squishy brakes

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Whenever I am at a full stop, such as a signal light, and put constant pressure on the brake pedal, the pedal will slowly move towards the floor. Let up on the pedal and the cycle starts over. Normal braking seems not to be affected otherwise.
This has been going on for quite awhile.
Any ideas?
Gary


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'92 250 LE 4x4,NV4500 5 spd,Borgeson steering shaft

 

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My opinion is that your master brake cylinder is leaking. I have had the same problem on one of my cars and a previous truck. Usually if you hit the brake real hard the pedal will hold but if you apply steady pressure your pedal will fall. Sounds to me like you need to replace or rebuild the master brake cylinder.
Cheers,
Al

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92-LE,Cummins,Tach,4x4,5spd,3. 54,Borgeson steering shaft,

[This message has been edited by Al Kungel (edited 10-26-2000). ]

 

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Al, should I see leakage around the master cylinder if it is fact leaking? Things look pretty clean and dry under the hood tho I have put 137K+ miles on it since it was new and still on the original brakes.
Still, master cylinder sounds like a good cluprit... . thanks.

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'92 250 LE 4x4,NV4500 5 spd,Borgeson steering shaft

 

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The same thing has happened to me last year... . exact same thing. I replaced the master cylinder and everything was great... for a while. Now it's starting to do the same thing all over so I've just learned to deal with the problem... . it's not that major to me.
cody

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91 4x4, 5 speed, 3. 54 gears, pw injectors, 12cm turbo housing, K&N air filter, "tweaked" pump, isspro boost and pyro gagues w/A pillar mount, straight piped 3' exhaust

 

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Gary, you will not necessarily see any external evidence. What is happening is your getting brake fluid by-pass (when you push the brake pedal the piston in the master brake cylinder moves to push fluid to the wheels, but some brake fluid is getting by the O rings on the piston and is thereby returning back to the reservoir and therefore your pedal will slowly bottom out).

At one time I didn't drive our car too much and I didn't know there was a problem. My wife really stomps on the brakes at the last moment before she comes to a stop light and then the brakes hold. I on the other hand will apply the brakes quite a bit before I come to the stop light and slowly glide to a stop. Well when I drove the car guess what happened all of a sudden the pedal is on the floor and the car is moving as I am coming up behind the car in front of me - lucky I was able to swing into the other lane and avoided rear ending collision.

In my opinion, brakes are the most important device on a vehicle.
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Al

 

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Better safe than sorry just replace your master cylinder. Personaly I don't like rebuilt units suggest cost aside that a new unit is better in the long run. You can do this job yourself, but consult the service manual first, there is a special proceedure to follow due to the antilock brakes. Also check your brake shoes,low pedal can be a result of worn or out of adjustment rear brakes, note if your truck has limited slip only one rear brake may be working and it won't pull.


regards Neil C

 

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I will get the master cylinder looked at and go the new route if necessary. Agreed that brakes are pretty darned important. Thanks for all the help.
Gary

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'92 250 LE 4x4,NV4500 5 spd,Borgeson steering shaft

 

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GLG, I have replaced 4 count um four master cylinders, all Brand New units to no avail.
I have even replaced the Vacuum Booster to no avail. You have described exactly what my truck has done since day ONE. I just can't help but beleive it is in the Antilock system in the rear. No leaks, never had a leak, anywhere. I have tested the pressure from the vacuum pump and it is right on with the Shop manual. My next step is to run new lines bypassing all Antilock equipment directly to the rear wheel cylinders.
Good luck, Walt

 

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Walt,

Keep us posted on the brake line re-route. Let us know how it works out.



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Stan
93 2WD extended cab, Banks Power Pack, K&N Air Filter, PW Injectors,Auto w/4. 10 rear with limited slip, US Gear Exhaust Brake, 31/2" Exhaust, 5K air bags, Boost/Pyro/Tach Gauges, Green/Silver, 146K