R/R Steering Gearbox Questions - PeachParts Mercedes-Benz Forum

donbryce · #1 03-13-2008, 07:45 PM

(My apologies to Meltedpanda for stealing the thread title)
OK, so if anyone has been following along, the other thread on this subject has progressed to the point where the box is now 'on the bench' and ready for new seals.
R/R steering box removal - scale of 1-10

The best write up on this IMO is that by David Petryk http://www.davidpetryk.net/Mercedes/Steering.htm What I'm asking here is some advice on a few of the steps in his procedure, which I will reference....

In Steps 3 - 5, removal of the pitman shaft, he undoes the locknut on the adjusting screw and turns the screw clockwise to push the pitman shaft bearing cap out of the gearbox body. Later, in steps 54 - 61, he describes how to set the torque, or freeplay, of the gearbox. Can the locknut be removed and the pitman shaft assembly pulled out without disturbing the freeplay setting, assuming of course that the socket screw is not disturbed throughout the procedure? I'd prefer not to mess with this setting.

In steps 9 and 10, he describes removing the steering shaft bearing cap and rack assembly, to "Turn the steering shaft fully clockwise", with a caution not to "by any means unscrew the steering shaft from the rack gear assembly. The balls will fall out and you don’t want that to happen.". He then advises turning the shaft so there is no gap between the bearing cap and rack assembly, as in the gap pictured in step 10 and none in step 12. Does turning the shaft fully clockwise not eliminate this gap before the unit is removed? Should this be the initial position of the gearbox before the pitman shaft bearing cap is removed?

Appreciate anyone's help who can answer these questions. My seal kit should be here next week, and I'd like to be sure of what I'm doing. (I also PM'd dpetryk...hope he can clear this up)

Edit Added: Would the initial turning of the pitman shaft adjusting screw, steps 3 - 5, create this gap in the steering shaft bearing cap/rack assembly?

donbryce · #2 03-14-2008, 11:48 AM

....for my W126 steering box "Reconditioning of steering gear", section 46 - 220. There is a procedure for checking the play of the pitman shaft while the box is on the bench. This would be steps 55 - 61 of Dave Petryk's article.

Mercedes uses a socket of some sort that slips onto the spline of the steering shaft, and a Ncm torque wrench that goes into the socket.

The procedure is (quotes from the manual)

(1) Screw in the adjusting screw "until the steering worm can be easily rotated, then measure friction torque of steering worm" and note value.

(2) Turn the screw to the left (CCW) until "friction torque has increased by 40 - 60 Ncm. That is, when the steering worm has turned beyond center position, the friction torque should amount to 110 - 160 Ncm."

I'll assume from this that the initial torque should be 70 - 100 Ncm.

All of this is with the box off the car. The values for measuring from the steering wheel, box in car, discuss an initial value of 60 Ncm, an increase of 30 - 60 in the center range, with a total value of 90 - 120 Ncm. These values are with the pitman arm off the box.

I find this slightly mind boggling, and I'd still prefer to leave this setting alone.

dpetryk · #3 03-14-2008, 12:22 PM

No way to leave the setting alone. It must be changed to remove the pinion gear. You will understand when you get it apart why the adjustment must be reset. The adjustment screw is connected to the pinion gear through a bearing and it must be removed with the pinion gear.

Just follow the procedure as written. It works.

Don't worry too much about the gap. Just don't let the worm gear come out far enough to let the balls fall out.

The setting is easily reset. Just follow the procedure.

donbryce · #4 03-16-2008, 06:46 PM

OK, the job is done. I started with a nicely cleaned gearbox, about 3/4 hour at the wash tank, at noon today, and I was inside around 4:30 following the last step of his procedure ("You are done. Great job. You have saved about $400. Go have a beer or two.").

I'd like to add a few observations and comments to the procedure.

- Before I undid the adjusting locknut and screw, I marked the screw, locknut and casing with a scratch awl and metal marker for later reference. I was/am paranoid about not getting this setting right. I also counted the exposed threads (5), and measured the exposed screw tip distance from the casing shoulder (18.04mm).
The 2 pictures below were taken after the operation. As you can see, the mark on the screw is slightly left of the other marks, and the final tip-of-screw is 18.03mm. The mark reflects that I tightened the screw up a bit more. The mm distance is +/- due to manual error, but it was close enough to ensure that the adjustment is very close to the setting before I changed it.
The business of following the Mercedes procedure to set this clearance (Petryk step 57, and my post above) was not possible for me, since I don't have either the special ruler-tool/weights, or a torque wrench that can read Ncm's. I also could not 'feel' any measurable change in the torque at the center of the pinion's travel vs. the beginning/end of travel. So, I'll have to wait until everything is back in the car to find out if it's correct.
Bear in mind that I only had from mid Sept. to the end of Oct. to drive this car, not much time, but it didn't feel loose, so hopefully it will be as it was then, only not leaking a liter of PS fluid every 50 miles..

- I too had to use a chain wrench for the big steering cap nut in the vice to get it started, Petryk step 14, with a piece of box tubing for extra leverage, but I finally found a use for my old plumbing 'spud wrench'. It was perfect for reinstalling the big nut!

- Unfortunately, the inside of the casing bore has lots of wear marks, and a couple of deep scores. I'm thinking that these might tear the teflon seal up and put me right back to square 1. I couldn't see any scoring on the old seal though, so here's hoping...

continued next post....

donbryce · #5 03-16-2008, 07:06 PM

- In step 30, it says to "Replace the O rings" in the control valve, but I only found 1, in the valve cap.

- Steps 7 and 51 - 53 discuss the overhaul of a valve, which my gearbox doesn't have. The manual addresses an 'automatic compensation' valve, which I assume is the same valve, found on a version 3 gearbox?

- I searched through 4 ice cream tubs of metric bolts and couldn't find one with the same thread pitch (1.0) and size as the closing plug bolt, to make a centering bolt-lock as shown in step 39. Finally, on a second pass, I did find a banjo bolt that matched. I ground down a zerk fitting and pressed it into the banjo bolt, which works great.

Well, that's about it. Thanks again to Dave Petryk for taking the time to document this procedure. It would've been a nightmare weeding out the unnecessary steps in the 99 step job in the Mercedes service manual!

Added: I guess it is possible to just replace the pitman arm seals with the box on the car, but after getting the kit, and removing the pitman arm, the extra steps to undo the steering shaft coupling, the 2 fluid lines, and the 3 frame mounting bolts don't really seem that much extra work for the benefits of having all the seals redone.

donbryce · #6 04-10-2008, 10:44 AM

Well, the box is back in the car, finally! I did an R&R odessey, still on-going, to remove the sub-frame and the oil pan, both subjects for another thread(s).
I wanted to add a note on something that I encountered on reinstallation of the shaft to the steering coupling.
As anyone who has been there knows, the spline is very tight at the coupling on the gearbox spline. I had to use a long 3/4" thick bar and hammer to pound it out, and even with grease, it needed to be pounded in as well, from the inside through the cover opening at the steering column base, even with a cold chisel in the spline opening. After about half an hour of pounding and going under to check the progress, it was nicely seated just where the bolt needs to go to re-attach at the box.
Then I checked the steering column at the top, where the wheel goes, and noticed the aluminum bearing carrier, the piece with the 3 allen bolts that had to be loosened to allow the shaft to come up for spline removal at the box, was turned left. The bolt holes didn't line up with the threaded parts in the column housing. I tried, but there is no way to turn this piece once the coupling is seated on the box shaft! I had to pound the thing off again, turn the piece to align it, then pound it on again.

The moral is: Use a couple of long (about 1 1/2") bolts to keep the bearing carrier aligned to the column bolt holes while working on the coupling. Remove after the job is done and reattach the stock bolts.

Also, I think I might be able to adjust the box while it's in the car by snaking a long extension, flex-end, and 6mm allen socket down to the adjusting nut between the exhaust manifold pipes on #7 and #8 cylinders. The nut should be able to be turned with a 3/4" crowsfoot from the top (same access) or a custom bent end wrench from the bottom (MB method). This is for the cursed cramped 560SL engine bay BTW.