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Username Post: More air in brake lines!!        (Topic#228256)
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-23-09 07:16 AM - Post#1792991    

I have had poor brakes on my 1990 Chevy 1/2 ton pick up and replaced the rubber lines this week, bench bled the master again to see if this would help. After bleeding the front they seem to be ok, and the rear had some air at first but I finally get solid fluid but when I go check the fluid in the reservoir (I never let it get too low) I put the lid back on, then go back to the old style bleeding where someone pumps the brakes while I open the bleeder and when I open the bleeder I get a big burst of air, I re-bleed them to solid fluid and then check the reservoir and once again I get a burst of air. I have gotten these results every time. I do not see how this can be connected but I can not get the rear brakes to bleed correctly. The brake pedal is never released before I tighten the bleeder valve! There are no leaks in the system that I can find and I have no fluid loss.

 
Jim.Biron 
"7th Year" Platinum Supporting Member
Posts: 2464
Jim.Biron
Age: 63
Loc: Saugerties, NY
Reg: 04-10-08
10-23-09 10:26 AM - Post#1793091    
    In response to BG

  • BG Said:
I have had poor brakes on my 1990 Chevy 1/2 ton pick up and replaced the rubber lines this week, bench bled the master again to see if this would help. After bleeding the front they seem to be ok, and the rear had some air at first but I finally get solid fluid but when I go check the fluid in the reservoir (I never let it get too low) I put the lid back on, then go back to the old style bleeding where someone pumps the brakes while I open the bleeder and when I open the bleeder I get a big burst of air, I re-bleed them to solid fluid and then check the reservoir and once again I get a burst of air. I have gotten these results every time. I do not see how this can be connected but I can not get the rear brakes to bleed correctly. The brake pedal is never released before I tighten the bleeder valve! There are no leaks in the system that I can find and I have no fluid loss.



The rule (As I always understood it) was to bleed the brake fatherest away from the MC first and then work your way forward toward the MC.
Jim
www.HudsonValleyCruise.com


 
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-23-09 11:03 AM - Post#1793116    
    In response to Jim.Biron

The way I bleed them is to start at the right rear, the left rear then move to the right front then the left front. I am still getting air at the rear.

 
Vaughn 
"12th Year" Gold Supporting Member
Posts: 15226

Loc: Colorado Springs, CO
Reg: 08-08-04
10-23-09 12:37 PM - Post#1793167    
    In response to BG

Your master cylinder could be bad. If the internal seals are damaged, air could be getting by the rear seal - making brake bleeding impossible.

Get a good AC Delco master cylinder from Napa. Up to 50 percent of other parts stores master cylinders fail right off the shelf.

 
52chevybob 
Dedicated Enthusiast
Posts: 5628

Reg: 05-27-08
10-23-09 02:01 PM - Post#1793203    
    In response to Vaughn

Could be that you don't understand how to bleed.
The process is to apply pressure to the brake peda, open the vlave for a bit, letting whatever escape and then close the valve before the pedal gets to the floor. Seal the valve and recycle to the pedal high and pressure position and reopen the valve. Check the MC to make sure that it doesn't get too low or you will be putting air back in again.

 
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-23-09 05:37 PM - Post#1793330    
    In response to 52chevybob

I have bled the brakes on different vehicles in the past without a problem but this one does have me questioning if I am doing something wrong. I am not doing anything different from when I have bled other brakes. I am wondering if the master cylinder has a leak as mentioned in the above posting.

 
tjn. 
Contributor
Posts: 882

Loc: louisville, kentucky usa
Reg: 02-16-05
10-23-09 05:41 PM - Post#1793332    
    In response to BG

BG, Sit in the car with the ignition off, hold your foot firmly on the brake pedal and see if the pedal drops. If it does drop and you don't find any leaks you're in the new MC business. TJN

 
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-23-09 06:01 PM - Post#1793349    
    In response to tjn.

tjn,
I just went out to my truck and tried the pedal and it will go down about half way then it holds. Earlier I was trying to bleed them again with a vacuum pump and all I could get was air out of the rear. I tried to gravity bleed them but I could hardly get a drop at a time. I do have better brakes backing up! The brake pedal does not return like I think it should, could this be part of the problem?

 
tjn. 
Contributor
Posts: 882

Loc: louisville, kentucky usa
Reg: 02-16-05
10-23-09 07:35 PM - Post#1793401    
    In response to BG

BG, don't know, but it sounds like the MC is o'kay or it would have let the pedal sink. TJN

 
wheelman 
Valued Contributor
Posts: 3081
wheelman
Loc: Long Island--New York
Reg: 04-14-07
10-23-09 07:51 PM - Post#1793408    
    In response to tjn.

How's the proportioning valve?Any leaks?
1968 Impala Sports Coupe
1997 Buick LeSabre Custom
Save a Classic - Crush an Import
My 68 Impala


 
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-23-09 08:07 PM - Post#1793421    
    In response to wheelman

There are no leaks and I just took out the proportioning valve because I was having trouble getting it to reset and swapped it with a used one that is supposed to be good but I am still having trouble getting the air out of the system. I have tried gravity, pressure on the pedal and vacuum to bleed these and have been thru 1and 1/2 gallons of fluid. I have bled brakes on different vehicles over the years and never had this kind of trouble.I am thinking of getting a pressure tank and trying it.

 
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-23-09 08:22 PM - Post#1793427    
    In response to BG

My brake pedal does not return like it should and I need to check this out. Could this be keeping the piston in the master cylinder out of the correct position and causing the problem with bleeding the brakes? This may just be a problem under the dash and nothing to do with the brake bleeding problems.

 
N8sToolz 
Very Senior Member
Posts: 2315
N8sToolz
Age: 28
Loc: N 42┬░ 53.290' W71┬░ 34.1...
Reg: 10-23-03
10-24-09 12:45 PM - Post#1793693    
    In response to BG

Fluid starts at the master, so you really have to start there. The pedal not comming back up is def a sign that something is not right.

  • Quote:
Up to 50 percent of other parts stores master cylinders fail right off the shelf.



My guess would have been higher on that number, forever getting bad ones. I have not used the AC delco ones though.

Does the rear of the truck have a load valve? It adjusts the rear line pressure depending how much weight is in the back of the truck. If it does I would delete it from the system.
1982 Chevy K20 Converted from C20.
355/700R4
2002 Yamaha XVS1100CL VStar
2002 S10 2WD


 
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-24-09 03:06 PM - Post#1793747    
    In response to N8sToolz

From what I can tell the truck does not have a valve for weight, it does have the combination valve without ABS. While using the pedal to apply pressure while bleeding the brakes the pedal would not come all the way back up so I would lift it the final inch or so but right now to check the pedal it seems ok.

 
Vaughn 
"12th Year" Gold Supporting Member
Posts: 15226

Loc: Colorado Springs, CO
Reg: 08-08-04
10-24-09 10:04 PM - Post#1793936    
    In response to BG

I've run into a lot of different brake problems over the years - and almost every time a brake system can't be bled via normal brake bleeding procedure, the master cylinder is the culprit.

Master Cylinders - even the high quality parts store units - are not that expensive. If nothing else, you insure that your master cylinder won't need to be looked at or changed out for the next 10 years or so.

 
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-25-09 11:35 AM - Post#1794145    
    In response to Vaughn

I plugged the ports on the master and it holds pressure. I did find what looks like a leak at the right rear wheel cylinder so I am going to replace both of those. Since the brakes have always been on the weak side can I change out the calipers or wheel cylinders to a different size to get more brakes??

 
tjn. 
Contributor
Posts: 882

Loc: louisville, kentucky usa
Reg: 02-16-05
10-25-09 02:42 PM - Post#1794226    
    In response to BG

BG, if you change out the calipers to "larger" then the rotors have to also change to "larger". Never heard of stouter/stronger wheel cylinders.

BTW, I readjusted my rear (disk) brakes so that the inner pads just contact the rotors and it made a marginal improvement in the pedal "drop". TJN

 
52chevybob 
Dedicated Enthusiast
Posts: 5628

Reg: 05-27-08
10-25-09 03:53 PM - Post#1794265    
    In response to tjn.

Generally wheel cylinders also need to change the backing plate as the backing plate sets the offset of the cylinder from the backing plate. Putting larger cylinders on there will make the cylinder push the shoes at an angle. It is also uusal to have the bolts at different locations from one size to another.
I'd suspect thaat calipers also have the same problem with differences between the rails.
The only real way to get stoonger brakes is to build a higher pressure in the system.

 
BG 
Contributor
Posts: 635

Reg: 09-12-07
10-25-09 07:01 PM - Post#1794387    
    In response to 52chevybob

I was just hoping there was a way to upgrade the brakes. Today I replaced the rear cylinders and while I had it apart I disconnected the rear line from the combination valve just to see if I could draw fluid thru the line with the small mighty vac hand pump and I could not draw the fluid thru the line, I reconnected the lines and used speed bleeder valves that have the check valve built in and was able to bleed the rear lines but the brakes are still bad even after this. The master cylinder checks out ok but there is something not right with these brakes.

 
64Bel Air 
Forum Newbie
Posts: 39

Reg: 07-08-09
10-27-09 04:47 PM - Post#1795380    
    In response to BG

You have remember there is many different styles of brake systems. And not all brake systems can be bled from the farthest from the master first. So please look up your style of brakes very carefuly. Also Master cylenders will hold preasure to lines even when your not on the pedal or anything so air in the master be prepared to reblead the master off the booster or off the car completely. Best bet, Draw on a peice of paper exactly how your brakes are run. Find out the style, and buy a power bleeader and ALWAYS check the master level

Edited by 64Bel Air on 10-27-09 04:50 PM. Reason for edit: No reason given.

 
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