94 S10 Blazer no back brakes

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  #1  
Old 12-20-08, 03:36 PM
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94 S10 Blazer no back brakes

Alright, well I got a 94 S10 blazer with a 4.3L. It kept losing brakes and it seemed like the master cylinder was to blame so we replaced that with a new one and it went fine for a few days until one day the brakes went out so we parked it and examined the brake lines and found two leaks.

So we repaired those and bled the front brakes just fine but couldn't get the back brakes to bleed so examined the master cylinder and fluid wasn't coming out the front part for the back brakes so we replaced that one with another. Then still got no where. The brake pedal was hard as could be. So we checked the combination valve and that was seized.

So we went and got another one and put that one and that brakes worked fine for a few minutes and then the pedal got hard again and the brakes stopped working. Does anyone have any idea?
 
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  #2  
Old 12-20-08, 03:50 PM
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sounds like you might have some debris in your lines causing problems with the combination valve, try flushing all lines and cleaning the combo valve then starting over, with some one pressing on the pedal can you open the lines at the master and cause the pedal to fall?
if so then you know the master is probably not at fault. I would start there and work out to each connection from there. also be aware some times old flex lines will start to degrade internally and small pieces of rubber will break off and plug orifices downstream from the flex lines. if any of your flex lines show any sign of wear replace them all. also make sure no one has added anything to the system but clean dot 3 fluid, occasionaly mistakes do happen and none dot3 fluids can cause major problems with seals and rubber hoses.

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  #3  
Old 12-20-08, 04:04 PM
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The only rubber there is is at each wheel. otherwise it's all hard lines. Could it be the brake booster?
 
  #4  
Old 12-20-08, 04:28 PM
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There should be a rubber hose at the rear axle going from the body to the axle, bolted with a banjo bolt to a block that sends fluid to both rear wheel cylinders. Also be aware that the rubber hoses can collapse on the inside, and not look any different on the outside, first thing I would do is replace the rubber hose at the rear axle, then try bleeding again.
 
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Old 12-20-08, 04:42 PM
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would that make the pedal hard though?
 
  #6  
Old 12-20-08, 05:37 PM
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when you say that the brake pedal is hard is it like you are trying to push it with the engine off? if it is then it might be the vacuum booster or the lines going to it. check the vacuum it should be around 15-17 in of vacuum. if you have the proper amount of vacuum then it might be the booster.
good luck
 
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Old 12-21-08, 03:43 PM
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It is possible for the hose to close up on the inside, and hold full brake system pressure, while not allowing any fluid to pass to the rear brakes. I would think if the booster was bad, it would affect the front brakes as well.
 
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Old 12-21-08, 07:55 PM
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yes booster will affect front and rear equally.

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  #9  
Old 12-25-08, 11:18 AM
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Alright. Time for an update. Still no brakes. We changed the master cylinder twice, changed the compression valve and changed the brake booster with a booster off of an 87 S10 pickup with a 2.5 in it. None of which help. Maybe its the ABS box? The pedal is still hard and we tried bleeding it but it didn't help much. Maybe there's a way to bypass that if its the problem?
 
  #10  
Old 12-25-08, 12:00 PM
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It certainly could be a valve hanging up in the ABS control valve assy. Your original post did not mention the truck having ABS, also is it just the rear brakes or all the brakes? The more correct info you post the better answers we can give you, there are some very smart guys that read these boards, they can help if you point them in the right direction.
 
  #11  
Old 12-25-08, 02:16 PM
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Well, it has ABS and it is all brakes that are not working.
 
  #12  
Old 12-25-08, 06:39 PM
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how much vacuum do you have at the hose from the intake manifold?
 
  #13  
Old 12-25-08, 07:09 PM
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Not sure if you're looking for an exact amount or something but it seems to be a good amount of vaccuum
 
  #14  
Old 12-26-08, 04:18 AM
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With the engine off, starting at the master cylinder, crack the lines loose at each fitting, and have a helper push the brake pedal. DO NOT pump the pedal just push and hold, you should see fluid come out and the pedal should go to the floor, tighten the fittings before you release the pedal to prevent air entrance. When you get to the point where no fluid comes out and the pedal stays hard you will have isolated the problem component. I am betting on it being the ABS control valve, not a big stretch since you have already checked or replaced everything else. Please do not try to bypass the valve assy. if it turns out to be the trouble brakes are not the place to try to save money.
 
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Old 12-26-08, 11:42 AM
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Not sure if this helps but when trying to pump, the fluid in the rear reservoir in the master cylinder becomes milky colored.
 
  #16  
Old 12-26-08, 12:03 PM
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sounds to me like your rear brake calipers are froze up only working when you release preasure off then when biult back up they quit again
 
  #17  
Old 12-27-08, 06:22 PM
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alright, today we took the back brake lines off and blew air through em with the air compressor and put it back together and they brakes started working but the pedal is extremely tight and you can barely stop the vehicle once moving. Tried bleeding it and everything. Perhaps the ABS hydraulic unit is part of the problem?
 
  #18  
Old 12-28-08, 05:48 PM
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Did you bench-bleed the master cylinder before installing? Do you have good engine vacuum to the master cylinder? It shouldn't be hard to depress especially when bleeding. Something is stuck closed somewhere. When you bleed a wheel, does the pedal drop and fluid come out of the hose? I'm still not clear on the underlined portion:
"but couldn't get the back brakes to bleed so examined the master cylinder and fluid wasn't coming out the front part for the back brakes so we replaced that one with another. Then still got no where. The brake pedal was hard as could be. So we checked the combination valve and that was seized."
 
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