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71 bus brake question

My 71 bus is giving me some weird brake problems. When I first start the bus and hit the brakes for the first time, the pedal resistance is light and stopping is excellent... similar to modern power brakes. After this first press of the pedal, the pedal comes up a little slow, and the brakes feel hard and stopping power is diminished significantly. I practically have to stand on the brakes to get the bus to stop. If the bus not running the brakes are *really* bad.. so I know the booster is working at least.

I was told by the PO that the brake booster is brand new, and that the front calipers are also new. I looked underneath and they do seem shiny and new. I noticed when trying to adjust the rear brakes that on the right rear the adjusting stars are frozen in place and can't be adjusted. I'm planning to pull it apart in a few minutes to loosen up the adjusters.

My question is: On a bus with front disk and rear drum brakes what would cause the symptoms I'm seeing? Could one brake being out of adjustment cause this due to the pressure regulator in the system?

Thanks, Tom

Reply to
Duck Fizz Bang
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I don't believe this problem is due to shoe adjustments or the pressure regulator.

Sounds like the new booster was not set up correctly to the M/C. There is an elaborate procedure in your Bentley manual. Something is preventing vacuum from entering the port on the servo (no boost).

(Sorry, this is a bit off the top of my head, but it's where I'd start looking...)

Speedy Jim

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Reply to
Speedy Jim

Hmmm..., sounds odd.

I don't think the rears are the cause of this problem, but this is still a very important thing to fix.

Check your brake fluid level. Check the vacuum hose all the way from the intake manifold to the MC. If it is collapsed, kinked, or pinched anywhere, fix it or replace it and make sure it stays fixed.

Sounds like you're not getting consistent vacuum to the booster. My guess is that there's a problem with the vacuum hose. It could even be something that is not obvious when you inspect the hose from the outside. You might want to try pulling the hose off the booster when the engine is running at idle. There should be lots of vacuum there with lots of air flow available. It might even cause the engine to die, just because the idle mixture would get very lean suddenly.

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Reply to
Jim Adney

Reply to
Ilambert

Easy test for your booster...........start engine, with engine running pump the pedal a couple of times to get a feel for the amount of boost.

Shut off engine and wait a minute or so. With the engine off press on the brakes and see if you still have some assist. It *will* go away after a few strokes (becuase there's no vacuum source with the engine off)...........*BUT* if you find a hard pedal on the first stroke then you know that the booster has a leak or if there's a check valve in the hose (usually on the booster itself) then that could be bad.

Here's another way to check, engine off, pump the pedal till there's no reserve boost, start engine WITH YOUR FOOT ON THE BRAKE. If the pedal sinks slightly right after starting then you know you're getting vacuum to the booster.

significantly.

Reply to
ANT

Here's what I'm getting:

After pumping pedal with engine off, I hold my foot on the brake, start the engine, and the pedal sinks an inch. After this the pedal feels hard again. I shut off the engine, and the pedal feels the same. I pump it a few times... no difference. The pedal always feels hard. I didnt take a drive with the booster disconnected (yet). Once I find something to plug the vacuum hose, I'll take it for a spin and compare.

Thanks, Tom

Reply to
Vic20Owner

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