Please help with brakes, replaced master cylinder
#1
01-17-2011, 01:49 PM
Please help with brakes, replaced master cylinder
I know there a lot of brake threads. I've read them all (I think) but still at a loss as to what to do next.
To keep it concise:
93 S10 Blazer, 4x4, 4.3w, 108k
Was driving and pedal went almost to the floor. Pulled over and checked fluid level. The front half of the reservoir (closest to the front of the truck) was bone dry and back half was almost out. I noticed seepage around where the MC bolts to the booster and also around where the reservoir is connected to the MC itself.
With engine off, I pumped up the brake pedal and it got hard. I held for a good minute and it didn't drop any. So I figured it must be the MC.
Replaced MC with a rebuilt unit from Advance. Instructions that came with it said it could be bled while bolted to the power booster and came with plugs you screw in and pump the pedal no more than 1" while the reservoir is full of fluid. The pedal finally got firm and I saw no more air bubbles. I removed plugs, reattached brake lines, topped off the fluid and bled all 4 wheels, starting with the rear right first. But NO air came out of any of the 4 lines. I had someone pump and hold 4-5 times for each wheel for me and did not see any air or any spewing of fluid, just a steady stream on each one as I loosened the bleed screw.
Started truck and drove around a few mins. Brake pedal still goes down farther than it should be is a LOT better. I got up to about 40mph and hit the pedal hard. The pedal did not go down near as far but the truck did not stop as fast as I thought should.
side note: some time ago, I unplugged the power to the ABS module because it would make a buzzing noise and the brake pedal would completely go to the floor and I had ZERO braking power until I pumped it, stopped, turned engine off and then restarted. This was done a year ago.
If I hit the brake pedal now gently I hear a 'swoosh' like air noise and the pedal goes way down, but if I hit it hard it's a lot firmer.
I have new brake lines in front, two new calipers in front. Brakes lines from ABS unit is still connected, only power is disconnected. Everyone around here wants $100 to bleed the ABS unit with a scan tool so I just disconnected. I don't go fast in this vehicle, I deliver mail so I do get up to high speeds, just a few mph between boxes so ABS is not a big issue to me.
So... why would I not get any air out of the lines when the reservoir was bone dry on one side? Do I need to bleed it MORE?
Could it be the booster?
To keep it concise:
93 S10 Blazer, 4x4, 4.3w, 108k
Was driving and pedal went almost to the floor. Pulled over and checked fluid level. The front half of the reservoir (closest to the front of the truck) was bone dry and back half was almost out. I noticed seepage around where the MC bolts to the booster and also around where the reservoir is connected to the MC itself.
With engine off, I pumped up the brake pedal and it got hard. I held for a good minute and it didn't drop any. So I figured it must be the MC.
Replaced MC with a rebuilt unit from Advance. Instructions that came with it said it could be bled while bolted to the power booster and came with plugs you screw in and pump the pedal no more than 1" while the reservoir is full of fluid. The pedal finally got firm and I saw no more air bubbles. I removed plugs, reattached brake lines, topped off the fluid and bled all 4 wheels, starting with the rear right first. But NO air came out of any of the 4 lines. I had someone pump and hold 4-5 times for each wheel for me and did not see any air or any spewing of fluid, just a steady stream on each one as I loosened the bleed screw.
Started truck and drove around a few mins. Brake pedal still goes down farther than it should be is a LOT better. I got up to about 40mph and hit the pedal hard. The pedal did not go down near as far but the truck did not stop as fast as I thought should.
side note: some time ago, I unplugged the power to the ABS module because it would make a buzzing noise and the brake pedal would completely go to the floor and I had ZERO braking power until I pumped it, stopped, turned engine off and then restarted. This was done a year ago.
If I hit the brake pedal now gently I hear a 'swoosh' like air noise and the pedal goes way down, but if I hit it hard it's a lot firmer.
I have new brake lines in front, two new calipers in front. Brakes lines from ABS unit is still connected, only power is disconnected. Everyone around here wants $100 to bleed the ABS unit with a scan tool so I just disconnected. I don't go fast in this vehicle, I deliver mail so I do get up to high speeds, just a few mph between boxes so ABS is not a big issue to me.
So... why would I not get any air out of the lines when the reservoir was bone dry on one side? Do I need to bleed it MORE?
Could it be the booster?
#2
01-17-2011, 03:00 PM
I know there a lot of brake threads. I've read them all (I think) but still at a loss as to what to do next.
To keep it concise:
93 S10 Blazer, 4x4, 4.3w, 108k
Was driving and pedal went almost to the floor. Pulled over and checked fluid level. The front half of the reservoir (closest to the front of the truck) was bone dry and back half was almost out. I noticed seepage around where the MC bolts to the booster and also around where the reservoir is connected to the MC itself.
Sounds like the master was leaking from the rear seal, it happens, good call on getting a new MC
With engine off, I pumped up the brake pedal and it got hard. I held for a good minute and it didn't drop any. So I figured it must be the MC.
Replaced MC with a rebuilt unit from Advance. Instructions that came with it said it could be bled while bolted to the power booster and came with plugs you screw in and pump the pedal no more than 1" while the reservoir is full of fluid. The pedal finally got firm and I saw no more air bubbles. I removed plugs, reattached brake lines, topped off the fluid and bled all 4 wheels, starting with the rear right first. But NO air came out of any of the 4 lines. I had someone pump and hold 4-5 times for each wheel for me and did not see any air or any spewing of fluid, just a steady stream on each one as I loosened the bleed screw
It takes more that 4 or 5 times to move the fluid at the master down those long lines to the back. Try 15 or 20 times... Eventually the bubbles will get to the back. They are there if you had a brake line off at the master, no question about that.
Started truck and drove around a few mins. Brake pedal still goes down farther than it should be is a LOT better. I got up to about 40mph and hit the pedal hard. The pedal did not go down near as far but the truck did not stop as fast as I thought should.
side note: some time ago, I unplugged the power to the ABS module because it would make a buzzing noise and the brake pedal would completely go to the floor and I had ZERO braking power until I pumped it, stopped, turned engine off and then restarted. This was done a year ago.
The ABS module is full of air, it trying to give you brake pressure, but all it did was compress air instead of apply brakes. When taking brake components apart and they are dripping, you must keep the resevoir full. As long as its kept full it cant get air inside and can drip as long as you like.
If I hit the brake pedal now gently I hear a 'swoosh' like air noise and the pedal goes way down, but if I hit it hard it's a lot firmer.
The woosh is normal for when the booster is moving all the way in one push, there is air in the lines, get that out and replaced with fluid to provide some resistance to the booster so it cant travel all the way
I have new brake lines in front, two new calipers in front. Brakes lines from ABS unit is still connected, only power is disconnected. Everyone around here wants $100 to bleed the ABS unit with a scan tool so I just disconnected. I don't go fast in this vehicle, I deliver mail so I do get up to high speeds, just a few mph between boxes so ABS is not a big issue to me.
This could be where the air is that you cant get out and it has been there since you did the front lines and it dripped dry?... Might be a good idea to drop the 100 on the bleed.
So... why would I not get any air out of the lines when the reservoir was bone dry on one side? Do I need to bleed it MORE?
Yes, lots more, like a whole litre bottle of fluid worth, the shop will do that when they bleed the ABS.
Could it be the booster?
If it was a booster problem you would have to push really hard to get any brakes at all.
To keep it concise:
93 S10 Blazer, 4x4, 4.3w, 108k
Was driving and pedal went almost to the floor. Pulled over and checked fluid level. The front half of the reservoir (closest to the front of the truck) was bone dry and back half was almost out. I noticed seepage around where the MC bolts to the booster and also around where the reservoir is connected to the MC itself.
Sounds like the master was leaking from the rear seal, it happens, good call on getting a new MC
With engine off, I pumped up the brake pedal and it got hard. I held for a good minute and it didn't drop any. So I figured it must be the MC.
Replaced MC with a rebuilt unit from Advance. Instructions that came with it said it could be bled while bolted to the power booster and came with plugs you screw in and pump the pedal no more than 1" while the reservoir is full of fluid. The pedal finally got firm and I saw no more air bubbles. I removed plugs, reattached brake lines, topped off the fluid and bled all 4 wheels, starting with the rear right first. But NO air came out of any of the 4 lines. I had someone pump and hold 4-5 times for each wheel for me and did not see any air or any spewing of fluid, just a steady stream on each one as I loosened the bleed screw
It takes more that 4 or 5 times to move the fluid at the master down those long lines to the back. Try 15 or 20 times... Eventually the bubbles will get to the back. They are there if you had a brake line off at the master, no question about that.
Started truck and drove around a few mins. Brake pedal still goes down farther than it should be is a LOT better. I got up to about 40mph and hit the pedal hard. The pedal did not go down near as far but the truck did not stop as fast as I thought should.
side note: some time ago, I unplugged the power to the ABS module because it would make a buzzing noise and the brake pedal would completely go to the floor and I had ZERO braking power until I pumped it, stopped, turned engine off and then restarted. This was done a year ago.
The ABS module is full of air, it trying to give you brake pressure, but all it did was compress air instead of apply brakes. When taking brake components apart and they are dripping, you must keep the resevoir full. As long as its kept full it cant get air inside and can drip as long as you like.
If I hit the brake pedal now gently I hear a 'swoosh' like air noise and the pedal goes way down, but if I hit it hard it's a lot firmer.
The woosh is normal for when the booster is moving all the way in one push, there is air in the lines, get that out and replaced with fluid to provide some resistance to the booster so it cant travel all the way
I have new brake lines in front, two new calipers in front. Brakes lines from ABS unit is still connected, only power is disconnected. Everyone around here wants $100 to bleed the ABS unit with a scan tool so I just disconnected. I don't go fast in this vehicle, I deliver mail so I do get up to high speeds, just a few mph between boxes so ABS is not a big issue to me.
This could be where the air is that you cant get out and it has been there since you did the front lines and it dripped dry?... Might be a good idea to drop the 100 on the bleed.
So... why would I not get any air out of the lines when the reservoir was bone dry on one side? Do I need to bleed it MORE?
Yes, lots more, like a whole litre bottle of fluid worth, the shop will do that when they bleed the ABS.
Could it be the booster?
If it was a booster problem you would have to push really hard to get any brakes at all.
Last edited by ohsofly; 01-17-2011 at 03:09 PM.
#3
01-17-2011, 03:07 PM
Wow that many times to bleed each one? Ok. I definitely didn't do it enough then. Will go get some more fluid 
Good thing Advance has buy one get one free right now on any size bottle
I've read about gravity bleeding. Would you recommend trying that since it seems I do have a lot of air in the lines? I don't have a handy assistance always to help.
Is there any way to completely bypass the ABS module? For safety's sake, I have no problem with $100 being spent, but if I can do without ABS to begin with, I'd rather find a way to by pass it then bleed it, since the ABS module is likely bad anyway.
Thank you for the info.
Good thing Advance has buy one get one free right now on any size bottle I've read about gravity bleeding. Would you recommend trying that since it seems I do have a lot of air in the lines? I don't have a handy assistance always to help.
Is there any way to completely bypass the ABS module? For safety's sake, I have no problem with $100 being spent, but if I can do without ABS to begin with, I'd rather find a way to by pass it then bleed it, since the ABS module is likely bad anyway.
Thank you for the info.
#4
01-17-2011, 03:13 PM
Bleed, bleed, and more bleed. I gravity bleed all my brakes, it works great and you can drink a beer while your doing it. Make sure the master cylinder cover is open while you are doing it.
#5
01-17-2011, 03:14 PM
Not sure about bypassing it, I love ABS myself and would have it fixed. Mine works great and has saved me from running a blazer up someones *** this winter already.
Gravity bleeding is a fancy name for leaving a bleeder open to drip, that might be what got you into this mess to begin with. Its ok for moving fluid and junk along, but bubbles will stay in high points unless you use some force to move them along. Im impatient and never do it. You could get one of those hand pump ones that you plug on the bleeder with a clear hose, then you can see the junk and bubbles coming out better.
Id just get a buddy to pump. You havent bled it out enough unless that person is complaining their leg hurts and wants a break. It takes about a litre to flush these trucks till it runs clear on all 4 corners. When there is no more air left that pedal will be hard as a rock.
Gravity bleeding is a fancy name for leaving a bleeder open to drip, that might be what got you into this mess to begin with. Its ok for moving fluid and junk along, but bubbles will stay in high points unless you use some force to move them along. Im impatient and never do it. You could get one of those hand pump ones that you plug on the bleeder with a clear hose, then you can see the junk and bubbles coming out better.
Id just get a buddy to pump. You havent bled it out enough unless that person is complaining their leg hurts and wants a break. It takes about a litre to flush these trucks till it runs clear on all 4 corners. When there is no more air left that pedal will be hard as a rock.
Last edited by ohsofly; 01-17-2011 at 03:17 PM.
#6
01-17-2011, 06:25 PM
i dont know if it was said. but try bleeding at the master cylinder itself. have someone pump it up a bunch then crack open one line let the fluid come out, close it then open the other and repeat a few times. also make sure you dont get hit in the eye that stuff comes flying out
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