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

Bob Mulry · 02-23-2011, 11:11 PM

Hi Art,

Since you have committed to a new M/C, why don't you consider going to a smaller diameter M/C if one is available for your application?

A larger caliper or a smaller M/C = the same thing. It's just a ratio of the areas...

One thing to be careful about with increased pedal ratio and a smaller M/C or larger caliper is the total brake fluid displacement per stroke.

Go too wild and you would have to pump the pedal to get enough fluid to apply the pads.

Just my thoughts,
Bob

A Closkey · 02-24-2011, 02:03 AM

You didn't use Silicone fluid, did you? This stuff will produce a crappy pedal.

art leong · 02-24-2011, 10:11 AM

I'm using a 7/8 master cylinder now. I've talked to some of the brake manufacturers, and they don't have anything smaller. That is why I'm going to see if I can change to a larger piston caliper. I now run a 54mm (2 1/8") pston. I'm hoping to use a 60mm (2 3/8) With the 22mm (7/8) master cylinder. The master cylinder (power brakes) for that application is 24mm (15/16).
I'm hoping to get the car to hold at a higher rpm against the foot brake.

Regular brake fluid not #5

chris ok · 02-27-2011, 05:28 PM

any new news yet?
Are you using factory stuff. mopar has some real light aluminum calipers made by trw of mexico it is I believe.
have you driven car around at all. I say you can't just run it without driving it to settle all brake parts and get a real feel. Good luck Art. Chris.

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, 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, 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

02-23-2011, 11:11 PM	#7
Bob Mulry VIP Member Join Date: Apr 2002 Location: Coarsegold, CA Posts: 1,016 Likes: 57 Liked 320 Times in 102 Posts	Re: Brake problems? Hi Art, Since you have committed to a new M/C, why don't you consider going to a smaller diameter M/C if one is available for your application? A larger caliper or a smaller M/C = the same thing. It's just a ratio of the areas... One thing to be careful about with increased pedal ratio and a smaller M/C or larger caliper is the total brake fluid displacement per stroke. Go too wild and you would have to pump the pedal to get enough fluid to apply the pads. Just my thoughts, Bob __________________ Bob Mulry 7516 STK A & M Motorsports

02-24-2011, 02:03 AM	#8
A Closkey Junior Member Join Date: Oct 2008 Posts: 1 Likes: 0 Liked 0 Times in 0 Posts	Re: Brake problems? You didn't use Silicone fluid, did you? This stuff will produce a crappy pedal.

02-24-2011, 10:11 AM	#9
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 using a 7/8 master cylinder now. I've talked to some of the brake manufacturers, and they don't have anything smaller. That is why I'm going to see if I can change to a larger piston caliper. I now run a 54mm (2 1/8") pston. I'm hoping to use a 60mm (2 3/8) With the 22mm (7/8) master cylinder. The master cylinder (power brakes) for that application is 24mm (15/16). I'm hoping to get the car to hold at a higher rpm against the foot brake. Regular brake fluid not #5 __________________ Art Leong 2095 SS

02-27-2011, 05:28 PM	#10
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 new news yet? Are you using factory stuff. mopar has some real light aluminum calipers made by trw of mexico it is I believe. have you driven car around at all. I say you can't just run it without driving it to settle all brake parts and get a real feel. Good luck Art. Chris.