Rear brakes won’t bleed

[BlazingBlue305]

Hey yall, I just replaced the whole brake system on my ‘81 Blazer. Went to bleed the brakes and found the rears have no pressure. I can only get small drops of fluid. Brake pedal will only build slight pressure up to a certain point. The proportioning valve is new so I don’t think it’s that. I believe it has something with the new master cylinder? I bled it in the vehicle and did notice the port for the rear wasnt putting out as much fluid as the front. I know that’s somewhat normal, but this was a big difference in fluid. Any ideas why pressure to the rear is restricted? Thanks in advance for any input.

 

[imiceman44]

Hey yall, I just replaced the whole brake system on my ‘81 Blazer. Went to bleed the brakes and found the rears have no pressure. I can only get small drops of fluid. Brake pedal will only build slight pressure up to a certain point. The proportioning valve is new so I don’t think it’s that. I believe it has something with the new master cylinder? I bled it in the vehicle and did notice the port for the rear wasnt putting out as much fluid as the front. I know that’s somewhat normal, but this was a big difference in fluid. Any ideas why pressure to the rear is restricted? Thanks in advance for any input.

2 things to look for.
I had once the wrong master and it had no pressure to the back, changed to the proper part and things worked.
The other thing that happens is the proportioning valve will shut off the rear flow and will need to be reset

 

[HankScorpio]

I had this happen on a suburban. There was a coupling about half way down the truck on the hard line. It was clogged somehow.

 

[imiceman44]

I had this happen on a suburban. There was a coupling about half way down the truck on the hard line. It was clogged somehow.

Ha was saying that at the master there was low pressure

 

[Wes Harden]

If you pressed the pedal hard or fast while bleeding the front brakes the porportioning valve has probably shifted.
It will need to be reset. You can try unscrewing the ground switch from the valve a couple turns, opening the front left caliper with a hose connected tight to bleeder, then stomp the pedal, if there is enough fluid in the rear side the shuttle will move.

 

[Wes Harden]

Low pressure or low flow ?

When cycling the brake pedal, if there is a small geyser in the reservoir wells the master is most likely doing its job

 

[BlazingBlue305]

2 things to look for.
I had once the wrong master and it had no pressure to the back, changed to the proper part and things worked.
The other thing that happens is the proportioning valve will shut off the rear flow and will need to be reset

When the new MC came in I compared it to the old one. Both were identical. Unless something with the internals is different. Proportioning valve wasn’t tripped when I tried to reset it the first few times either.

 

[BlazingBlue305]

Low pressure or low flow ?

When cycling the brake pedal, if there is a small geyser in the reservoir wells the master is most likely doing its job

It’s slowly dripping out fluid from rear screws when opened. If I leave it open for about 10 seconds, nearly nothing comes out anymore. I am getting the geyser in the mc on the side for front brakes. Should there be a geyser on the side of the rears as well?

 

[Wes Harden]

yes both sides should geyser