On our way back from Robert Treman in November, I stepped on the brakes to hold the bus on a hill, and felt a suspicious drop. There was still a good, hard pedal there, but the power assist was gone, confirming for me that the whooshing sounds that I'd been hearing for a couple of weeks every time I stepped on the brakes were definitely NOT GOOD.
The engine started to loose rpm's and run rough every time I stepped on the brake, an obvious sign of a vacuum leak.
We stopped as soon as possible at a nearby scenic overlook, where I improvised a vacuum plug from an Ommegang beer cork, a short length of hose, a clamp, and some electrical tape. With the intake manifold port plugged, we had plenty of brakes, but no assist, & that's how we drove it home. It was spring before I took it all apart to see what happened.
Apparently, a good check valve is more important than I thought. I could blow through mine in both directions, a clear sign that it was shot. When I pulled the brake booster out, I was able to drain a cup or so of nasty gassy-smelling goo out of it, which I surmise to be an amalgam of gas fumes that had migrated up the tube due to the broken check valve (nothing is ever supposed to travel in that direction; the valve is one-way) and brake fluid, plus a fair amount of dissolved diaphragm.
The whooshing sounds I heard before the total failure must have been from a partial rupture.
While I was taking the booster out, I also found I was having trouble with the proportioning valve, which was leaking from the seam between the two halves of the valve, and with the seal between the tube from the top to the bottom brake fluid reservoir, causing the tube to leak on the bottom end. I was able to source a used valve from a local enthusiast (Hi, Brian!) and you can see me cleaning it up for installation in some of the
pictures; brushing off scale, cleaning out mounting holes, putting homemade plugs in the openings to keep debris out& make sure the threads were good. Upon installation, it didn't leak! Hooray!! Still don't know why the original one leaked; though I suspect a gasket failure between the halves. These cheesy German parts, you know; won't last more than 35 years, give or take...
The booster had to go in for rebuilding, through Bus Depot. NOT CHEAP, and it was only 2 years old! Lesson Learned: Verify check valve function at every oil change, or a malfunctioning $12 part could cost you $300 or so. Ouch!
The Garage Gnomes made off with the installation pictures, and undoubtably hid them in the same place they keep all my Vise-Grips, but the new booster went in pretty much the same way the old one came out. The sequence I used for booster removal was: Remove the short line from the proportioning valve to the master cylinder. This will allow the master cylinder enough movement to let the booster get by, after which the MC can hang by its lines. At this time, I replaced the rubber sleeve inside the tube that connects to the lower reservoir, since it had been leaking. Also, I
changed out the proportioning valve, which involved disconnecting the rest of the lines to the valve. With the MC out of the way, disconnect the vent hose from the top of the booster, and the vacuum hose from the rear-facing face of the boooster. After that, the booster disconnects from the frame with 4 nuts, and can be guided/wrestled/persuaded out. One thing that I discovered while playing with brake parts & waiting for my rebuilt booster to come back, was that the smaller, earlier unit that's found on '71 Busses can be interchanged with the larger unit used on the '72 - '79 Busses. It will bolt up without modification, and there is just barely enough room for the emergency brake cable to squeak by.
Sadly, the late model booster that I had lying around was bad, too. But, next time I send one in, I'm sending that one, for a little extra power assist. Couldn't hurt. Oh, in case anybody's wondering, I ordered a NEW check valve from Bus Depot, and installed it with the new booster. Ouch! Braking just fine, though.... DISCLAIMER: I am not a professional mechanic. My advice should be considered non-expert! Before you try any of these procedures, for Heaven's sake go out & get yourself the Bently manual for type II's. Section 8 (Brakes & Wheels) pages 7 through 13, have WAY better pictures than mine, and probably better instructions, too. And, please remember to bleed the brakes thoroughly, at the proportioning valve bleeder & all fittings, too, as well as the wheels, before you take her out on the road. After all, I might be out there, too!
Sunset over Lake Ontario.
Mark celebrated a birthday.
