yamahondarider

Okay, so my car is a 1969 Oldsmobile Cutlass S, with 4 wheel drum brakes. Until a few weeks ago it was sitting since 1988. I got the brakes working and working well, and the master cylinder is clean as a whistle. It has power brakes, and what I think is happening is the actual vaccum brake booster, is "sucking" the brakes on when I push the pedal and not releaseing them unless I pull the pedal back with my foot. Is there some sort of check valve or one way valve that could be stuck open inside the booster? Or is there supposed to be an external one? There is only a straight hose going from the manifold to the booster, and it looks like the rubber part was replaced shortly before the car was parked. Any ideas?

Heres a video:


also, a semi-helpful picture of the booster line:
booster_zps89b8e010.jpg

MDchanic

Sometimes a little touchiness and stickiness can be caused by the pushrod being a bit too long, but I've never seen a booster hold the pedal to the floor like that.

I'd say you've got a failure of one of the booster's internal valves. Others may know more about it.

I'd bet if you read through the booster section of the CSM, you might find the answer, and you might be able to fix it by just taking it apart and messing with it, too.

- Eric

don71

You got to remember on old cars like these that sit a long time, the brake system is the first to go. I know you said the master is clean as a whistle. But what you can't see is inside. The bore is probably nasty, causing the pedal not to return.

I think your problem is the master cylinder. At this point, I don't think its the booster. Boosters or the vacuum lines have seldom given me a problem.

My suggestion to you is replace the master cylinder and bench bleed the unit and the system.

Go from there and expect to replace the wheel cylinders (all four) and the two front flexable/rubber brake lines at some point. You should just do this all at once and be done with it.

Problems with the metal lines along might creep up later, but you should start here.

yamahondarider

Yeah I was thinking of getting a new MC, I just thought I'd give the old one a shot before I take it out. I rolled the car with the engine off to get it down a set of ramps and the brakes stopped it fine without sticking, that was engine off with no power brakes, keep in mind, stopping from about the same speed as when I putt around the yard. Thats why I think its the booster. I don't wanna buy a new MC and find the same problem and then spend more cash on a booster.

yamahondarider

I guess what I'll do tomorrow is pull the MC off the booster and see if the pedal loosens up at all. I may as well pick up one at autozone, their $25 for a reman'd MC plus core charge, and I'll bring in my core.

yamahondarider

Okay, so, today I took the master cylinder off the break booster. I pushed the MC in and it sprayed fluid out of both ports (frontmost port first, the one with the biggest resivour). It also sprung back and operated smoothly, so I don't think theres any problem with the MC. However, the pedal didn't get any smoother to operate without the MC, until I pumped the pedal a lot working it loose. From the floor, the pedal springs back quickly to about halfway, then you have to pull it back another 2-3 inches to make contact with the stopper/brake light switch. When you push the pedal, you hear the sound of air escaping, and when you pull it back, the sound of air rushing in. Is that an indicator of a stuck valve inside the booster?

joe_padavano

This is almost certainly caused by a bad control valve in the booster. It's easy to test (well, it WOULD have been easy before you took the M/C off...).

Simply disconnect and temporarily cap the hose from the engine. If the brakes work fine (except without power assist), the booster is bad. Always try the easy troubleshooting before wasting a lot of time removing and replacing parts.

yamahondarider

Okay, thats what I figured. I mentioned in another post briefly, but before I took anything apart, I had the car on a set of ramps when changing shocks, and when rolling the car off the ramps, the brakes (with the engine off, no power) worked fine with no sticking. Now, going about the same speed idling thru the driveway with the engine on and power brakes, the pedal would sink and not return unless pulled like shown in the first video. I guess I'm gonna have to buy a booster then, but getting the pin out of the brake pedal arm is gonna be a pain!

MDchanic

I believe you can just fix the valve, but Joe would know that better than I.

Also, I don't think you have to mess with the pedal - just remove the invisible nuts and pull the booster off.

- Eric

joe_padavano

Actually, you do have to disconnect the pushrod from the pedal. The rod is held to the pedal with a pin and spring clip. It is a PITA to get the spring clip off.

You can fix the valve, but you have to disassemble the booster to do it.

MDchanic

Whoops. Guess I must remember the pushrod from manual brake cars.

I had thought that the valve was repairable, but I've never done one myself. Seems reasonable to try before shelling out for a new booster.

- Eric

yamahondarider

I took the booster out and everything rubber/plastic was old and dry and nasty, so I went ahead and ordered a new booster. Its only $86 at Autozone, after 44 years in the car I don't mind replacing the old booster. I'm picking it up tomorrow and plan on getting that and the MC installed, then putting in the new rubber brake lines up front, bleeding everything, and HOPEFULLY my brake system will be back in order. I'm also picking up a B&M Z gate shifter and a Barry Grant Street Demon 750 CFM carburetor from a guy not too far away for $125, both in great shape. I don't need em yet but I will soon

yamahondarider

Good news, got the new booster and put it in and seems to have solved my problem. pedal feels like a brand new car. I haven't RAN the car yet so I don't know how it'll do under power but we'll find out. I need to get a battery, the one I was using was borrowed from dad's van but he needed it back. Looking for one local I can pick up tonight.

newbooster001_zps069f2f15.jpg

newbooster002_zps69b0c782.jpg

MDchanic

Great! You'll be hitting the road soon!

- Eric

yamahondarider

Great news! Borrowed the battery out of another car in the driveway and hooked up my temporary gas tank and fired it up. It stops smooth and no major sticking but it hangs a tiny bit at the end which I blame the pedal for. I'm gonna hook up a light return spring on the pedal and call it good. So glad Im that much closer to being on the road!