What a feeling it will be! A properly adjusted W123 / W116 / W126 power steering box - PeachParts Mercedes-Benz Forum

Stretch · #1 08-11-2011, 04:14 AM

Here's what I did recently to try and regain that fresh out of the box feel for my W123 power steering.

The power steering pump had long been resealed and cleaned out (see http://www.peachparts.com/shopforum/showthread.php?t=278649) but as I was busy cleaning up the engine bay during an engine rebuild I thought I'd have a go at doing the steering box as well. I mean why not? I obviously didn't have enough to do...

I was influenced by this DIY (see http://www.davidpetryk.net/Mercedes/Steering.htm) that has been talked about quite a bit on Peach Parts. I like this DIY but I think the adjustments can be done a bit better.

When I looked at the FSM I found that the chapter is split into two PDF files on the CD. Reading through this chapter you could be mistaken for thinking that adjusting and resealing a W123 power steering box is really complicated – a bloody nightmare in fact – but I now think otherwise.

Performing ALL of the adjustments specified in the FSM does take time and you need to be patient but I think it is a straight forward DIY job with the exception of one bit => tightening the working piston. This does need a difficult to replicate special tool – but I've got a solution for that too; but it isn't a quick, easy or a really cheap one.

Stretch · #2 08-11-2011, 04:14 AM

Whilst I'll be covering most of the information in the chapters for resealing and adjusting the steering box in the FSM I encourage you to read through the chapters as well. Especially if:-

You have a W126 steering box
You are building one box from many others => Many parts are NOT interchangeable
You are replace parts (other than seals) within the box with new ones

There are subtle differences in these steering boxes, such as steering stops, no steering stops, self centring, no self centring etc. There is a whole chapter about this – chapter 46-010 and loads of information in chapter 46-220.

In the W123 FSM there are two chapters that are concerned with measuring the friction in the steering system. One is covered in the refurbishment of the steering box chapter 46-220 (which is the subject of this thread) and the other for measurement of the steering system fitted to the car with the wheels on the ground: This is chapter 46-120 which can be briefly summarised as wheels on ground, engine at idle => force required to turn steering on steering wheel nut should not exceed 5-7 Nm.

Please note chapter 46-120 is a check. It is only a check – not a method of adjustment. From comments on this forum I understand that adjusting the steering box play in accordance with the check procedure in 46-120 or just nipping up the adjustment screw is quite commonly done. Fair enough – but – before you do that please have a look at the final adjustment procedure at the end of this DIY... I have some extra information and a warning for you!

For the record my steering box has the following identification marks next to the “drain” bolt (which is actually a cover for a hole where a special tool pin is used to locate the centre of the steering):-

YY

This means that I have a second version steering box with an internal stop. It just so happens that it does not have the automatic compensation for play. The part number for the main casting is 116 461 04 01. This might seem like trivial information but it might help some of you out there.

Stretch · #3 08-11-2011, 04:17 AM

I'd like to be able to give a definitive list of the tools that you'll need. Unfortunately there are many different variants of this steering box depending on whether it was meant for the W123 or the W126 or whether it was an early or a late version.

65mm open ended spanner => for most W123 steering boxes ONLY – W126 is different and so are some of the earlier steering boxes!
6mm Allen key
Special tool – to remove and tighten the nut on the working piston
Pin spanner with 4mm pins
Self made special tool to measure friction => Strong but light bits of wood, 2 wood screws, some wire and some 'heavy things'!
Kitchen scales that measure in intervals of 1 gram
Instead of the wood and kitchen scales listed above you could alternatively get a fancy torque wrench and expensive special tool attachments that fit on splined shafts... or any of the other special tools listed in the FSM...
Circlip pliers
A vice / method of holding the steering box (so that you don't damage it)
A set of old fashioned hanging scales if you decided to tighten the steering nut

Stretch · #4 08-11-2011, 04:17 AM

I've set the names of the parts of the steering box in the following photographs.

Stretch · #5 08-11-2011, 04:18 AM

First drain the steering fluid. Turn the steering wheel all the way to the left...

...and undo the little screw on the steering box...

Catch the oil as it pours out.

Disconnect the supply and return hoses from the power steering pump.

Disconnect the centre steering stay ball joint from the Pitman arm.

Centre the steering wheel if you wish and then disconnect the rubber flex joint between the steering box and the steering wheel shaft.

Whilst supporting the steering box remove the four bolts that hold it onto the side of the engine bay. The heads for these bolts are in the wheel well. Warning:- the steering box is heavy and awkward – mine weighs 14kg.

If you struggle with these stages, stop and ask yourself if you really want to continue. Adjusting a steering box does get a bit harder than this! (Please note I've given you a bit more information than that presented in http://www.davidpetryk.net/Mercedes/Steering.htm, but I do agree with the “If you can’t figure how to get the gearbox off the car you don’t need to be taking it apart” comment)

Clean the outside of the steering box if necessary with your favourite engine degreaser.

Remove the Pitman arm.

For removal of the Pitman arm there is a special tool / puller for it – but chatting with the chief mechanic at the dealer he said that you usually have to resort to using heat (and lots of it). I tried with a Butane blow torch but it didn't work – shame of shame I got the mechanic to remove it for me. I don't think he bothered with the special tool.

Stretch · #6 08-11-2011, 04:18 AM

Not really rocket science this bit.

There is a control valve at the back of the steering box, where it attaches to the inside of the engine bay. The sealing cap on mine was pretty rusty. After removal of the circlip it took a lot of persuasion and penetrating oil to remove the sealing cap.

Inside you'll find two springs on either side of a shuttle valve. The FSM says you are NOT to dismantle this part any further. I didn't.

Next remove the bolts that hold the output shaft cap in place. This is the part from where the Pitman arm shaft / output shaft emerges.

Remove the little O ring on the back of this cap. Remove the large seal on the outer surface of the cap after removing the circlip.

Next remove the lock nut on the adjusting screw which is positioned at the other end of the shaft that holds the Pitman arm (see photo below). You will probably need to hold the screw thread still with a 6mm Allen key. Next screw this thread all the way into the steering box with the 6mm Allen key. The whole shaft will come out.

Stretch · #7 08-11-2011, 04:19 AM

At the end of this shaft you'll see two small circlips. Remove them so you can clean and inspect the end of the adjusting screw assembly.

If you haven't already removed the steering shaft flex disc assembly from the input shaft of the steering box, do so now.

You can now remove the 15mm hex headed bolts from the cap and remove the cap from the steering box.

You can now remove the working piston and steering worm assembly.

Now that you've removed the working piston assembly – slow down and take it easy. The steering worm / input shaft can still turn. If you unscrew this bit then the ball bearings will fall out.

Time for the first adjustment measurement!

Once you've removed the steering worm and working piston assembly (complete) the FSM says to check the over all condition of this part of the steering gear by measuring the friction / wear of the ball bearings and the races in the working piston.

If you have a fancy torque wrench that can measure between 5Ncm and 50Ncm and special tool attachments that will connect your toque wrench to the splined input shaft; or the special tools detailed in the FSM skip these next bits, measure the torque on the input shaft and go to the continuation of the dismantling procedure.

Stretch · #8 08-11-2011, 04:20 AM

From the picture above you can see that this special tool is essentially a notched ruler that attaches to the splined shafts on the steering box. Weights are positioned in the notches of this ruler to apply a torque.

I replicated this tool by finding a bit of soft wood with approximately these dimensions 30mm X 10mm X 300mm. I drilled a 16mm hole in the centre and then carefully cut along its length – through the centre of the hole – to split it into two parts.

I then held these two parts together with two wood screws, one on either side of the central hole, which can be tightened to improve grip on the splined shaft of the steering box.

Instead of notches on the upper surface of the special tool 116 589 03 21 00, I just marked the distance from the central hole on either side in centimetres. You probably won't need to go further than 12cm but that depends on the weights that you have available.

You now need to find some suitable weights that you can hang from wire off of your newly made special tool. I just so happened to have some wheel balance weights that are conveniently marked with their weight. But you can also thread nuts, washers, spanners, sockets or whatever onto bits of wire or string. This is where your kitchen scales come in handy.

Stretch · #9 08-11-2011, 04:20 AM

I'll go through this once – and only once because it is a bit tedious!

Prior to dismantling the steering worm gear from the working piston and the cap a measurement should be made to assess the condition of the ball bearings and bearing races in the steering nut. The torque should be in the range of 5Ncm to 50Ncm.

Please note – we are often quite used to torques with the units of Newton metres but here we're talking about Newton centimetres – this is why the messing about with a balance tool is necessary in the absence of a smart (and probably expensive) torque wrench that can measure these low torques.

Torque is defined as force multiplied by distance.

From this relationship we can find the force needed to apply a given torque at a known distance. To help with my mathematical abilities I've chosen 10cm.

For the lowest torque of 5Ncm the force required is:

You can go through the same process shown above for the highest torque of 50Ncm and you should come out with a required force of 5N.

We now know that if we need to apply a force at a distance of 10cm marked on the balance tool in excess 5N in order to move the input shaft something is wrong.

We also know that if the input shaft moves with a force smaller than 0.5N at a distance of 10cm marked on the balance tool then there is also something wrong and the assembly is out of limits.

In order to apply the forces calculated above we need to convert these force values into equivalent weights (strictly speaking masses) using this equation:

Here 'g' is the gravitational constant which is equal to 9.81m/s2

We can now convert our maximum force valve of 5N (only applicable at a distance of 10cm) to an equivalent weight.

And the minimum force value of 0.5N (only applicable at a distance of 10cm) comes out at 51g. Don't forget to convert kilograms into grams! There are 1000 grams in a kilogram.

I've written this out as simply as I can so that hopefully everyone who reads this can understand what to do. If you feel confident enough you could combine the equations above into one. Have fun!

Stretch · #10 08-11-2011, 04:21 AM

You now need to rummage through your tool box and find two items – one that weighs 51g and the other that weighs 510g. Attach these items to a bit of wire or string and hang them at the 10cm point on the balance tool.

Position the balance tool on the end of the input shaft and make sure that this connection does not slip.
I wrapped a piece of masking tape around the splines of the shaft and drew a mark on the tape and the balance tool so that if the joint moved I could easily see any misalignment.

Hang a weight on one side at the 10cm mark and then move the same weight to the other side of the balance tool so that you get an idea that the force you are applying is resulting in the same response on either side.

Example:-

You can now work out the force required to turn the shaft. Say for example the shaft is loose enough that at 10cm the 510g weight just falls off – the balance tool spins from the horizontal position towards the vertical and the weight falls off. You can now reset the balance tool to the horizontal position and re-hang the weight at say the 5cm point. Say for example this time the balance tool moves slowly from the horizontal position until the weight eventually slides down and falls off.

However when you reset the balance tool to the horizontal position and put the weight at the 2cm point the balance tool stays level. You find that placing the weight at the 2cm point on the other side of the balance tool also results in the same – the balance tool stays level. So using the equations above you can “backwards calculate” the torque that you are applying.

And because we're hanging the weights at the 2cm point (instead of the 10cm point)

You can see that by applying a different weight at a fixed point or moving a weight along the length of the balance tool you can adjust the applied torque to a value that you require.

The trick is to position the weights on the balance tool so that it “just doesn't” move.

You could use this same method for setting up the pre-load torque on a W123 / W126 differential input shaft – so it is worth remembering.

Stretch · #11 08-11-2011, 04:21 AM

After you've checked the wear in the working piston you can continue taking the rest of the steering box to bits.

Get a 65mm open ended spanner to remove the lock nut on the cap that covers the input shaft (or the equivalent tool for your steering box). It might be necessary to hold the inner part of the cap with a pin spanner.

Here's a picture of the input shaft and cap in bits

Remove and replace the rubber and plastic seals in the cap.

Place the working piston and worm gear in a plastic bag and unscrew the steering worm so that the ball bearings fall out. There should be 24 balls. (PHOTO)

You can then unbend the tabs on the working piston to gain access to the screws that hold the detachable bearing races in place.

Stretch · #12 08-11-2011, 04:22 AM

The working piston, worm gear and ball bearings are supplied as a single part. This part is still available at the time of writing but it costs in excess of 500 Euros plus tax. If your steering box failed the torque test made during dismantling, now is the time to work out why and what on earth you are going to do.
Look out for the usual damage such as corrosion, pitting, wear marks etc. To my mind if you are in a cash poor time rich situation and the working piston failed the torque test described above it might be worthwhile fitting the sealing kit and see how you go – so long as there is no visible damage to the steering box. All I'm saying is that a reseal kit is cheap compared with the cost of proper replacement parts and will probably be cheaper than a second hand steering box in most areas in the world. This however is your choice – your decision. Post up some pictures on this forum if you're not sure – perhaps the input of others will help you make up your mind.

Warning – what ever you decide to do – do not refit parts that are obviously knackered. Worn input splines and Pitman arm splines should not be reused. Broken / re-welded / botched parts should not be reused. Parts with heavily worn bearing tracks should not be reused. This is a steering box folks – make sure it will continue to work as intended for you. Just like brakes it is a very important part of your car.

If you are in the habit of thinking “oh it will be OK” think again!

Stretch · #13 08-11-2011, 04:22 AM

If you've followed the procedure to this point, the working piston will still be in one piece. Inside there is a protruding “foot” that is called the steering nut in the FSM.

The steering nut is held in place by a large 8 sided lock nut on my W123 power steering. Officially you are meant to use several special tools to undo this but I got a local CNC machining company to make my version of a “special tool” socket. You can read all about this in this thread http://www.peachparts.com/shopforum/showthread.php?t=298612.

The steering nut has a bearing that sits inside the working piston. The steering nut should not be flopping around in the working piston under its own weight. Adjustment is made by tightening the steering nut assembly via a 35mm hex head and the large 8 sided locknut.

I'm not 100% sure if this totally necessary. I did go through the trouble of getting a special socket made and I did adjust the steering nut as prescribed in the FSM so that essentially it doesn't flop about (the prescribed torque is 6-10 N cm).

It is a lot of work, and I'm not sure what the result would be if this bit was left in an out of adjustment state. The only thing that concerns me is that if the steering nut is flopping about it is difficult to tell if the bearings inside are damaged or not. If the steering nut is stiff or moves unevenly / jerkily then it is definitely unserviceable.

Here are some pictures of the special tool socket I had made and the plans (use these at your own risk!)

Stretch · #14 08-11-2011, 04:23 AM

Clean all the parts before assembling. I used brake cleaner. Make sure all seals and plastic rings are clean and dry before applying a smidge of power steering fluid before fitting them.

Starting with the steering nut. Assemble the bearing and bearing race in the bottom of the working piston assembly...

...fit the steering nut and tighten with use of your special tool (home made socket – or MB tools) so that the torque required to move it is in the range of 6-10Ncm...

A tip for this bit is not to bother too much about clamping the working piston – work the self made socket against a 35mm socket and T bar. Tighten the 8 sided nut to 200 – 240 Nm.

To do this I used my open ended 60mm spanner on one side of my self made socket and attached my old fashioned hanging scales to a hole in the end of the spanner so that I could measure the torque applied.

Using the formulas given above, for a distance of 47cm between the centre of the open ended spanner's mouth and the hole on the handle, I calculated that my scales should be reading between 43 kg and 52 kg to apply the correct torque.

Please note unlike a torque wrench, calibrating scales is quite easy to do so long as you have some known weights to test it. This might look like a bit of a dodgy way of applying a torque but if you are careful (and you have to be) you can safely apply a torque as well as you might with a torque wrench – in absence of a torque wrench – particularly if you are given a nice wide range between 200 and 240 Nm.

Stretch · #15 08-11-2011, 04:23 AM

If you didn't take the steering nut and working piston apart you'll be starting here.

Start by fitting the input shaft cap onto the steering worm. Make sure you've replaced all of the O rings and the plastic rings.

The input shaft / steering worm has several bearing races that fit within the cap. Make sure that these are fitted in the order shown. The FSM doesn't say to do so but I lubricated these bearing prior to fitting with power steering fluid.

Fit the main outer seal into the central plug section of the cap by carefully tapping it into place with a suitable sized mandrel (or socket). The FSM does say to fill the gap under the seal with grease.

Fit the circlip to this central plug and tighten loosely with a pin spanner. Fit the external locking ring (in my case this is a 65mm hex nut). Now you need to tighten the central plug with the pin spanner so that the input shaft friction is less than or equal to 12Ncm. Then tighten the plug to have an additional 4 – 7Ncm. From my understanding this process in the FSM is to make sure that you don't over tighten the delicate bearings in the cap. If you have assembled the input shaft and cap in such a way that it fails the first test (<= 12Ncm) then you need to take it to bits again to find out why. If I ever get the chance I'd like to check the original German version of the FSM as I get the feeling that some meaning has been lost in the translation. Once you've gone through this fiddly process tighten the lock ring to 140 - 160Nm.

After torquing the lock ring recheck the torque of the input shaft to make sure it hasn't moved.