New here and wondered if anyone can help I have a 1992 freightliner chassis diesel pusher Rv Motorhome. (Damon challenger) It has a single spring Lucas girling hydraulic parking brake system Has bendix hydromax booster Eaton BB pump Bendix HR1 relay valve Metric steering box (lhd) Issue is. When hydromax is depressed all steering is lost. (Steering locks) The steering is gradually affected with increasing brake pedal pressure. When the brakes are not pressed the power steering works perfectly fine. When the steering wheel is not used the hydromax works perfectly fine. Ok so What I've done so far Replaced the hydromax for a new unit Stripped and cleaned pump Flushed fluid and replaced filter a few times I tested max pump pressure at 1000psi Pressure while using steering is 500psi Pressure with no load is 300psi Pressure with hydromax pressed hard is 1000psi. Anyone got any ideas? I'm really running out of ideas with this one and I could really do with it back on the road ASAP. Massively appreciate any help or insites. Many thanks. Mark
Sounds like your pump is worn and not producing enough volume for both systems. or you have a flow divider that's not working properly. The pressures seem low to me. Do you have the specs for what the proper pressure and flow should be?
Well in the hydromax manual it says that the power steering source should be capable of supplying 1000psi to the brake booster. Which it is doing properly I wondered maybe if the restriction was too high in the hr1 valve. 300 psi seems a lot to me for no load considering I ran the test with the transmission in park. Surely the pressure should only be created by the restriction in the filter or something? I was expecting more around 50 psi no load pressure. I have no specs for the power steering pump or what it is designed to produce. When I stripped the pump it all looked in very good condition with a "hone" surface on most of the parts. The pump looked surprisingly good. The vehicle is an American import and I am based in England so getting specs as parts seems to be quite a struggle over here. Cheers.
The pumping sequence goes in this order Resivoir - pump inlet Pump outlet to steering gear input Steering gear output to hydromax input Hydromax output to HR1 valve HR1 valve to filter Filter to cooler Cooler to HR1 valve HR1 valve to resivoir HR1 valve to park brake valve Park brake valve to HR1 x2 pipes HR1 valve to Parking brake Spring That is all I can see in the system There seems to be no pressure bypass around the hydromax and I see some systems have a second return from the steering gear but this system does not. Hope that makes sense.
https://www.haldex.com/en/na/power-...mp---newremanufactured/spline-shaft/rp70106x/ This BB pump shows 1500 psi and 8gpm although it may not be the pump you have
Thanks jonas302 That is the pump I have but I'm not sure if for my application they have fitted a different pressure regulator Spring. The hydromax manual doesn't mention anything about a high limit pressure for the hydromax but it does say if pressure is too high or flow rate too high the brakes will self apply. Hydromax says it needs 1000psi and between 3.2 - 5 gallons per minute. I don't have a way of testing the flow rate though.
I believe the parking brakes are pressure release, are you testing with the park brake released or engaged? Maybe check it both ways if you can?
The parking brakes are pressure release so with the brake engaged there should be no pressure applied to the Spring. Will try with the brake released tomorrow.
I have found a page that tells what pressure the pump was built for but I can't seem to find the corresponding codes stamped on my pump! http://dudamobile.srtp.us/?url=http...eavy_duty/eaton_steering_pumps_bb_series#2676
Just because a pump can make the pressure doesn't mean it can push the fluid too. It sounds like pump has lost its flow to me. Or you have a problem in the steering gear
The steering should not lock up, it should lose power steering just like if the engine stopped. This sounds like one mess of a system to diagnose. I understand that the system started as power steering and then added a brake booster, which is fine, power steering boosted brakes are simple enough. But then you add a third system in series hydraulically and make it that complicated with the prince of darkness badge on it... I have to disagree with the new dude who claimed "there are no suicidal parts". This is one system that sounds like it degenerated to suicidal. So I have no idea how the HR1 valve works and google isn't much help. Apparently, this parking brake system was widespread but short lived in production so you should be able to find some diagnostics? For now, I'd disconnect it and see what the steering and service brakes do, connect the hose from the brake booster to the reservoir, plumbing the parking brakes out of the circuit. If that fixes it, then you go through the parking brake diagnostics... "I wondered maybe if the restriction was too high in the hr1 valve" that's my suspicion too, but just because it's creating restriction doesn't mean that it's not doing it's job, ie the brakes are calling for pressure so the valve is supplying pressure. Once you narrow it down to "downstream of the brake booster" then you can diagnose the parking brake.
Ford used this Lucas girling crap for a long time way to long and it is hard to find diagnostic info for that setup also . I wish the op the best of luck on his issues if I come across anything I will get a link posted
Yeah, a lot of the info that came up was from Ford super duty, or RV sites. It sounded like Ford used a separate "power steering" pump to run the parking brake, is that true? That would make the OP's Freightliner chassis that much harder to find info on, the combination system makes the diagnosis exponentially harder.
I have worked on alot of the Ford systems and about a 2 years ago i found the manuals on them in a junk or antique store it was the best $5.00 i have spent in a long time. The place i work at has 2 of the Fords they try and use. I would bet that in this country they couldnt get by useing one pump to run both. I would replace the pump.
I helped a friend who runs a truck shop fix a Sterling that would periodically have the steering lock up and superman couldn't turn the wheel. After the driver ditched it up a couple times he refused to drive it again. My friend changed the steering gear a couple times to no avail. He asked me for a fresh look and I told him to change the power steering pump. It seems the pump would apply pressure to the return line and seize the steering, after the engine was restarted, all would be normal for a while. Long story short, check the return line pressure!