Replacing PD4106 Front Brakes

The first time I changed the oil in the bus I hired Robert Moore, who knows these buses inside and out, to teach me the process. While we were at it we jacked up the front of the bus and crawled underneath to do the front end lubrication and inspect the components, including the front brakes. One thing that Robert pointed out was that the front brake linings would need to be changed "before too long". Several thousand miles later (I am not very hard on brakes) in early April we finally got nice enough weather to allow us to do the job in my driveway.

Bus securely lifted onto jack stands

Robert showed up early one morning in his service truck. The fact that he can come out to my place rather than my having to take my bus somewhere is a nice thing. Of course that means working in the dirt, but he has a big sheet of plywood that he slides under the bus so it is not that bad. His truck has a big gasoline-powered compressor, ramps to drive up on, an air-operated jack, and jack stands to hold the thing up. The compressor also runs the air wrench; I would hate to try to get those lug nuts off without that tool.

Getting the bus up in the air and secure on jack stands took a little over a half hour. Because we did not know yet what issues might come up during this little adventure, we needed to make sure we had everything secure enough to hold it up there for multiple days if that became necessary. The next thing was to get the wheels off. The chrome wheel covers are held on by some of the nuts but the air wrench made quick work of removing the lug nuts on the passenger side, exposing the brake drum. You can see the drum with the lug bolts sticking out and the hub cover that holds a bit of oil to lubricate the wheel bearings. I am used to wheel bearings being packed in grease so this was something new. Robert said that the oil in the hubs needs to be re-filled every 5000 miles or so because it slowly leaks out.

Hub assembly with drums on showing retaining screws

The brake drums are secured by some flat-headed screws. Because the previous owner had been good about coating the threads with anti-seize compound when he re-installed them the last time, the bolts came right out after being "bumped" with an air chisel to loosen them. Once those bol
ts were removed, the drum was lifted off to expose the brake components. While disk brakes are more common on newer vehicles (including buses), back in the 60s when this bus was built, drum brakes were used on most vehicles, including the PD-4106. Disk brakes clamp down on the outside of a rotor (like the hand brakes on a bicycle) while drum brakes like these operate by pushing brake shoes out against the inside of a drum. The brakes in larger vehicles like this bus are air-operated, while the brakes in most smaller vehicles are activated by a hydraulic cylinder.

Removed drum

Once the drum was off, it was just a matter of pulling off the retaining springs and two rollers and then the brake shoe assemblies could be "flopped" out. On more modern brakes, the lining material is generally bonded onto either the shoes (drum brakes) or the pads (disk brakes). The brake lining in older vehicles were usually removable and were attached to the shoe with either bolts or rivets. On this bus the linings are bolted onto the shoe so it is very important to replace them before they wear down to the point where the bolt heads start to contact the brake drums, ruining them. Replacement parts for antique vehicles are never cheap and are often unavailable (such parts in the busing world are often said to be made of "un-obtainium). An inspection of these shoes revealed that the bolt heads were still between 1/8" and 1/4" from contacting the drums, so this was the perfect time to replace them since this is obviously not a repair you want to have to make out on the road.

Once the brake shoes were "flopped out" it was easy to use air tools to remove the retaining nuts and bolts. Robert said that in most cases some of the bolts will have to be broken out to remove them but on this bus every one of them was able to be unscrewed with minimal effort. A little bit of wire brushing and we bolted the new linings on with the new brass bolts I bought. We also replaced the springs and rollers when we reassembled and installed the brake shoe assembly.

Newly installed linings showing recessed bolt heads

I was able to buy all the parts from Mohawk for less than $150, which for a bus like this seemed pretty good. We moved on to the other side and things went smoothly. We took advantage of the opportunity to lube the undercarriage (it was sure easier with the wheels off. Robert adjusted the brakes after he installed the drums, put the wheels back on and after removing the bus from the jack stands we were done in record time (about 3.5 hours). It is always a pleasure to work with someone who knows what he is doing!

The old linings and springs, ready for recycling

We have a trip to the NC mountains next month and I look forward to having new brake linings.