4 years ago..I found a custom 89 E350 Extended van (5.8L) in storage, with a verified 9,835 miles on it. Water pump impeller was rusted away..a few hoses were rotten..batteries were toast...the usual for a long..long term stored vehicle. Ive now got 32,000 actual miles on it as my service truck (I fix machinery in machine shops). Only a few problems over the last couple years...mostly electrical and traced to dirty connections etc. Yesterday..I was driving along in traffic and hit my brakes..and the pedal went right to the floor. I pulled over and crawled underneath..and..no leaks are showing. I pumped the pedal a couple times..and the brake pedal went back to full height and pressure. I watched carefully the rest of the day and nothing changed. I parked on a hill later that evening..and I got a Brake warning light..that went out the moment I hit level ground. No changes until this evening when the brake light went on and has stayed on. No changes in braking have been noticed..good pressure and so on. I do notice however..a very faint moisture on the face of my vacuum booster around the end of the master cylinder. It appears to be brake fluid..maybe, but there is no signs of dripping whatsoever. Brake fluid in plastic resieveor bottle on top of master cylinder now appears to be down 3/8"..so its going somewhere. Why did I get the brake pedal to the floor...why did it come back..and why does the Brake warning light now stay on? Id have thought that if the master has failed..it would have failed "hard" and not come back. its not..not missing much brake fluid...what is the threshold? Im assuming the brake warning light is only for fluid level on this older OBD-1 vehicle? Any suggestions are greatly appreciated as to what is going on with this 30+ yr old vehicle.

 

the "Brake" Light should illuminate in the "Start" position of the IGN Switch as a Bulb Test ... IF it is on in the ACC or RUN position it indicates Low Fluid in the Master Cylinder or the Park Brake is engaged.

Some also have a Rear Anti-Lock system and that has an "ABS" lamp that will light for a few seconds in the ACC or RUN position as a Bulb Test, I Think the E-Series all used a Height sensing Proportioning Valve mounted near the Differential.

from your description .... I would first Replace the Master cylinder, Change the Fluid and Bleed the system.

it's possible for a seal to stick and roll and then recover....but IF this has happened the Master Cylinder is Failed and needs careful inspection.

 

Thanks LW. I just found it wierd as hell that Id loose all pedal suddenly..then be able to pump it back up in a few pumps and it being just fine after that. I filled the master with new fluid a few ago...and now Ill start looking for a leak. Much obliged.

 

check those Drum Brakes on the back end sometimes you can see fluid on the inside of the rear tires, it cleans em up pretty good if the Wheel Cylinders are leaking.

Fluid leaking from the back end of the MC can also collect inside the booster and will rust the push rod.


MC is not very expensive from Rock auto. anyway you're quite welcome ..

 

@Lonewolf : you mentionned the heightsensing proportioning valve. Mine is leaking. do you think it's possible to repair it or should it be changed ?