2nd Gen Non-Engine/Transmission Help Brake pedal goes right to the floor

[Neibe]

When I start my truck up the pedal goes to the floor without me touching it.

 

[Lightfoot]

First thing I'd do is make sure there is not a fluid leak. Then maybe see if the vacume booster has vacume. The master cyl. is collapsing without pedal pressure. It would seem that that cannot happen without a fluid or a vacume deficiency. I just went through some weird "soft pedal" stuff with my truck after a front rotor, pad, and brake hose install. Ended up having the lines power bled. That seemed to fix the problem. Also had to adjust the rear wheel cyls. a few clicks.



96 2500, 4x4 ,AT,4"exhaust,354gears,Power Loc rear diff. ,Pac Brake

 

[Neibe]

The thing is I don't touch the brake pedal I can wathc the pedal when I start it up. The pedal is being pulled to the floor with out me touching it the brakes are locked up I can't move jacked up the front end can't spin the wheel.

 

[Stamey]

The thing is I don't touch the brake pedal I can wathc the pedal when I start it up. The pedal is being pulled to the floor with out me touching it the brakes are locked up I can't move jacked up the front end can't spin the wheel.

Does it have a hyroboost or vacuum brake booster?



Chris

 

[Neibe]

Hydroboost I'm thinking the power steering pump gave out and it isn't getting pressure to power the hydroboost. Is this likely? Except I still have power steering.

 

[Stamey]

With a hydroboost, you probably have a valve stuck open in the hydroboost, so the "assist" part has now taken over. I can't tell you exactly where that valve might be, but hopefully someone else here can get into more detail so maybe you can fix it yourself, without replacing the unit.



Chris

 

[Dave M]

I replaced the hydroboost unit in my 97 about 2 months ago with a new one from www.hydroboost.com . I didn't want to deal with rebuilt failures. The way the hydroboost works is the brake pedal is connected to the rod coming out of the hydroboost unit which is mounted on the firewall. The master cylinder is bolted to the front of the hydroboost unit. A small rod comes out of the hydroboost unit and pushes into a cup of the master cylinder.



The hydroboost unit has power steering lines going to the power steering pump and steering box. As you can see there is just a mechanical connection from the pedal to the hydroboost and from the hydroboost to the master cylinder. I separated the master cylinder from the hydroboost to replace my hydroboost unit and left the master cylinder connected to the brake lines even tho the manual said to disconnect it and the combo valve below it. There is a cast metal spacer between the master cylinder and hydroboost with bolts holding it on and bolts from master cylinder to the spacer.



If the hydroboost doesn't work the brakes will not. If you don't have an obvious leak somewhere then it might be the hydroboost. If you separate the master cylinder from hydroboost you may be able to see if the rod sticking out of it is moving forward when the pedal is pressed. The hydroboost wasn't too bad to replace... and I'm a novice at this.



Heres a link to a thread that has 2 pics of the hydroboost unit.



http://www.tdr1.com/forums/showthread.php?t=130868&page=3



One pic is of the hydroboost in the truck. You can see the gold anaodized can on my new hydroboost unit. Thats the accumulator which is gas pressurized to give you 3-4 pedal presses with engine off. The old accumulator was blue. The other pic is my new hydrobooost out of the truck before I installed it.



Good luck, Dave

 

[Neibe]

Well it was the Hydroboost. I didn't have time to fix it so I payed $450. 00 to have it fixed. The brakes are much better it must have been getting weaker over time cause now it stops on a dime. Thanks for all your help!!! The TDR is great.

 

[Dave M]

Well it was the Hydroboost. I didn't have time to fix it so I payed $450. 00 to have it fixed. The brakes are much better it must have been getting weaker over time cause now it stops on a dime. Thanks for all your help!!! The TDR is great.

Glad to see you got it fixed. My brakes are great too with the hydroboost working. Now we know a defective hydroboost can cause the brakes to lock up. I learn something new everyday



Dave