94 F150: Over-sensitive brakes not tripping brake switch?

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Mike - 16 Nov 2006 23:10 GMT

Hello all.

I picked up a 94 F150 (5.0 litre, auto, 2wd) this spring and have an
unusual situation: the brakes are too sensitive! I barely have to
touch them before the pedal goes down. It goes down about half way
before there is any resistance. Odd thing is, the brakes work fine.
(nice even skid patches on the street) Nice even braking.

At first, I thought air in the lines, so I bled them, twice. (a fluid
flush couldn't hurt anyway..) On the off chance that the master is
defective, I replaced that. No change. Replaced pads, shoes, drums and
rotors. No change. (front calipers and rear brake cylinders were good,
no leaks).

Is it possible for the brake booster to fail this way? Any other ideas?

The problem with all this is that the tiny amount of foot pressure on
the brake pedal does not trip the brake switch. Thus no brake lites,
and since I also tow a trailer with electric brakes, no brakes and brake
lites on the trailer either. I'm worried that one day I'll be
rear-ended by a semi...

Thanks in advance for your help.
Mike

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Bill Schwab - 16 Nov 2006 23:38 GMT

> Hello all.
>
[quoted text clipped - 11 lines]
>
> Is it possible for the brake booster to fail this way? Any other ideas?

Dumb question: is it simply that the pedal/linkage is way out of
adjustment? What you are describing sounds a lot like the correct
behavior for the very top of the motion, assuming you don't get any
braking until you feel resistance???

Good luck!

Bill

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Mike - 17 Nov 2006 23:04 GMT

The brakes work almost right away. At idle and in drive, I need only push
about 1/2 inch to stop the truck. If I we to puch till I felt resistance, it
would be about the same as doing a PANIC stop.

Another test I tried was with the engine off, the brake is very firm, I could
only push about 1/4 inch. I know that this is really just testing the spring
inside the brake booster.

Thanks.
Mike

> > Hello all.
> >
[quoted text clipped - 20 lines]
>
> Bill

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Teddy Bear - 18 Nov 2006 06:34 GMT

Try restricting the vacuum to the booster by putting a clamp on the hose.

Report back.....

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Bill Schwab - 18 Nov 2006 16:25 GMT

Mike,

> The brakes work almost right away. At idle and in drive, I need only push
> about 1/2 inch to stop the truck. If I we to puch till I felt resistance, it
[quoted text clipped - 3 lines]
> only push about 1/4 inch. I know that this is really just testing the spring
> inside the brake booster.

Thanks for replying, though based on the later replies to your question,
I'm not surprised at the results.

Good luck with the repair!

Bill

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lugnut - 17 Nov 2006 00:41 GMT

>Hello all.
>
[quoted text clipped - 20 lines]
>Thanks in advance for your help.
>Mike

I just replaced the booster on my CV for that very reason.
At least it started that way and soon did not completely
release unless iI lifted it with my foot. It wasn't too
long that it would just apply the brakes as soon as I
started to push the pedal. Wife damn near burn't the pads
off it driving to the store. Called me complaining that car
wouldn't move. She took it while I was out of town for a
day or two. I guess I should have told her but, who'd have
known she would have taken my car to the nursery for compost
since she a perfectly good car of her own.

Lugnut

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