Cleaning/replacing the servotronic hydraulic unit

[fritzenos]

Does anyone know how much pentosin is lost when cleaning the screen in the servotronic hydralic unit? Or do I have to emty the resovoir?

My power steering cuts out often, so I figure I'd start with cleaning the screen, then check the control unit for component failure.

[shogun]

Use a turkey buster and suck the Pentosin container empty. Then you lose very little. I used a paper filter to filter the Pentosin before I added the old one again, but new fluid would also be a good idea to add. Instead of Pentosin CHF 7.1 or Pentosin CHF 11S you can use the hydraulic oil from Febi Bilstein, that can be mixed with Pentosin.
Check the Febi Bilstein site which of their products fits to CHF 7.1 and which one to CHF 11S.

Maybe the servotronic control unit is the problem, repair on my website.

[fritzenos]

Exactly what I'm going to do. I've looked at your site, it seems to be straight forward. I have new pentosin 7.1 in it already so I'll turkey baste it out. Got CHF 7.1s from BMW in Sweden the other day for 170S SEK, around 25USD/litre.

Is it possible to do test mesurements for known values on the control unit without de-soldering components first?


Shogun, your site is great!

[shogun]

One of my friends built a tester, but he is the electronic experts, I have no plans or whatsoever to build it http://www.bimmerforums.com/forum/sh...94-Servotronic

Do you have the old unit for the control? The square box with the 2 round plugs? Unplug these and connect them together, then the servotronic should be always full power. If that works then, then the control module might be the problem.
The newer one is a relay type. Older one is no longer available, to convert, you need the relay type and a short wire looms, see for example www.autohausaz.com

[fritzenos]

Power steering is back! 100%. The servotronic control module behind the driverside kick panel speaker is default. But the best thing is that the unit can be bypassed without any modifications. Just unplug the control unit and reconnect

[shogun]

Repair the old unit as per the info on my website or buy a new used one. The older square version is no longer available (that is the one with the 2 yellow plugs). You can also buy the newer version. New style relay last year after I found out that also Audi / VW use same relay http://www.bimmerboard.com/forums/posts/1217078
ZF relay # 7038 900 223 BMW 32.43-1 162 705, BMW 32431162705
one old style like this you can buy from Germany, but of course we do not know if it works, best is repair
BMW 1134870, ZF 7038 900 145 with yellow plugs and some wires
or black color old style BMW 1134316, ZF 7038 900 142

Here is how you can connect the new relay style Servotronic to replace the old style without buying the expensive conversion wire loom
http://www.kawasuki.net/fotos/servo2.JPG
http://www.kawasuki.net/fotos/servotr.JPG
On the relay version there are the connections shown like 15, 31 etc, then there are only 2 more wires to connect .
2 large pins for the valve at the bottom of the steering gear (32411134770 ZF OEM - Servotronic Control Unit; Torque Converter for Servotronic Steering Box) and a smaller pin for the speed signal.

New version:
CONTROL UNIT SERVOTRONIC up to 04/1990 32431162703 $213.23
only in conjunction with Repair kit up to 04/1990 32431162736 $81.04 (that is the new wire loom with plugs) http://www.ecstuning.com/BMW-E34-525i-M20_2.5l/ES55404/

pinout from old to new relay style, translate
da ich vom alten STG zum Neuen in Relaisform umwechseln muss, braeuchte ich die Belegung vom Relais. Könnte mir da jemand Auskunft geben, damit ich den Relaissockel belegen kann? Es hat ja leider einen Pin mehr als das alte STG.
Vorhanden sind: Kl 15, Kl 31, W1, W2, V, OI (oder DI?) (kleiner Pin).
Kl15: Eingang, Plus
Kl 31: Eingang, Masse
W1:
W2:
V:
OI:
------------------------------------------------------------
Antwort von 518iA
Kl15: Eingang, Plus, PIN4
Kl 31: Eingang, Masse, PIN2
W1: Ausgang Lenkgetriebe; PIN5
W2: Ausgang Lenkgetriebe; PIN8
V: Eingang Geschwindigkeitssignal; PIN6
OI: bleibt offen, könnte der Programmierung der Kennlinie dienen

[fritzenos]

Wow! Great information! Too many choices maybe? I guess I like the idea of repairing my original unit as described on your website from Yuriy. The two components I can get from Elfa at thier local store in Stockholm for less than 1 Euro.

https://www.elfa.se/elfa3~eu_en/elfa...toc=0&q=ztx753
https://www.elfa.se/elfa3~eu_en/elfa...oc=0&q=bc33740

I'll verify the components when I desolder them.

[fritzenos]

So all,

Repairing the first servotronic control unit, as described on Shoguns site is very straight forward. BUT! First go out and buy some Samtex other other dynamite (haha). The unit to my surprize is realy contained, glued, molded together. So, use a candel to heat a razor knife, melt through the case along the assumed seam. Had I known this beforehand, I would not have been too upset.

Why is this unit so enlcosed? Higher voltage? Anyway,part costs only cents......a new or replaced old cost $$$$$. Cheers!

[fritzenos]

Just finished replacing two transistors in my original Servotronic Control unit, located behind the drivers side kick panel. Took her for a spin, beautiful to have the correct powersteering at all speeds again. I was driving with 100% assitance for a few days while waiting for the transistors, but I realy don't recommend doing that on icy roads or snow, you can't feel the traction up front. I also did clean the small filter in the servotronic hydralic unit just in case.

So, you realy don't need to be an electronics expert, just be patient. I would mention two things which could be added to Shoguns write-ups on his site for steering fixes.

A) the old "first" servotronic control module is not realy serviceable, you have to cut/melt your way into it to get it open
B) If you are going to clean the filter in the servotronic hydralic unit, make sure you have a 2.5mm HEX-bit.

Cheers!

[markostam]

Great info on the 2.5mm hex bit as I’m also about to tackle the filter cleaning due to intermittent / unpredictable boost.

[shogun]

does anyone have the no longer working pics downloaded? Pls post them, thanks