Kennyjai

iTrader: (3)

I'm still having a soft brake pedal after bleeding my brakes four times (using the two man method). I recently upgraded my front brakes to the 11" mini cooper rotors & legend 2 pots with hawk hps pads. I did the bed in procedure on the pads correctly and bled the system four times in the right bleeding sequence (i have a 01 DC) but I'm still having a soft pedal. Someone suggested gravity bleeding but I have yet had the time to try that out.


Here's some things i notice:

-brake booster should be good, the pedal holds firm after I pump it several times while car is off and drops a little when the car is started
-brake vacuum holds fine, no rpm jump
-the pedal doesn't drop to the floor while at a stop light so I'm pretty sure the master cylinder is OK and yes it is original

On a side note...my rear's have been squeaking while driving. It's because the pad's are low, about 1cm left. This should have no effect on the pedal right?

So what could it possibly be that is causing my pedal to be so soft now? Internal leak in master cylinder?

mark@silbernage

were you able to rotate the calipers to get the bleeder up top?

If so, I wonder if it's worth taking it into a shop to bleed them under pressure and force the air out... ?

TREESnoseeds787

http://www.bmw-m.net/TechProc/bleeder.htm

Those are worth making ^

I'm not a brake expert by any means, but it looks like you have done most of the troubleshooting. The only other thing I could think of is the possibility of a weak rubber brake hose possibly expanding under pressure? Causing the pedal to slowly get soft as you mentioned. Hopefully others will chime in on this subject.

JOE_DC4ever

For one, one centimeter of pad life left is more than most pads come with brand new... You mean one millimeter? As for the bleeding. Have you gotten the brakes to work properly before the pedal issue? If not, then the problem probably lies in the modification you did, not the bleeding. The pedal pressure loss is most likely due to the fact that you upgraded caliper (piston) size but did not upgrade the size of your MC. All these components are designed to work with each other, change one, and you change the dynamics of the system..

sebTeggy

FSM:

Not sure if you have done all this.



BRAKE BOOSTER INSPECTION

Functional test:
1. With the engine stopped, Depress the brake pedal several times, then depress the pedal hard and hold that pressure for 15 seconds. If the pedal sinks, the master cylinder, brake line or a brake caliper is faulty
2. Start the engine with the pedal depressed. If the pedal sinks slightly, the vacuum booster is working. If the pedal height does not vary, the booster or the check valve is faulty

Leak Test:
1. Depress the brake pedal with the engine running then stop the engine. If the pedal height does not vary while depressed for 30 seconds, the vacuum booster is OK. If the pedal rises, the booster is faulty
2. With the engine stopped, depress the brake pedal several times using normal pressure. When the pedal is first depressed, it should be low. On consecutive applications, the pedal height should gradually rise. If the pedal position does not vary, check the booster check valve.

Check valve test:
1. Disconnect the brake booster vacuum hose at the booster.
2. Start the engine and let it idle. There should be a vacuum available. If no vacuum is available, the check valve is not working correctly. Replace the check valve and retest.

END TEST

JOE_DC4ever

The way hydraulics work, is that the force applied to the MC gets multiplied by the ratio between the sizes of the two pistons (caliper piston/s and MC push rod). The output piston (the caliper piston) moves much less but with more force while the input piston (MC push rod) moves much more but requires less force.

So let say your original caliper piston area is 1 square inch and your MC push rod area is .25 inch. In this instance if 100 pounds of force is applied to the MC through the pedal, then the force at the caliper will be 400 pounds (ratio of the areas of the pistons is 4:1)

So now you upgraded to lets say 1.5 square inch caliper pistons. Since the MC is the same, the force at the caliper is now 600 lbs. Which sounds good until you realize that your car is going to start slowing down with roughly the same amount of pressure on the pads as before... So ASSUMING that the car only NEEDS 400 lbs to slow down as before, then you calculate backwards and find out that that with the new ratio of piston sizes (6:1) your foot only needs to input 67 lbs.. this effectively reduces the pedal pressure you are used to.

DirtyDA9

Brake pads are measured by 32nds of an inch. The lowest a pad can be to pass inspection is 2/32nds, most pads new are about 6-8/32nds. For example, take a penny, 2/32nds is from the outside egde of the penny (above abe's head) to the top of his head.

JOE_DC4ever

Good to know.. ^^ but also validates my point. At most you say a new pad has 8/32 on an inch.. that is only 6.35 millimeters.. he said he had low pad life with 1 cm (10 mm) of pad left...

Kennyjai

iTrader: (3)

Sorry guys, I probably meant 5mm of pad since they are already starting to squeal. I believe the min thickness is no less than 2mm of pad in order to be considered "safe". I don't think pad has to do anything with the softness of the pedal, maybe the initial bite only.

I had already swapped sides of the calipers so now the bleeder valve is at the top, about 10 o clock. I completed the bleeding sequence four times and the pedal is still soft.

I understand that it's important to upgrade the master cylinder to a larger size if I have bigger piston calipers but I have an 01 integra..isn't my master cylinder a full size already? I thought about that once, having a bigger calper with two pistons vs one would mean I would have to push the pedal farther?

And I will try to complete the brake booster test. What other reasons could it be?

JOE_DC4ever

You are correct, the MC and brake booster should be sufficient to run those calipers. Try using a vacuum bleeder and a clear tube to make sure no air is left in the system. I'm sure the MC, Brake booster, and hoses are all fine... Things don't just go bad coincidentally after you modify something. That means the problem should lie in the bleeding procedure, the alignment of the calipers/rotor, or possibly just bad calipers..

standy xsi

Im assumeing you refiled your brake fluid after bleed? jus asking as you didnt say it

Kennyjai

iTrader: (3)

Correct, the resevoir was topped off every now and then during the bleeding process and I did have the resevoir cap closed until the pedal was fully released.

What will a vacuum bleeder do that a two man method can't? I don't want to buy it if it's not going to help at all =/

TheRealTegger

You did mean to say you meant that you kept the caliper bleeder screw closed until the pedal was released, yes?

Kennyjai

iTrader: (3)

Yes, closed bleeder before pedal released but I am saying that the resevoir is closed until the pedal was released before I ever topped it off, that way I wouldn't be sucking in air.

I honestly can't think of any other reasons that make cause the pedal to be soft still. I also noticed that when im at a stoplight, the height of the brake pedal is about EQUAL to the free gas pedal (meaning no foot on gas pedal). Is this normal? I think the brake pedal's about half way depressed.

90_EX_Civic

does your car still have abs? if it does, did you bleed your abs unit?

Kennyjai

iTrader: (3)

Yes I do, but I don't know how to bleed it. I don't even think I can, don't only the older teg's have a ABS resevoir? I thought the new tegs have a smaller ABS unit.

DirtyDA9

Did you bleed them in the correct order?

Edit: nevermind, you said you did it in the proper sequence...

1998GsRIntegra

Well now that you have me contemplating returning every part I just bought to do the exact same upgrade you did...lets just say I will be following this thread closely.

Your saying that your pedal is spongy and you have much less pedal travel? If I understood you correctly.

And yes, the newer tegs (can't remember exactly what year) no longer had the seperate bleeder on the abs module.

Have you tried a hot bleed yet?

Kennyjai

iTrader: (3)

what's a hot bleed? I kind of hate my new calipers too, I drove in the rain today and they got all rusted...like the rain water on rotors look (the orange powder)

1998GsRIntegra

A "hot bleed" would be bleeding the brakes on a car as soon as it gets back in the paddock from an on track session. When the system is hot any air will have expanded more so than under normal use making it easier to bleed out. Basically go to a safe area and do 60 to 5 or 10 mph stops until you get some brake fade. Drive around and let them cool down a bit. Then go and bleed the brakes. Don't actually come to a complete stop though during the process as you will leave an imprint of the pad onto the rotor.

Also, not sure if you went with SS lines when you did the install, but I would highly recommend them. The OEM lines deteriorate and flex more when they age resulting in a spongy pedal.

You may want to consider changing out the brake fluid as well. Over time mositure builds up in it reducing its boiling point, and thus rendering it not as effective.

Out of pure curiousity, did you buy raybestos re-manned calipers? I ask because I did and if you also did and they rusted that quick I'll paint mine with some g2 paint before I install them.

EDIT: Having low rear pads will effect your pedal travel a bit as the piston needs to be pushed out farther to clamp the pads thus using more fluid and as a result increasing the pedal travel.

Corollz

Was about to say the same thing

90_EX_Civic

there should be a bleed valve on top the abs unit. and hate to say it, but do a how to search on bleeding the abs unit.

brownboi512

i had a similar problem last year. brake pedal kept going to the ground even after bleeding multiple times. fixed it by replacing the brake master cylinder and bleeding from there. i didnt see a leak in the MC, but it was failing. just a thought to check it out if bleeding doesnt fix your problems.

fd380ps

I had that same problem after i replaced my master cylinder on my race car. I fixed it by removing the master cylinder and bleeding it off the car.

I used table vise to hold the master,
I stuck to 1/4" hose on the outlet of master and had it returned to the reservoir.
Used a screw driver to pump the master until the bubbles are gone.

hope this helps

Andrew

Kennyjai

iTrader: (3)

bumping this thread up. never replaced the master cylinder but i plan on doing so very soon because the spongy pedal is really bothering me.

i notice that the very first pedal pump i can hear a hiss air sound and now when i release the brake pedal i hear a little squeak. pads and rotors are all new, no brake fluid drop in master cylinder, prop valve is not leaking, brake lines are not leaking, bleeders are tight.

I've done the brake booster functional and leak test and it holds pressure. With the car off, I pump the brakes a few times until it gets "firm" but it isn't completely firm to the point I can't push it down anymore like my friends lexus. I can still push it about another 1in, is this due a internal seal leaking inside the master cylinder? or is it my brake booster?

or is just the nature of the legend 2 piston calipers? does a brake pedal feel different when you upgrade from one piston caliper to two piston?