Having a brake problem with my 98.5 dually. When you press the brakes it starts stopping normally then the pedal goes to the floor leaving me with only a little bit of rear brake but nothing in the front. Feels like the front brakes are bypassing. Abs light is on , seatbelts are locked. not losing brake fluid , new front calipers , new mastercylinder. Don't know much about these abs brakes or the hydroboost system . Any ideas would be appreciated. Gotta get this thing stopping.

 

You have air in the system. Bleed them again to get all the air out..

 

Could be air, but if after checking the bleed, find out if you have 4WABS for sure. Either look for the build tag or look for the front sensor wires. If you have only 2 WABS, might well be the dump valve. I am not sure how the 4WABS system works, could be the same. I had the same issue with one of mine, Chrysler no longer sells the valve, Junkyard is your only option. At least on my 97, the 2WABS valve is the same from 1/2 ton up.

 

just had a chance to get back to the truck, had to work through the holiday. checked the bleed . good . 2wheel abs . if I hit the brakes hard i will come to a good fast complete stop. then sitting there still holding the pedal it will just release to the floor to where i have no brakes at all . under a normal gradual braking condition it will release before i come to a complete stop. where is the dump valve located.

 

Dump valve is right after the MC, lines go to it first ( I think, then to the proportioning valve. ) Basically it is right next to the MC, will have 2 solenoids and a wiring harness plug. The way it works is it is an accumulator that bypasses fluid into the accumulator when the ABS condition is called for.

 

Found a dump valve in the junk yard. Installed it today. Still having the same problem. Brakes start strong when first applied then just go away. bled them till both of my boy's legs were tired. good clean fluid at all 4 corners. Scratching my head on this one.. any more ideas? thanks.

 

Also the pedal comes back very slowly and it does the same thing with the abs unplugged.

 

That almost sounds like the new mastercylinder is leaking internally.

 

Yep.......

 

I believe that also. filled the reservoir to exactly the full mark.got one of my sons to apply the brakes until they released to the floor. level raised above line. Guess I'll get a new one from napa instead of o'reilly's . Thanks guys..

 

The dually is now stopping . thanks .