GregC
05-08-2005, 07:28 AM
Hello,
I am having a problem with the brakes on my 1982 GMC 7000, 366 CID (gas). I bought the truck late last summer. When I took it in for safety they replaced 6 wheel cylinders and 1 drum (cleaned the shoes). They passed it but missed that the plastic check valve (mounted near the master cylinder) was no longer working. The system wasn't holding vacuum when the engine was shut off. I replaced that with a new one from GM. Now the problem, I seem to have intermittent boost assist. Sometimes it works and sometimes it doesn't. There doesn't appear to be any leaks, the vac gauge always reads above 15 even when I have no boost, the gauge works. If I press the pedal with the engine off eventually the gauge will read zero (boost working at that time). When it doesn't work I can pump the brakes and it doesn't help. If I wait a bit I may get boost the next time I need to brake. The pedal is hard, I don't believe it is air in the system, I know what that feels like. Fluid level is right at the top in the master.
I would think that a booster would either work or not. The system consists of the master, remote booster and an additional vacuum reservoir cylinder. I am not familiar with the type of vacuum booster that is remotely mounted from the master. It has a bleed port on it. I guess there is a piston in it that could be gone. I am going to try to suck some fluid out of it and see how clean it is.
Anybody have any ideas what could be the problem? I can post pictures of the parts if needed.
Picture of truck (http://www.carter-engineering.com/images/truck/GMC7000/roofdump.jpg)
Thanks
Greg.
I am having a problem with the brakes on my 1982 GMC 7000, 366 CID (gas). I bought the truck late last summer. When I took it in for safety they replaced 6 wheel cylinders and 1 drum (cleaned the shoes). They passed it but missed that the plastic check valve (mounted near the master cylinder) was no longer working. The system wasn't holding vacuum when the engine was shut off. I replaced that with a new one from GM. Now the problem, I seem to have intermittent boost assist. Sometimes it works and sometimes it doesn't. There doesn't appear to be any leaks, the vac gauge always reads above 15 even when I have no boost, the gauge works. If I press the pedal with the engine off eventually the gauge will read zero (boost working at that time). When it doesn't work I can pump the brakes and it doesn't help. If I wait a bit I may get boost the next time I need to brake. The pedal is hard, I don't believe it is air in the system, I know what that feels like. Fluid level is right at the top in the master.
I would think that a booster would either work or not. The system consists of the master, remote booster and an additional vacuum reservoir cylinder. I am not familiar with the type of vacuum booster that is remotely mounted from the master. It has a bleed port on it. I guess there is a piston in it that could be gone. I am going to try to suck some fluid out of it and see how clean it is.
Anybody have any ideas what could be the problem? I can post pictures of the parts if needed.
Picture of truck (http://www.carter-engineering.com/images/truck/GMC7000/roofdump.jpg)
Thanks
Greg.