We have a 2001 pickup and when we start it up the brake pedal depresses and the brakes automatically apply....on it's own.
Any explanations would be greatly appreciated.
Thanks.

 

I'm no brake expert, but I can only think of 2 reasons why a brake pedal would/could apply on it's own.

1. Faulty/stuck valve in your hydroboost unit.


OR


2. If you have vacuum brakes, you might have a tear in one of the diaphrams.


Are the 2001's 4 wheel disc?


You're gonna like this site. Watch how many responses you get. It's wild.



Good luck.

 

Hey there check for a vacume leak at the master cylender . and does the pedal go all the way to the floor ?

 

now thats an interesting gremlin. Ive heard of the engine running away when it is first startred, but the breakes engageing is a first.

 

This forum is great! Thanks DieselDemon and i11m10c2 for the responses.
Here is more detail on our situation....
The 2001 pickup does have 4 wheel disc brakes but not vacume brakes. We started out with no brakes at all. Then after putting in a new master cylinder and new brake booster the problem started with the brakes automatically coming on. We suspect it may be the booster but not sure. Through deduction we put the old booster back on and it still is doing the same thing. We even tried bypassing the booster and the problem is still the same.
Does this help in narrowing down the problem?

 

you may have the suply and return lines from the hydrobooster backwards, if thats possable.

if not that the hydrobooster may be air locked, I can see that causeing the porblem.

 

I am pretty sure the Rams use two different sized, inverted flare fittings at the hydro unit. Even if they were plumbed backwards, you would simply have no assist.

I'm not being a wisenheimer, but you're positive you have a hydroboost unit attached to the master cylinder? It has three hoses and a cylindrical nitro can, that looks like it would hold 2 midget tennins *****. No offense to midgets.....or their *****.

How well did you bleed your brake system? Is there any special procedure to follow for ABS? It takes a lot to damage a master cylinder to the point where it is faulty. Did you replace the exsisting mc with a mc of the same bore? If not, THEN you would have issues. Nothing which would cause the "mystical pedal" routine...lol.


I am stumped at the moment. We need to narrow down which type of booster you have. You mentioned bypassing something. There's nothing to bypass and a hydro unit. And there's only a check valve on a booster. The mc is bolted to one or the other.

Keep us advised.


Good luck.

 

all the hydro boosters Ive messed with did have two different sized fittings, however I realy havent studdied the one on my ram to know. I just threw that out there casue I know how engineers can develop some part very well on CAD, but it is hell to change when your haveing to wrench on it. (brake job on a military hummer, may arms are too long and there is no way I can contort myself to break the bolt loose[:@])

the ABS only works off a sensor and a geared wheel bolted to the axel. it has nothing to do with the mechanics of the brakes, but I still believe you have an air lock somewhere.

 

I have no Idea what the issue is but keeping conversations PC can be fun!



[sm=icon_rofl.gif]

 

No brake man here either, but I would definitely check the plumbing again with a shop manaul in hand.