Ford brake system

[jkindt]

Does anyone know about the hydraulic brake system used on the Ford B600 chassis in 1981? My bus has what appears to be a power-steering type pump that runs to the master cylinder, also an electric motor attached to the master cylinder. I have a single brake light that is on constantly when the bus is running, although I have functional brakes. The previous owner claims that the brake light has been on for as long as he can remember and figures it has something to do with a 'redundant system' component. I would prefer to find out why the light is on and correct the issue, safety first! I wouldn't want to lost brakes on such a heavy unit in traffic, not for my own safety, but for the safety of others around me. (And for my own, I don't want to crash a bus! Got rear ended by a police car once and it really messed me up!) Not a lot of information about these busses online, that I can find anyways. 8)

 

[lapeer20m]

Ford liked to use Lucas Girling hydraulic over hydraulic brake systems.


They work good, but i have heard they are expensive to repair.

 

[SHORTS]

check on the schoolbus fleet forums, or the local ford truck dealer and ask someone to help.

from your description you have a hydro boost system with an electric backup brake system, the power steering/hydraulic pump supplies pressure to boost the standard brake hydraulics instead of the old style vaccum boosted master cylinder, the electric motor is a backup system in case of engine/pump failure. the vaccum systems had an auxillary vaccum tank for emergency service. the light is probably a system balance indicator that got out of whack when the brakes were being bled, look for a block connected between the front and rear brake lines with a sending unit on it, their is a shuttle valve that moves when one side of the system looses pressure,(open bleeder) and the light comes on. if you disconnect the wire and the light goes out, reconnect the wire and then bleed the brakes, after the brakes are bleed go to the opposite end of the bus and slowly bleed 1 cylinder until the light goes out.You can remove the switch and test it for continuity when you press the plunger in the circuit should be closed. the other easy place to look is on the parking brake assembly, is their a switch for an idiot light that is out of adjustment or malfunctioning?

 

[frank-id]

A wild ass guess

Many vehicles of that era used a mechanical switch that is controlled by the brake pedal under the dash. The switch bracket can get bumped or become loose and the switch will not turn off. Look at the wiring and any switch near brake pedal. Next try to fix stop lite is to go to any parts store and ask for a look at the switch. Looking at a switch will allow you to know if the switch is hydraulically operated or mechanical. Some parts stores will have a catalog that tells some parts location. Frank

 

[jkindt]

What I was able to find out about this system is that it is a Hydro-Max system. This one uses a dedicated engine driven hydraulic pump that is very similar to a power steering pump. This provides the assist needed to provide sufficient 'power brakes' to bring the bus to a stop without literally 'standing' on the brake pedal. Without the engine running, or if a hydraulic hose ruptures or leaks, there is an electric pump attached to the booster that provides backup hydraulic power to the system to stop the bus, although not as powerful as the engine driven hydraulic pump. It is this electric system that I am having issues with. According to Bosch, the makers of the Hydro-Max system, I have a type 1 system. This system uses a relay near the electric pump motor to provide up to 50 amps at 12V to power the backup pump. I found that this relay is MISSING from my bus. It is simply not there! There is a binding post on the firewall where the 12V supply to the relay hooks up, but there is nothing attached other than a heavy gauge wire from the chassis battery. Also in the same area is a connector that goes to the 'flow switch' which is used to turn the electric pump motor on in case flow is lost from the engine driven pump or if the engine is not running. There is another wire from the control module that provides the lower current power to activate the relay. I tested the motor by running a jumper wire to the binding post for a couple seconds and it turns and sounds just like an electric over hydraulic pump, which is a good thing. I will try to find an appropriate relay and wire it in tomorrow. Hopefully this is all it takes to fix my brake light problem. And make the bus safer for everyone. As a side note, I found one of the four bolts holding the brake system to the firewall was loose enough to unscrew by hand!!! Time to go over every bolt and make sure there are no other loose bolts or nuts! 8)

 

[jkindt]

So I wired up the relay and it seems like everything is going to work! With the engine off, the electric pump comes to life and provides brake boost when the brake pedal is pressed. With the engine running, the engine driven pump provides the boost. If I press the brakes hard when the engine is running, the electric pump kicks in and provides some extra boost pressure. Is this normal? Could my mechanical pump be worn and not puting out enough flow? Or maybe the pressure switch is out of calibration? I just want to ensure my brakes are functioning properly and safely. 8)

 

[talk2cfs]

I have a 89 Ford B700 with air brakes. Ive never had any problems with the braking system until a buddy of mine said he tried to move the bus and didnt wait for the air presure to build up and could release the parking park and still tried to move the bus by putting it into gear for a little bit and then decided to call me for help. I told him you cant move it or try until the brake system warning light and buzzer stops and you then can release the parking brake. Hestopped what he was doing and gave up . A couple days later when they were ready to move it again, the air gauge wouldnt move and the system just keep buzzing and would pump up. I have checked the compresor and looked for leaks and still cant figure out what went wrong. Anyone else have this problem or know what possible could be the problem? Any help would be great. Thanks/

Jeb

 

[jkindt]

You may want to post this in a new thread. 8) Air brakes are a lot different than the hydraulic systems.

 

[talk2cfs]

I will. Thanks!