Lost all brakes on my 88 Dakota last night. There is fluid in the Master Cylinder and no leaks from any brake lines. Master cylinder was replaced about 2 years ago. Looks like the MC moves when the brake pedal is pushed. My guess is the brake booster. What should I look for as a cause or is it a simple replacement of the B booster?

 

i am thinking it is the master. a seal has failed and it does not push the fluid it just leaks past the plunger...........my best guess, see who else might chime in......

 

Does the pedal sink to floor, or does it seem to almost fight you?

 

Sounds like it is the Master Cylinder is leaking internally. Very common problem with cheep replacements. It is easy to replace just you have to bleed all 4 brakes.

 

The brake pedal goes all he way to the floor and I can hear a hissing sound as I depress the brake pedal. Pressure doesn't build up as I pump the brakes. So the thought is the Master Cylinder not the brake booster? What about the Master cylinder moving back & forth as the brake pedal is pumped?

 

does the booster move as well? if not the master should be fastened to the booster some how if it is still intact then the master sems to be shot if it was the booser then you woldnt be able to push the pedal down. i had the booster go on my other car when i was backing out of a parking space and it threw my knee into the steering wheel

 

Ya, with my recent experience with MC rebuilds in my first year apprentace course. Like the earlier posts, the seals most likely have went, without the tapered seals working as needed nothing can build in the primary and secondary chambers. The fluids will just by pass back over the lip and right up the vent port. For the hissing, the booster could possibly have a split diaghram or a buggered vaccum line, kinda have to do some inspecting but the MC seals for sure!

 

i agree with all replys thus far. the booster is just that, a "force multiplying device" essentially. you should still have manual brakes (with no assist) if the booster went as the same if you were to loose vaccum @ the booster. id change the master and go from there. to save yourself some time and hassle id bench bleed that master prior to install

 

What about wheel cylinders? Had one go out on my Dakota and two on the Durango with no signs of leakage on either and the pedal went straight to the floor.

 

he still hasent said what the pedal was doing once he says that we will know for sure