the proportioning valve regulates the amount of fluid that goes to your front brakes on cars with both disc and drum brakes like yours. The valve is designed as to allow more pressure go to your drum brakes right when you brake so that your drum brakes activate right before your front disc brakes. If it is clogged it could block the brake fluid from going to one or more of your wheels causing the other wheels to experience an increase in pressure.

 

how was your brakes intially with the new rotors and pads.........your "break-in" period?

 

its always worse when new rotors and/or pads go on. The surfaces haven't had time to bond together yet so i'd say the braking during the break in period was like 35% of what it should be normally. It was honestly kinda dangerous, i had to brake WAY early when coming to a stop.

Has anyone ever had a proportioning valve get clogged? I've never heard of this being a problem in any brake system, until a few days ago i'd never even heard of the part. However, it does seem to describe some of my problems. During one of my visits to my mechanic, I drove it around for a while till the brakes got hot, then took it to them. They took a temperature gun to my rotor/brakes through the wheel, and my front left brakes were at like 470 degrees and the front right side was only like 240. My front left brake pads always wear out faster. That much is consistent.

 

I'm not a Honda guy, but I've replaced many brakes and taught people how to replace it as well. I'm actually here because I'm fixing my gf's '93 accord.

I'm just wondering if you notice that your braking gets worse as you drive the car longer? This could be a problem if your calipers are stuck, or even cheaper the brake cable is rusted. See how brake behaves. Do a quick stop right at the beginning, and compare it to hour later.

I had a problem with my Maxima where after driving for some time, the braking becomes dangerous. Turned out that the brake cable was corroded and one of my brakes was constantly rubbing. Now, this causes your brake system to heat up, and form bubble in your brake fluid and you know what.

I'd suggest the following. After you drive the car for a while, touch each wheel. See if one of them is a hotter then others. This will give you a hint as to which wheel may be causing the problem. If you think one of them is hotter, jack the car up, block the other end's set of the tires (brick/tire/what ever), and try to move the wheel without the emergency brake and your gear in neutral. (Make sure you put something on the other 2 tires!!!). Now check to see if you can move your wheel. It should move freely. Now, try the other end and compare. If it's harder to move or stuck, then it's a caliper, or maybe even the brake line. Isolate to see if one wheel is causing a problem. This should help your isolate it to one of the wheels.

Now the other test is overall braking. If everything is consistent across all wheels, you may be looking at air introduced in the master cylinder, or your master cylinder going bad. I'm not an expert at this and I can not comment or suggest ways to isolate that problem.

I drove with crappy brakes for a year and nobody could figure out that it was a brake line until the day it corroded and got stuck completely. Then I saw smoke coming from the back tires and my rims were super hot. I pulled into Midas (I think) and the idiots at the shop forced me to replaced the calipers, even though I insisted them to just replace the brake line. After they replaced the calipers, the guy came back and said "Oh yeah... The brake line's bad. Sorry, just get the cable, and we'll put it in for free.". Ever since then, I never trust my brakes to just anyone working in a garage.

I hope you the best!

 

i have to say that i HIGHLY doubt the problem is air in your brake system. even with air in the system the brakes still should perform very well at least much better than what you are describing. I have a honda crx which currently has a problem where the brakes engage on me on their own and the only way i can drive it is by loosening one of my brake lines either at the master cylinder or at the proportioning valve as to let brake fluid leak of and alleviate some of the pressure in the system. now even when i loosen the the brake line and leave it like that for a week my braking is still great and im sure that it acquires lots of both air and moisture. so for your problem to be caused by a slightly loose master cylinder cap i find very to believe. my bet is on the proportioning valve. you are supposed to buy them new from the dealer but i would just go to the junk yard and pluck one.

 

yea, that is what i was tihnking...possible just stuck calipers?

i know mine get stuck every once in a while because i didnt lube the shit enuf. i already have heat marks on my rotors

tried de-glazing the pads? (sand them on a flat surface) and proper break-oin procedure?
i think it is 30 to roll for like 10 times and super easy breaking after that.

i didnt do it correct the first time and i couldnt stop worth shit because of the glaze on the pads.

 

but dont you think his mechanic would hve figured out that easy solution.....? he deals with rotors and pads and sticking calipers pulsating pedals all day long. what he doesnt deal with all day long is master cylinders...pro valves...boosters ...pedal switches. i dont know how good this mechaic is but a glazed rotor and pads are easy to identify. also if the pads get extremly hot like he says, he would be complaining of a mushy soft pedal, and he isnt. i really wnat to figure this question out for him and have done some research. go to http://auto.howstuffworks.com/disc-brake.htm and at the end of the explanation of brakes there are a couple of links that might help you. good luck and please keep us all informed....im scratching my head.

 

In your original post you said every component had been replaced but the booster.

Replace the booster. Might as well.
A faulty booster could sure cause this problem.
As far as your mechanic saying nothing is wrong with it.....well.....nothing else he replaced has fixed your problem.

 

booster or proportioning valve...choose one...if that doesnt work...choose the other....

 

I'm gonna go with the proportioning valve. All the brake booster tests showed it was good.

Today was really weird. Like two times tonight when I stopped it stopped like a real car would. Then it would just mysteriously go back to suck mode. I don't understand at all.

I'm gonna get the proportioning valve done and then see what happens. Thx for the help guys, this one's been stumping me for a long time.