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6.9 steering box overhaul

Started by s class, 16 September 2007, 06:33 AM

s class

Well, the 6.9 was suffering from severe leaking from the steering box, and the usual play. 

I decided this would have to be dealt with before the roadworthiness inspection. 

Removal went pretty smoothly. 

This is 'as removed'




I immediately saw 2 things :

a) the steering coupling is knackered
b) the sector shaft adjustment was quite well in, suggesting the box might have quite a bit of life left in it. 

Yippee!!

Then I peered under the car to inspect the steering box location :




Again, 2 things obvious :

a) behind the steering box was mud, crap and some small creatures.
b) the rear most exhaust manifold stud has no nut on it!  Presumably someone thought it was too inaccessible and didin't bother.


Then I cleaned the box up :






[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

#1
I tried adjusting the sector shaft setdown and was dismayed to find that even slightly adjusting it caused binding off centre, and yet had minimal effect on the large amount of play in the centre.  This box certainly has no high-point left. 

Now my experience is that generally, the sector shaft teeth wear long before the teeth in the piston.  So the trick is that one can often just replace the sector shaft, either with a decent used one, or if you are flush enough, a new one. 

I then stripped the box to examine the situation.

Summary  - the sector shaft teeth are VERY worn, and so are the piston teeth.  Oh bugger. 

This box is about beyond it. 

Its not very clear in the photos, but the contact surfaces of the teeth are eroded and brinelled.







The valves are OK.  Well that's something at least. 





[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

#2
The problem is there are exactly zero LHD 6.9 steering boxes in scrapyards here, so I realised I needed to be a bit creative.  I had recently scored a pretty good 280SE (RHD) steering box at the breakers.  This was before I even bought the 6.9, I took it just because reasonable ones are few and far between. 

LHD and RHD boxes are the exact mirror image of eachother, BUT some of the internal components are the same, just assembled in reverse order.  I decided to strip the 280SE box and see if I could scavenge its sector shaft and piston. 

The photo below shows the two input screws. 

The 280SE item is on the left, the 6.9 item on the right.  You can see the more heavy duty carrier sleeve that the 6.9 uses. 

Also see how the screws run the opposite ways, due to the differences between LHD and RHD. 



I will be retaining the 6.9 screw for its handedness and heavy duty design. 

Below are the pistons (top view) .  280SE on the left, 6.9 on the right.  The input bearings are different diameters to account for the 6.9's heavy carrier sleeve.



Below is a bottom view of the pistons.  It doesn't show up in the photo, but the 280SE items teeth are in very good condition.  Note how the two are mirror images of eachother.  The 'tab's sticking out to the side are the valve actuators. 



OK then a top view :

280SE on left, 6.9 on right

You can see the opposite handedness of the ball return loops.



I am going to transplant the ball cage and return loop from the 6.9 piston into the 280SE piston to give it the handedness I need. 



[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

#3
The 280SE sector shaft has teeth in a pretty good condition.  Its a direct drop-in replacement for the 6.9 shaft. 

Another bonus from reversing the handedness of the 280SE components is the sector shaft will now engage the piston's teeth at the opposite end of the cuts, where they have not been used.  SUPPOSING I can actually reverse the handedness of the piston, things should work well. 

sector shafts : 6.9 item at top, 280SE below. 



To distract myself from the misery of all this I decided to get on with the aesthetics of the box.  The components were degreased, derusted, and then primed with Standox etch, then painted with 2K black gloss.

looks better than before :







[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

CraigS

Very creative. I just hope it works with all the trouble you are going to, but then again, what choice do you have  - other than to buy a new one. The EPC doesn't even list a price for it, but I know the 6.3 one is in excess of USD 2500.
[url="http://s109.photobucket.com/albums/n77/Aegeanfoods/My%20Cars/"]http://s109.photobucket.com/albums/n77/Aegeanfoods/My%20Cars/[/url]

s class

#5
Craig, indeed.  I could get one from the US I suppose but that's a lot of trouble and expense.  I do think this will work, but before I get ahead of myself too much, I need to strip those 2 pistons to be sure their internals will interchange. 

You can buy a sector shaft separately, but if memory serves its something daft like US$1000.  In any case, the sector shaft isn't really my problem, as the 280SE one is good and will drop straight in.  Its the piston teeth that are the real issue.  I've never seen them worn like this.  I have a suspicion that this car has gone most of its life without a PS fluid change - see the discolouration of all the internals - perhaps that's why the wear has been excessive.  I also think that is has been running with excess play for a long long time, and perhaps all that rattling around has chewed off the teeth.

Who knows. 

Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

CraigS

[url="http://s109.photobucket.com/albums/n77/Aegeanfoods/My%20Cars/"]http://s109.photobucket.com/albums/n77/Aegeanfoods/My%20Cars/[/url]

s class

Gee thanks Craig,  you really are quick at finding stuff. 

'fraid I was even quicker though.  I bought one at the dealership this morning for the equivalent of that ebay price plus shipping.  So at least I didn't get ripped off. 

Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

CraigS

Sometime I come across these things by coincidence - others by design.

Have a look at this also. Probably too late, but ..........

www.300sel.com/pdf/StarBrochure11_05.pdf

Scroll down almost to the end. Reco Steering box.
[url="http://s109.photobucket.com/albums/n77/Aegeanfoods/My%20Cars/"]http://s109.photobucket.com/albums/n77/Aegeanfoods/My%20Cars/[/url]

s class

HI styria,

Thanks for your encouragement and praise.  As I'm sure you know, resolve and enthusiasm are easier to come by in the early stages of a project.

Indeed I really enjoy discovering every aspect of a car and how it all works.  There is no substitute for getting one's hands dirty to achieve that. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

#10
OK progress update - I have not played with the 6.9 much in the last week because such mundanities as work got in the way. 

As stated above it was my intent to disassemble the pistons. 

At this point I feel I must include a disclaimer and a 'don't try this at home' warning.  Stripping a steering box further than the photos above is not even done by the professionals.  If the piston components were to be disassembled, during reassembl, the installation of the crown and lock ring determine the end play in the internal bearings in the piston.  This setting of end-play is CRITICAL to correct, safe operation of the steering box.  Realise that the steering box is a safety item.  Your manufacturer recommends replacing the entire steering box as a unit if wear is excessive.  I would advise that steering boxes should only be resealed by professionals, or replaced as appropriate. 

Contact me offline if you want more information. 

Ryan



[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

s class

Michel, I've slacked off on the pace because my left front strut will only arrive from Germany on about 18 October.  I have to wait for that before the inspection. 

First priorities are to patch up the rust in the sill, and complete the steering box.  Then I will do the struts and spheres once everything has arrived.  I HOPE the struts, spheres and reco pump will do the trick. 

Yes I'm late for the inspection but these things happen.  I've gone as fast as I can. 

Ryan


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan


A question for "s class" regarding transplanting of the ball nut.

What tool did you for undoing the locking slot nut in the recessed end of the piston?

A bought tool? I can't find anything suitable.

A DIY tool, a bit of pipe and an angle grinder?

(Realise this is an ancient topic but it has appropriate pictures.)

koan
Boogity, Boogity, Boogity, Amen!

s class

Koan, I cut down a suitable socket to make a 4-pronged tool.  I think the socket was 50mm.  I can take a photo if you like, but it really isn't too pretty. 


[color=blue]'76 6.9 Euro[/color], [color=red]'78 6.9 AMG[/color], '80 280SE, [color=brown]'74 350SE[/color], [color=black]'82 500SEL euro full hydro, '83 500SEL euro full hydro [/color], '81 500SL

koan

Don't worry about the photo, I did the same with a pipe coupling to get some drive line (diff?, hubs?) apart, Wasn't pretty either. It failed in the tightening and had to get the Sirtools real thing.

Couldn't find anything in any of the online tool stores.

A 46mm socket fits the nut, a piece of tube 2.5 in ID fits over the socket. I'll start with that and the angle grinder.

koan
Boogity, Boogity, Boogity, Amen!