Brake Issues

[72blazerguy]

I am having braking issues. Intermittent, no brake pedal, but brakes always return when pumped once or twice. I have checked the brake lines for leaks and am fairly certain the rear wheel cylinders are ok.

I'm thinking master cylinder, but maybe the brake booster.

Looks like I could replace the master cylinder, power brake booster, and the brake booster check valve for about $150 thru rockauto.

71 blazer, disks in front, 14bff drums in rear.

Anybody have any ideas on deciding which part is failing?

 

[ChrisPerry]

If pedal goes to floor it won't be the booster. Booster only affects how easy the pedal is to push. Most likely gonna be the master cylinder.
I would replace the booster and master cylinder together though. If the master cylinder is leaking brake fluid into the booster it will go in short order.

 

[chulisohombre]

Is the check valve on the tube going to vacuum on the intake still working. If not your booster will loose vacuum and will require you to
Pump to get pressure in there before braking comes back. Possible lack of fluid capacity from bigger rear drums or needs bleeding good to double check flow to all wheels. Just a couple thoughts.

 

[Fordum]

If it worked OK before, and you have not changed any major components, such as converting drums to disks, things like that, then its most likely the master.

Vacuum to the booster does not matter if you are losing pedal. With no vacuum to the booster, you should still have lots of pedal, just really hard.

I have replaced lots of masters while keeping the booster, but that is a good price, so you might as well get the whole thing.

There should be some instructions for bleeding the master before installing it. That is separate from bleeding the brakes themselves.
A dry master can have bubbles inside parts of it that would not come out when bleeding the wheels, but can cause problems.

 

[dyeager535]

Concur with master being bad. Had a failing master cylinder in my truck, always was a bit spongy, could never bleed that out, one day pedal went to floor. Was able to pump the brakes to get enough pedal to stop, but immediately got a new one in there, problem gone.

Bad booster (lack of assist) symptom would be a rock hard pedal.