Classic GMC Motorhomes had very advanced brakes... for the 1970's. Brake systems have come a long way in the last 40 years and most modern vehicles simply stop faster. Most coaches have also suffered corrosion and wear that has gradually reduced the brake function even further. Add that to a 12000 pound vehicle, and you end up with a dangerous situation.
One way to improve the old system is by installing disc brakes in place of the
original drums. Disc brakes are much less susceptible to brake fade than drum brakes
and perform far better in prolonged or repeated braking or wet conditions. They are simpler to install and maintain,
inexpensive, and generally require no adjustment after they're installed. For service
braking, disc brakes are a superior solution.
To see more about disc vs drum brakes, brake fade, and stopping distances, see this US Department of Transportation article:
http://www.fmcsa.dot.gov/about/outreach/bus/safety-technologies.htm#5
For an excellent article on the topic by fellow GMCer Frank Condos, see:
http://www.gmcws.org/techcenter/00-08tc30.html
Whether you have discs or drums, a serious shortcoming of our classic coaches is that when braking hard as in a typical panic stop, the weight of the coach is shifted forward, causing the rear set of wheels to lift upward and skid. The usual result is flat spots on the tires and substantially reduced braking. The reaction arm system is designed to regain control of the back of the coach by counteracting the upward lift during hard braking.
The reaction arm concept has been around for decades and used extensively, especially for racing applications. In early 2007, Norm Jestico and Chuck Aulgur independently developed prototypes for a reaction arm brake system for GMC motorhomes. Based on Chuck's work, Rick Flanagan, working with Jim Kanamota, later developed kits for production.
The Manny Brake Kit is also based upon Chuck Aulgur's original designs, but is Manny Trovao's own version. The kit is meant to be an effective, quality upgrade that is cheaper and easier to manufacture and install. It includes all the parts needed to add disc brakes to all four rear wheels PLUS a reaction arm system to improve brake function. The kit includes two standard GM calipers for the middle wheels, and two GM parking calipers for the rear wheels. These calipers are the same sizes used in the popular TSM kit (tsmmfg.com), which have been installed on GMCs since at least the 1990's. When combined with 80mm front calipers, these calipers provide about the same balance of front-to-rear braking as the OEM system, which should help maintain stability in wet or icy conditions. The two dual-action parking calipers provide both hydraulic and mechanical activation for use as a parking brake on the rear wheels, and are attached to the OEM brake cable system.
NOTE: Mechanical parking brakes are required in most jurisdictions. The hydraulic line locks sometimes provided with
other kits are not street legal by themselves.
HOWEVER: the parking brake calipers are unlikely to hold a 12000 lb vehicle on any significant grade.
A line lock can be added, but is not part of the kit.
The standard brake hoses included with the kit are reinforced rubber, but stainless-reinforced/teflon hoses are available as an option. Additional parts to add a stabilizing track for the front bogie arms are also availble. See B-Track kit.
These instructions describe how I installed Manny's combined rear-disc/reaction-arm kit, affectionately known as "Manny Brakes". Special thanks to Kerry Pinkerton and Kelvin Dietz for testing, proofreading, and extra pictures, to Ken Henderson for patient technical advice, and to Albert Branscombe for help understanding master cylinders and parking calipers.
THANK YOU Manny Trovao for another great and very cost-effective upgrade!
These instructions are available on the web at http://www.machinesoflovinggrace.net/gmc/brakes. Email suggestions and comments to molggmc at sonic.net.
DISCLAIMER: THIS IS A WORK IN PROGRESS. 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.
Working around and under a 6-ton vehicle or modifying brake systems can be hazardous.
BAD BRAKES CAN KILL YOU!
The instructions are as correct as I can make them, but I OFFER NO GUARANTEES ABOUT ANYTHING!
What you do to your coach is your business. I have no monetary interest in the sale of any products mentioned in this document.
Before you change the rear brakes, take a look at your master cylinder. The master cylinder provides the hydraulic pressure needed to activate the brakes. It must be properly sized to the rest of the system and in good working order. Old master cylinders are likely to have corrosion and worn rubber parts. Disc calipers require more fluid than wheel cylinders, so the master cylinder piston will move beyond the range of its prior travel. If there is corrosion in the bores where the piston hasn't been before, that rough surface will damage the old seals. The result is that shortly after installing new brakes, your master cylinder will start leaking and stop working. If you don't know the age, size, or condition of your master cylinder, it is best to replace it. Master Cylinders are inexpensive, readily available, and critical to the function of the brake system.
For more information, please see Master Cylinders
The Combination Valve on our coaches was designed for a mixed disc and drum brake system. Please read the section about Combination Valves.
© Copyright 2013, 2014, 2015, 2016 K. Bradley
Before beginning work, please read and understand the instructions and verify you have all the parts. The list of parts included in the kit can be found here.
In addition to the kit, you will need the following parts:
Begin by parking the coach on a flat spot with adequate room to work. Securely block the front wheels so the coach can not roll!
Inside the coach, release the parking brake.
Place a thin piece of bar stock between the bogie arms and the bogie housing to keep the arms from dropping as you jack up the coach.
Place a jack under the bottom of the bogie housing, or use a jack hook, and raise
the coach just enough to take most of the load off the air bags. Break the lug nuts free
at each wheel, but don't remove them yet. Let the air out of the air bags
to avoid stressing the shock absorbers as you raise the coach. Keep raising
the coach until the tires are free enough from the ground so they can be removed.
Securely support the coach by placing stands or blocks under the frame
just in front of and behind the bogies, at the part of the frame where the cross
members bolt to the side members. This will leave the bogies free
of obstructions so you can work.
Make sure all jack stands and blocking are extremely stable. Your life can depend on it.
Remove the rear wheels. Put one wheel on the ground under the coach frame in back to act as a safety in case the jack stands fail. If you are replacing your brake lines at this time, you'll need to get the coach high enough to work underneath. If not, it only has to be up enough to remove the rear wheels.
Wire brush and apply penetrating oil such as atf/acetone to the parts you'll be removing:
Pry off the dust cap at the center of each wheel. Remove the cotter pins and castle nuts from the spindles. Put the dust cap back on to protect the outer bearing and keep it from falling out as you remove the drum. This will also keep the correct bearing with each hub and prevent them from getting mixed up.
Pull the drum/hub assembly off of the spindle. If it's stuck on the brake shoes, go into the coach and try setting and the re-releasing the parking brake to work it free. If it's still stuck, try twisting the drum as you pull it off, as though you were unscrewing it. If all else fails, adjust the brake ratchet mechanism to pull the brake shoes inward (see manual).
Set the drum/hub assemblies aside, but protect the bearings from dirt and water.
Underneath the coach, just behind the front wheel on the driver's (left) side inside the frame rail, is the main parking cable adjustment. Back the nuts off to the end of the threaded adjustment rod, but leave the cable attached. This will provide additional slack in the cables and help with adjustment later.
Locate the brake cable yokes on either side of the coach outside the frame rails in front of the back wheels. Free the cable from the yokes by removing the nuts from the threaded rods, sliding the yokes off, and pulling out the cable. Put the nuts and yokes back on the threaded rods so they do not get lost. Detach the two cable ends from the metal clip that holds them together.
Remove the clips holding the cable sheathes to the supports on the frame rail at each rear wheel. This will allow you to pull the sheaths out of the support brackets when you remove the drum plates.
Remove the bolts that hold the small clips supporting the hydraulic brake lines at the middle of each bogie arm. If the clips are big enough, you may be able to reuse them for the new rubber brake hoses.
Wipe the old grease off of the spindles. Remove the 4 bolts and nuts holding the drum backing plate to the bogie arm.
Gently pull the drum backing plate off the spindle while guiding the hydraulic lines and cables out of the way and free of their supports. Guide the attached hydraulic line around behind the bogie arm and set the whole backing plate assembly out of the way under the coach. By leaving the hydraulic lines attached, you'll avoid dripping or contaminated brake fluid. The lines can stay attached to the drums until you're ready to install the new rubber hoses in their place.
Wire brush the back of the spindle housing at the bolt holes. Scrape off any rust that may be stuck to the base or back of the spindle to make sure nothing will prevent the new parts from seating properly. Thoroughly clean the spindle bearing surfaces and the flat base of the spindle.
The caliper plates are all identical and mount with the cutout facing AWAY from the center bogie housing. There are two different torque boxes that are a mirror image of each other, one for the mid wheels, and one for the rear wheels. The boxes mount with the curved cutout at the bottom, facing TOWARD the center bogie housing. Select the correct box for the spindle you're working on. Powder coating has reduced the size of the un-threaded holes in the torque box and caliper plates, so assembly will be easier if you remove the coating from the interior of the holes. Do not remove metal.
Thread the four long 3/8" bolts into the block to clean up the threads. Remove the bolts.
NOTE: If you are installing a B-Track kit, the blocks for the front bogie arms are replaced with the B-track angle block. See B-track Installation
Thoroughly grease the torque box washer, stud, the hole in the block, and all sides of the bearing. Place the washer on the stud. (Early kits had small legs on the washer. These are omitted in later kits.) Place the bearing over the stud on top of the washer.
NOTE: The bushings supplied with later kits are longer than the ones shown here and may extend past the end of the stud. This is a design improvement to keep the bushings in place better. There may not be hash marks on the blocks since those were to retain the shorter bushings.
Orient the steel block so that the 4 hash marks around the hole are facing up. These help retain the bearing. Slide the block down over the bearing on the stud.
Mount the assembled box to the back of the bogie arm by bolting through the holes in the spindle base with the four long 3/8" bolts. Apply loctite to the bolt threads. Torque the bolts to 40 to 44 ft-lbs.
Remove the bronze bushing from the back of a caliper plate. Thread the 4 short 3/8" bolts into the holes in the plate to clean up the threads, then remove the bolts. Test fit the caliper plate on the spindle. The center hole in the plate should be just big enough so you can slide the plate all the way back to the base of the spindle. If needed, lightly sand or file the hole until it just clears the spindle.
The front caliper cutout should face toward the front of the coach. The rear caliper cutout faces the rear of the coach. While holding the plate oriented correctly on the spindle, test fit the four short bolts through the torque box into the caliper plate. If you have trouble getting the holes in the torque box to line up with the ones in the plate, try inserting a long metal bar into the large hole at the bottom of the torque box and applying leverage to get the holes aligned. If needed, the bolts holes in the torque box may be enlarged slightly, but keep them as small as possible. You may also be able to clamp the torque box slightly to improve the alignment, but usually a lever is sufficient. Once the fit of everything is tested, remove the caliper and plate.
Clean the spindle and apply grease to the bearing surfaces at the base.
Thoroughly grease the caliper plate bushing and place it into the caliper plate with the beveled edge facing up.
Install the caliper plate on the spindle with the caliper cutout facing forward on the middle wheels, and backward on the rear wheels. The recesses on the back of the plates fit over the spindle bolt heads. Insert the four short 3/8" bolts with lock washers through the holes in the torque box and into the threaded caliper plate holes.
Tighten the bolts uniformly about half way so there is an even gap between the caliper plate and the torque box. Be careful to tighten these evenly, but don't tighten them down all the way yet. You need to be able to move the torque boxes by hand while you install the reaction arms.
Install the remaining torque boxes on the other spindles the same way.
Select the correct caliper for the spindle you're working on. The parking brake calipers go on the rear wheels, the regular calipers go on the middle wheels. Each caliper type also has a right and left version, so there are four different calipers. When installed correctly, the bleeder fittings will face upward, and the brake line fittings (Banjo Bolt) will face downward. Ignore any markings on the caliper body.
Use the caliper pins to temporarily bolt the calipers to the plate.
Test the fit the caliper against the support arms of the caliper plate. When bolted in place, there should be 0.13 to 0.30 mm clearance to the caliper body.
Note: A piece of copier paper is about 0.1mm thick and can be used to test clearance, as shown in the picture.
File or sand the inside tips of the plate cutouts slightly if needed for clearance. Remove the calipers and set them aside.
Clean the inside of the center bogie housing around the slot at the bottom. Wire brush the outside bottom of the bogie housing to remove dirt or rust.
Thread the short 3/4" bolt partially into the T-nut to clean up the threads. Don't try to thread it all the way through the nut. The back of the nut is deformed slightly so it can act as a lock nut. Remove the bolt.
The curved shoulders of the T-nut face the back of the bogie slot to match the curve in the slot cutout.
Position the T-nut inside the bottom of the center bogie housing, all the way at the back of the slot. Place the lock washer on the bolt and apply loctite to the threads. Hold the center anchor block under the bogie, parallel to the frame rail, with the notch in the block facing upward. Bolt the anchor up through the slot into the T-nut, but don't tighten it all the way yet.
Insert a long 3/4" bolt into the hole in the back of the torque box, and push it about halfway through. Position a reaction arm so it aligns with the curve of the bogie arm, with the large hole toward the torque box. Slide the hole in the arm over the bolt in the torque box, and finish pushing the bolt through to the front of the box. Install the lock nut on the front of the box, but do not torque. The long bolt in the open space inside the torque box provides clearance for the reaction arm to follow the movement of the bogie arms, which can move in and out from the coach a surprising amount when the coach is turning.
NOTE: Variation in the alignment of the flats on on the ends of the reaction arms will not affect operation. All it has to do is ride on the long bolt and there is plenty of room in the torque box for this.
On some coaches, the bracket that supports the parking brake cable may interfere with the reaction arm when it lifts during braking. If necessary, trim the bracket back so the arm clears. As you can see in the picture above, the bracket left a scar on the reaction arm. The picture was taken from underneath the coach, looking outward.
Grease the bushing that's pressed into the other end of the arm (do not remove the bushing from the arm). Push the end of the arm up into the slot in the center anchor block. Align the bushing with the hole in the anchor block, and insert the bolt through the front. Wipe the grease off the threads and put the lock nut onto the bolt in back, but do not torque yet.
Attach the remaining reaction arms to the other torque boxes the same way.
At each spindle, tighten the 4 caliper plate bolts to pull the plate down uniformly against the torque box. Be careful to tighten the bolts evenly. Torque to 40 ft-lbs. It's hard to get a wrench on the upper bolts, so you'll need to use a box wrench on these. A socket swivel adapter may also be helpful.
Make sure the T-nuts are still positioned at the back of the bogie slot. Torque the 3/4" center bolts into the T-nuts to 150 ft-lbs.
NOTE: Once the T-nut bolt is tightened, there should be a small gap between the bottom of the T-nut and the top of the anchor block. If there is no gap, remove the T-nut and grind or file a little off the bottom. There are minor variations in the thickness of the bogie castings. The T-nut needs to be firmly bolted so it can not move.
Torque the 1/2" pivot bolts on the ends of each center anchor block to 70 ft-lbs.
Torque the long 3/4" bolts at the torque boxes to 70 ft-lbs. Avoid over tightening these bolts since they can deform the torque boxes.
Place the drum/hub assembly upside down on one of your removed wheels with the wheel studs through the holes in the wheel. This will hold the drum still while you work. Remove the eight bolts holding the hub to the drum. If there are washers under the bolts, set them aside for reuse. The bolts will not be reused.
Lift the drum up off the hub. Clean the rust and dirt off the hubs, especially at the base around the bolt holes where the drum was bolted.
Place the hub so the inner bearing end is facing up. Slide a spacer ring over the hub and align the holes.
Make sure the spacer seats all the way onto the hub. Early coaches may have a radius/shoulder at the center that prevents the spacer from seating properly. For these coaches, you will need to file or grind the inner edge of the spacer to clear the obstruction.
Place the disc on top of the spacer and align the holes. If there were washers, reuse these with the new grade 8 bolts. Install 4 new bolts per wheel.(Early kits had 8 bolts per wheel. Only 4 are needed.) Use loctite on the bolt threads. Torque to 65 to 75 ft-lbs. Be careful to tightend the bolts evenly.
Clean both sides of the disc thoroughly with brake cleaner and wipe dry with clean paper towels. Some people recommend using sandpaper on the disc surface. The problem with this is you risk contaminating the surface with aluminum oxide from the sandpaper. A scotch-brite or scrubby pad is sufficient if the surface is very dirty. Always use brake cleaner as the solvent.
Thoroughly grease the bearing. It must be completely filled with grease. An inexpensive plastic cone for packing bearings makes it much easier to really fill the bearing.
Put the clean, greased outer bearing, washer, and castle nut where you can reach them by the spindle. Apply grease to the spindle bearing surfaces. Disposable gloves are helpful.
Carefully guide the hub over the spindle and push it all the way back onto the base of the spindle. Push the greased outer bearing onto the spindle, lifting up on the hub as needed.
Place the washer over the bearing with its tab aligned with the slot in the end of the spindle.
Thread the castle nut onto the spindle and tighten by hand while turning the hub. Keep turning while you torque the nut to 25-30 ft-lbs to seat the bearing onto the spindle.
Check that there is still clearance between the back of the hub and caliper plate. If the hub is hitting the plate, the bearing will not be able to seat properly onto the spindle. Early coaches seem to have more issues with clearance at the back of the hub than later coaches. Removing one or more of the shims between the backer plate and bogie box may help improve clearance.
After the nut is torqued, back the nut off one-half turn and finger tighten the nut to align the hole for the cotter pin. Do not over tighten! Turn the disc/hub to check for any excess tightness, looseness, or grinding, and adjust as needed.
Install the cotter pin and bend the end over to secure the castle nut. Install the dust cap.
Clean the disc again with brake cleaner and clean paper towels to remove any grease.
Once again, select the correct caliper for the spindle you're working on, with the parking brake calipers on the rear wheels and the regular calipers on the middle wheels.
Make sure bleeder fitting will be at the top of the caliper and the hydraulic brake line connection at the bottom when the caliper is installed.
Remove the caliper from the plate to apply caliper lube. Push the caliper sleeves out of the caliper body and grease the outside of the sleeves and the inside of the o-rings. Also grease the outer o-rings and the smooth part of the caliper slide pins, but keep the grease off the threads. Reinstall the sleeves in the caliper body.
If the pads you got for the rear wheel parking calipers have a clip riveted to the back of the inner pad, break the clip off as close to the rivet as possible. The pad needs to be able to sit flat against the piston face so the small pin can engage the indentation and allow the piston to adjust when the parking brake is operated.
The parking brake calipers are provided with a circular clip that holds the inner pad in place. This clip fits around the edge of the piston.
Install the inner parking caliper pad by tucking the edge of the pad under the clip fingers. The clip and the caliper slide pins hold the inner pad in place. The outer pads are all held in by the slide pins when installed.
The mid-wheel calipers have a clip that holds them to the hollow piston cup when pressed into position. If your pads don't have this clip, use the one provided with the mid-wheel caliper.
Hold the caliper oriented correctly at the slot in the caliper plate, with the installed pads on either side of the disc. Push the guide pins through the threaded holes in the plate and into the holes in the ears of the calipers and pads. Make sure the pin doesn't push the outer o-ring out of place. Tighten the caliper bolts and torque to 28 ft-lbs with a 3/8" hex wrench. Check that the gaps to the caliper plate are still correct.
Select the correct rubber brake hose for the wheel you're working on. The middle wheel hoses have more bend at the caliper attachment, and each has a right and left version. This means that all four hoses are unique.
With the hose held horizontally, the loop that attaches to the caliper should angle downward. The end with 90 degree bend and threaded fitting should face outward, toward you.
Position the hose along the back of the bogie arm and through the center of the torque box to the bottom of the caliper. Remove the plastic protector from the caliper brake connection hole.
With the banjo bolt facing upward, place a copper washer on the bolt, then the loop fitting on the end of the correct hose, then another washer.
Thread the bolt up into the bottom of the caliper. Make sure the brake line doesn't run where it can get pinched or damaged. Tighten the banjo bolt until snug.
Remove the old hydraulic brake line from the center support by using a 3/8" flare nut wrench to loosen the fitting, then push the line out of the way. If you can't get the nut loose, remove the two bolts anchoring the fittings to the bogie so you can pull it out to where it's easier to work. Install the end of the new brake line where the old one was, and angle the hose down gently toward the arm. Anchor the hose to the arm in the same place the old line was supported. Cable ties can be used to secure the cable if desired.
Repeat the disc and caliper installation at the other wheels.
Partially disassemble the drum shoes and arms from the REAR wheel drum plate assembly enough so you can get to the end of the long brake cable. Detach the end of the cable from the drum brake arm. Remove the cable sheath from the plate by squeezing the four tabs and pushing it through the hole. Pull the whole cable and sheath assembly off of the plate.
Cut the forward stop end off the cable as close to the end as possible. Use a hacksaw to make a clean cut. (An angle grinder with a cutoff blade just frayed the cable and ruined it.) Keep the conical rubber tip from the end of the sheath to reuse.
Pull the cable out of the sheath, and slide the spring off the cable.
Discard the spring.
Thread the cable back through the sheath from the side that was attached to the drum brake where the spring was.
The cable sheath is not long enough to reach the new parking brake location, so threaded tubes are provided as extensions. There are variations in the ends of the cable sheaths where the clips to the frame supports were attached. On early coaches, all the sheath ends have a flat tip. On later coaches, the sheaths from the middle wheels have a rounded tip. The rounded tips fit better against the end of the tube, but either will work. The sheaths on the middle wheels are the same length as the rear ones, so can be interchanged. You can also grind or file the metal tip of the sheath so it fits into the tube better. You can also fit a short length of hose with a ½-inch internal diameter over the tube and the end of the sheath to keep out dirt and help provide alignment. Since the tube and sheath are fairly well constrained by the supports, any of the sheaths will work and it's mostly a matter of preference.
Slide the (optional) short length of rubber hose over the end of the supplied threaded tube. Thread one nut onto the rod about a third to a quarter of the way from the other end. Slide the rod and hose over the cable and butt them up against the end of the sheath. If you're using rubber hose, work it over the fitting at the end of the sheath.
Thread the loose end of the cable through the hole in the bogie from the rear side, and through the support tab on the frame near the bogie. Keep going until the threaded rod fits through the hole in the tab. Slide the other nut over the cable and thread it onto the rod loosely to secure it to the tab. Slide the old rubber conical tip you pulled off the sheath over the cable, and work it down over the end of the threaded rod.
On the caliper end of the sheath, pull about 6 inches of cable out from the sheath. Run the sheath and cable up behind the bogie arm and through the top of the torque box to the caliper. Guide the cable through the hole and spring at the caliper lever arm. Work the end of the cable into the recess at the end of the lever arm. Pull the cable back until the stop is butted up against the end of the arm. Push the fitting on the end of the sheath into the hole until it locks in place. Adjust the nuts on the threaded extension at the bogie so the sheath has a little slack. Tighten the nuts against the bracket in the frame to secure the sheath in place.
Route the other end of the cable forward through the supports along the frame as far as possible. Slide a 1/8" ferrule/crimp connector over the cable to about 12 inches from the end. Run the cable through the yoke at the end of the side cable rod. Loop the cable back through the cable ferrule. (You can use a pair of wire rope clips instead of the crimp ferrules if you prefer.)
Do not crimp the ferrule until you've got both sides prepared. You need to be able to adjust the cable loops and make sure there's enough cable available. The cables should be installed as tightly as possible without pulling on the parking caliper lever arms.
Repeat with the cable on the other side, then crimp the ferrules to secue the cable loops. Tighten the adjustment nuts at each cable adjustment yoke until the cables are snug and evenly distributed, but not pulling on the parking calipers.
The parking calipers on the rear wheels are adjusted automatically every time the parking brake is set. To adjust them initially, use a wrench to grasp the bottom end of the caliper lever and work it back against the spring a few times. Be careful not to bend the small tab at the top of the lever arm that secures the cable end.
To keep the parking calipers properly adjusted, you MUST use the parking brake regularly.
Bleed the brake system thoroughly to remove all trapped air. There is no need to remove the calipers since the bleeder screws are already located at the top of each caliper. Check all connections to make sure there are no leaks.
Seat the middle wheel caliper pads against discs by pushing the brake pedal after the system has been bled.
DO NOT ATTEMPT TO MOVE THE VEHICLE UNTIL THE PEDAL IS FIRM!
When you first move the vehicle, verify that nothing is dragging or hanging up. An infrared temperature tool is helpful for checking the temperature of each disc.
When first driving the vehicle, the pads will not yet be broken in and the stopping distance will be much greater than normal. BE VERY CAREFUL WHEN FIRST DRIVING THE VEHICLE!! The pads should be broken in by gradually increasing the speed and braking aggressiveness with each stop.
Time to go camping! :-)
Copyright © 2013, 2014, 2015 by K. Bradley
For more information, please see B-track Installation
