bleeding master cylinder

[FlatBlackBurb]

ok so ive looked at a couple archives and people have advised people in situations like me to bleed the master cylinder.... when i go to put on my brakes, if i stomp on them hard enough there is a loud whooshing sound coming from underneath the dash and the pedal goes almost all the way to the floor before i get any response. if i pump the brakes hard enough, i get better response from the brakes. so what do you think is the problem? im guessing its the master cylinder. we bled the brakes and the brakes work better but the whooshing sound is still there... so how do u bleed the mc?

 

[AZ79K5Project]

Unbolt it, remove the brake lines, drive to Autozone or your favorite place, give the man $20.00 and drive home with a new one, repeat the steps above in opposite order.

It sounds like you MC is bad.

You need to bench bleed the MC before throwing the new one on the truck. Very Easy. Here's a good little article on it:
http://www.superchevy.com/technical/chassis/brakes/0509sc_bench/

I would recommend flushing the whole system with clen fluid while you have it apart if its never been done.

just my $0.02

 

[slyguy_22]

Unbolt it, remove the brake lines, drive to Autozone or your favorite place, give the man $20.00 and drive home with a new one, repeat the steps above in opposite order.

ummm not sure you wana unbolt it and remove the brake lines than drive to autozone!? though it would def bleed the system!

lol couldnt resist. when i replaced my mastercylinder the directions said to prime the cylinder (been a while) buy i just used a screwdriver or something to push the cylinder than i bolted it all together and cracked the rear bleeders and filled up the new one. than went around and bleed the brakes worked fine.

 

[Leper]

The whooshing sound is from the booster.

How long has it been sinse you replaced the brake fluid?
Done any brake work recently?
Did the problem just start one day, or has it been getting worse for a while?

You can just go and replace the master cylinder, bench bleed it and bleed the entire system after you install it.
Or you can spend a few minutes looking for other problems.
How old are your hoses? Are they cracked or have a bubble on them? What is the fluid level at? Are the rears adjusted properly? Are there any leaks? Are the pads and shoes close to needing to be replaced? Are the calipers and wheel cylinders moving freely?

IMO it is better to know what is wrong than to just start hanging parts. I am not saying it's not the MC, just want you to know what else to look for.

 

[FlatBlackBurb]

well to answer the questions... i opened up the resivoirs to take a look at the fluid level and it was pretty much full. i put a little more inside there just to see and it came overflowing out when i put the lid back on. i had this problem when i got the truck, and luckily we had a 78 3/4 ton parts truck sitting in my friends driveway. we swapped the boosts over and i noticed a little bit of a change but the whooshing sound is still there. also we bled the brakes immediately after putting the new boost in... if this gives any info to my problem

 

[AZ79K5Project]

Press and hold the brakes without pumping. Does the peddle hold or drop down?

Pump them up and then hold. Does the peddle hold or drop?

A peddle that drops may indicate a bad MC. A bad booster will make a stiff/hard peddle push. The vacume booster provides a mechanical advantage to the driver.

If your lines are dry, you're not leaking fluid, there is no fluid level drop but your peddle drops while holding a brake application, bad MC.

 

[jones]

So,how/why does a master cylinder go bad,and can I take the one from an '80(the metal style )and bolt it in place of the plastic style on my '84?

 

[lectric80]

Master cylinders are just a piston that pushes the brake fluid into the lines. They have seals and rings that wear out over time, that is how they fail. Don't know about using the older master cylinders.