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Need help - problem with brakes


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11 replies to this topic

#1 danas

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Posted 13 February 2004 - 01:20 AM

I cant figure out what is wrong with brakes. Brake pedal has to travel all the way to the floor until it starts to brake.

Then the engine is off you can pump the brakes , but it still feels spongy. then depresing the pedal, in the middle of pedal travel feels small resistance, but it clicks and goes deeper.

Did bleeding - didn't helped.
Had a dealer inspect it - he said it's master cylinder.

I instaled a new Master Cylinder myself, bled the system - same thing, nothing changed at all..

Now I'm quesing it's brake booster. But it's pretty expensive, I don't want to throw any more money replacing good parts.

When I was changing master cylinder, noticed one thing - then I touched the pin coming from power brake booster I heard the air coming out. (That pin supose to push the master cylinder). Could it be, that it's leaking vacuum thru here ?

Inspected vacuum hoses for leaking , but didn't noticed anything.


Could any one explain how to check brake booster if it works
properly?

Could something else be wrong ?


Thanks,



1995 Subaru Legacy L, 2wd, 2.2 , automatic. front disk, rear drums.

#2 hb_kim

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Posted 13 February 2004 - 03:00 AM

If booster is NOT leaking, then you should feel the difference in resistance when you depress brake pedal a few time, while engine is off. According to what you said, this is not the case.

Quoting from Haynes manual:
Other than faulty master cylinder, Spongy pedal might come from
- Faulty hoses
- Master cylinder mount
- Rear drum brake not adjusting properly

#3 Tolerance02

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Posted 13 February 2004 - 06:49 AM

A failing booster should result in high and hard pedal pressure.
There is air in the system or pads or shoes are mounted incorrect.
Sometimes the rubber dust cap on the front brake pistons can be wedged between the piston and the pad, this causes the same effect as if there is air in the system.
Also the shim plates on the pads may cause the same problem, if
placed incorrect they work like a spring that pushes the piston backward.

Hope this may be some help.

Urban.

#4 Setright

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Posted 13 February 2004 - 07:56 AM

Engine off, pump the brake to relieve the booster of vacuum. Pedal should become harder.

Rest your foot on the brake as you start the engine, the pedal should drop further toward the floor. If this happens, then the booster is most likely okay.


Your problem could sound like faulty seals on the pistons in the master cylinder, but since you replaced the MC...?

Check the condition of your brake hoses, the ones that lead from the lines to the caliper at each wheel. If the reinforcement inside these hoses separates a "ballon" will form on the hose and will be easy to see. It will also give a very spongy brake pedal.

#5 yohy

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Posted 13 February 2004 - 11:52 AM

danas,

From the FSM for my '97 Legacy, these are the various checks for the Brake Booster:

AIR TIGHTNESS CHECK
Start engine, and run it for 1 to 2 minutes, then turn it off.
Depress brake pedal several times applying the same
pedal force as that used in ordinary braking operations.
The pedal stroke should be greatest on the 1st depression,
and it should become smaller with each successive
depression. If no change occurs in the pedal height while
in a depressed state, brake booster is faulty.

OPERATION CHECK
1) With engine off, depress brake pedal several times
applying the same pedal force and make sure that the
pedal height does not vary with each depression of the
pedal.
2) With brake pedal depressed, start engine.
3) As engine starts, brake pedal should move slightly
toward the floor. If no change occurs in the pedal height,
brake booster is faulty.

LOADED AIR TIGHTNESS CHECK
Depress brake pedal while engine is running, and turn off
engine while the pedal is still depressed. Keep the pedal
depressed for 30 seconds; if no change occurs in the pedal
height, brake booster is functioning normally; if the pedal
height increases, it is faulty.

Hope this helps.

#6 danas

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Posted 13 February 2004 - 01:06 PM

Thanks a lot for recomendations how to check power booster.
Booster is really working. I even reconected vacuum hose, and diference is tremendous, pedal became very very hard.


Gonna try to remove and inspect supports, rubber lines.. have no idea, what else could be wrong :(

Thanks once more ;)

#7 Phillip

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Posted 13 February 2004 - 01:32 PM

When did this problem show up? Have you done anything to the vehicle recently that might have caused this problem (ie replaced brake pads or a hydraulic line)? Spongy pedal feel and pedal traveling to the floor but being able to be pumped up are classic symptoms of air in the system. Modern vehicles with ABS brakes can be difficult to purge all the air from the brake system. I'd try bleeding the brakes again if it were me.

#8 danas

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Posted 13 February 2004 - 01:59 PM

My wife drives this car, but she never told me about this until I took this car for a ride.
I changed brake fluid and brake pads about a year ago and I'm sure it was fine after that. Once in the while I check everything, but this problem starter recently.

First what I did, I changed and bled the system.
After that changed master cylinder and bled system again.
Nothing changed..

Have to look at the pedal mechanism itself too, because this free play is really so big. Doesn't feel any braking untill pedal reaches the floor (maybe 1 inch to the floor)


and this car has no ABS..

#9 SevenSisters

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Posted 13 February 2004 - 06:29 PM

Check the adjustment of the rear shoes. If the shoes have to move to far,to reach the drums, you really have to pump up (fill) the cylinders. Hence, all the symptoms you describe.

#10 tcspeer

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Posted 13 February 2004 - 07:22 PM

Did you bleed the master cylinder? It has been a while since I chg. one but if I remember correctly you have to bleed that separate from the other cylinders.

#11 Hank Roberts

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Posted 12 July 2005 - 05:29 PM

Ever solve this one???? Happening to me, found this thread belatedly after starting a new one, in the Older Generation area (1988)

#12 danas

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Posted 12 July 2005 - 09:53 PM

Hi,

It's really embarasing to admit.. problem was in brake pads.

I didn't took them off to inspect. Just looked over the hole and they seemed to be thick enough.

But acctualy the ones sitting next to the cylinder were stuck and not moving at all. The other side pads were worn out and only ones moving.. so thats why I had to press brake pedal so deep...

:banghead: stupid me..




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