I totally agree. The low pedal is annoying, but I'm more concerned about the lack of friction.
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.
Brake pedal pushes back??????
- Thread starter K85 Octane
- Start date
I totally agree. The low pedal is annoying, but I'm more concerned about the lack of friction.
I'm not using a prop valve on mine and my brakes work great. I was under the impression that the prop valve controls the pressure front to back not the amount of fluid.
Pressure would be fluid.
Are the calipers new ? May be a bad one ? What about how much fluid is going to the calipers ?
Are the calipers new ? May be a bad one ? What about how much fluid is going to the calipers ?
readymix
3/4 ton status
Look what I just found....
Ok, either I missed something, or something is not adding up. Just to verify, with no boost, does the pedal go either to the floor, a long way, but not all the way, or short distance but spongy?
If, like Chris says, it goes about 3 inches and then gets hard enough that you cannot press it farther with both feet, then I suspect I know what the problem is.....
First, I am pretty sure that we do not have an air problem. If there was air, you would get the geyser when you release the pedal.
The geysers at first are normal. They occur when the piston is starting to pressurize the fluid, but the intake ports have not fully closed off yet.
If he is now getting a hard pedal with no boost, and good travel with boost, then I do not think there is a defect with the hydraulics anymore.
The booster may be causing a problem, but his replacing it should handle that. If he can still not lock up the brakes, then it is either really slick brake pads, the wrong size MC, or a combination of the two.
It could also be a bad wheel bearing, but I suspect you would have noticed that.
He may wind up needing a prop valve, but not because the brakes are not working well, but because the front or back is working too well and locking up too fast.
BTW, many of the boosters have an adjustable shaft. Making it longer will give you more pedal, but you have to be careful not to cause the brakes to drag.
If its too long, the MC will not retract fully, and hold pressure on the calipers. But, if its too short, you will have to push the pedal too far to engage the brakes.
If, like Chris says, it goes about 3 inches and then gets hard enough that you cannot press it farther with both feet, then I suspect I know what the problem is.....
First, I am pretty sure that we do not have an air problem. If there was air, you would get the geyser when you release the pedal.
The geysers at first are normal. They occur when the piston is starting to pressurize the fluid, but the intake ports have not fully closed off yet.
If he is now getting a hard pedal with no boost, and good travel with boost, then I do not think there is a defect with the hydraulics anymore.
The booster may be causing a problem, but his replacing it should handle that. If he can still not lock up the brakes, then it is either really slick brake pads, the wrong size MC, or a combination of the two.
It could also be a bad wheel bearing, but I suspect you would have noticed that.
He may wind up needing a prop valve, but not because the brakes are not working well, but because the front or back is working too well and locking up too fast.
BTW, many of the boosters have an adjustable shaft. Making it longer will give you more pedal, but you have to be careful not to cause the brakes to drag.
If its too long, the MC will not retract fully, and hold pressure on the calipers. But, if its too short, you will have to push the pedal too far to engage the brakes.
y5mgisi
1 ton status
KG, i hear ya, but it sounds like he cant get his rears to lock either. And i dont know too terribly much about the prop valves, but i feel like i would run one. Dont know if its needed, but i have never had a truck without one.
FWIW, on my 78 suburban 1/2 ton 4x4, i swapped to a 3/4 ton front, and rear discs/calipers from a k20. Stock half ton master cylinder/booster/prop valve. Those brakes were the best brakes i have ever had on a truck with regard to stopping power. The best FEELING brakes i have ever had on a truck was a k5 i had that had 100% all new brakes from master to pads. The truck was all original save for a 6" lift and 35s. Those brakes flat rocked! Hooking a trailer to it showed its lack of braking power, but in normal traffic or cruising, they just felt like a brand new truck. It was crazy.
FWIW, on my 78 suburban 1/2 ton 4x4, i swapped to a 3/4 ton front, and rear discs/calipers from a k20. Stock half ton master cylinder/booster/prop valve. Those brakes were the best brakes i have ever had on a truck with regard to stopping power. The best FEELING brakes i have ever had on a truck was a k5 i had that had 100% all new brakes from master to pads. The truck was all original save for a 6" lift and 35s. Those brakes flat rocked! Hooking a trailer to it showed its lack of braking power, but in normal traffic or cruising, they just felt like a brand new truck. It was crazy.
readymix
3/4 ton status
This also.
I just wasted a full Sunday. 
I wasn't comfortable with my brakes last year, figuring I'll take another year to work out all the bugs before BB. I'm frocked this year.
Today I.....
Replaced Booster
Re-sanded the discs with 80 grit and aggressively sanded the pads
Bled the brakes to the best of my abilities.
Checked U-bolts
Cut out some of my old wiring, since I'm not running an electric fan or AC anymore.
Put the tires back on and started the truck.
No difference.
Here's a video. I'm in 4L BTW. I'm done for tonight. I feel like grabbing a bucket of KFC chicken and whatever else will kill me quicker. So off I go for some food, first food of the day
I wasn't comfortable with my brakes last year, figuring I'll take another year to work out all the bugs before BB. I'm frocked this year. Today I.....
Replaced Booster
Re-sanded the discs with 80 grit and aggressively sanded the pads
Bled the brakes to the best of my abilities.
Checked U-bolts
Cut out some of my old wiring, since I'm not running an electric fan or AC anymore.
Put the tires back on and started the truck.
No difference.
Here's a video. I'm in 4L BTW. I'm done for tonight. I feel like grabbing a bucket of KFC chicken and whatever else will kill me quicker. So off I go for some food, first food of the day
Last edited by a moderator:
All calipers were replaced ~3,000 miles ago. Even if one of them was seized, I'd still have better pedal feel.
Food time
Food time
Maybe vacuum bleeding the brakes will work better in your case?...
I made a vacuum bleeder because I never have a helper around to pump the pedal,and using other methods dont always work by yourself..
Have you replaced all of the original lines?...I'm wondering if one might be crimped or blocked inside by some rust or crud...also wonder if the calipers and wheel cylinders are "free" and not seizing up in their bores...
I made a vacuum bleeder because I never have a helper around to pump the pedal,and using other methods dont always work by yourself..
Have you replaced all of the original lines?...I'm wondering if one might be crimped or blocked inside by some rust or crud...also wonder if the calipers and wheel cylinders are "free" and not seizing up in their bores...
Have you considered cutting a hole in the floor and using your feet like Fred Flintstone?
I actually have one more thing for you to try. Well, really two, but one will require a second person........
OK, three if you consider a can of gas and a match.......
If you can find a smaller MC, try it. 1-5/16 is pretty big. You need the volume for the bigger calipers, but you can oversize it.
The advantage of hydraulics is in the ratio between the the two pistons. That is where you get your stopping force.
Making some numbers up, 100 lbs applied to a 1 square inch surface area piston attached to a 10 square inch piston, yields 1000 pounds of pressure.
100 lbs on a 5 inch piston yields only 200 lbs on a 10 inch one.
The smaller the MC piston, the more force you get at the pads. As long as there is enough fluid transfer to move the calipers the required amount, you are good.
If there is a number you could look up, I suspect that one deep hole MC you got by accident is going to be a smaller dia piston than the others.
Since it was designed for nonboost systems, it will need the smaller piston to give more force with less pedal pressure.
I actually have one more thing for you to try. Well, really two, but one will require a second person........
OK, three if you consider a can of gas and a match.......
If you can find a smaller MC, try it. 1-5/16 is pretty big. You need the volume for the bigger calipers, but you can oversize it.
The advantage of hydraulics is in the ratio between the the two pistons. That is where you get your stopping force.
Making some numbers up, 100 lbs applied to a 1 square inch surface area piston attached to a 10 square inch piston, yields 1000 pounds of pressure.
100 lbs on a 5 inch piston yields only 200 lbs on a 10 inch one.
The smaller the MC piston, the more force you get at the pads. As long as there is enough fluid transfer to move the calipers the required amount, you are good.
If there is a number you could look up, I suspect that one deep hole MC you got by accident is going to be a smaller dia piston than the others.
Since it was designed for nonboost systems, it will need the smaller piston to give more force with less pedal pressure.
Anybody ever wrap the bleeder threads with Teflon tape? I want to make sure I'm not sucking air between the threads and either giving a false "air" reading or even drawing air back into the caliper while bleeding on my own.
samsterman99
1/2 ton status
Yes, but I used the bleeder with the press fit threads, and actually put a one way check valve in the line so it sucked clean fluid from the resivoir because I couldn't get the air out of the plastic bleeder lines
y5mgisi
1 ton status
Yep
Hmmm even those speed bleeders mention thread sealant.
I vote Speed Bleeders and that you have air in the lines. Having done massive amounts of brake work in the past few years you can't bleed your brakes with one person and gravity bleed only goes so far.
I've had good luck with the speed bleeders myself, I also don't see any reason for the Teflon tape to hurt anything as long as you make sure it stays on the threads only.
I have also loaded the race car on the trailer with brakes that we thought needed to be bled more, only to arrive 800 mile later and think they were way better than it's little trailer ride. The vibrations and moving on the trailer worked the air bubbles to the master is my theory.
