I have been cruising the site for quite a while research my recent purchase of a 1987 F800 Dump Truck. I quickly realized there wasn't a whole lot of information regarding the brake pump the supplies pressure to the hydromax unit. After much research, I wanted to pass what little information I gathered, and frustration I found while replacing the pump to those who are also ignorant to the ways of the hydromax brake pump.

The brake system consists of a engine mounted brake pump (really a power steering pump), the hydromax unit, the brake control setup, and an electric backup pump should the engine pump quit producing pressure (engine die or lose a belt).

The electric backup pump can be easily replaced and I found mine at Oreilly Auto, but can be ordered offline as well. There are two models, but the difference is based on how the electric wire attaches. The pump is held on by two bolts. Disconnect the electric wire and remove the two bolts, and the backup pump will drop. The new pump came with two new orings. Install the new orings and reinstall the pump. Reconnect the electric wire and the pump is replaced. Sounds simple, but installing the the two bolts is a major PITA.

The engine driven brake pump is a saginaw style power steering pump used in many different applications from ford to GM to international. After much research and cross referencing, I found the following pump at O'Reilly Auto Part # 731-0125. If you have looked at your brake pump and are looking at the picture on the website and they look different, you are half correct. The engine driven brake pump sits inside of a housing that is connected to a remote reservoir. To replace is not terribly bad but be prepared to take a day to replace.

First is to the loosen the belt tensioner and take the belt off of the power steering pump pulley. The pulley is "pressed" on and requires a power steering pump pulley puller. You might be able to use a jaw puller, but I recommend either buying or renting the power steering pulley puller because it works better in this situation and requires less room which you have little. Using the puller, remove the pulley from the pump. You will also need to remove the remote reservoir from the pump. Four bolts hold the reservoir to the bracket. My bolts had locktite on them so be prepared. A short section of hose connects the two. Loosen one of the hose clamps and you can pull the two apart, but be prepared for all of the fluid to empty out of the reservoir. Now would be a good time to remove the other two lines from the back of the pump as well. One used a hose clamp, the other was equipped with a flared nut (high pressure line to the hydromax unit). Four bolts hold the pump, and the bracket the reservoir was bolted to, onto the motor. Once you remove these four bolts, the pump should come out.

Now that it is out, this would be a good time to clean the pump. Mainly because most of what you see will be reinstalled onto the motor, and will minimize fluid contamination. Once cleaned, place the pump with the shaft down into a vice. There will be a threaded stud extending from the back of the pump, as well as the female flare the high pressure line threads in to. The threaded stud will screw out, but the flare nut has a spring and is under slight tension so be ready to catch if necessary the piece screws out. With both removed, you may have to gently tap the housing to remove the actual pump. I spent some time making sure the inside of the housing was clean and free of debris. If your new pump does not come with a new magnet, then clean and reuse the existing. Assembly is pretty much the reverse.

This may be common sense to some, but for the others, I hope this saves you some headache. Also, if I have any information wrong, I apologize and please let me know so I can correct it.

Keyword: brake pump, saginaw, lucas girling, power steering, bendix, haldex, f600, f700, f800

 

Thanks for the info. Might need this down the road.

 

Thanks for the info. I also have a 97 f800 with what by your description has the hydromax? braking system. As you can tell I am not to familiar with these systems.


The problem I have is that over the winter the reservoir that holds the power steering fluid for the brake system leaked out. the truck was driven for about 5 miles with it empty. As I was driving the brake light came on on the dash and the brakes seem to still work but only as if there was no assist and had to push hard to get any brake action. When I filled up the res with oil it took about a quart and a half!! I started the truck but the light is still on and brakes still don't work properly. I drove it for a couple miles hoping it would come around but no such luck. The brake fluid In the res was full to the top and never lost any over the winter. As near as I can tell the power steer fluid leaked out of the little control unit that is hooked to the parking brake. When I pull the yellow **** out on the dash it is hooked to this. The little shaft that goes into this little unit directly hooked to the park brake seems to be leaking very slowly. I am guessing this is where the oil leaked out as it sat for about 5 months over the winter with no use. Also when I push the brake pedal with the engine not running the electric motor runs and I think I can hear little bits of air passing through as it working. If I hold the brake pedal for about a minute or so it will eventually go to the floor. could be a separate problem?


Any ideas as to why it wont work? Do they need bleeding after they have run out? Or will driving it bring it back?