Need Expert opinion

[ubtripn]

I just installed a new Master cylinder. I have 4 wheel drum power assist braking. I did have some squealing initially like a balloon being emptied by stretching the opening when braking but way louder. I removed the MC and lubricated the dish in the power booster that the MC mounts to and it went away. It was braking GREAT but I still had a little air and travel. I could not get one bleeder screw in the rear out so I had it bled by a machine at a shop. I think but am not sure that the front tires are braking as before but I am now using more force than I do in my 66 that is not power assisted. Is it possible the booster went bad or the MC? Thanks in advance for your info and help.

[demian5]

You still have air in the rear.
You mentioned nothing about why the master was replaced or if the brakes worked fine before.
Did you adjust the brakes?
I had the same noise, it was a bad vacuum check valve on the booster from CPP.
If master failed and fluid was ingested into the booster, the booster may be damaged (suck the fluid out and spray brake cleaner in there)
Maybe the seal on the master side isn't sealing properly causing the vacuum noise.

[ubtripn]

Vacuum noise is gone but I replaced the master due to a leak. Here is where things get tricky for me. I have about 3 inches of travel on the pedal with no force then its like hitting a rock. (I'm not hitting the floor but close.) When I stand on it at that point it brakes correctly but not easily. When I had them bleed the truck they replaced one bleeder screw. What bothers me is I know what good feels like, as long as I kept fluid in the bad MC it braked good, now I have a new MC and it i shop bled and it brakes bad. How are you sure the rear still has air? I will bleed it myself if that is the case.

[ubtripn]

It feels like the booster failed when the new MC held pressure. Almost as if the leak was like a relief valve. Can new MC's kill old boosters?

[Andy4639]

With your foot on the brakes start the truck if the pedal drops a little then the booster is working.
It sounds like either the rod in the booster is not long enough are you have air in the system.

[LockDoc]

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Bench bleeding the master is important....

On the drum brakes, one thing I found on mine is when you put everything back together and adjust the brake shoes you can’t just adjust them out until they start rubbing and quit. You have to adjust them out as far as they will go and you cannot turn the wheel or drum at all. This centers the whole assembly in the drum. (I even tap around the drum as I tighten them to help them center themselves) Then you back them off until the wheel just turns, and stop. If you only adjust them out until they start rubbing and quit, the first time you press on the brake pedal the brake shoe assemblies will center themselves and you will have too much clearance between the shoes and the brake drum. I also put three lug nuts on backwards to hold the drum tight against the axle on the rear.

I know it is a pain in the butt to try and hold the self adjusters off of the adjuster wheel while you back them off, but this is the only way I could get my drum brake shoes adjusted correctly.

LockDoc

[B. W.]

X2 what Andy said
X2 what LocDoc said

if brakes work but require extra effort & the pedal is rock hard then the booster is bad

in a drum brake system (even disc/drum) if you have a low pedal (assuming no air in system) the drum brakes are out of adjustment

replace the booster & adjust your brakes

[ubtripn]

Thank you. I will do just that. What is weird still to me is that I did the front shoes two years ago and it has been braking just fine but leaking at the MC. All I did was replace the MC. No brake work so why so much travel now I wonder. Either way I am going to rebuild all four, replace the booster, adjust and go. Thanks all.