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F700 Lucas Girling system brakes

J

Jeffro_bodine2000

New User
I know this is a Ford tractor forum and I"ve looked online in other places but I was curious if anyone here has had any dealing with the Lucas Girling brake system on the F series medium duty trucks. We recently purchased a 1990 F700 with the 6.6 diesel and it has this system and I"ve been told that it is pure crap and they are expensive and a nightmare to troubleshoot. The issue with our truck is that the electric motor light stays on and when the truck is warmed up when you press on the brakes it makes a loud whining noise near where the brake pump is. The fluid levels are okay. Where should I go from here?
 
I have worked on these systems quite a lot. Brake Pressure is supplied by a power steering pump.No or low pressure, the brake presure light stays lit.The electric motor /pump is a back-up system should the engine die or you loose pressure.Some also have a hydraulic park brake system on the rear brakes. They are a little expensive to work on but not really that hard to work on once you know how the systems works.Diagrams are available,if you will take the time to troubleshoot the systems. They are not something that can be fixed in 10 minutes with a screwdriver and a pair of pliers.
 
The brake pressure light stays lit up all the time. The truck will stop when the brakes are pressed and the power steering pump appears to be new. It just makes a loud whining/grinding noise when it is pressed. It appears that the bottom reservoir is trying to overflow? What should I start with first?
 
Does it have one power steering pump or two. Are you sure the the grinding /whining noise you are hearing is not, the electric pump energizing when you press the brakes. The electric pump is fairly noisy. If the main pressure is low the electric pump will run.
 
I'm thinking that it has only one pump. It really sounds like the p/s pump is making the noise. Is the electric pump the one located close to the firewall that resembles a wiper motor? The cranks and runs fine and operates well all but the danged brake system.
 
The electric motor is mounted on the booster and yes it looks like a wiper motor. Here is a diagram of the system.You will probably have to copy it and enlarge it.
a114151.jpg
 
Is this the same as the Hydro Max brake systems used on Motor Homes. Searching on that term brings up some hits that might be useful.

The ones I worked on where pretty straight forward, but auto mechanics are not familiar with them. The brake side is standard, but the power boost comes from a power steering type pump with a electric motor pump backup. Sound familiar?

They are really nice systems and trouble free. Work great on heavier vehicles that don't have air brakes.

I think you are on the right track with the belt driven pump, but I'm no expert.
 
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