Brake System Help

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Jun 28, 2008 | 04:35 PM

RoyalFord

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From: North Carolina

Brake System Help

I’m having some issues with my brakes that I just can’t figure out. The problem is that my brake pedal is low. I can stop fairly well, but I must travel great distances with my foot. This is a major problem because I’m lazy. When I bleed the system, the firmness of the break pedal is immediately restored but to no avail, around three to five days later my pedal is low again.

I’m not losing any fluid, so I was guessing it was the master cylinder. I’ve already replaced it three times in the past month from different parts dealers and none of them fixed the issue. My hypothesis is that I’m getting air in the system somewhere, but for air to get in fluid has got to go out somewhere, right?

Let’s just assume that it isn’t the master cylinder. What can I check?

Truck = 1998 F-150 4x4 Lariat (Front Disc & Rear Drum) ABS

Jun 28, 2008 | 05:02 PM

Bobby82490

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From: N. Fort Myers,FL

Maybe there is air trapped in the ABS controller...?

Jun 28, 2008 | 05:32 PM

RoyalFord

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From: North Carolina

That is something the dealer is going to have to take care of, right? Power bleed it?

Jun 28, 2008 | 07:32 PM

Club Wagon

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Pretty unlikely to get 3 bad MC in a row, presuming they were new. How did the bench bleeding go?

Quote:

Originally Posted by bvoncannon

replaced it three times

My hypothesis is that I’m getting air in the system somewhere, but for air to get in fluid has got to go out somewhere, right?

No. Air that gets in does not equate to fluid going out. Air in the lines & components acts like a spring, increasing pedal travel. The fluid that's displaced doesn't "go out" it returns to the reservoir.

There's been considerable discussion on rear drum brake adjusters. Seems that many people have had a lot of trouble w/them. If your rear brakes are out of adjustment you'll have a lot of "travel" before shoes contact drums.

Jun 28, 2008 | 08:07 PM

Bobby82490

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From: N. Fort Myers,FL

Quote:

Originally Posted by Club Wagon

... If your rear brakes are out of adjustment you'll have a lot of "travel" before shoes contact drums.

I was thinking about mentioning this, but if it is firm right after he bleeds it then shortly after it starts getting a mushy pedal.. i would think out of adjustment shoes would be unlikely.
Now if you couldnt get a firm pedal, then out of adjustment shoes could be a likely culprit.
How many times have you bled the brakes and then they get mushy?

Jun 28, 2008 | 08:12 PM

RoyalFord

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Bench bleeding went fine. I had plastic lines coming out of both ports and placed the other end of the line back into the reservoir submerged in fluid. Then after about 10-15 slow pumps, no bubbles.

I've checked through peep hole on the backing plate on the rear drums and the shoes are all the way against the drums. Also, I pulled the drums off and adjusted the shoes out as far as possible to the point where the drum wouldn’t even go back on... so I then backed the shoes off a little.