Backyard Bus Braking Repair
by Crash the Busdriver
Brakes are an integral part of bus operation. Without them you might
not be able to stop. This page is for people who want to stop. But if
you can't stop, go faster.
SAFETY WARNING: Servicing large equiment can be extremely dangerous if proper safety procedures are not observed. Never perform any service procedure without the appropriate safeguards in place. Think carefully about possible consequences before you try to do something clever. Be advised that any information on this page may be erroneous or incomplete. I cannot be held responsible for your safety should you choose to attempt any of these procedures, though I will have a good chuckle if your mangled corpse ends up on rotten.com. You have been warned.
Brake Systems
There's a couple types of brake systems that you might commonly find on a bus. Some newer buses have disc brakes, but almost all have drum brakes. Drum brakes use a set of pads or shoes that create friction against the inside of a rotating drum attatched to the wheel. They are a very well-proven technology, but have a few general faults. They often require frequent adjustment and the driver must be careful not to cause them to lock up or fade. Otherwise they are often very reliable.
Hydraulic Brakes
Some smaller buses, rvs, and delivery trucks use hydraulic brakes similar to those on most four-wheeled autos. These have a hydraulic fluid reservoir, a master cylinder, steel brake lines, and use one or two cylinders to push the shoes. Some have a wratching self adjustment and some don't.
Hydarulic brakes are a big pain in the ass on a bus. They don't typically require alot of real maintainence, but HYDRAULIC BRAKES DO NOT HAVE ANY SORT OF BUILT-IN FAILSAFE. This means means that if you're going down the side of a mountain and one of your rusty brake lines bursts because you never bothered to replace it, much less look at it in the first place, you will be totally fucked. Yes. Totally fucked.
Servicing hydraulic brakes is a messy and time consuming job. They should be bled and adjusted any time the lines are opened. Speed Bleeders help with this, though you may not be able to find sizes that fit both front and back cylinders. Brake fluid should be flushed through with clean fluid yearly. Be sure to keep plenty (like a half gallon) of fluid handy. Check your brake lines and cylinders for rust and leaks every time you change your oil. Check your shoes for wear at this time, too.
Air Brakes
Air brakes are often designed for heavier duty than hydraulics. As far as I know, all air brake systems use drums. Air brakes are powered by compressed air which is generated by a compressor attached to the engine and stored in a tank. Depressing the brake pedal opens a valve that lets the air press against a diaphram, which pushes a lever, which turns a cam, which presses the brake shoes against the drum.
Most air brake systems on buses have a failsafe. This means that when air pressure is lost the rear brakes engage. This can cause some confusion to the inexperienced operator trying to move the bus immediately after a cold start. Until the air pressure reaches about 90 psi, the bus will not move and attempting to move it will stall the engine. Usually there's a big red warning sign or light and an annoying buzzer that come on when the pressure is too low.
Air brakes require frequent, but simple maintainence. Brakes must be bled every day after operation. All this means is that you have to open the drain cock (valve) for each tank. If you're unlucky you might have to crawl under the front and rear of the bus to reach a valve on the underside of the tank, but most buses have the drain routed to a valve under the skirt. Tanks are usually located at both ends of the bus, for front brakes, rear brakes, and air accessories, like powered doors or windshield wipers. Some air systems have automatic drying or bleeding systems.
Adjusting air brakes is a fairly simple and straightforward procedure. On the actuating lever is a 9/16" bolt head with a collar. The collar holds the bolt in place until it is depressed (usually by your wrench). Clockwise rotation of the bolt head should tighten shoe to drum clearance. About every 30 degress of rotation, the collar should pop back out, locking the bolt again. This is one notch. The correct way to adjust the clearance is to jack up the wheel and spin it, adjusting the shoes outwards until some drag is felt. The shoes are then adjusted back one notch. Old truckers will tell you that, in a pinch, you can adjust shoe-to-drum clearance with a matchbook cover. Some buses have self-adjusting rear brakes and don't require any manual adjustment. Please note that in order to adjust the clearance on your rear brakes you have to turn off the emergency/parking brake. PLEASE BE SURE TO CHOCK THE WHEELS BEFORE DISENGAGING THE PARKING BRAKE AND GETTING UNDER THE BUS. We lose more bus drivers that way...
Air compressors have filters that should be changed once a year, or even more often if you drive in really dusty conditions. Changing them at the same time as the engine air filter is probly not a bad idea. If you don't change them, then your compressor wears out and leaks alot of oil into your air tanks. This is something to look for when you bleed the tanks. Also note that there's usually a regulator on the back of the compressor that fails sometimes.
Servicing air brakes is alot less messy than servicing hydraulic brakes, unless your tanks are full of compressor oil (doh!). Large leaks can be easily heard. Small leaks can be found with a spray bottle of soapy water (but you didn't even notice you had a leak because the brakes still work anyways). Be sure to let the air out of the tanks before disconnecting any air lines. Air hose is pretty cheap and can be purchased by the foot at truck parts stores, or at NAPA. All plastic air hose fittings are compression type. For best results, use a new brass collar and insert after you disconnect a line.
Common Service Procedures
These procedures only cover older and more common buses with all-wheel drum brakes. If your bus is different, you are advised to review these instructions anyways, as some procedures are still similar. When in doubt, ask for advice from somebody who has serviced this type of equipment before proceding.
Hydraulic Brake Bleeding
Front Wheel Disassembly
Park the bus on a flat surface. Chock the rear wheels with chock blocks or any
object that can keep the bus from rolling forwards or backwards.
Jack the wheel up with an appropriately sized jack under a solid part of the axle,
and secure the axle on blocks or jack stands. If using blocks, railroad ties or other
very large pieces of lumber are good blocks. Using cinder blocks may not be advisable.
Never work under a bus supported only by a hydraulic jack (especially the cheap kind we
use). Hydraulic jacks can fail. There are many horror stories about this on the internet.
Once the wheel is lifted and secured, get somebody to apply the brakes (if they still work) so
you can remove the lug nuts. If the brakes don't work, you may have to jack the wheel down
a little so that some of the weight of the bus is resting on the tire. Break the torque on the lug
nuts then jack the wheel up and secure the axle. It takes a big bar and a lot of torque to turn
the nuts, or a 1" air impact driver. Cheap tools will bend easily when applied to this purpose.
Break the torque on the nuts by turning them 1/4 rotation. Loosen all the nuts in a criss-cross
pattern around the wheel. When all nuts are loosened, then they can be removed. Please note that
lug nuts on the drivers side of the bus (left side) are left-hand threaded and loosen by turning
counter-clockwise. These lugs usually have an "L" stamped into the end for easy identification.
The wheel is very heavy and can fall off the drum with nothing to secure it, so watch out!
With the tire and rim off we must now prepare the drum for removal. The first step is to loosen
the break shoe clearance as much as possible so that when we try to pull the drum off later we
don't snag a ridge in the drum. Hydraulic brake shoes are adjusted with a toothed wheel, accessable
through a slot in the inside cover plate. Use a scredriver to turn the wheel until the shoes are adjusted
well inward of the drum. For air brakes, adjust the shoes in with the adjustment bolt located on the
actuating lever (sorry. no pictures).
The next step in removing the drum is removing the outer wheel bearing. Remove the wheel
bearing cover plate in the the center of the hub (this may be filled with oil). This allows you
access to the nut securing the outer bearing. The nut shown below is of the castle type,
secured with a cotter pin. Yours may be secured differently. After the nut and any other
components securing the bearing are removed you are now ready to remove the drum. You
may need a partner to help with this, as the drum is pretty heavy. You will probly have to
work the drum back and forth to get it off. This is because the inner wheel bearing and
seal fit very tightly onto the spindle.
Drum and Bearing Inspection
Check the inside of the drum for any large cracks or grooves. The braking surface should be very smooth
Rules to Live By
- Always check your brakes before going down a mountain. There's usually a brake check area near the top for doing this. Be sure to smile and wave at the truckers.
- Never ride the brakes down a long grade. This will severly reduce braking power as the drum heats up and expands away from the shoes. This is known as "brake fade". Apply the brakes firmly, slowing by about 5 mph, then let off for a couple seconds and do it again.
- Never take the bus out of gear when going down a grade. You probly won't be able to get the gears to engage again until you slow way down, which is alot harder to do without using the natural braking power of the engine. Even though your bus only goes 65 mph on a flat, getting it up to 88 mph on a grade will not send you far enough back in time to avoid the nauseating carnage that may exist in your near future.
Luv, CrAsH
