500E (124.036) — rock-hard rear end, and I just found power steering fluid in the SLS reservoir

[dinbirb]

Hi guys,


l've been dealing with a power steering fluid leak for a while now, and my rear suspension feels super stiff/rock-hard.


Today, while the engine was running, I opened the hydraulic reservoir for the suspension, and power steering fluid shot right out of it.


Is that supposed to happen, or shouldn't these systems be strictly separated? Could a bad tandem pump or air in the system be causing this blowback? Also, I'm guessing my stiff rear end means the accumulator spheres (accumulator bulbs) are completely shot?


Any advice on what to check first would be greatly appreciated!

 

[gsxr]

Yes - if the rear suspension feels super stiff/rock-hard, the problem is failed pressure spheres (located in the spare tire well) for the rear SLS system. This may also cause other issues. Change those immediately as driving in this condition could cause other parts to fail.

The PS and SLS fluid often look the same, how do you know PS fluid is squirting out of the SLS reservoir? New OE SLS fluid is very light color, almost clear,;new OE PS fluid is light amber/golden (a bit like maple syrup).

The tandem pump does isolate the two systems, but a failed seal between the 2 halves could cause fluids to mix.

 

[dinbirb]

When I opened the hydraulic oil reservoir for the SLS, oil came out, and after that I saw there was no oil left in the steering reservoir.

 

[500AMM]

The seal between the two chambers in the tandem pump is likely shot. Gerry made a very well described HOW-TO about resealing the tandem pump, scroll down to post #46 and #48:

Post in thread 'HOW-TO: Removing and re-sealing ZF tandem pump (SLS and power steering)'

Mar 23, 2013

Re: Power Steering Pump Leak Investigation

Tonight I moved into pump disassembly and rebuild mode. I spent about 3 hours out in the garage disassembling the pump and got a good part of the way back toward reassembly. Unfortunately I didn't get to the cam advance solenoid re-seal, but I plan to get to that tomorrow (Saturday). I will also finalize the parts order that I need to make for the steering box seals and transmission cooler hose. Seems like a job that isn't going to be done anytime soon, mostly dependent on having to wait for parts orders.

I'll post photos below that...

• gerryvz

• 

IIRC a leak between the two chambers will cause a pressure build-up in the SLS circuit compressing the spheres and fill them with oil. Maybe not completely, depends on whether the membrane inside the spheres collapses or not. I don't know how the hydrostruts manage that pressure increase. Anyway, the suspension will be rock hard.

 

[maw1124]

Hydrostruts are some of those "other parts" that may fail, and the hoses running to them as pressure spikes go unchecked.

maw

 

[dinbirb]

I just checked again, and after topping it off, the hydraulic reservoir for the suspension is completely full to the brim, and the one for the steering is half full. So that's the problem. What else should I replace besides the pump seal kit, given that I've had this oil leak for an extremely long time?

 

[gsxr]

Sounds like a tandem pump seal kit, plus short hose below the reservoir, and probably the nitrogen spheres for the SLS. And a few liters of fresh SLS juice.

Remember, the pump seal kits are different between ZF and LuK/Vickers, check your pump brand before ordering the seal kit. The center shaft seal which separates the 2 fluid circuits is a RPITA to extract.

 

[dinbirb]

Ok thank you, but do i have to flush the system after

 

[gsxr]

Ok thank you, but do i have to flush the system after

The SLS system will need to be depressurized in order to replace the spheres. Follow the FSM procedure. There's a bleed screw at the top of the SLS valve. I'd drain the reservoir and also replace the short sections of braided hose at the reservoir and tandem pump. Refill with new fluid. Normal level is about half of the reservoir. Use the dipstick for the final fluid level adjustment.

 

[dinbirb]

Thank you, how do i get the manual for the SLS

 

[gsxr]

Thank you, how do i get the manual for the SLS

Everything should be here, down in the lower section:

https://www.500eboard.co/forums/misc/Manuals/Servicev3.2/W124/Index/Groups/32ShocksSprings.htm

 

[dinbirb]

Is the ASR system also part of the Oilsystem of the suspension?

 

[Efraim]

Is the ASR system also part of the Oilsystem of the suspension?

No.

 

[gerryvz]

Is the ASR system also part of the Oilsystem of the suspension?

No.

As said, the ASR system is an extension of the braking system of the car, and the ASR pump uses regular DOT4 brake fluid. The pump's fluid should be changed at the same time that the car's brake fluid is changed, but it is a separate change/bleeding operation. There is a HOW-TO here on the forum specifically about how to do this.

The rear SLS (self-leveling system) is completely self-contained and uses a plastic hydraulic fluid reservoir up front on the 500E/E500 engine, on the passenger side of the engine. It uses a radial piston pump that is part of the combined "tandem" pump that has the SLS and power steering systems combined (but separate) as part of the same pump assembly.

The SLS fluid reservoir should be approximately 50-60% full (just above the metal spring band on the outside) when it is fully filled up at the correct level.

The power steering reservoir should be filled up to the flat portion of the plastic insert that screws onto the center threaded metal stud.