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i have a 1977 buick lesabre with brake issues. Ive replaced the brake booster, master cylinder, bench bled it as well as while on the car. bled the complete system at least 3 times. I have firm brakes when the car is off, but soon as i start the car i have no front brakes. Could the hoses from the front calipers to the main line be bad/clogged? all help is welcomed, as i would like to be able to sort this out and drive the car again. I have changed both front brake flex lines with no change. I have looked up that my car came with 2 different sized brake boosters, and feel the parts store sold me the smaller of the 2. I checked at the parts tore the other day if the booster and LF caliper were under warranty, and they are so will be swapping these out. Is there anything that i could be missing/overlooking?
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I’m having a little trouble understanding what you mean. How do you know you have no front brakes? If the pedal goes to the floor you have no brakes period.
I owned a couple of GM cars from this time period and I remember that when you got air in the system between the master and the proportioning valve you had trouble. As I recall there was a little valve covered by a rubber boot on the proportioning valve that had to be depressed when bleeding. There was a special tool for this. I had the tool and still had trouble.
If you have the calipers installed on the wrong sides with the bleeders at the bottom the car will be an antique before you ever get the air out.
Ok to those that asked about if the caliper bleeder screws are on the bottom? no there in the proper location on the top and know there on the proper side. Yes i know i have brakes but no fronts, because when i move it in the driveway the fronts don’t stop but the rear locks up. So i have plenty of rear braking. I’ve replaced the brake booster check valve and it helped some, but still don’t have front braking. when i get the bigger brake booster and re bleed the LF caliper i will know more on what i have. prior to having these issues and when i had brakes i could tap the fronts and it would drop the front and i could stop almost on a dime so to speak. Also not sure if i mentioned this but after bleeding the front and turing the car on and checking the pedal travel and go to see if i can move the rotor, it wont move until i crack the bleeder screw and bleed the brakes. So seeing that i may have manual brakes, but with the booster being so small it may not be big enough to release the pads.
Your thinking is wrong in your last sentence. The pads are released by you taking you foot off of the pedal. There really is no mechanism in the master, booster or caliper that releases the pads. Only the lack of hydraulic pressure. That and the square seal may pull the piston back a little.
So you release the brake pedal and as it comes up the port in the master is uncovered and fluid under pressure is vented to the master’s reservoir. That’s all that happens. If you still have pressure there that is not happening meaning something is wrong.
If only one caliper I would suspicion a brake hose. If both calipers I would suspicion the master. Either the port is plugged or the push rod is out of adjustment or wrong.
right, i saw in ETCG video about the calipers and hoses so i was like ill check the flex hoses, they were like 4-5 bucks a piece so i replaced those and bled the fronts with my mightyvac bleeder and i was able to get some fluid through it and then started to go clear, meaning the good fluid was coming through. stopped and started the car and tried them, but went to the floor. so i did the bleeding and trying for like and hour and felt like i was making progress, but not a firm pedal where used to when you apply the brakes.
[quote=”barneyb” post=104092]
I owned a couple of GM cars from this time period and I remember that when you got air in the system between the master and the proportioning valve you had trouble. As I recall there was a little valve covered by a rubber boot on the proportioning valve that had to be depressed when bleeding. There was a special tool for this. I had the tool and still had trouble.[/quote]+2 on the proportioning valve.
I have seen a few steel lines clogged by rust, but IIRC that was a Ford issue.[quote=”BigDaddyChris81″ post=104166]Ok to those that asked about if the caliper bleeder screws are on the bottom? no there in the proper location on the top and know there on the proper side. Yes i know i have brakes but no fronts, because when i move it in the driveway the fronts don’t stop but the rear locks up. So i have plenty of rear braking. I’ve replaced the brake booster check valve and it helped some, but still don’t have front braking. when i get the bigger brake booster and re bleed the LF caliper i will know more on what i have. prior to having these issues and when i had brakes i could tap the fronts and it would drop the front and i could stop almost on a dime so to speak. Also not sure if i mentioned this but after bleeding the front and turing the car on and checking the pedal travel and go to see if i can move the rotor, it wont move until i crack the bleeder screw and bleed the brakes. So seeing that i may have manual brakes, but with the booster being so small it may not be big enough to release the pads.[/quote]
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This is one of the most confusing posts I have read in a while.First you say you have rear brakes but no front brakes.
Then you tell us – as above – that in fact when the brakes have been applied the pads locked onto the front rotors (either 1 or both). To do that the brakes worked at least on one application.
You then mentioned that to have the calipers release the pads from the rotors you had to open the bleed screw on the caliper. When you did the pads released.
What this tells me is :
1. The calipers are fine as they released and operated as normal when you opened the bleed screw.
2. There is a blockage in the line between the master cylinder and the brake caliper (which is not in a collapsed flexible brake hose as you replaced both). There is a blockage up the line from the flex hose as the fluid is not returning to the master cylinder when you release the brakes. Thus to release pressure from the pads to enable the brake disc to rotate you had to undo the brake bleeder.
I don’t know what the blockage in the line is to one or both front brakes. Is it debris, an air lock ?
If you had good brakes previously, I suspect that blockage has happened when the master cylinder was replaced and whatever brake bleeding system you are using I suspect you are not purging all the air out either.since i’m not bleeding the brakes right and my one man brake bleeder vacuum isn’t working, even though money is tight and didn’t want to take it to a mechanic, i will and figure out the rest afterwards. i have a used prop valve, have yet to install it as uncertain of its condition. I’m not trying to be rude or sound like an ass, if it came off that way sorry in advance. Just at my wits end of what is causing this on my car.
My experience is that when a proportioning valve from this era of GM car goes bad the rear brakes start locking on moderately hard stops. When I tried to fix mine I first tried a used valve and then a new one. GM no longer made the correct valve so they sent a substitute. I ended up putting the original back on and living with it.
Why I mentioned the proportioning valve is because if air gets into the line above the proportioning valve it is hard to bleed out. You probably need a pressure bleeder.
GM’s of that vintage required a special tool to hold the proportioning valve in place when you bled the brakes. Failure to use this tool means that you won’t be able to bleed the brakes properly and set the proportioning valve to it’s correct position.
http://www.jbtoolsales.com/otc-7853-abs-brake-proportioning-valve-depressor/#oid=1002_1
Good luck and keep us posted.
I have the brake issue fixed, turns out the remaned brake M/C was bad and needed a new one. shop replaced it/bled the brakes for $90, and did a front end alignment since i have new tires for my buick rally rims for $60. i’m glad im able to drive it again. Once i have the cylinder head replaced( I will be doing that myself) If anyone has any tips or advice when i do that is welcomed. I have almost all the parts for that. Thanks for all that chimed in on there help and advice, i will be posting again in here when i have a problem.
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