I have an interesting problem with my passenger side rear brake on my 88 f350. I've had the truck for 6 or 7 years now and it's never leaked a drop of brake fluid but the parking brake has always been a little loose. You had to push it all the way down to get it to hold the truck and when you pulled the release there was enough slack in the cables to keep the pedal from lifting high enough to make contact with the switch that turns off the BRAKE light on the dash.

So the other night I had a moment of boredom and decided to tighten the nut on the bracket where the cables split from one to two, not entirely sure what it's called to be honest. I tightened the nut about 1/2 an inch and it did what I wanted. The pedal engages better and when released comes all the way up and shuts the light on the dash off. Good right? Apparently not. I set the brake and called it a night, next morning I go out to the garage and find a pretty good size puddle of brake fluid on the floor under the passenger rear tire, leaking from between the drum and backing plate. The next night I parked the truck overnight without setting the brake and there wasn't a drop of fluid on the ground. BTW there isn't any sign of leakage from the driver's side rear brake.

I looked through my Haynes manual to better understand how the parking brake works and I just can't understand how my parking brake adjustment could cause a leak. Maybe someone here can help me understand what's happening here a little better, and what needs to be done to solve the problem?

 

I just rebuilt my whole rear drum brakes last weekend. The only thing I can think of is that your wheel cylinder in that wheel is leaking and having the parking brake engaged agitates it. I would just replace it. They're cheap.

 

In normal operation the brake springs pull the brake shoes back retracted, thus pushing the pistons in the wheel cylinder back against the rubber sealing cups in the wheel cylinder. When you apply the parking brake the brake shoes are pushed out slightly without the use of the wheel cylinder, therefore the pistons in the wheel cylinder are no longer pressing against the rubber sealing cups in the wheel cylinder applying pressure.

That's my guess as to why the cylinder leaks when the parking brake was used. The bottom line is if you replace your wheel cylinder or put a kit in your present wheel cylinder, your leak will probably stop.

 

Thanks! The leak started again without me using the parking brake so I guess it must have just agitated something. Oh well, time to replace the wheel cylinders!

 

Just for S&G, the next time AFTER you set the parking brake jam down a couple times on your regular brake pedal, this will push the seals in the wheel cylinder tight and square against the piston. I would be very curious to see if it still leaks.

 

I will try it and see.