Another poster kindly asked if my power booster was failing in my breaks. I went and reads the FAQ and these are my questions:

THE PROBLEM:

The breaks seem to have two stages. First they slow the vehicle down, but once it is almost to a stop or even after it has stopped (about a good two or three second count after putting on the breaks to begin with) the pedal begins to sink further and the car will begin to move unless I put more pressure on the breaks. After reading the FAQ I seem to recall hearing a sucking noise when applying the breaks.

THE QUESTIONS:

I read and re-read the FAQ about the check valve and power booster. As a result I have some questions. First the big one; Will my breaks fail in a spectacular fashion regarding this issue? It might be some time before I can address this issue and I am bereft of cash at the moment. I am not certain I understand the procedure to examine the check valve. Can I just yank this piece out of the master cylinder and blow it out with compressed air to see if it is working or to clear it? How is it set into the master cylinder? The check valve does look original to the car (1988) as does the vacum hose going to the engine block. Both do not look defective...I do not see any cracks or failures in them. I am trying real hard to conserve cash as I am really broke and will be so until at least October...next paychecks come in October. I am hoping this issue is not the power booster. Following the procedure for the power booster check I pumped the break pedal. Started the car, put the break pedal as far down as I could push and then turned the car off. The pedal came back up but it seemed to be under normal pressure and not like it was pushing my foot up. There is an air sound when the break pedal comes up that is coming from that pedal area...what does that indicate?

THE REMEDIES:

I am new to Volvos so please outline my remedies as explicitly as possible. Taking the car to a mechanic or the Volvo dealer is not possible (I might as well push it into the ocean as I do not have the money to spend for that). Please explain in great detail my options and places I can find parts to solve this issue. Also what tools might I need? Thanks!

OK all three responses were fantastic and very helpful. So I am looking at replacing the master cylinder. I do not yet have any of the books and I searched the FAQ for the directions to do this but turned up nothing...perhaps I was looking in the wrong places. Please outline the materials I will need, where to obtain these materials and the tools I will need to execute this repair. Again, I am new to Volvos so please be explicit as possible. Is it possible to rebuild the master cylinder or should I just chuck it in and start over? Again, all helo is very much appreciated. Thanks!

I believe the check valve is there to allow air to be sucked out of the booster by engine intake vacuum but prevent air rushing in as from a backfire. If you don't have to press super hard to brake then the booster is working. If you get a sinking pedal with moderate pressure but none or less with hard pressure then the master cylinder is bad. Fluid is leaking around the master cylinder piston internally do to wear. Hard pressure on the pedal expands the seals more so the problem is reduced.

What you describe are classic symptoms of a failing master cylinder. Under good braking pressure, the pedal holds OK, but with lighter pressure the pedal slowly moved toward the floor.

A test is to do that, in a safe environment. Engine running, hard pressure, pedal should hold fine. Lighten up a little and see if the pedal sinks down.

You can drive like that a while, but it will get worse. Also a situation requiring light braking and you won't stop until you stomp on them, can be surprising and uncomfortable and dangerous.

Rebuilding a master cylinder (MC) has about the same cost as a new one and more labor. T'aint worth it.

Doyou have any books? Haynes Manual or the Bentley Service Manual? A book will make the job a lot easier.

The job is relatively easy, and can be done in a way that avoids the need to bleed the system afterwards.

Post back if you (1) are sure it's the MC, (2) you have a book, which one?

Regards,

Bob

:>)

it sounds like your master cylinder, although it wouldn't hurt to just replace the check valve. the check valves are less than $15 from FCP Groton I believe, and is about a 5 minute job at most. if you want to check the valve before you replace it, you can pull it out from the booster and remove the hoses. then just blow into it. air should only be able to go in one direction. if it goes in both, it's not working properly.

last time the MC went on my car which was about 5 years ago, it exhibited the same symptoms that yours did. tight pedal at first, and then suddenly sinking.

don't delay fixing your brakes. this is your life you are gambling with. if you can't afford to fix it yet, then don't drive the car at all.
--
Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'