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Username Post: brake Problem        (Topic#346855)
Troylure 
Silver Supporting Member
Posts: 12
Troylure
Age: 26
Loc: Ashland
Reg: 03-27-17
08-27-17 08:21 PM - Post#2705815    

So, Im having a problem with my brake system. I don't have any pressure in my brakes when my truck is started. it will build up pressure and hold it when the truck is off, but as soon as i start the truck up the petal gets soft until the last 2 inches of travel. i have changed the brake pads, soft lines to the calipers, and power booster and master cylinder. they were all bled properly after installation.



 
Low priced Genuine GM Auto Parts
stumppuller 
"7th Year" Gold Supporting Member
Posts: 794
stumppuller
Loc: Canada
Reg: 11-01-04
08-29-17 03:57 PM - Post#2706063    
    In response to Troylure

Check to make sure the rear drums are properly adjusted.

If the are, get the truck on jack stands. With the engine running, transmission in neutral, have someone press and hold the brake pedal with only moderate force. See if you can rotate any tires by hand. Then put the truck in drive and see if the rear brakes will keep the rear tires from rotating. Make sure the brake pedal does not slowly sink to the floor.

-91 Sierra C2500, now K2500
-81 Chev K20


 
Troylure 
Silver Supporting Member
Posts: 12
Troylure
Age: 26
Loc: Ashland
Reg: 03-27-17
08-31-17 05:26 PM - Post#2706338    
    In response to stumppuller

thnxs for the reply, but does this matter with the E-brake? because i could set my e-brake and they will hold my truck, even when im in gear and try to go. but i will try your advice.



 
Troylure 
Silver Supporting Member
Posts: 12
Troylure
Age: 26
Loc: Ashland
Reg: 03-27-17
08-31-17 06:09 PM - Post#2706347    
    In response to stumppuller

okay i did the test with the truck in the air, and with the pedal pressed, i could rotate the rear tires with some effort, but could not rotate the front tires. so is that air in the lines? or do i need new shoes. my E-brake will hold my truck pretty good. i could park on a pretty good slope and they will hold. the only problem that its giving me is a sinking brake petal upon startup of the engine.



 
stumppuller 
"7th Year" Gold Supporting Member
Posts: 794
stumppuller
Loc: Canada
Reg: 11-01-04
08-31-17 07:36 PM - Post#2706353    
    In response to Troylure

First I would make sure those rear brakes are properly adjusted. The E-Brake holding is not really a guarantee that the rear adjustment is good.

It could be some air in the system. Did you bench bleed the master cylinder before replacing it?

It may also be a bad "new" master cylinder. The failure rate is over 50% right out of the box. I can personally vouch for this.

What you can try is to lift the rear again, with the engine running and in neutral, cut a piece of 2x4 to wedge between the brake pedal and seat. This will hold the brake pedal in one place, if the rears get easier to turn by hand over a few minutes then the pressure is bleeding off and it may likely be the master cylinder.

It could also be a leak, or issues with the ABS unit. In this scenario, pull the rear line off the master and plug the port. The pedal should be much stiffer and not move nearly as much if the master is good.

Did you have this brake issues before replacing all the parts in your original post, or did this start after the full brake job?

-91 Sierra C2500, now K2500
-81 Chev K20


 
rockfangd 
"4th Year" Gold Supporting Member
Posts: 2215

Age: 31
Loc: Utica ny
Reg: 04-13-10
09-01-17 06:32 PM - Post#2706452    
    In response to stumppuller

Would not be surprised if it is a bad master cylinder.

How far does the parking brake pedal have to be pushed down to hold?
Should be no more than half

Old School GM fan FOREVER


 
Troylure 
Silver Supporting Member
Posts: 12
Troylure
Age: 26
Loc: Ashland
Reg: 03-27-17
09-13-17 04:00 PM - Post#2707597    
    In response to rockfangd

Okay, so i was rechecking the brake lines and decided to re-bleed the rear brakes,

but as i started bleeding them the fluid that came out almost looked like gear oil, just not as thick.

So i continued to bleed them for about 1/2 hr and it started getting better except the color stayed the same,

but the petal got alot better i got back about 2/3rds of petal travel back. not sure if im on the right track or not.



 
rockfangd 
"4th Year" Gold Supporting Member
Posts: 2215

Age: 31
Loc: Utica ny
Reg: 04-13-10
09-14-17 05:00 PM - Post#2707672    
    In response to Troylure

I would say so.
Make sure your brakes are adjusted up.

Old School GM fan FOREVER


 
Troylure 
Silver Supporting Member
Posts: 12
Troylure
Age: 26
Loc: Ashland
Reg: 03-27-17
09-18-17 12:00 PM - Post#2708040    
    In response to rockfangd

Okay, so how would I go about adjusting my rear drums, as they are not exactly my strong suit.



 
rockfangd 
"4th Year" Gold Supporting Member
Posts: 2215

Age: 31
Loc: Utica ny
Reg: 04-13-10
09-18-17 06:51 PM - Post#2708077    
    In response to Troylure

I remove the drums,
grind off the lip at the edge, to be even with the rest (if they are worn)
Reinstall drums,
set the parking brake about a quarter of the way.
Turn star wheel until the drums will not turn by hand easily.
You can do it by removing the drums also.
Slide the drum off, turn the star wheel. Keep adjusting til the drums just slide tight onto the hub. Remembering to leave the parking brake set a quarter of the way
I have done it both ways with good results.
If you tighten it too much you will have to push the clip out of the way to turn the star wheel back

Old School GM fan FOREVER


 
va_samiam 
Contributor
Posts: 101

Reg: 11-15-10
10-01-17 05:09 AM - Post#2709351    
    In response to rockfangd

I struggled with brakes for a couple of months on my 92 C2500. The big thing that helped was bleeding and grinding off the grooves on the wall of the rear brakes. I made sure on assemble everything was lubed well. Then assemble with wheel off and you can feel/see when they are adjusted properly, not to tight that they drag but not to loose that they will not work.
It is a job that is best to take your time.



 
Junkyardwarrior 
Contributor
Posts: 247

Loc: Yuma AZ
Reg: 02-25-15
10-02-17 12:50 PM - Post#2709513    
    In response to va_samiam

When I did mine I had to tighten the rear shoes until they were tight (my parking brake cable is broken so there was no quarter setting) and then bleed them until I hit the pedal and got basically no give at all. Then I put the truck in neutral and loosened each side until the wheels would spin freely. Been great since.



 
Low priced Genuine GM Auto Parts
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