stud. Using a close fitting (possibly metric) wrench, turn the the puller bolt to apply pressure to the ball joint until it pops free. It takes a lot of force and you may need to also hammer the stud and/or eye. Once the ball stud is loose, remove the tool and the castle nut and lower the knuckle and hub assembly off the stud.
Note: If you still can't remove the lower ball joint, remove the three bolts that hold the disc/hub retainer to the knuckle. The bolts are behind the disc and a little hard to get to, but shouldn't have a lot of torque on them. Slide the disc/hub assembly outward off the knuckle. The manual shows using a slide hammer, but I was able to just slide if off with a gentle tap on the back. This will remove most of the weight from the lower A-arm and make it easier to handle while you're working on the lower ball joint.
If you're replacing your sway bar front frame bushings, now is a good time to do that. (see manual)
Remove the bolts and adjusting cams from the upper A-arm and pull the arm out of the frame brackets. You may have to wiggle the front cam around to get the bolt past the shock absorber bracket. Check the cam adjustment bracket surface for weld splatter, dirt, or rust, and clean up as needed to avoid affecting the alignment.
Note: If you broke a hard brake line as I did, now is a good time to repair or replace it, with the upper A-arm out of the way.
There are a lot of different ways to get the A-arm bushings out, but here's how I did it: Using a hammer and chisel or small crow bar, pop off the metal ends of the upper A-arm bushings by working the tool under the lip of the metal. Try not to bend them since you'll still need one set per arm. Use a screw clamp and a short (about 2") 3/8" socket extension with about a 3/4" socket to remove the old bushings. You want a tool that won't get stuck once the sleeve and bushing are pushed out. There are many other combinations of sockets and tools that can do the job. You'll also need a spacer to give the bushing a place to go, such as a big socket or steel plumbing cap.
Clean up the rear hole in the arm really well and remove any burrs, rust, paint, or dirt. It may help to lightly sand or file the hole, but don't remove too much metal. Align the new offset bushing in the rear hole of the upper A-arm with the arrow pointing AWAY from the ball joint.
Once the new bushing is fully inserted into the arm, put the new small cap on the small end of the bushing and seat it into the inner metal sleeve. The new big cap goes on the big end.
Before installing the front bushing, clean the interior of the old outer metal sleeve on the A-arm. Lubricate the sides of the new urethane bushing with the provided grease. Use a mallet to drive the new bushing into the old A-arm front outer sleeve. Make sure it's completely seated. Grease the outside of one of the old inner metal sleeves and drive it flush into the new bushing. Put one of the old big caps on the big end and the little cap on the little end and seat them into the old inner metal sleeve.
Clean and inspect the old cam assemblies you removed. If the bolt threads are stripped, replace them. Otherwise, you won't be able to torque them properly and will have alignment problems. Apply anti-seize to the bolts and threads.
Guide the upper control arm into the frame bracket and re-install the cam assemblies. The cam bolts should be installed from the center of the A-arms so that the bolt heads are both in the middle of the arm, facing in opposite directions.
Note: It is harder to install the cam bolts this way because the shock mounts are in the way, but makes it easier to get a torque wrench onto the nuts later. You may need to pull the a-arms outwards and separate stuck cams from the bolts in order to insert them into the adjustment slot.
Torque the cam nut to 80 ft-lbs. Hold a wrench on the cam bolt head to keep the cams from turning.
You may also want to spot weld the upper ball joint plate to the top of the A-arm, but this is not required.
Before you remove the lower A-arm, clean off a spot on the torsion bar just behind the A-arm socket and clearly mark the top of the torsion bar with paint or a marker. This is just to prevent confusion later if anything shifts or becomes misaligned.
Lower the jack from under the A-arm. Removing the jack will release most of the load from the torsion bar.
Note: If you can't get the jack out after lowering it, you can remove it after the torsion bar is unloaded.
If you want to weld on extra support, see Notes:A-Arm Reinforcement. This is not required, and not something I chose to do.
Install the grease fitting onto the side of the new lower ball joint, angled toward the rear of the A-arm so you can reach it later. Seat the lower ball joint grease boot onto the ball joint. There's a small indentation on the boot that should line up with the grease fitting.
Clean out the torsion bar socket on the new A-arm and apply a generous amount of chassis grease to the inside of the socket. Place the new A-arm near the coach in the correct orientation, ready to install. Be careful to keep dirt out of the ball joint and torsion bar socket.
Get under the coach at the rear of the torsion bar and measure how much the adjuster bolt sticks out of its special square nut. (There should not be any other nuts or Loctite on the adjuster bolt, though I ran into both.) The manual says to count turns, but I found it too easy to lose track while struggling with rusty stuck bolts and awkward access. Later GM manuals say to measure or "matchstick" (or "story stick", i.e. mark the length on something else.) You can also paint the bolt to mark it, but then you won't be able to clean the threads.
Note: Now is a good time to inspect the torsion bar and make sure you have a "right" bar on the right, and a "left" bar on the left. Some coaches have had a problem with this, resulting in an inability to properly set ride height. The bars should be stamped on one end with "L" or "R" and have an arrow indicating direction. It may not matter whether the stamp is at the front or rear, but the bars must be on the correct side.
Hold the new A-arm in the same orientation in which you removed the old one. Place the socket of the new A-arm over the end of the torsion bar and and seat the socket all the way onto the torsion bar. Work the arm back into the frame brackets. A small crow bar is useful for getting the holes aligned. Install the bracket bolts. Install the nuts but do not torque.
Note: If you decide to remove the torsion bar from the pork-chop for any reason, it's probably best NOT to apply any grease between the pork-chop and the torsion bar when you reinstall it. You don't want it to move out of the pork-chop.
Pull up the lower A-arm to about its normal height and put a jack under it. If you don't know what that height should be, hold up one of the shock absorbers to where it will mount as a reference.
Install the sway bar links and torque to 15 ft lbs.
While you have it out, clean and inspect the threads of the torsion adjusting nut and bolt. If you have a thread cutting tool, use it to clean up the threads. Apply a liberal amount of anti-seize or chassis grease to the threads. Use the torsion bar unloader tool to pull the pork-chop back up so you can fit the square nut into its slot. The indentations on the square nut face downward and rest on the crossbar edges. Install the adjusting bolt back to the same measurement it was before. Remove the unloader tool.
Clean any rust or dirt out of the tapered holes (eyes) of the knuckle. Degrease the knuckle eyes and the upper and lower ball joint tapers with brake cleaner.
Do not try to reinstall the old brake hose support bracket on the upper ball joint. There will not be enough room to install the cotter pin if you use the bracket.
Get some help with installing the knuckle if at all possible. It's heavy and hard to do by yourself. Also, when I got the kit the wheel spacer was already bolted to the hub. If yours isn't, I'd wait to install the spacer until after the knuckle is installed. It's heavy enough as is.
Guide the knuckle assembly onto the lower ball joint stud. Attach the new ball joint nut and hand tighten. Lower the knuckle so it's hanging from the ball joint. Tighten the lower ball joint nut, but do not torque.
Note: Do not try to re-use the old nut on the new ball joint; it does not have the correct thread. Use the new nut provided with the kit.
Guide the end of the axle shaft into the back of the hub, being careful not to damage the rubber boots or over-bend the CV joint.
Place the big washer on the axle shaft. Install and securely tighten the new axle nut, but do not torque. It's easier to torque later when the weight of the coach is on the wheels.
If it's not already installed, align the holes in the wheel spacer over the studs on the rotor and guide it into place. Use the 8 nuts provided in the kit to hold it on. Torque the nuts to 120 ft-lbs. If the spacer was installed previously, check the torque of the nuts. Remove the crowbar.
Torque the new upper ball joint nut to 40 ft-lbs. You'll need a really short socket to get between the nut and the CV boot. Do not try to re-use the old nut on the new ball joint.
Note: I couldn't find any way to move the CV joint enough to make this any easier and couldn't fit a 1/2" torque wrench and regular socket. I ended up using a regular 3/8" socket wrench. Since the tie rod end nuts require about the same torque, I used them as a reference to feel the force needed on the 3/8" wrench.
Install the cotter pin in the upper ball joint stud and bend the ends of the pin so that it can't damage the outer CV boot. It may be difficult to insert the pin due to the thickness of the knuckle eye. Try curving the cotter pin to get it through the hole. Do not back off the nut to install the cotter pin.
Torque the lower ball joint nut to 100 ft lbs. Install the new cotter pin and fold back the ends. Do not back off the nut to install pin.
Use a grease gun to lubricate the upper and lower ball joints through their grease fittings.
Note: If you have trouble getting grease into them, remove and inspect the grease fitting. It may be too long and running into the interior joint or just installed too tightly. Back it off and try again.
Put the inner sleeves back in. Apply a little grease to the caliper bolt body (but not the threads) and put the bolts back into the sleeves.
Turn the knuckle so that it's easier to get at the back of the caliper mount.
Note: If you can't turn the knuckle, try jacking the lower A-arm up a little higher.
Flush the front brakes as described in the manual. If you don't have a pressure bleeder, be sure to place a board under the brake pedal to avoid pushing down too far and damaging the master cylinder.
Check all the brake fittings for leaks. Tighten as needed.
Clean the brake rotors with brake cleaner and paper towels.
Once both brakes are installed and bled, pump the brake pedal to seat the pads against the rotors. Do not try to move the vehicle if you have a low pedal problem.
Torque the nuts to 40-50 ft-lbs. Install new cotter pins and fold back the ends. Do not back the nut out to install the pin.
Note: It may be difficult to get the outer tie rod cotter pin inserted due to the thickness of the knuckle eye. Curving the cotter pin may help.
Lubricate the tie rod ends through their grease fittings. If you can't get grease to go in, check the grease fittings.
Work the lower shock absorber eye onto lower control arm shock mount and install the nut. You may need to jack the A-arm up or down to get the shock inserted. Slide the upper end of shock absorber into the frame bracket and install the bolt and nut. Torque the nuts to 90 ft-lbs
Reinstall the wheels. Tighten the lug nuts to the extent possible with the coach off the ground.
Raise the coach and remove the jacks stands. Lower the coach to the ground.
Torque the axle nuts to 170-180 ft lbs. There is no cotter pin on the new axles.
Torque the wheel lug nuts per specs, depending on what wheels you have.
Drive the coach around a little bit to settle the parts. (Go easy on the new brake pads.)
Re-check the axle and lug nut torques.
If you're not comfortable aligning the coach yourself, you should still check and adjust the ride height as described in the manual. Also check that the wheels are approximately parallel as described in the Alignment section of this document. Re-install the dust caps, and take it to an alignment shop. Tell them you want 0 toe, 0 camber, and as much caster as you can get with the caster equal on both sides. For maximum caster, the rear adjustment cams should usually be left as close to the frame as possible.
Note: The alignment and ride height may take substantial driving to settle to their final positions. This may mean miles of driving, not just a few blocks. You should periodically re-check and re-adjust until everything stabilizes. It may be more effective for you to do the alignment yourself than to have to keep taking it to an alignment shop, especially if it's a shop you don't know and trust.
GMC Motorhomes can be aligned using simple tools. Done carefully, many people report getting better results than alignment shops provided. While there are endless variations of tools and techniques, the procedure given below is the simplest, cheapest effective version I could derive. If your coach has a bent frame or suspension issues, it will probably not be sufficient. For a more complete alignment kit and recommendations on good but inexpensive digital levels and gauges, see the article by Jerry Work in the GMC Motorcoach section of his website. Special thanks to all the very helpful, knowledgeable people who contributed to this document.
If you have just installed the new front end, the adjustment cams should initially be set with the rear cams as close to the frame as possible, and the front cams approximately centered in their slot with the cam plates above the bolts. This is just a starting point, but should provide close to maximum caster and 0 camber.
Check that the tire pressure on all six wheels is correct. The water and fuel tanks should be filled to the levels at which you normally travel.Check that the front wheels are roughly parallel by measuring from a good tread at the front and rear of the wheels. Small changes in tie rod length have big consequences at the wheels, so they may be significantly out of alignment. If needed, adjust the tie rods as described below so you can drive the coach safely. You'll be checking and adjusting this more carefully later.
Drive the coach to settle the suspension and then park it on a level paved surface, preferably concrete. The wheels should be pointing straight ahead.
When doing an alignment, always check and adjust in this order: 1) ride height, 2) caster, 3) camber, 4) toe. Re-check all measurements after driving the coach. It can take many miles of driving before everything has settled properly. Since you want maximum caster, you can cheat a little by setting the cam bolts for maximum caster as described above and then worry about the other settings.
Check and adjust the ride height as described in the manual using the unloader tool. This should be done on a level concrete surface because asphalt surfaces are usually not flat enough to get an accurate reading. Block the rear of the coach to the correct height and release the air bag pressure to prevent the rear suspension from compensating for changes to the front suspension. The ride height should be 13 1/8" +/- 1/4" to the top of the slot located behind the front wheels, and 11 11/16" +/- 1/4" to the top of the slot behind the rear wheels. One inch of ride height equates to roughly six turns of the adjustment bolt.
Once you have figured out what change in height is needed, it is very helpful to jack up the front of the coach at the center frame member under the engine to take up most of the front end weight. This saves both you and the tool from having to work so hard against the weight of the coach. For safety, always be sure to put jack stands or blocks in place before getting under the coach. In order to keep the front weight balanced correctly, both adjustment bolts should be kept approximately the same number of turns so that the pork-chops are held at equal heights. If one pork-chop is higher than the other, the weight will shift to one side. This can dangerously overload the tires and cause handling problems even though the ride height may seem correct. Although uneven loading can also be a result of interior weight distribution or, very rarely, a weak torsion bar, one sign of an unbalanced front end is that the rear airbag on the side opposite the overloaded front tire consistently requires more air pressure than the other side. To keep the front weight balanced, whenever you adjust one pork-chop bolt up or down, count the number of turns and make the same adjustment to the other side.
Note: If you have non-stock wheels or tires, you may need to adjust the ride height to compensate for the difference in the radius of the wheels. Stock sizes are OEM wheels with 8.75/16.5 tires, or 16" wheels with LT225/75R16 tires. These are usually about 29.5 inches in diameter though there is variation between brands.
Alignment work is best done with the wheels resting on turn plates, but anything that allows the wheels to slide more easily will work. Some examples are metal or plastic plates with grease in between, sheet metal, floor tiles, several layers of plastic sheeting, or garbage bags with a little oil or water inside.
Center the steering by turning the steering wheel all the way to the left, then all the way to the right while counting turns. Divide by two and move the wheel back this number of turns.
Caster is defined by the relationship between the upper and lower ball joints. The lower ball joint is in a fixed position, so the only adjustment we have is to move the upper ball joint. The further to the rear the upper ball joint is set, the greater the caster. Camber is the amount the wheels tilt in or out at the top. We measure caster indirectly by measuring the change in camber when the wheels are turned to specific angles. For our coaches, we want as much caster as possible and it should ideally be the same on both sides, but the actual numbers are not very important.
Check the accuracy of a digital level by turning it around end for end on a level surface and re-checking the reading. It should produce consistent results. Some levels can be recalibrated.
To compare caster on the right and left sides, center the steering wheel and then turn it one complete turn to the left. This will turn the wheels approximately 20 degrees. Using a digital level or gauge, measure the camber of one wheel. You can calculate the angle changes, but it's much easier and less confusing to let the gauge do the work. Hold the gauge to the flat face of the wheel and push the zero button on the gauge. Keep track of exactly where you placed the gauge on the wheel so you can do it again. Now turn the steering wheel back to center and then one complete turn to the right. Measure the same wheel in the same place to get the change in camber. Repeat the procedure for the other wheel.
The measured change in camber is a fraction of caster and should be close to equal on both sides. On most coaches, the passenger (right) side has less maximum caster than the driver (left) side. You will need to reduce the side that has more caster to match the other side. How close they need to be is debated. Caster and camber will cause a pull toward the more negative set side of the vehicle, so you can use these settings to compensate for road crown or other conditions.
If you want to measure the actual caster instead of just the relative caster side to side, you'll need to be more exact in the angles you turned the wheels. Multiply the change in camber by a fixed amount according to the angle you used. For example, if you turned the wheels 20 degrees left and then 20 degrees past center to the right (40 degrees total), multiply the change in camber by 1.43. If you used 15 degrees, multiply by 1.91.
Camber and caster are both adjusted by moving the upper A-arm cam bolts in their slots. To maintain maximum caster, all camber adjustments should be made with the front cams only. To maintain a set caster however while adjusting camber, move both the front and rear cams an equal distance in the same direction. For example, to make the camber more positive while maintaining the same caster, move both the front and rear cam bolts outward from the frame by the same amount.
Adjust the wheels as close to plumb (0 camber) as possible, or very slightly negative (tilted in toward the coach at the top). If negative camber is used, the right side should be slightly more negative than the left. For example, left = 0, right = -1/4 to -1/2 degree, or left = -1/2, right = -1 degree. Once you've got the right settings, torque the cam nuts to 80 ft-lbs while holding the bolt head to keep the cams from moving.
Toe is determined by measuring how parallel the right and left wheels are to each other. Put a mark on the rear of each tire as high up as allows a tape measure to run under the coach without touching anything but the tires. You want as precise a mark as possible, so use a thin line on a piece of masking tape or the edge of a sharp tread and mark it clearly on both tires so you can easily find it again. It helps to measure starting at the 1-inch mark on a tape measure rather than the end since it's easier to see and usually more accurate. Measure the distance between the marks on the right and left tires. Also measure the distance from the mark to the ground. Roll the coach straight forward until the marks on the rear of the tires come to the front at the same height as they were in back. Measure the distance between the marks on the front of the tires. If the measurement is the same plus or minus 1/16th inch, the toe is correct.
If needed, adjust toe by loosening the clamps on both tie rods and turning the center sleeves. It doesn't take much to make big changes at the wheels. The right and left tie rod assemblies should both be adjusted so they are kept as close to the same length as is possible. Before you re-tighten the clamps, move the tie-rod end ball joints all the way in the same direction. This is to keep them from binding when in normal steering range. When adjusting the tie rod lengths, the gap in the clamps should NOT line up with the slot in the center tube. Torque the tie rod clamp nuts to 20 ft lbs.
Drive the coach and re-check and re-adjust as needed. This may take several miles and repetitions before everything settles into a stable configuration.
If after driving the coach you find your steering wheel is not centered, you can fix it easily if you have an adjustable drag link. If not, the tie rods can also be used to center the steering wheel. For details see http://www.bdub.net/center_steering_wheel.html .
Though not required, you can weld on extra reinforcement to the A-Arms. Here are some pictures and ideas courtesy of Gary Worobec. Again, not required. I didn't do any of these changes and have had no problem.
You'll need to use the tension between upper and lower A-arms to help pull apart the lower ball joint, so must do this earlier in the process while they're still connected. Remove the cotter pin on the lower ball joint and back off the nut until it's flush with the end of the threaded stud. Place a jack or block under the A-arm for safety in case the threads strip, but don't apply pressure to the A-arm. Hold a big heavy weight (like an 8 or 10 pound sledge hammer) against once side of the lower knuckle eye. Use a smaller (4 or 5 pound) hammer to hit the other side of the eye. This should pop the joint loose. I had no success beating the joint apart, but include it here for completeness since more than one person mentioned it.
Note: Energy Suspension Kit 3.3181 includes 4 each upper and lower urethane bushings.
Replacement outer CV joint boots are part number BT-257