Vacuum brakes hard after parts added

[captflash]

Ive had my T Type for 8 years and drive it quite often. Over the years I've gone through the whole system, from booster to master cylinder to brake lines to pads ect. They worked great and anytime I had an issue I fixed it. Recently I installed a front mount intercooler TA performance headers and a 6870 Precision turbo. Prior to the new parts the brakes worked great. After the parts they are hard. The pedal is hard and I have to lay on the pedal to stop. I've tried backing up adjustment, checked the check valve and it was good. Pulled the check valve out of the booster and there was vacuum. My boost gauge shows 17-18 lbs vacuum and still a hard pedal. Thanks kindly in advance for your suggestions and help.

 

[whitehot1]

Could be the master cylinder,wheel cylinders,proportion valve causing the problem. Not sure how to test those though.

Maybe someone who knows will chime in or you could do a search to find out.

Sorry i can't be of any help to fix the problem. I've had vacuum brakes for a long time and the only problem i had with having a hard brake pedal was vacuum related.

 

[1986 Buick GX1]

Have you done a vacuum test on the booster itself to see if it holds vacuum? It might be just a coincidence that your booster started to leak.

George

 

[SICK_SIX]

A hard pedal with vacuum brakes usually means there's a problem with the booster -- less or no vacuum assist = hard pedal

 

[Turbo6inKY]

A hard pedal with vacuum brakes usually means there's a problem with the booster -- less or no vacuum assist = hard pedal

Yup. I'm going to venture a guess that the booster diaphragm is leaking.

The check valve that comes with these boosters can't hold up to positive manifold pressure. They're cheap, designed to handle a normal car. They'll leak above 15psi, pressurize the booster, and damage it. Been there, done it. Got rid of it for a manual master.

 

[captflash]

Thanks for the replies and the suggestions. The accumulator appears to be holdin a vacuum. I say appears as after sitting through the night I pulled the check valve out of the accumulator and it definitely had held the vacuum overnight. Is there any further test I can perform to check the accumulator or any other part of the system? Thanks in advance for your help

 

[Turbo6inKY]

Thanks for the replies and the suggestions. The accumulator appears to be holdin a vacuum. I say appears as after sitting through the night I pulled the check valve out of the accumulator and it definitely had held the vacuum overnight. Is there any further test I can perform to check the accumulator or any other part of the system? Thanks in advance for your help

If the booster is holding vacuum, then you need to look for some other things. Seized wheel cylinder or caliper?

 

[captflash]

If the booster is holding vacuum, then you need to look for some other things. Seized wheel cylinder or caliper?

The brakes are not seized and the hubs and calipers are not hot.

 

[Turbo6inKY]

The brakes are not seized and the hubs and calipers are not hot.

Attach a vaccuum pump to the booster, suck it down, and hit the brakes. If they feel normal, then you've got a leak in the intake tract that's preventing adequate vacuum from building in the booster while its running. If it's still hard, then start replacing parts, starting with the booster and working your way out to the calipers and wheel cylinders.

Not much more diagnosis we can do over the interwebz.