Brake goes to floor when truck is started on a 1998 Jimmy with ABS

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  #1  
Old 09-21-11, 04:27 PM
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Brake goes to floor when truck is started on a 1998 Jimmy with ABS

Hi all.
Hopefully someone can help me. When I press the brake pedal, it works good when truck is off. When I start the truck, it almost goes to the floor. Maybe I need to spend more time bleeding the brakes. But I'm sure I did it right.

Here is what I've tried so far:
1. Replaced bad rotor, caliper, and pads.
2. Replaced master cylinder.
3. Bled the brakes <with truck running and a helper>.

This is a 1998 GMC Jimmy 4WD with ABS. 4.3 ltr V6 Engine SLT model.
Thnx in advance
Tim
 
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  #2  
Old 09-21-11, 04:51 PM
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you didn't bleed the master, did you?
 
  #4  
Old 09-21-11, 04:55 PM
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Sorry for my ignorance..what do you mean by the master? The master cylinder??
No..just the four wheels. Don't see a spot to do it on the master cylinder.
 
  #5  
Old 09-21-11, 04:57 PM
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yes, of course. I should have been more explicit, my bad.
 
  #6  
Old 09-21-11, 07:21 PM
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Thats' ok. Thanx for the quick responses. Maybe I'll just try bleeding them longer and see what happens. Don't see any leaks anywhere at all, although the lines are pretty rusty looking.
 
  #7  
Old 09-22-11, 04:34 AM
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Bleeding the master (bench bleeding):

Master Cylinder Bleeding - How To Bench Bleed Your Master Cylinder - Remove Air Bubbles

A lot of masters will come with the little plastic fittings and hoses included to to this.
 
  #8  
Old 09-22-11, 12:07 PM
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you can bleed master on car using same kit. thereafter, you have to bleed brakes again.
 
  #9  
Old 09-22-11, 03:52 PM
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Thanx again guys. Will try this and see what happens. Also, someone mentioned to me it could be the power assist hose or something.Check to make sure there is a vacuum in it when you apply the brakes or the hose/valve could be no good. Hope you know what I"m talking about here
 
  #10  
Old 10-08-11, 09:03 PM
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Well, still trying to get these brakes fixed. Bleeded the brakes about 10 times now and still nothing. The brake peddle is a little bit harder to push now when the truck is running, but not much better. I checked and there is a vacuum on the hose that leads to the master cylinder housing. Any more thoughts before I have to give up on this project
 
  #11  
Old 10-30-11, 10:07 PM
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you may have to use a scanner to bleed the ABS hydraulic control unit
 
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