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73-87 Chevy _ GMC Trucks => Brakes, Frame, Steering & Suspension => Brakes and Braking Systems => Topic started by: 1976blazer on September 24, 2018, 11:01:02 AM
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Okay new to this site and doing this but I needed some help with a brake problem I have it's a 1976 Chevy 2 wheel drive Blazer I have replaced the master cylinder the rubber lines to the calipers ,calipers and the front pads also have replaced the proportioning valve, the problem is the pedal still goes to the floor but will stop the vehicle just slowly, back brakes work front brakes work just not like they should I think there is still air in the system but I've bled it multiple times and it seems to come out with no air in the fluid. I have bled all four corners using the two-person pump the brakes a couple of times and then crack open the bleeder valve method what else could be the problem or how do I get the air out if that's really what's going on. I replace the master cylinder twice thinking the first one was bad , bench bled then both first, only to have the same problem, pedal has brakes but goes to the floor slowly like a bad master cylinder. Any help or suggestions would be great I've worked on my cars since I was 16 years old I'm now 45 I've done this lots of times and never had this problem. Thanks :o
Ok make sure you read all the way to the second page bottom to get the solution it will surprise you and the back brakes were never adjusted. Unlike some, it was not the problem ever but good job on trying to get me to do unnecessary work lol. Neck braking stopping power now, YA BABY!!! Thanks again everyone for all the help.
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Welcome.
Have you checked the booster for vacuum leaks, and or check valve?
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Vacuum booster seems to be working just fine has vacuum when the engines running and after shut off and the pedal firms up when you take all the vacuum out of the booster and the pedal goes about three-quarters or more way to the floor without the vacuum booster
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http://forum.73-87chevytrucks.com/smforum/index.php?topic=33548.0
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Have you adjusted the back brakes to take out any excess clearance?
The oil is going somewhere, could be that.
If there is still air, you would pump the brakes and the pedal would rise. Is it doing that?
And please, for us older guys, please use periods.
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Hi 76Blazer:
The 76 service manual says that the combo valve must be held open while bleeding...this is the little button on the end of the combo valve. You can either make a tool to hold it open or rig up some clamping tools to hold it open while you are bleeding.
Regards,
Henry
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You can thank the phone I'm using for not adding punctuation I'll try to do a better job. I have not fully adjusted the back brakes, although they do lock up when I press the pedal and I'm traveling on a wet surface.
I have never had to have the back brakes fully adjusted to get the front brakes to work on a half ton, seems like something the proportioning valve should be taken care of.
Thanks for the help.
To the second part of your question the pedal never pumps up it always go to the floor. That is what's baffling me and I'm not losing fluid anywhere the fluid level stays at the same height once the brake is released.
I've been trying to fix this problem going on a year now and I can't seem to find it. It's a project truck so it's when I have time to work on it.
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Ok, i did check the button on the valve before and after the bleeding and it did not moved but I will try to hold it while bleeding and see if I get any change in results. I assume you mean to hold the button in not replace the switch with something else while bleeding the brakes like the instructions say for the aftermarket proportion valve. Thanks
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Okay here's an update on the Blazer. I'm not sure about the proportioning valve but I did take the Rubber off the button end and have somebody step on the brakes the little Rod pokes out when you step on the brakes. The brakes still go to the floor but not quite as bad as when the vacuum booster has vacuum but they still go most of the way to the floor I would guess 90 to 95%. I was assuming that you wanted to keep the rod IN while pumping the brakes so I cut a nail and wedged it between the frame and that Rod so it could not come out. Now on second examination I'm wondering if I should have had somebody step on the brakes put a vise grip on that rod and keep it out while pumping the brakes to bleed them. I bled the whole system with no change in the brakes. The pedal still goes to the floor. I will try it the other way Tuesday. Thanks everyone for the help.
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Did you check the rear brakes? Are the drums true and shoes properly installed and adjusted?
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Hi 76Blazer:
Combo valve: on the factory combo valve you should hold the button in while bleeding. If you have an aftermarket combo valve, what do the instructions with this valve tell you to do while bleeding?
On the factory combo valve, pushing the button in overrides the metering function of the valve which insures that full flow of brake fluid goes to the front and rear brakes simultaneously. Not pressing the button allows the metering function to work which closes off the front brakes from the master cylinder until a certain pressure is arrived at. So this could cause a problem while trying to bleed.
Regards,
Henry
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Thanks Henry
It is a factory proportioning valve. And I did hold it in using a nail wedged against the frame into that hole to hold the rod from coming back out when the person pumping the brakes pushed on the pedal. After all that and bleeding everything I did get a little bit more air out of the rear, but still the brakes go to the floor kind of like you're pushing fluid not just falling completely to the floor right away but there is no pressure building up in the system no matter how many times you pump it. I get plenty of fluid out of the bleeder valves at the wheel. The person pumping the pedal told me when it got to the floor but it didn't always go to the floor or barely even moved, though I was getting fluid out of the bleeder valve in the front.
makes me think that rubber line that goes to the back brakes may be expanding inside somehow and absorbing some of the pressure and throwing off the system but does not explain why the pedal still goes to the floor and can't build any pressure. Thanks again for all the helpful advice ,the more things I try and the more things I do I will let you guys know.
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Did you check the rear brakes? if not you can bleed it for the rest of your life. Pedal travel is impacted by the brake shoe adjustment. Seems like you continue to ignore this advice which is step 1!
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Did you check the rear brakes? if not you can bleed it for the rest of your life. Pedal travel is impacted by the brake shoe adjustment. Seems like you continue to ignore this advice which is step 1!
OP, it will behoove you to heed this man's advice ^^^^ and diagnose the issue in the proper order! You won't find anyone more knowledgeable on these trucks.
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thanks but the back brakes work just fine that's mostly what stops the truck if they're that far out of adjustment would that fix the front brakes, so the breaks wood we applied pressure and then I would crack up in the bleeder and sometimes the pedal go to the floor other times cuddled wouldn't move yet I would still get pressure out of the caliper what would be the problem with that? that's something new?
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Sorry about that last post. I didn't proof read it before I posted it but the brakes still don't work even after keeping that Rod that sticks out of the portion valve in and bleeding and I think I must have air bubbles in more than one spot because when I bled it sometimes the pedal would go to the floor sometimes it wouldn't move at all yet I would always get fluid out of the bleeder valves. I will try to work on it again this weekend.
Thanks
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Hi 76Blazer:
Do you have some rubber brake lines at your rear drum brakes?...If so, inspect them if they are old...if they are starting to crack outside, they may be delaminating internally. I have heard about them delaminating internally which can cause the brake fluid a place to go which causes brake sponginess and inability to bleed.
Regards,
Henry
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Thanks Henry,
That is how this whole process started one had collapsed in the front driver side stopping the fluid from going to the caliper I replaced both front rubber lines and have not been able to get pressure in the brake system ever since I'm going to check the rear rubber line from the frame to the rear end this weekend hopefully I can find the problem.
And just in case anybody is wondering I have tightened all the fittings to make sure that there isn't any leaks. I see no fluid dripping or seeping out of anything.Everything
is perfectly dry there's no puddles under the truck and nothing leaking from any lines or connections.
Thanks for all the good suggestions I will also double check the adjustments on the back brakes this weekend. It seems that a lot of people think that those need to be adjusted perfectly for you to be able to bleed the front and back systems I'm not sure I'll try it
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If you think there is residual air trapped in the system, try a gravity bleed (http://forum.73-87chevytrucks.com/smforum/index.php?topic=36528.msg307687#msg307687). Are the front wheel bearings properly adjusted?
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Thanks :D
I'm not sure if the front wheel bearings being out of adjustment would really make the pedal go all the way to the floor. I can't foresee them being so far out of adjustment that I could drive it and not notice it. I did have it jacked up and the tires on the discs, seem to not have any wobble to them so there should not be enough air in there to make the pedal go to the floor but that fluid has to go somewhere from the master cylinder and then it comes back so the only thing in a hydraulic system that can compress or expand is the rubber lines and or air but thank you :-) good thought.
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You might have to bite the bullet and try a new master cylinder.
If the pedal goes to the floor but there is no leakage at any of the wheels, then the seal or lines at the master cylinder are not holding pressure. Its a closed system and there is nowhere else for the pressure to go.
Wipe down the body of the master cylinder very carefully and make sure there is absolutely no evidence of a leak at the lines. Any fitting with even the slightest drip or seepage means that its losing pressure.
If that seal inside the master cylinder is bad, it allows pressure to bypass it. I've seen it happen on used master cylinders when bleeding brakes because someone pushes the pedal and cylinder seal beyond the built-up ridge in the bore and it mangles the seal. It should not happen on a new master cylinder.
A weak rubber line will also allow expansion, but it sounds like you have already replaced them.
Bruce
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Thanks
That was the first thing I did.The first one I purchased was a rebuilt one so I thought it may have been bad out of the box. I purchased a new not rebuilt one the second time and nothing changed. I also have checked for small leaks and have not found any. I will check the back rubber line from the frame to the rearend this wkend. I have replaced the front already.In a closed system there is only 2 placed that could let the pressure change, air will compress or a rubber line can expand, or a leak or blown seal somewere.
Thanks for the great idea.
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Did you bench bleed it first?
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Yes I did bench bleed it thanks.
Here's the way I finally got it fixed. Started with the master cylinder, bench bled and it held pressure, then put it on the truck and the peddle went to the floor still.
Then put clamps on all rubber lines and the brakes held pressure right at the top of peddle travel. So the air or leak must be trapped at one of the wheels.
Next I released the rubber line clamp to the rearend and checked the peddle and it was right on top.
So the air must be at the front somewhere.
Next step is to release the next farthest point, the front passenger side rubber line clamp. Checked the brakes again and they were right on top.
Next I released the drivers side rubber line. Then the brakes went to the floor again.
Next I clamped the front passenger line again and checked the peddle again, it went to the floor, must be a problem with the drivers side caliper, but it is brand new not rebuilt.
It trurns out that the pin that holds the caliper in on the bottom had been changed out for a longer one with more threads and it was keeping it from centering it self on the disc so no fluid could get in the piston back. It would go in from the brake line hit the bottomed out piston and send it right out the bleeder when I cracked it open to bleed.
I ground the longer threads off and put it back in and now the caliper centers it self just fine. I will replace it with the right one befor I drive it for thoughts thinking it's unsafe.
Once I ground the threads and got it to center it self, then bled them they were right on top. I never ajusted the back brakes, and the vacuum booster works great, just so everyone knows. I thought I was never going to find the problem!
Thank you everyone for all the help and knowledge it was very enlightening. Hope i have been posting this right, I'm not sure if it's in the right place or not and i was not sure how to do this to begin with.
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Hi 76blazer:
Good info...another story about the great interchangeability of GM parts that can cause problems!
Regards,
Henry
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Wow
Glad you persisted and found the problem
Sometimes it’s a bizarre problem
I’ve also run into a couple times where you had to remove the caliper and put some wood in between the pads so you could rotate the caliper and tip it over a little to get the bleeder screw at the very top
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Ya that's what happens when you buy a used car, you never know what the last guy did just to get by.
I hope nobody ever has to chase down that problem! It was starting to keep me up at night racking my brain. I do have to that the guys working on that general Lee car on youtube for the idea to clap the rubber lines. Without that idea i would have not found it so easy.