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.

 

If you found rotted rubber hoses, lines etc etc then its quite possible the booster diaphragm has suffered those same ravages of time.

I'd double check the vacumm line and check valve running from the booster to the intake---and the grommet in the metal case of the booster.

You could also post this in the brakes and chassis sub-forums here on FTE---this sort of thing may have been discovered, diagnosed and fixed by another, perhaps in the F-Series camp.

Do let us know what you find---might be helpful in the future--good luck with the repairs.

 

Thanks. I filled the master..the Brake light went out..but its leaking somewhere..gotta find it. I was just shocked to find the pedal go to the floor...but pump back up again,..and no problems so far in 2 days...in heavy So. California traffic.

 

Make sure all hard lines and hoses are dry. Also check on the back side of the rear brake assemblies or tires. Leaking rear wheel cylinders are also a fairly common problem on vehicles that have been stored.

Most likely you'll need to replace the master cylinder. The seals on the master cylinder piston are probably leaking fluid past them and into the booster. You can verify this by unbolting the master from the booster ( leave lines hooked up ) . Pull it forward off the booster and check for fluid on the part that seats in the booster. If it's wet the master is toast.

 

If the booster fails you will get a rock hard pedal not one that drops to floor. If the diaphragm ruptures or you loose vacuum some other way, you just loose the power assist.

 

So what would have caused the pedal to go to the floor...then pump up and stay as normal?

Thanks!

 

Something happened with the piston seals on the master cylinder that let the fluid by them, thus didn't hold pressure. Then when the piston returned the seals moved and sealed back up. The same thing can happen with the rear wheel cylinders. I've had quite a few that would seep fluid and then seal back up and work fine for a while. But once they start leaking they need to be replaced. The brake system is one thing you don't want to chance it with.


Do what I said in my last post to check the MC. If you want to check the rear wheel cylinders you need to jack up the back of the van, put it on jack stands. Then pull the rear wheels off and remove the brake drums. If it looks wet or sludgy at all you either have a bad wheel cylinder or axle seal. You can usually tell where the wetness is coming from by the staining.

 

When the master cylinder is low on fluid, and you don't see fluid leaking anywhere, it's because it's leaking into the brake booster.