brake issues

[Benz300]

It's for a non mercedes, mitsubishi montero.
after 3 new master cylinders the pedal still is spongy, pedal engages half way through and the stopping power is 35% of what it used to be before this problem occured. However, if i pump slightly and then press the brake pedal again it always is firm. Though the braking poewr still comes and goes even with this double pumping action. at times the brakes engage perfectly but subsequent brakings are back to less power.
the dealer service center and also the private shops i went to, bleed the system with the two person method. they donnt even use a bottle and pipe at the bleeding screws. they just squirt the fluid out.
with zillions of posts on shops having actual gadgets to bleed the m/c and the brake lines properly , I wanted to know if anyone knows of such specialty brake shops in central NJ area.
really would appreciate any input on the problem and also a recommendation for the shop.
thnx.

[t walgamuth]

like air in the system. no way to know if they are bleeding correctly. did you watch them?

tom w

[Benz300]

yea i watched them. at two private shops i actually was sitting inside while thhe mech. opened annd closed the valves. the pedal feels firm once you push on it twice with engine off. however, the moment the engine is turned on, the pedal drops about 6 inches towards the firewall.
that is with constant pressure. The drop was never more than 2 or so inches when the system was performing well.
all the process in this article has been followed.
http://www.classicperform.com/TechBook/BrakeBleed.htm

[Benz300]

allright, bled the brakes thoroughly over the weekend.
no change whatsoever,
once the brake is pumped, the pedal is high and stays high.
with the engine off, the pedal firms up and doesnt drop at all.
so the m/c is not the problem here.
that leaves the brake lines or the callipers.
without air in the system, what else could be causing this ? any ideas ?

[yal]

Bad brake booster?

[Benz300]

the second application of the pedal always gives perfect pedal and brake power.
had the booster been bad wouldnt the pedal be rock hard and difficult to press rather than being so soft on first application and then OK on every subsequent applications ?

[Richard Wooldridge]

Hi there,
It still sounds like air in the lines to me. It's real easy to get a bubble of air trapped in a high spot that won't get pushed out during a normal bleeding process. Try to eliminate any possible air in high spots. Sometimes a very fast, forceful depression of the brake pedal when bleeding will move the bubble along. Sometimes one can very slightly loosen the lines at the master cylinder and force a bubble of air out there.
It is very normal for the pedal to be hard with the engine off, and go down when the engine is started, it is just a testament to the help the power booster is capable of giving you.
Sometimes a reverse flush will eliminate those pesky air bubbles.

[Matt L]

I don't know if that car has rear drum brakes, but drum brakes can do this if they get out of adjustment. They're supposed to self-adjust, but on some cars, it's necessary to use the parking brake to make them work.

[wbain5280]

Does the car have ABS brakes? If so, check for proper bleeding procedures.

[Benz300]

rear are discs as well.
yes the suv does have abs but the abs stopped working years ago. brakes were finne even after that though.
as for bleeding, the abs modulator doesnt have any bleeding screws so can't be bled.

[Ralph69220d]

I wasn't quite clear whether you bled the new MC's you installed. A new MC does need to be bled. Some MC's come with a fitting & rubber hose to bleed the fluid back into the MC; then follow the other member's suggestion of getting any residual air at the top of the line where it connects to MC. If all air is out of lines then it sure sounds like the pads are too far from the rotors causing the need for a second pump. Even with the two person method stubborn air bubbles can be hard to move to wheel cylinder / calibers for bleed off. A high pedal with the engine off is normal, even with an incomplete bleed. Again, make sure you've bled the MC properly in all reservoirs.

[autozen]

Have the front calipers been replaced recently like just before the problem started?

[Benz300]

two different master cylinders have been tried. they were all bench bled before installation. no change on the pedal height.
the callipers were not changed, and there was no brake service done right before the problem occured either.
..... what else...

[t walgamuth]

bleeding is no substitute for bleeding after installed. it just makes it quicker and easier.

tom w

[cunix]

Hi there Benz300,

I had gone through exactly the same experience, also on a Mitsubishi.
It turned out the master cylinder's piston was wrongly inserted. During assembly, the mechanic seems to get confused which is the correct end as it looked the same. Try to sort that one first.

On another occasion, also with the same car, I had experienced the one way valve (located in the vaccum line going to the servo) failure. The symptom was, the pedal became very-very stiff during braking whenever the turbo kicks in (positive vaccuum).

Finally, also with the same car, I had replaced the brake booster. This time the symptom was the car could not idle properly because of vaccuum leak.
This was by far the most difficult to solve as I never suspect the bad idle to be caused by the brake booster. Well after replaced the booster, it cured the engine idling problem and I also notice the pedal has less travel, less spongy feel and more bite during braking. Upon disassembling the faulty brake booster(had to hack to open it though). I foungd the diaphram had torn thus causing the leak.

Sorry for the long post, but I seem to think that your problem could relate to one of the experience that I had gone through.

Cheers