Brake problems?

art leong · 02-19-2011, 10:42 PM

I recently changed the brake ratio on my car It has stock 4 wheel discs. With the power booster removed. Kept the stock mastercylinder.
The original ratio was less than 4 to 1, I changed it to 6 to 1.
I now have 1000 pounds of pressure on the drive wheels (had 600 before) While applying fairly hard pedal pressure.
With the car off I have a hard pedal. But when I start it up and put it in gear. The pedal gets spongy, and slowly sinks.
I've bleed the brakes 3 times and have no air coming out. I didn't disconect the brake lines from the master. I did take out the bleeder valve to install gauge to check pressure.
I can't figure why this is only happening in gear?

BTW the car in on jack stands not on the ground.

gmonde · 02-20-2011, 11:24 AM

are still running the vacuum booster or is it manual ???

gmonde · 02-20-2011, 11:34 AM

it sounds like whats happening is when the wheels are rotating the rotors are pushing the pads/pistons back into the calipers ,so on your first brake application the pedal is low because the pistons have to move the extra distance to contact the rotor ,,just check your rotors for run out and also are they floating rotors???? was the wheel bolted on???

gmonde

art leong · 02-20-2011, 12:20 PM

Originally power brakes, took off power booster, and all abs equiptment.
On first application the pedal is high, and hard. I put car in gear and it starts to get spongy.
Wheels are on tight. Calipers were put on new when I built the car, pads are the cheaper (more organic) didn't have any problems except for the need for excessive pedal pressure. I'll check runout, but they look okay

I'm beginning to wonder if the vibrations some how cause leakage in the master cylinder.
I've thought about replacing the master cylinder next. But not sure if I should get a stock replacement, or an aftermarket one. I originally figured the stock one should be fine because I'm using the stock calipers etc. All I did was remove the power booster, and the abs stuff. put in a proportioning valve. Then change the pedal ratio.
Another thing i had to change was the stock system was right front, left rear on one part of the master, left front right rear on the other. Now it is both fronts off one end both rears off the other.

gmonde · 02-20-2011, 01:54 PM

also check your brake pads for sitting in the brackets and calipers ,some times the aftermarket pads do not sit correctly and this will cause a spongy pedal due to the caliper piston flexing the brake pad and acts like a spring pushing the piston back in ,,,,if the master is bad the pedal will slowly make its way to the floor under constant brake pedal presure

to isolate the caliper(s) block off each wheel with line clamps (if you are using rubber hoses) check the pedal each time you remove one of the lines ,this will help locate the issue

gmonde

mopar · 02-20-2011, 02:13 PM

sound like to me , the master clyinder is your problem. ( not holding presser at all time)

Ron Waters 1346 s/st

art leong · 02-20-2011, 02:41 PM

I just went out and tried the brakes with the motor off.
When I pushed hard (2 feet) the pedal slowly sank.
When I tried it before I got a firm pedal and just figured it was good.
So now I'm pretty sure it's the master cylinder.

Phillip marvetz · 02-20-2011, 10:09 PM

Either the master cylinder or you have a small leak that is letting air in. Did you put in a hydraulic switch or pressure gauge? My vote is the master cylinder though.

chris ok · 02-21-2011, 02:49 PM

any time you bleed a used master cylinder you have to be careful to not bottom it out.
Are you moving to much volume of fluid? Don't manual brakes use a smaller diameter bore piston. One possibility.
Honda an some other companies screw their hat rotorrs to the hub. One screw w a tapered head, supposedly helps with the pedal. saw it saturday at work. they screwed it together and corrected a shimy and a pedal issue. These are lightweight rotors with heavy clamping on the calipers from your ratio and line pressure. second possibility
Any time I've taken brakes apart you always have to re seat them too.

art leong · 02-21-2011, 03:27 PM

I'm changing the master cylinder, And see if that helps.
I also am wondering if I used a bigger piston caliper (now 54mm change to 60mm).
Would this increase the static ( against the converter) holding? I'm not sure if a larger piston would increase the static holding with the same rotor?

02-19-2011, 10:42 PM	#1
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Brake problems? I recently changed the brake ratio on my car It has stock 4 wheel discs. With the power booster removed. Kept the stock mastercylinder. The original ratio was less than 4 to 1, I changed it to 6 to 1. I now have 1000 pounds of pressure on the drive wheels (had 600 before) While applying fairly hard pedal pressure. With the car off I have a hard pedal. But when I start it up and put it in gear. The pedal gets spongy, and slowly sinks. I've bleed the brakes 3 times and have no air coming out. I didn't disconect the brake lines from the master. I did take out the bleeder valve to install gauge to check pressure. I can't figure why this is only happening in gear? BTW the car in on jack stands not on the ground. __________________ Art Leong 2095 SS

02-20-2011, 11:24 AM	#2
gmonde Senior Member Join Date: Nov 2007 Posts: 615 Likes: 56 Liked 165 Times in 59 Posts	Re: Brake problems? are still running the vacuum booster or is it manual ???

02-20-2011, 11:34 AM	#3
gmonde Senior Member Join Date: Nov 2007 Posts: 615 Likes: 56 Liked 165 Times in 59 Posts	Re: Brake problems? it sounds like whats happening is when the wheels are rotating the rotors are pushing the pads/pistons back into the calipers ,so on your first brake application the pedal is low because the pistons have to move the extra distance to contact the rotor ,,just check your rotors for run out and also are they floating rotors???? was the wheel bolted on??? gmonde

02-20-2011, 12:20 PM	#4
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Re: Brake problems? Originally power brakes, took off power booster, and all abs equiptment. On first application the pedal is high, and hard. I put car in gear and it starts to get spongy. Wheels are on tight. Calipers were put on new when I built the car, pads are the cheaper (more organic) didn't have any problems except for the need for excessive pedal pressure. I'll check runout, but they look okay I'm beginning to wonder if the vibrations some how cause leakage in the master cylinder. I've thought about replacing the master cylinder next. But not sure if I should get a stock replacement, or an aftermarket one. I originally figured the stock one should be fine because I'm using the stock calipers etc. All I did was remove the power booster, and the abs stuff. put in a proportioning valve. Then change the pedal ratio. Another thing i had to change was the stock system was right front, left rear on one part of the master, left front right rear on the other. Now it is both fronts off one end both rears off the other. __________________ Art Leong 2095 SS Last edited by art leong; 02-20-2011 at 12:30 PM.

02-20-2011, 01:54 PM	#5
gmonde Senior Member Join Date: Nov 2007 Posts: 615 Likes: 56 Liked 165 Times in 59 Posts	Re: Brake problems? also check your brake pads for sitting in the brackets and calipers ,some times the aftermarket pads do not sit correctly and this will cause a spongy pedal due to the caliper piston flexing the brake pad and acts like a spring pushing the piston back in ,,,,if the master is bad the pedal will slowly make its way to the floor under constant brake pedal presure to isolate the caliper(s) block off each wheel with line clamps (if you are using rubber hoses) check the pedal each time you remove one of the lines ,this will help locate the issue gmonde

02-20-2011, 02:13 PM	#6
mopar Junior Member Join Date: Sep 2010 Posts: 11 Likes: 0 Liked 0 Times in 0 Posts	Re: Brake problems? sound like to me , the master clyinder is your problem. ( not holding presser at all time) Ron Waters 1346 s/st

02-20-2011, 02:41 PM	#7
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Re: Brake problems? I just went out and tried the brakes with the motor off. When I pushed hard (2 feet) the pedal slowly sank. When I tried it before I got a firm pedal and just figured it was good. So now I'm pretty sure it's the master cylinder. __________________ Art Leong 2095 SS

02-20-2011, 10:09 PM	#8
Phillip marvetz Senior Member Join Date: Oct 2008 Location: Lynden ,WA Posts: 820 Likes: 0 Liked 3 Times in 3 Posts	Re: Brake problems? Either the master cylinder or you have a small leak that is letting air in. Did you put in a hydraulic switch or pressure gauge? My vote is the master cylinder though. __________________ 2009 V/SA Record Holder

02-21-2011, 02:49 PM	#9
chris ok Senior Member Join Date: Jul 2002 Location: Long Island, New york Posts: 592 Likes: 131 Liked 46 Times in 29 Posts	Re: Brake problems? any time you bleed a used master cylinder you have to be careful to not bottom it out. Are you moving to much volume of fluid? Don't manual brakes use a smaller diameter bore piston. One possibility. Honda an some other companies screw their hat rotorrs to the hub. One screw w a tapered head, supposedly helps with the pedal. saw it saturday at work. they screwed it together and corrected a shimy and a pedal issue. These are lightweight rotors with heavy clamping on the calipers from your ratio and line pressure. second possibility Any time I've taken brakes apart you always have to re seat them too.

02-21-2011, 03:27 PM	#10
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Re: Brake problems? I'm changing the master cylinder, And see if that helps. I also am wondering if I used a bigger piston caliper (now 54mm change to 60mm). Would this increase the static ( against the converter) holding? I'm not sure if a larger piston would increase the static holding with the same rotor? __________________ Art Leong 2095 SS