Steering system flushing procedure

[shogun]

ZF recommends:
The steering system is an important safety component in a vehicle and must be properly maintained. With this in mind, a steering system must be flushed EVERY TIME a component of the system gets replaced, no matter if the components are new or remanufactured.
ZF Recommended Steering Systems Flushing Procedure
Equipment Needed:
- Safety Glasses
- Empty Bottle for contaminated oil
- Screwdriver
- Manufacturers’ Recommended Power Steering Fluid
1- Clean the outside of the oil reservoir and the surrounding area to ensure no dirt or foreign particles get into the oil reservoir.
2- With a screwdriver, loosen the clamp holding the return line connection between the steering gear and the oil reservoir. Disconnect the oil line from the oil reservoir.
3- Insert the end of the return line into an empty bottle and cap the oil reservoir return connection with a plug.
4- While wearing safety glasses, start the engine and fill the oil reservoir with fresh power steering fluid while turning the steering from side to side to purge all oil out of the system. (Use recommended fresh fluid to flush the system.)
5- Turn off the engine and remove oil reservoir from bracket. Flush out debris or particles from reservoir into container. Check oil contamination for metal or foreign particles by filtering the contaminated oil with a coffee filter.
- Fine metal shaving means a normal wear and tear of the power steering pump.
- If metal chips are present, replace power steering pump.
- If black rubber particles are present, the pressure/return line inner lining is disintegrated. Replace the pressure/return line.
6- Check the oil reservoir condition for cracks. If the oil reservoir is cracked, replace the oil reservoir. If reservoir has no cracks, just replace the oil filter. If filter is integrated inside the oil reservoir and cannot be removed for oil filter change, replace entire reservoir.
7- Check the condition of the pressure/return oil line for cracks, soft or sweat spots. If any of these conditions exist, replace lines.
8- Check all banjo bolt connections for blockage. If blocked, clear connections by appropriate method (air hose, fluid, etc.)
9- Reconnect oil reservoir into bracket.
10- Connect return line to oil reservoir.
11- Top off oil reservoir with manufacturers’ recommended fluid.
12- Start engine and turn steering from lock to lock to purge air out of the system.
Caution:
Do not hold steering gear from lock to lock for more than 30 second. This could cause the steering system to overheat.
12- Check for oil leakage and top off power steering fluid to recommended level.
The smallest particle can cause the system to leak or even fail. A clean system is a REQUIREMENT for acceptable service life.

ZF pump and steering catalog, which contains all BMW parts numbers as well as the corresponding ZF numbers for each model

http://www.unofficialbmw.com/images/steering-flush.pdf

[Waylander131]

Sorry for bringing this 1 year old post up again, but I have few questions regarding the flush procedure:

Let me first point out that I have recently bought my 1993 740iL, I've noticed that in the steering reservoir the fluid is yellowish in color, not green as CHF7.1 should be. This brings me to the thought that the previous owner has replaced it with unknown (for me) type. I would like to flush the system and replace the fluid with the recommended Pentosin CHF 7.1. Here are the questions:

1. I've read a lot about pro's and con's of replacing 7.1 with 11S, as the latter is lacking some lubricant components that 7.1 has and could degrade the system performance (not confirmed). As 7.1 is now discontinued, can I assume 11s is a suitable replacement?
2. My car has the LAD system which uses the same fluid to adjust rear shocks height. Is the flush procedure the same?
3. How much fluid should I purchase prior commencing the flush?

Cheers!

[shogun]

1. A 1993 740iL never had Pentosin CHF 7.1, definitely Pentosin CHF 11S. Pentosin is greenish/Yellowish on a white tissue paper. Pentosin CHF 7.1 was only used in the older E32 and then they switched to 11S
2. LAD uses the same fluid as the power steering, all from the same container/reservoir = Pentosin CHF 11S. But here the problem starts, flushing an LAD system is not that easy, AND you do not want to open old, rusty connections which might then leak. The above is the official ZF recommendation, I would do the following:
avoid opening connections as much as possible, they could leak later, it is also difficult to get to the connections to open. Here is a diagram with possible places where to open the lines, and when you had a look at it, you do not want to do that
http://www.bimmerboard.com/members/s...mSchematic.jpg
I would use a turkey buster and suck the fluid out of the reservoir, fill it with the right stuff, run the engine, turn the steering wheel from left to right and vice versa so that the pump works, then suck the stuff out again, refill, drive, and then check the color and do that some more times. You could also losen the lines on the steering box so that the old fluid drains, or even open the bolt on the steering box to drain it, but that is more difficult, you need new copper washers there etc pp, so the turkey buster method is the easiest in my opinion.
Or:
Open the return line to the Pentosin container, extend it with another hose/pipe so than you can fill the returning fluid into a container. Open the Pentosin reservoir, drain it, fill with Pentosin, start engine and let someone fill the reservoir with Pentosin while you turn the steering wheel, so with this method it might be faster to change.
3. How much fluid: If I remember correctly, for my 750 iL with LAD 1.8 liters are required in total.

Instead of Pentosin CHF 11S you could also use the corresponding product from Febi, they have something for 11S as well as for 7.1, 2 different products. That is a bit cheaper than Pentosin.

[Waylander131]

Thanks a lot man, I really appreciate your help!

[shogun]

schematics of the hydraulic system E32 with LAD once upon the time made by Ice Tea in 2004, I saved a copy, 1991 E32 750iL Hydraulic System Schematic, shows pressure lines, return lines, possible flushing points. Some points are unclear yet like return line
From the ZF catalog steering pumps ..
Vehicle Year... Application............. OE Part No........ OE Service Part No. ....Gear Part No......... Pump No.
1986-89... 735iM30/735iLM30.. 32131132278...... ..32131468049......... 8054955203ZW
1986-89...... 735i/735iL.......... 32134403688..................................... 8054991112ZW*
1990........... 735i/735iL.......... 32131136807...... 32131136825........... 8054991115ZW
1991-92..735i/735iL Servotronic. 32131138273.... 32131138565.......... 8054991119ZW
1986-94.. 735i/735iL w/self-leveling 32411132277.. 32411132726............................... 8692955106ZW
1986-90........... 735i.................... 32411131239.. 32411130556................................ 7682955102ZW*
1992-94.. 740i/740iL.................. 32131138685..... 32131138695....... 8054955226ZW
1992-94.. 740i/740iL Servotronic.. 32131138687.... 32131138697....... 8054991126ZW
1986-89...... 750iL...................... 32134403688............................... 8054991112ZW
1990..... 750iL Servotronic........... 32131136809.... 32131136827........ 8054991116ZW
1991-94.. 750iL Servotronic ............1138274........ 32131138566....... 8054991120ZW
1986-94.. 750iL w/ self-leveling.... 32411132277.....32411132726....................... ........ 8692955106ZW
* Some of the above ZF part numbers may have interchanges. Please refer to the ZF Interchangeable Cross Reference list at the back of the catalog.

BMW750E32HydraulicSystemSchematic.jpg

[Cactuar]

What a useful diagram, thanks Shogun.