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.

Re: Brake problems?
 

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

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

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.

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

Re: Brake problems?
 

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


Ron Waters 1346 s/st

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.

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.

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.

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?

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

Re: Brake problems?
 

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

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

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.

Re: Brake problems?
 

Put a new mastercylinder. Still have the problem. Bench bled the new master. Bled the brakes over and over. Doesn't seem to make a difference. The pedal seems a bit spongy. Checked all the fittings there doesn't seem to be any leaks.
On the jack stands I can ony hold the brakes to 3000 then the wheels start to turn.
I think it would be a little bit more rpms with the wheels on the ground.
Going to try to bleed them one more time. Tomorrow. With someone that I know can pump and hold. If it doesn't get better I'm going to put it on the ground, and try it.
If not I'll just leave at 2500. I doubt there will be any trouble stopping at the finish line.

Re: Brake problems?
 

Put a pressure gauge on them today. With left foot only pedal I got 1100 psi on the front.
600 on the rear. Before I changed the ratio I needed 2 feet pressing as hard as I could to get to those numbers..
Does the difference from front to back seem correct? I have an adjustable proportioning valve.
Hoping that when I put it on the ground I will pick up a few hundred rpms in holding against the converter.

Re: Brake problems?
 

Re: Brake problems?
 

Thanks for this I read it and it answers some of my questions.
But the Chrysler FWD cars. are biased brakes (?) the front part of the master supplies the right front and left rear wheels, the back chamber supplies the left front and right rear.
I have changed all that and and now my 2 front wheels are supplied by the rear part and my rear wheels are supplied by the front section.
One thing that the article brings to light is that my fronts have 54 mm pistons my backs have 34mm pistons. The stock setup would supply a 54mm and a 34mm piston. Now my fronts call for two 54mm pistons. I wonder if I have the volume to supply them? The master cylinder is 22mm. Not sure of the stroke though.

Re: Brake problems?
 

Art,

I found this blog that may give addition insight to your situation: http://forums.nasioc.com/forums/show....php?t=2076386

Re: Brake problems?
 

Thanks. I'll look that over. Ironicly I was looking on that forum to see about hood Subaru hood scoops. To cover my four throttle bodies when I put them on.

Re: Brake problems?
 

Art, forgive me for asking a dumb question, but are your bleeders all on the top side of the calipers? I had a friend with similar issues on a Ford, and the calipers were installed on the wrong sides. Once he changed them, the pedal was firm on the first pump.

Re: Brake problems?
 

Thanks Arnold. I'll check that first thing tomorrow. I think they are on right but anything is possible.

Re: Brake problems?
 

There's your problem Art...you should have two on the right and two on the left.

Re: Brake problems?
 

Thanks to all for your help. With the car on the ground they worked fine. Stalled to over 3500 without my left leg shaking, and driving around the pits it feels like a normal manual brake car.