Just bought a 95 F250. The brake pedal will go to the floor when the engine is running. The truck will stop but the pedal is real scary. When I shut off the engine, the brakes will be good and hard. Turn on the engine and the pedal goes right to the floor. I replaced the master cylinder and rebled the brakes. I have also checked the rear drums and fixed one of the adjuster along with setting the brakes up.

I cant figure out if the problem is in the vacuum assist module or someone said that it could be in a valve on the frame rail for the rear ABS brakes. What is the best way to check each. Also if the valve is to blame can it just be removed or does it have to be replaced. This is mostly a work and plow truck for me so I am not sure if ABS is really needed.

Any help would be appreciated.

 

what engine do you have?

 

5.8L with auto

 

check to see if you are getting vacuum to the power booster behind the master cylinder. if you have a vacumm gauge or can borrow one, check to see if the booster will hold a vacumm. If not will need to be replaced. The auto parts store when I had to change mine on a 93 f350 said to replace both the booster and the master cyl. at the same time. Then they would warranty the whole unit, but not separately. Good luck

 

A brake booster can't cause a soft pedal. Only a hard pedal. So you can rule that out based on what you're describing.

Your brake hoses could be stretching, you might be leaking fluid somewhere, you could have a bad master cylinder, or you could still have air in the system. Did you use a powerbleeder or the manual method?

 

I manually bled the system. I am going to go through and do it again. Is there any special procedure for doing this?

 

Start with the wheel furthest from the MC and work your way closer. Have someone sit in the truck. Pump the pedal three times and hold it down, open the bleeder, close it, release the pedeal, and repeat. I'd do this until either clear fluid runs through that line or about 20 times, whichever is more.

 

That is how I bleed the brakes also. What is the deal with some ABS valve. Someone told me that this could cause this. What does this do and how can I check it?

 

People blame ABS because they don't understand it, superstition.

https://www.ford-trucks.com/forums/s...d.php?t=335183

This is a link to a thread that I started to help understand ABS.

Does your red brake warning light work and does it light when the pedal goes to the floor?

 

I am not sure if it works or not. It does not go on at all.

 

It should come on when you start the truck like the other idiot lights. It should also come on when you set your parking brake.

 

Flushing/Bleeding your rear brakes is a little different because of RABS. After you bleed them take the truck out on dirt and lock them up several time to make the RABS cycle. Go home and bleed them again.


Your RABS controller has an accumulator that holds a quantity of fluid and can give your pedal a mushy feel but I wouldn't expect it to do that in normal service, only after maintenance until the brakes are properly bled or after a leak in the rear circuit.

.

 

It's in the bleeding. You've got to get that part right or you will have no pedal. When your pedal goes all the way to the floor it's cause there is air in your system. Air compresses which is why your pedal goes to the floor. Brake fluid does not compress. When you turn off the engine your pedal is hard cause you no longer have a power boost. You can buy a little check valve thing to bleed the brakes yourself with no help. I have one I got from Checker (I think) years ago. It has a rubber hose on one end and clear tubing on the other. You just slip the rubber end over the bleeder valve and drop the other into a jar and pump the brakes yourself. I used mine just the other day after I changed front calipers in my Suburban. You just pump the pedal til the fluid coming out is solid with no air bubbles. Then re-tighten the bleeder valve. And like andym said, start with the wheel furthest away and work your way closer. It should go passenger-rear, driver-r, pass-front, driv-front. Get the air out.

 

you said that you just bought the truck. If you purchased it from a dealer I would go back to them and have them fix it. They are resonsible for providing the customer with a safe vehicle. Other wise I would talk to the person that you purchased it from. They may know what they problem is.

Tom

 

I think that I got it fixed. I rebled the brakes. Finally got air out of the right rear. I also bled the abs valve and that seemed to really help. The brakes seem to be good now. No more pedal to the floor. Thanks.