HELP!!! Multiple brake problems

A brief background: Just installed hydroboost while simultaneously trying to solve spongey brakes. Replaced the master cylinder and both rear calipers. Flexible lines are stainless and fairly new. All other lines and proportioning valve are original.

The hydroboost is in place and plumbed. the fluid has been topped up and the power steering works fine.

The problem. I have intermittent spongey brakes. Drove it last night and it was soft. Tried to take the wife for a drive this morning and it went to the floor. Moved the car this afternoon (fairly hot here) and the pedal is nice and hard.

Symptom number two. With the engine off, the pedal feels fairly normal, though spongey. With the engine running, the pedal goes down but does not come back up. I can stop the car, take my foot off the pedal and the car will stay stationary until I pull the pedal up with my foot. Not easy to pull up either.

Last symptom: I got a power bleeder. Works great but the flow rate is VERY slow. Upon sitting for a few minutes, I'll get a short burst of good flow followed by very slow, almost to a stop. This is the case at all four corners.

I'm guessing that there is a blockage at the proportioning valve or the valve itself is gummed up. Is this a reasonable conclusion? Should I just do all the original lines while I'm at it? Am I simply missing the real problem?

As to the pedal issue, I'm new t hydroboost and have no real idea of what the issue is.

Any help would be appreciated.

By the way, I also have an issue with traction. The tires can't seem to stop spinning when I stand on the throttle. :yahoo: Pretty pleased with the engine if I can only get the car to stop. Tired of using the e-brake. Thank God I fixed that well.

With that power bleeder, you should have quite the stream coming out when opened.
You need to isolate the lines, the valve, and the M/C to see where the one or more problems lie first.
Start with the basic system, then check the hydro-boost.

big2bird said:

With that power bleeder, you should have quite the stream coming out when opened.
You need to isolate the lines, the valve, and the M/C to see where the one or more problems lie first.
Start with the basic system, then check the hydro-boost.

Click to expand...

That sounds reasonable. I can verify that I have good flow up to the proportioning valve from both MC lines. I think if I have good flow there, it is reasonable to assume the issue is in the block though. I'm not sure it's practical to brake lines open and verify after that.

Having said that, it probably wouldn't hurt to open up one of the flex lines. It't be a shame to replace all the hard lines and find out that the flex lines were the problem, however unlikely that is.

I'll do it in the morning and report back.

By the way, my Raiders stunk onight. We left after the start of the 4th awhen it was 24 to 0.

Don't know much about hydroboost but I have heard that it takes a while to get the air out of the system and you have to watch how the return is plumbed into the reservoir. Hydratec used to have a forum for user issues but I see that it is gone now.

The problem that you are having where you have to pull the brake pedal up to release the brakes doesn't sound good at all. I still guessing here but sometimes the accumulator (little can on the HB) goes bad. The procedure to test the accumulator involves turning the car on, then off and slowly pumping the brake pedal. If you loose assist quickly, the accumulator is bad. Sorry, don't know any more details but maybe someone else does.

Thanks Shark. That's something to look for as well. I did get a rebuild kit when I got the hydroboosts including a new accumulator. I'd have to find instructions as well but judging by the number of parts, it can't be that hard.

I'll have a look around for test procedures. This will certainly be complicated though because of the brake system problems. Never simple :banghead:

EDIT: Found a pretty good web site outlining the workings of the hydroboost unit

http://www.babcox.com/editorial/bf/bf030542.htm

It also outlines the accumulator test procedure that you were describing. Sounds to me like the accumulator is the equivalent of our vacuum reserve to give you one or two power assists when the engine cuts out.

73 Mike said:

It also outlines the accumulator test procedure that you were describing. Sounds to me like the accumulator is the equivalent of our vacuum reserve to give you one or two power assists when the engine cuts out.

Click to expand...

Precisely:beer:

I had a bit of an epiphany last night. I was checking the brake lines to make sure that there were no dents or kinks. I wanted to make sure that I only have to order parts once.

Although I noticed this before, I never thought anything of the fact that the stainless flex hoses that attach to each caliper have mild steel adapter blocks. On closer inspection, at least the two front blocks show noticeable signs of corrosion (couldn't easily check the back two). I applied PB Blaster on one of the fittings and, if I get home early enough, I'll test the flow on either side of the blocks. These are on all four corners so this could easily be the issue.

Regarding the hydroboost unit, I've done a fair bit of reading from a large number of sites that people have been forwarding to me (thanks all :thumbs. Although there are a few possibilities, it is clear that until I resolve the issues with the brakes, I probably won't be able to properly diagnose the hydroboost. The most likely causes though are binding in the pedal linkage, which I've never been happy with, or simply air in the hydraulic lines. I've read a number of references that suggest that air can stick in this system for quite some time. Once basic priming is done, only run time will completely remove all traces of air.

73 Mike said:

I had a bit of an epiphany last night. I was checking the brake lines to make sure that there were no dents or kinks. I wanted to make sure that I only have to order parts once.

Although I noticed this before, I never thought anything of the fact that the stainless flex hoses that attach to each caliper have mild steel adapter blocks. On closer inspection, at least the two front blocks show noticeable signs of corrosion (couldn't easily check the back two). I applied PB Blaster on one of the fittings and, if I get home early enough, I'll test the flow on either side of the blocks. These are on all four corners so this could easily be the issue.

Regarding the hydroboost unit, I've done a fair bit of reading from a large number of sites that people have been forwarding to me (thanks all :thumbs. Although there are a few possibilities, it is clear that until I resolve the issues with the brakes, I probably won't be able to properly diagnose the hydroboost. The most likely causes though are binding in the pedal linkage, which I've never been happy with, or simply air in the hydraulic lines. I've read a number of references that suggest that air can stick in this system for quite some time. Once basic priming is done, only run time will completely remove all traces of air.

Click to expand...

Carefull Mike. ANY contamination could be serious. Flush with brake cleaner thoroughly, followed by brake fluid.:thumbs:

You're right about the contaminants, but it is the flow restriction that I'm trying to resolve. Either a small orifice or, as I suspect, a corroded orifice would acount for this. If it is the case, I'll just replace the lines and then flush copeously.