dear V8buick community, 1967 Buick Special I have a new M/C cylinder installed (old one leaked) and also upgraded from the original distribution only valve to an inlinetube distribution/proportioning/Holdof combo valve. That hadn‘t been installed when converted to disc/drum yrs ago. Now I have the issue that on the left front side the brake pressure does not go away when I get off the pedal. Any ideas? How would you go about analyzing what‘s wrong? Thanks Patrick
Brake hose. (Especially if it releases after a while). If so, jack up that side, spin the wheel (to verify it’s free), mash the pedal to lock it. Crack the bleeder and see if it releases. Patrick
Brakes hoses appeared fine. I am suspecting the proportioning valve. Do these valve require any adjustment after installation? If so what exactly needs to be adjusted and how? At the front of the valve the is a rubber grommet and a screw underneath it. Patrick
Just because they appear fine, doesnt mean they are. Theres a quick and dirty method to diagnose this. Like Patrick said, mash the brake pedal and get the wheel to stick. Crack the bleeder. If the wheel frees up, its the hose. If you want further confirmation, mash the pedal again and this time crack the steel line going into the rubber brake hose. If the wheel is still stuck, its definitely the hose
Alright many people pointing in the same direction. Will do the quick and dirty tetsing and get new hoses first thing next year, just to be safe. Functionality of brakes is crucial. However what I did was to open the rubbercap and screw and I heard a pppfffft sound like air under pressure getting released. After that many things improved: - cars doesn’t pull to the left anymore when cruising (basically unrivaled) - cars stays straight when braking - so caliper is now willing to retreat as it should Overall driving felt good to normal (haven’t driven the boat in 18 months and boy these cars are veeeery different from my modern Skoda Octavia). Any idea what that sound was and how it cured my issues? This is the proportioning valve I am talking about https://www.inlinetube.com/products/pr100 Thanks Patrick
Jason, So that properly cured the issue? Or does it rather confirm there is something dodgy about the hose? What is the actual purpose of the screw I opened? I drove home for about 20km and couldn‘t feel any troubles... Man I hate it when I know there is something wrong and can't get it sorted in the near future.... Thanks for your help and hope the winter will be short. Patrick
We bled the brake system several times before and after the issue which included opening the bleeder screws on the caliper. Not sure I answered your question, Jason....
Having found this picture on the internet it seems I opened the metering valve which released pressure and I would now also assume the combi valve is not properly centered.oooppsss.... And I also understand I should buy a proportioning valve bleeder tool in order to properly center it. Like this: https://www.speedwaymotors.com/Speedway-PV2-PV4-Proportioning-Valve-Bleeder-Tool,296895.html Does this make sense?
No, as long as you have proper pressure on each side of the valve, it centers itself. If you trip the warning light while bleeding the brakes, a simple brake application will re center it and turn the light off. That picture you posted looks like the rubber cap covering the metering pin. The metering portion of the combination valve holds off the disc brakes until a set pressure is attained in the rear brakes. This is because disc brakes are essentially instant acting while drum brakes need to overcome springs and clearance of shoes to drums. The Chassis manual says you should depress the metering pin while you bleed the brakes. Not sure why there is a screw? under the rubber cap? The metering valve is separate on the 70 and earlier braking systems. (Next to Master Cylinder). In 1971 and later, it was incorporated into the combination valve.
Thanks Larry. Good info, I am getting there... collecting information. Wish it was spring and I could actually work on the car.. ;-( What are you guys using to measure the pressure (at the end of brake lines)? Is there a specific tool? Patrick
