HowTo -> Overhaul a ZF steering box

[Max Lumens]

Yes, they are. There is lots of interchangeability among the models. Earlier e24s and e28s had big nuts that held the pitman arm on, but the internals were the same as later boxes. There are dozens of ZF part numbers, but they mostly specify very minor differences like port connections or torsion bar specs.

Does anybody know if E32 box fits E31? I know that ratio is probably different, but are they physicaly the same?

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Have a look in the sections for OTHER cars in the BMW online manual; there were lots of chapters left out of the e31 manual.

BMWTIS -- Repair Information

Is there any official spec for the gear lash adjustment?

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Totally. The spiral on the worm gear is the opposite direction, since the sector shaft is on the opposite side of the box.

So the RHD is useless for me?

[janimaki]

A seal kit was obtained, definitely without any thanks to the oem.
The part numbers shown in pics below were assigned arbitrarily as I inventoried the kit and wrote out a spreadsheet.

Where did You obtain those White square gaskets and O-rings beneath them.
My box is from B12 Coupe without servotronic bun I think the inner parts are the same ?

[shogun]

Is that seal kit available somewhere as a kit or is that bought all separately, and where?
I am especially interested in the white square gaskets for the chambers C->E which allow control pressures to be passed from the rotating shaft to-and-from the stationary housing.

[Hyper]

In a fantasy world, someone would have picked up the (american style) football and ran with it, doing an around-end of the opposing team, the OEM protecting their rebuilder channel.

In reality someone has to own the unenviable project of visiting seal manufacturers and convincing them to produce all or part of a kit. And in reality, no one is being sponsored to accomplish such a job.

My instinct is that it is not incorrect to focus on the pressure zones C->E as these would have inordinate influence over operations.

It had caught my attention (with no further proof) that in my case, 1) the white square-section bands may have been contaminated/embedded with metallic debris, perhaps delivered from elsewhere by the circulation in the hydraulic fluid, and that 2) this may lead to a failure to isolate the control chambers.

Note also that within each of the 3 radial slots, that the white band covers a standard round-section O-ring, which I assume to be the ultimate source of force pressing the white bands against the inside wall of the housing. Hence, any degradation in the O-ring properties might also show up as a failure to seal chambers C->E. Hence, the restoring of such properties might lead to properly sealed chambers.

In a fantasy world, on the bench top, you would apply remedial action and then immediately verify the result (via leak down), but in the real world you might have re-install the unit and just hope that anything has changed for the better.

[moroza]

You mention removing the wormshaft, which is back-loaded on these. My question concerns the front of the wormshaft and where it meets the housing: what goes on there? Is the paint-marked bolt on the very front of the steerbox housing a wormshaft lash adjuster? I did this once on an ancient Mazda steerbox, after we had replaced every last steering component, tightened the normal (sector) lash, started to tear our hair out, removed the box intending to replace it... and found a giant nut around the worm (input) shaft. Tightening that was the cure. Did this on my Yota, too, which required a special tool but minimal disassembly. I'm chasing a steering slop problem on an E34 with a similar situation (and the same box as your E31), looking for info.

[Hyper]

...Is the paint-marked bolt on the very front of the steerbox housing a wormshaft lash adjuster?...

The mission in this thread is/was seal replacement, hence its titled "overhaul" rather than "rebuild" where we would check clearance and wear, follow procedures and testing to achieve factory spec.
We, the public, lack such tools and documentation.

So, although I can't say what that nut is, what it does, or how to use it, I can say it did not involved seals and therefore it got only a casual glance during the project.
I sort of recall staring down the input/worm barrel and not coming to any obvious conclusions.




Just now I pulled the box out of storage to check if had the allen/hex wrench thing going on.
Yep, but I exhausted my entire bin of allen wrenches, both metric and imperial, and yet didn't find a satisfying fit.
It's half-way between a smallish 2.5mm and 3.
Anyway, paint plus allen probably equals adjustment feature.
Use at your own peril or delight.

[moroza]

Excellent; I couldn't see the allen hole before, but that's a lash adjuster if I ever saw one. Peril and delight await!

[Hyper]

Since you fancy wild guesses, here is mine...

It's an adjustment to the end stop of the rack travel.
And rather than just a mechanical stop, it forces open a ball valve (that I think I'm detecting) in the end of the piston, cutting to zero the pressure difference across the piston seal.
Why an adjustment? Well, that would take another guess, and I'm a busy man.

[moroza]

3mm was a perfect fit on mine. Your guess seems right; tightening or loosening didn't seem to do much, but any effect may have been masked by the rather heavy steering (car in the air and off), possibly because the balljoints and tierods are nearly brand-new and still stiff. I played with it a bit, reset to paint mark, found and fixed the problem elsewhere. Thanks!

So there is no wormshaft lash adjustment?

[Hyper]

Doesn't seem likely.

I did not observe that the worm was anything but continuous from end-to-end, although I suppose it could be a two-piece {edit: duh, has to be 2-piece, otherwise we can't sense and react to torque}.
Once the control section is affixed (someway/somehow) to the shaft, the control section and thus the entire worm assembly is constrained by a torrington...


...and a ball-in-race...


...keeping the control section chambers centered on holes in the housing.
We would not want the chambers moving with respect to these housing inlet/outlets.

So your only hope is if the control section can be re-positioned along the shaft (someway/somehow).
This hypothetical procedure would require complete disassembly of the entire box down to bottom level components and therefore couldn't be called "an adjustment".
*****
I'm an analytical thinker and use the word "guess" if I am merely 99% certain.
The hazard in disabling with the assumed piston stop is that, if hydraulic pressure is not killed at the end of travel, then the piston attempts to force the case apart with (hydraulic pressure x bore area ='s) perhaps 3 tons of pressure.
Going the other way I'll guess there is some comparable fail safe, possibly the end of the worm shaft popping yet another check valve inside the piston.
****
Others have mentioned that if one runs out of sector/output shaft adjustment, then one might consider swapping imperial balls for the original millimeter.
Can't comment on that problem or solution, especially in this thread about seal replacement.

[ZesCoupe]

Hallo Hyper.

Had the same mysterious problem with the lack of steering assistance and also braking assistance on my '86 E24, although occasionally on my way home after it started it would suddenly all be there again. Initially changed the pump as it was worn, also tried a replacement accumulator which didn't help either. Sounding familiar? I found this thread after a discussion on bigcoupe.com and avoided the rather expensive regulator replacement. Although slightly different to my steering box the internals look more or less identical so the strip down was a breeze. having said that I did spend a day removing the pitman arm. Looks like only a nut holding it in place (E24/28 model) but mine was so tight that a typical puller ended up twisting itself out of shape. I had to construct a steel cage to support the whole box suspended from under the pitman so I could press the shaft out on my hydraulic press. When it eventually freed there was a crack like a gunshot, scared the crap out of me.

So OK - the inspection. The white piston seals looked remarkably similar to yours, plus I found more residue in the rack chamber. I'd earlier found residue in the reservoir so that wasn't really a surprise. One advantage of the stripdown is that I was able to flush all the old contaminated fluid from all corners of the box. Now there used to be a repair kit (oem 32131126887) which I presume included all the various o-rings and piston seals but as of January this year it is NLA.

The problem: I noticed that there had been one or two other requests (also in the other post in the E32 section) for the source of the 2 kits used for the write up but there had never been a definite answer except maybe the rather cryptic response (fantasy world?) but I'm not quite sure what was being implied. I have ordered the gasket kit (oem 32131126888), although I, like you, had no external leaks, and have been looking for sources for the square section piston seals without much luck. I have been unable to even ascertain the type of material they are made of, that would be a start anyway. What I did find still available from BMW are what looks to be the same sets of 3 o-rings/piston seals (control valve section) but as fitted to a number of older vehicles. Couldn't find any definitive size details but other parts have the same sizes, it looks like certain things are reused in design improvements. I ordered them and if they aren't correct it is only a few dollars (euros) wasted.

So the question is (again) where did the seal kits come from? Were they the same or similar to the kits I mentioned as there is nothing listed for the E31 or E32? I got the idea from an earlier post that maybe Max Lumens was involved in some way. It was suggested that he was rather knowledgeable in this area so maybe he could help if he reads this.

Thanks for a great write up anyway (as far as I got) and I'm sure that if I can find the rings the assembly will be just as easy. Worse case scenario is replacing the underlying o-rings and giving the piston seals a clean-up with some fine scotchbrite.

Regards,
Martyn
Netherlands

[Hyper]

...So the question is (again) where did the seal kits come from?...

The answer is (again), the kits referred to in this thread from years ago were bootlegged out of the rebuilder supply channel in spite of the factory thumbing their nose at owner/operators.

A couple other sidebar notes...
* The square section rings are commonly referred to a "lathe cut" and there are suppliers that can deliver to your specs, providing the bottom line of the deal is big enough to include NRE and production setup. Once you've paid for 1,000 of each seal in the box, you will then sell a dozen per year while the remaining rot with the passage of time.
* What is missing from our DIY bench is any performance specification, and any means to test whether a box conforms to the specs. This could become a big deal if we are on a quest to source seals that may or may not work properly. Our current method of testing is to spend the time to install the box and then see whether we can properly get down the road. Besides the time involved, it is not a pure test of the box, because there are other questionable components that go into the higher level system. IOW's the box has not been sufficiently isolated with all other variables removed.

[rjjablo]

This is what I just used, Does not come with the White Square Rings, Way to expensive for what it is but it had what I needed. Mine was just seeping and I don't think I had any internal Leaks

https://www.ecstuning.com/b-genuine-...t/32131134768/

[ZesCoupe]

Thanks for the reply Hyper. I thought that was more or less what was implied, maybe I need to try and find a contact at ZF in Delftland, Netherlands. I get the point about special orders as well, I have seen Google results with this sort of offer. I'll have to try plan B and reuse them with new o-rings underneath which I have been able to source. I seem to have now flushed out all the old fluid and any contaminants so maybe that should help, it did seem to be somewhat intermittent.

Also Rjjablo, as I mentioned in the post I have a gasket set (for the E24) on order at present from the local dealer. Mine, as far as I had seen, was not leaking but having opened it I thought it would be best to replace the external oil seals and anything else supplied in the kit.

[petejk]

As I understand it, there is a lot of similarity between steering boxes from the e31, e32, and e34.
From reading this thread, and others, there seem to be 3 kits that could be sources of components with which to completely reseal/rebuild.
Of course, if I'm barking up the wrong tree, please let me know

BMW directly - kits are apparently still available

32131134768, e31/e32 with servotronic
e31 and e32 with servotronic.jpg

32131134714 e31 without servotronic
e31 kit non-servotronic.jpg


The above are external seal kits only


...and aftermarket kits.

From ebay I saw two kits which might prove to be sources for the white internal seals referenced earlier in the thread:

Both kits are from the same Russian supplier, but the second picture in each auction shows a pretty complete looking kit. They are listed as for the e34 box, but there is potentially commonality with some or all of these internal seals between the e34 and e31/32 boxes.

Firstly https://www.ebay.com/itm/164183975606 - e34 steering box with servotronic

e34 repair kit with servotronic.jpg

and https://www.ebay.com/itm/164553883861 - e34 steering box without servotronic

e34 kit without servotronic.jpg

and then finally, a well known source for bearings and recirculating balls

e31 rebuild kit with bearings.jpg
http://duesenklinik.de/uberuns/proje...w-850i-ci-e31/

[Goodguyili]

There is a lot of play in my steering, thanks for sharing petejk, im pretty certain the ball bearings in my steering box are worn so that last kit is a must for me. Do you know how to overhaul and remove the box itself?

[affa]

Yes the bmw kits are just seal kits. They don't include the Teflon seals (those white rings) and back up o-rings to do a thorough job. Depending on your box's condition the recirculating balls and bearings might or might not need to be replaced.

The way i look at it if I'm getting in there then they're all getting replaced. What you found in the last pic looks very interesting indeed...

iirc for the full bmw experience (lol) i did mine with the seal kit and the E28 rebuild kit which has the internal wear parts, but no bearings or balls...

Thanks, that's a good find. I have a csi box on the healing shelf. This find might come in handy.

[petejk]

There is a lot of play in my stearing, thanks for sharing petejk, im pretty certain the ball bearings in my stearing box are worn so that last kit is a must for me. Do you know how to overhaul and remove the box itself?

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I removed the original steering box from my car, when I had the engine out, so it was a much different experience from what my future experience will be replacing it again from the under the car.

The process as I understand it is to remove the X-brace, along with the center link, idler arm and pitman arm and then to unbolt and remove the steering box.

As far as overhauling my old box goes, I haven’t crossed that bridge yet, but I’ll be making use of Hyper’s reference photos to do so.

It looks like the e28 bmw repair kit mentioned above that included the white rings is now NLA, which is why the Russian eBay kits caught my eye. Who knows how long they will be available for..


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[shogun]

Here is an interesting article in the German language magazine Auto Motor Sport with good pics https://www.auto-motor-und-sport.de/...-restaurieren/
translated
Recirculating ball steering systems are generally regarded as convenient and robust. Nevertheless, after several decades of operation, a thorough refurbishment is usually necessary. Here are the most important tips. And it clears up a common misconception.
Excerpts:
"On the steering wheel," says Mercedes-190 SL expert Fritz Wallner from Munich, "the play should not exceed 25 millimeters." If this is the case, the complete steering system with its tie rods including their linkages should first be checked. Often, the faults lie here and not inside the steering gear, which is robust in principle. This, however, comes under suspicion if slightly grinding noises can be heard when the steering wheel is turned at a standstill.

Steering systems all die the same way
Fritz Wallner says this from experience: "First their oil leaks out at the hardened lower sealing ring. Then friction causes severe damage inside." It would be a miracle if resourceful tricksters hadn't discovered a solution decades ago that can conceal this damage. Instead of the correct lubricant, heavy-duty hypoid oil 85 W-90, they fill tough grease into the steering housing. The result is unconvincing: although the grease holds in the steering gear, wear nevertheless progresses rapidly.
In addition, a popular misconception clings to the recirculating ball steering system. People repeatedly try to minimize play in the steering wheel by adjusting it. But if the wear of the balls and their raceways is responsible for this play, correction is impossible. However, it can be eliminated. To do this, balls of the right oversize must be used. There are between 60 and 64 of them in Mercedes steering systems. Their diameter is correct if the nut runs tough but round. It must not get stuck under any circumstances.

However, this repair requires that the surface of the ball races is undamaged throughout. Cracking usually occurs in the middle area (see photo show). This is not surprising, because the steering engages here when the steering wheel is in the center position - it is the standard situation when driving. In the event of such damage, a steering gear can only be repaired if a suitable steering worm together with nut is available.
Nevertheless, recirculating ball steering systems offer two possibilities for adjustment. The axial play of the steering worm can be corrected; the correct dimension is a maximum of 0.01 millimeters. In addition, a pressure screw (see photo show) minimizes the axial play of the steering shaft. This allows the cup in the arm of the steering shaft and the ball of the steering worm nut to mesh without air. It is important to note that the steering shaft should not jam under any circumstances as it passes through the center position. The bottom line is that defective steering systems remain a job for professionals. Even small errors can be dangerous - or at least expensive. One incorrect setting is enough.

Subtitles to some pictures:
Overhauling recirculating ball steering systems is feasible, but also quite expensive: around 1,200 euros must be paid for an overhauled replacement steering system for Ponton or 190SL, for example.

Beautiful as pearls: The dimensions and size of the steel balls are regulated by DIN 5401. Oversize balls can be used if the running surface is still intact.

Disassembling a recirculating ball steering system usually causes few problems. However, a special pivot wrench is needed to loosen the adjusting ring. If there is grease inside the steering, this is a clear indication of wear: the viscous grease should conceal the play that has occurred.

Cracks in the hardened ball race cannot be repaired. They are caused by wear and are found particularly in the center area of the steering worm, because this is where most steering movements take place.

In addition to the bearings, the seals and the two bushings of the steering shaft, which are pressed into the housing, are also replaced. The balls are also replaced. The remaining parts can usually be reused.

Before the steering system receives new balls, the steering nut is turned onto the steering worm. Suitable balls to DIN 5401 are available in increments of 5/1000 millimeters in diameter. Choosing the right size can only be done by trial and error. The steering nut must run tightly, but without hooking.

There is a big misunderstanding about this pressure screw: It is often tightened when there is too much play in the steering. But this is caused solely by wear of the balls and their raceways - it cannot be eliminated by adjustment. This screw alone minimizes the axial play of the steering shaft. Translated with www.DeepL.com/Translator (free version)

[Goodguyili]

http://duesenklinik.de/uberuns/proje...w-850i-ci-e31/

Can somebody guide as to how to buy this kit? I'm having a hard time figuring out where to check out.

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[petejk]

Just send an email to the info@ email address


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[cartoonz]

There is a lot of play in my steering, thanks for sharing petejk, im pretty certain the ball bearings in my steering box are worn so that last kit is a must for me. Do you know how to overhaul and remove the box itself?

You will be far better served to just ship the box to Benchworks in Phoenix. They will rebuild it like new.
www.benchworksteering.com

[Goodguyili]

You will be far better served to just ship the box to Benchworks in Phoenix. They will rebuild it like new.
www.benchworksteering.com

You're right I probably would be better off paying for someone to rebuild it, thank you for the link.

However, I do enjoy working on this car and wouldn't mind rebuilding it myself if I could. If if turns out to be far too complicated and I'm way over my head I'll give that link a go.

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[cartoonz]

You're right I probably would be better off paying for someone to rebuild it, thank you for the link.

However, I do enjoy working on this car and wouldn't mind rebuilding it myself if I could. If if turns out to be far too complicated and I'm way over my head I'll give that link a go.

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For some added perspective, I have specialized in these cars for 20+yrs... and even I will send the steering boxes there vs doing it myself.

[Auraraptor]

^^^^ What he said.

Same on this end (over 20+ years with various BMW V12s and V8s and now my second 8er)....I just sent my spare box to them for a rebuild as well.