Author Topic: Blazer brakes go to floor  (Read 2098 times)

Offline 1976blazer

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Re: Blazer brakes go to floor
« Reply #15 on: September 26, 2018, 10:42:51 AM »
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

Offline Henry

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Re: Blazer brakes go to floor
« Reply #16 on: September 26, 2018, 12:16:53 PM »
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 

Offline 1976blazer

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Re: Blazer brakes go to floor
« Reply #17 on: September 26, 2018, 01:10:46 PM »
  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

Offline bd

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Re: Blazer brakes go to floor
« Reply #18 on: September 26, 2018, 08:12:15 PM »
If you think there is residual air trapped in the system, try a gravity bleed.  Are the front wheel bearings properly adjusted?
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)

Offline 1976blazer

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Re: Blazer brakes go to floor
« Reply #19 on: September 26, 2018, 08:41:01 PM »
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.

Offline 75gmck25

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Re: Blazer brakes go to floor
« Reply #20 on: September 27, 2018, 07:32:03 AM »
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
« Last Edit: September 27, 2018, 07:36:40 AM by 75gmck25 »

Offline 1976blazer

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Re: Blazer brakes go to floor
« Reply #21 on: September 27, 2018, 09:06:01 AM »
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.

Offline VileZambonie

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Re: Blazer brakes go to floor
« Reply #22 on: September 27, 2018, 07:28:00 PM »
Did you bench bleed it first?
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Offline 1976blazer

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Re: Blazer brakes go to floor
« Reply #23 on: September 29, 2018, 10:40:28 PM »
 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.

Offline Henry

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Re: Blazer brakes go to floor
« Reply #24 on: September 30, 2018, 12:50:28 PM »
Hi 76blazer:
Good info...another story about the great interchangeability of GM parts that can cause problems!
Regards,
Henry

Offline roundhouse

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Re: Blazer brakes go to floor
« Reply #25 on: September 30, 2018, 08:21:55 PM »
Wow

Glad you persisted and found the problem

Sometimes its a bizarre problem

Ive 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

Offline 1976blazer

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Re: Blazer brakes go to floor
« Reply #26 on: September 30, 2018, 09:52:09 PM »
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.