Conversion from CHF 7.1 to CHF 11S

[gmu525i]

Hello everyone,

I am about to do an almost complete overhaul of the power steering system in my e34: everything but the pump, box, and cooling pipe is getting replaced. This relatively drastic step is being taken as all of the lines are leaking. As I will be removing ALL of the old fluid, this raises the question of what fluid to use to refill.

Based on a couple of points I am considering using CHF 11S:
- CHF 7.1 was discontinued by Pentosin.
- Pentosin states that 11S may be substituted for 7.1 in a system as long as ALL of the old fluid is removed, as they are not miscible.
-- The source for that is this document from Pentosin: http://pentosin.net/pressreleases/PE...UIDE3_Rev1.pdf
- The new ZF reservoirs that are available from Pelican and BAV appear to be labelled for 11S.
- Pentosin states that the characteristics of 11S are better, being synthetic rather than mineral oil based.

The argument on the other hand is:
- There is the Febi/Bilstein M6162 fluid that is 7.1 equivalent. Some argue that it is the exact same stuff just with a different label, but I don't know that for a fact.
- I can probably just use the cap from the old reservoir that is marked for 7.1 on the new reservoir.

The question is, has anyone on the board encountered this same situation, and what did you do? The car does not have self-leveling suspension, so at least I don't have to worry about that.

Stephen

[gmu525i]

Just for the record, I decided to go with the Febi/Bilstein M6162 fluid for the refill.

These are the reasons why:
- After a lot of internet searching I couldn't find anyone documenting having switched their system to CHF11S.
- Two different people at Bavarian Autosport encouraged staying with original spec fluid, citing lack of documented success.
- I realized that I could replace the gasket on the old (correctly labelled) reservoir cap and reuse it on the new reservoir.

Accordingly, I decided this was not the car that I wanted to use to verify the single sentence compatibility statement on a single obscure Pentosin document. Maybe on the next car.

I hope to get the job done in the next week or so, and I will put something up when I know how everything fit.

Side note on parts ordering:
BAV got the parts order over Pelican as they actually had all the part numbers in their online catalog for easy ordering, while Pelican had some where you had to call and truly "special" order, and they aren't open on Saturdays. BAV also didn't charge shipping for any of the stuff that had to come from Germany. To be fair to Pelican though, their online messaging system works well, and they did put in some time helping me confirm the part number list that I put together off of RealOEM.

Stephen

[gmu525i]

Got the work done on this the other week... It wound up taking two days because I was missing some tools that it didn't even occur to me to think about, like 19 and 22 mm shallow 3/8 drive sockets, and the crimp tool for Oetiker clamps, but I did get it done and everything is working well. It turns out Grainger stocks the crimp tool.

That said, here are a couple of little details that came up:

The Meyle high pressure hose for steering pump to steering box (BAV #359-202-0016) was a significantly different shape from the OE part that was in there, which wound up requiring some additional work to ensure that it didn't encroach on the steering column as it approaches the steering box. See attached picture for a comparison of the two parts.

The A14x20 seal rings (#32-41-1-093-596) are not correct for the M16 bolts on the low pressure fittings, steering pump supply and steering box return. In retrospect it seems somewhat obvious that 14mm rings don't work on 16mm bolts, but the correct seal ring part is A16x22 (#32-41-1-093-597). It tore my soul to do this, but I wound up reusing the old seal rings in order to get things back together. It does not appear to be leaking so far though. The source of this problem was partly RealOEM, since they don't list a part number for that particular seal ring in the steering lubrication system diagram. However, both Pelican and BAV did not catch this when I sent the the parts list and asked for a double check, and said I would need 8 of the 14 mm rings.

The Continental ContiTech hose shipped by BAV as "Power Steering Hose - sold by the meter - 12MM x 18mm" (#32-41-1-131-524) actually has an outside diameter of 21 mm. As a result the OE specified 16-20 mm crimp type clamp (#16-12-1-180-242) is not large enough, and it's necessary to either use the 20.9-24.1 mm clamp (#32 11 1 131 345) or, switch to a worm gear style. As it's a neutral pressure fitting it is not extremely critical, but still something to be aware of. I wound up having to use regular US spec worm gear clamps from NAPA, which hurt my OCD, but they work fine.

The instructions in the Bentley manual regarding filling the system and bleeding the air are just a wee bit vague. Certainly not the first time any of us have encountered this ("installation is the reverse of removal"), but still slightly annoying. Firstly, just pouring in the new fluid will result in a _very_ partial fill due to the trapped air, only about a 1/3 liter. However turning on the engine/pump briefly sucked most of it in and freed up space for more in the reservoir. The instructions say to turn lock to lock twice to bleed air, but does not say this needs to be done _on_the_ground_. Perhaps this is obvious to others, but up in the air there isn't enough resistance to force the pump to really do anything, so the air doesn't get bled. Also, I had to do this several times over the course of several days to really get the air out, progressively adding more fluid. The manual states the capacity is 1.2 liters, but I still haven't even gotten a full liter in it. I didn't fully evacuate the system so I have to account for what was left in the cooling pipe, but still this is less than I would expect.

Finally, removing the radiator fan, air box, mass air, and intake boot was key. If I did this again I would definitely also consider removing the brake booster, as it was _really_ in the way when working on the steering box.

The result is totally worth it though, because the steering is no longer leaking, parts are nice and clean after a great deal of engine degreaser, and the groaning from the pump is much reduced.

Stephen

[John in VA]

I wound up having to use regular US spec worm gear clamps from NAPA, which hurt my OCD, but they work fine.

Although they cut into the outer surface of the hose.
Nice write-up. What car was this performed on?

[gmu525i]

Absolutely agreed that they cut into the hose... It tore my soul to use them but I was at the point where I needed the car back together, and after determining that the OE spec crimp type clamps I bought wouldn't fit I wasn't able to find the Euro spec clamps on short notice. I have to admit though I didn't try going to BMW Arlington. I am slowly learning that I should just go ahead and order a bunch of those little parts and have them available since it seems like this sort of thing happens every time.

This was all done on my Island Green '91 525i 5spd, purchased from a fellow NCC CCA member in Burke a couple years ago. I guess I should put up a picture, but the paint is pretty gone so really doesn't look like anything special so far. I am planning to go through all the systems one by one, and hopefully get her painted next year sometime.

[John in VA]

I wanted to get official BMW hose clamps from the dealer a few years ago - gotta have the roundel on them! The parts dept. suggested getting the ones from Norma, Zebra, Wurth, etc. The BMW ones had a high failure rate. Olympus Imported Auto Parts sells them, or you could probably snag a few from your local independent import repair facility or internet vendor.
I've not been concerned with replacing clamps with the crimp-style clamps (they commonly leak over time), but have a few spots on the 2002tii that I probably should, for originality's sake.