brakes will not work

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Hi, I need some advice please on how to sort my brakes. I have a 1979 BJ40 with drum brakes all round. Recently I overhauled all the brake cylinders some of which were seized. I put on new rubbers etc. It is my first time working on the brakes. When it came to bleeding the system I started at the wheel cylinder farthest from the master cylinder and worked my way to the cylinder closest to the master cylinder. Everything seemed fine, pressing the brake before I started the engine the brakes felt firm. But as soon as I started the engine the brakes were all spongy. They would only firm up slightly with repeated pressing of the brake. Also the brake warning light came on and the buzzer sounded. I bled the system again using a large quantity of brake fluid but the same thing happened. The tandem master cylinder does not have a bleed nipple. Should I try and bleed the brakes with the engine running? Needless to say I have not tried to drive the cruiser in this condition. Help would be much appreciated.
 

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Have you adjusted the brake shoes? I would say that they are not properly adjusted, giving you this situation. I would adjust them porperly, and see how things work.
 

jm

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When you re-bled the brakes was there any sign of air actually being in the system? If not this may not be an air issue. If there is air in the system... did one of the reservoirs on the master get too empty and allow air in? Are the shoes all properly adjusted? Those may be the easiest places to start.

jm
 
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My leaking brake booster didn't show up until we replaced the 4 seized cylinders. What you describe: the malfunction with engine running, makes me think vacuum and therefore booster problems.
 
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I bet the issue is with the adjustment. With a few lug nust on tighten each cylinder until it will go no further. Back them off 10 clicks. See if the drum will turn. it should be tight but not too tight. If it feels like it is a bit too tight you are about there. If the MC was drained you must bleed it.
 
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[quote author=IDave link=board=1;threadid=6889;start=msg56800#msg56800 date=1067484363]
My leaking brake booster didn't show up until we replaced the 4 seized cylinders. What you describe: the malfunction with engine running, makes me think vacuum and therefore booster problems.
[/quote]

But isn't the connection between the pedal and the master cylinder a fixed length? (I mean pedal to pushrod to center of booster diaphram to pushrod to cylinder piston.) The booster only reduces the effort required. You can disconnect the booster and still have full use of the brakes. That would mean the booster is giving him a better feel for the extra travel that is either air being compressed or the shoes having too much travel. My .02, correct me if I'm wrong, which is not an uncommon thing.
 
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Theo, I am not certain, but he says things work/feel fine with the engine (therefore booster) off. My booster leak occurred/developed as I pressed in the pedal. No hiss until the pedal was halfway to the floor. No leak until all 8 cylinders were working and the pedal travel was longer. Once the leak occurred, after pedal travel, things got spongy. I agree he should do the usual cylinder adjustment as described, but if the cylinders are so far off, things shouldn't be working "engine off", right?
 
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That seems right to me. I need to look at an exploded view to refresh my memory about how the booster operates. Could have sworn it used a diaphram to just apply additional force without changing the actual travel.

Either way, if adjustment and bleeding don't get it done, the booster becomes highly suspect, eh? And your experience backs that up. :)
 
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He can do the booster test fairly easily:

[glow=red,2,300]When pressing on the brake pedal a hissing sound, a rapid change in idle or a rough idle are signs of a brake booster malfunction. Bad boosters will burn the exhaust valves in #5 & #6 cylinders. To Check Your Booster: Engine Off - press the brake pedal several times, pedal travel should not change. Start engine, pedal should move down a little and the pedal pressure will get softer. Press the brake pedal all the way down, shut off the engine, the pedal should not change position. Restart the engine, run for a minute and shut off, press the pedal several times, the pedal pressure should get harder each time. If your booster does not work this way its time to rebuild or replace it. Before buying the repair kit please refer to the factory Chassis/Body manual for the repair procedure[/glow].

He never said whether or not he adjusted the cylinders, so of course he has to do that if he hasn't.
 

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