Thread: Front brakes locking.

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Well I took my car or should I say I tried to take my car for it's first long run today. I got about 2 miles and came back for an unrelated problem and fixed that but on the way back on the way back it felt like the car was slowing down on its own awful quick. So after the car sat for about a 45 minutes I tried to leave again but only got about a block and not over 25 mph and had to come back to burning brake smell and smoke coming from the front brakes. I let it sit for a couple hours and picked up a new residual valve for the front. When I started to work on it the right front was still a tight and I backed off the bleeder valve to see if it would free it up but it didn't.So I took the caliper off and compressed it then I changed the valve but that didn't help. I backed off the pedal adjustment but then the pedal went to the floor as soon as I pushed it with the car running. I have disk all the way around. The strange thing is, or at least it seams strange to me, when I start the car the vacuum will suck the pedal down about an inch on it's own. And when it isn't running I can lightly press on the pedal and it sounds like air is pumping then the pedal is stiffer.
I have a non adjustable proportioning valve and 2 pound pressure valves on front and back. the back brakes are fine. Not sure if the front calipers got too hot and ruined but the car has been sitting about 45 minutes now and the front wheels are still hard to turn.
Any ideas?

You say you have a non-adjustable proportioning valve. I would put in an adjustable one. That way you can dial in the proper feel for the brakes.

Originally Posted by Mr Smith

The strange thing is, or at least it seams strange to me, when I start the car the vacuum will suck the pedal down about an inch on it's own. And when it isn't running I can lightly press on the pedal and it sounds like air is pumping then the pedal is stiffer.
Any ideas?

This statement "bugs" me! I think the weight of the pedal mechanism is closing the valve in the booster and causing the brakes to drag / be on.

A lot of people don't realize or don't know how a booster works but there is a equalization valve inside and I'm thinking your pedal assembly is closing that valve and giving you a headache.

I would add a spring temporarily to hold the pedal to the full off position and try again. I hope I'm wrong but it shouldn't hurt to try.

try it with the vacuum line unhooked from the booster

I gather this is a new system you are debugging? You didn't use .5 synthetic fluid on a non-compatable system did you? Some 'o' rings swell up with the synthetics.
Another tought is when the vacuum hits the brake pedal and pulls it down just make sure that the master cyl piston isn't being affected - i don't think so from your description but something to check. What'll happen is if the master cyl piston cannot fully return to ist' seat then it'll act like a check valve and the fluid won't return to the bowl - when that happens all the wheels will remain tight, not just one.
A stock proportioning valve is more complex than you think, there is an internal floating balance bar inside it. If one side or the other has no fluid when pedal is depressed that flaoting bar will go to its' limits of travel and cannot return and needs to be reset. I don't recall how to reset it, sorry, this subject came up one time and i didn't catch the whole thing as i am slow and was absorbing that there was more to a proportioning valve than i thought.

Thanks guys you gave me a lot to try. Yes this is a new system. That is everything accept the back brakes which ironically are fine. No I did not use dot 5 fluid. I just checked and my right front is still dragging,I guess I will have to tear that apart but not sure I will be able to fix it from the heat damage. Now that you mention it ojh I have also heard that about the proportioning valves. It looks like I will be replacing it with an adjustable one. I think I will also find a way to put a return spring in. Although I don't know how with the little room I have to work with.

Originally Posted by Mr Smith

I think I will also find a way to put a return spring in. Although I don't know how with the little room I have to work with.

It doesn't take much room, depending on the type and location of your master cylinder, it can be as simple as this example. Look at the 'Universal Brake & Clutch Pedal Return Spring Kit' shown near the bottom of this page.

Mike

Originally Posted by Mike52

It doesn't take much room, depending on the type and location of your master cylinder, it can be as simple as this example. Look at the 'Universal Brake & Clutch Pedal Return Spring Kit' shown near the bottom of this page.

Mike

Those are some cool return springs!! Good link, Mike!

Thanks Mike my mind was wrapped around thinking I had to somehow dangle some sort of spring from my firewall to my pedal. Any idea if those will work with boosted brakes?

Louey I agree that I have a caliper problem but I also need to fix what caused them to hang up in the first place. Since both fronts are doing it. the right is just got hotter then the left so the left releases most of the way after who knows how long.You are also right that I should hold off on the valve until everything else is tried.
I am going to take a few days off of this since I have been working every day on it for over a year this kind of knocked the wind out of me.
Thanks again

I just talked to a brake and clutch place near by to see if they would have a return spring and he didn't but he told me that he has heard of guys having problems with adding residual valves with these none adjustable proportioning valves because those valves have built in residual valves. Anyone heard of that?
Oh I also found these springs http://www.brucesspeed.com/kingmaste...springkit.aspx and speedway has them as well on sale for 14.99. The only thing is I would have to remove the rubber dust cover to install it.

lots of check valves, metering valves and residual valves in lotsa places in modern brake systems---they can be check/residual valves in the master cylinder, in the combonation metering valve you will find portioning , check and meter valve pieces and of course if your master cylinder isn't returning all the way your brakes will drag and most times probably the fronts as more pressure is sent to the front so if the master doesn't return you will have a lot of drag---

In your case----just what parts do you have on the car, and how are they plumbed????

Also did you bench bleed the master???

Are your calipers new???? If they have been setting a long time the pistons can get stuck.. I'd rebuild both fronts and see what happens. The other things are worth checking but if the calipers aren't good all the rest is a waste of time and money.

As far as parts go I have the brass non adjustable proportioning valve that according to speedway is used in a lot of 70's GM cars. I didn't get mine from them though. I don't know if mine is a 7 or 8 inch booster with a dual master cylinder. from the master cylinder I have the proportioning valve about 6" away then the residual valves are about 6" away from the proportioning valve. Yes I bench bled my master cylinder. I must say that even though I bench bled it and then vacuum bleed my lines a few times my pedal has always had a lot of travel. I just read an ad for a master cylinder proportioning valve set that said with the same type of proportioning valve residual valves are not needed for disc brakes.Not sure if theirs was for under the floor mount though. I think the first thing I will do is rebuild the calipers which are new but have been sitting in my dry garage for a couple of years. and if that doesn't work I will remove the residual valve at least in the front and go from there. I also read somewhere today that boosted master cylinders remove the need for pedal return springs.

Well I was just out working on my brakes again. I found out the brakes are not dragging because of fluid pressure but they are actually binding up. Not sure how it happens but after I apply the brakes there is a lot of drag that won't release when removing fluid pressure but if I pry up from the hub against the bottom of the caliper the brakes free up. Anyone ever had that problem before?

Check to see if your slider is sticking, (where the through bolt slides through the bushing0,Brian