The brakes on my '89 Suburban never seem to be right. I replaced the master cylinder and took it to a shop to bleed the brakes (seemed like my MityVac wasn't able to pull all the air out at the rear cylinders.) The shop said they bleed the lines for a really long time before they got a firm pedal. It is two weeks later, and the brakes are getting soft again. Any idea what is really wrong? The level of fluid in the master cylinder never seems to get any lower, and I have not found any visible fluid leaks.

I bought this truck from my father-in-law because it has a new GM engine and transmission, and parts are cheap. I have found so many things wrong with the engine install that I am starting to lose patients. If I could just iron out the brake problem, I feel like I can get through the other nit picky problems. Help save this Suburban and myself from an early grave!

 

Have you checked the rear wheel brake cylinders for leakage? The front brake flex hoses may need replacing.

 

I attempted to bleed the brakes yesterday. Lots of air in the lines. So much so that after an hour of pumping my brake bleeder, I gave up. No rear cylinder leaks, but I will check into front hose flex. Any idea how the air is getting into the system?

 

Don't forget about the rear brake hose. Might be swelling up. would explain soft pedal, low pressure for unsuccessfull bleeding, and no loss of fluid...

 

I have a 93 Suburban and if I remember correctly there was a brake related recall. Not sure if it included the 89 year model.

 

You need the "Pressure Bleed" treatment. Brake shops have a tool that forces fluid through your system via a Master Cylinder Cover that has an Inlet Port where Fluid can be pumped-in under pressure.

Bleed the FURTHEST Wheel Cylinder away from the Master and work your way to the closest. That ought to do the trick and get all that Air out of there. It will also find any leaks that you may have failed to detect during previous bleeding attempts.

 

I found that when I was using a Mityvac to bleed brakes, that it was actually sucking air past the piston seal into the caliper. That's when I decided to put an air fitting on a master cylinder and pressure bleed like RickCoMatic suggested. A lot easier to boot.

 

The first and most important step in doing a master cylinder is to bleed all the air from the master cylinder in a vise before installing it. pumping the brake pedal will not get all of the air out because of the slight angle of the unit once installed in the car. I know most of the aftermarket kits come with bench bleeding kits and have instructions telling you how to do it.

Could also be a bad master.....did you get a new or Reman? The were huge problems with the reman units a while back, and even though remans were way cheaper....they were not worth the headache.

 

hey sorry not sure how to make my own new thread but i blew my front brake line to the right side. i replace the line as along with the other front and the lines running to the abs pump. i have gravity bled and vacumm bled the system, after that i have pressure bled the the system as well. I started at the master bleeding it then did the pump the the 4 corners starting fartherest from the master cylinder.
i cannot get a pedal no matter what i do when the vehicle is running. i cannot pump the pedal up to get it hard (to see if there is air in the system as air compresses then fades slowly) the pedal falls almost completly to the floor.
im leaning towards a master cylinder? any idea would be great thanks!