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Steering knuckle rebuild...

Started by s class, 09 September 2011, 12:37 PM

s class

W116, W126 and W123 all use the same basic steering knuckle *, ** as in the photo below :



Note * The W116 6.9 and W126 with full hydraulic suspension, and armoured versions, use an apparently identical, but high strength version

Note ** The horizontal links differ slightly in geometry for different chassis.

If one looks at the rear side of the knuckle, the so-called supporting joint is visible :



This joint is the primary wear component of the steering knuckle, but the good news is that it is replaceable.  The bad news is that it is difficult (very) to replace.  The joint is a press-fit into the steering knuckle.  This photo shows the underside of the steering knuckle, and the base of the joint is visible.  When correctly installed, it projects a few mm through the underside of the knuckle. 



[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

I was recently working on a W123 that has had these joints replaced in the past.  In chasing a clonking suspension problem, I found that the LHS joint had collapsed, and had about 3mm play in it.  I proceeded with the stripping, which involves removing and supporting the brake caliper, releasing the wheel bearing safety nut, and withdrawing the disc/hub/wheel bearing assembly. 

Next the supporting joint, guide joint and tie rod ball joints are released with a ball joint separator.  The steering knuckle is then removed, and the horiziontal link can be separated from it. 

The first thing that was apparent is that the ball-joint's dust jacket was perforated in multiple locations, caused by poor previous installation technique.



The next concerning (very) observation was that the joint was not fully inserted  - compare this photo with the one in the previous posting which showed a correct installation :



[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

On the upper side, it was evident why the joint was not inserted fully :







Ham-fisted previous installation techniques involving hammers had distorted the rim of the jount such that it was prevented from being fully inserted. 

Normally it takes a huge amount of force to remove one of these joints.  This particular joint needed only one smart smack with a 5lbs hammer and suitable drift to get it out - proof that it was dangerously close to pulling out during normal driving. 

Once removed, the damage to the joint was clearly visible :



That collar that has been bent downwards is about 5mm thick.  I believe there were two reasons this joint failed in service :

a) the distortion of the housing increased the clearances in the joint inside
b) the compromised dust jacket allowed dirt in.

You will note that the failed joint was manufactured by Meyle.  I think the main ingredient in the failure here was not necessarily a parts quality issue, but rather the failure seems purely due to poor workmanship on the part of the mechanic who installed it. 


[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

When I replace these joints, I like to start by having the parts media blasted clean :

These next photos show a W126 unit, which is the same, except that it has an additional bore for the ABS sensor :



Prior to blasting, the stub axle bearing surfaces, bolt threads, and the joint bore must be protected by suitable blanks etc.



Next, the new joint is inserted into a self-made installation jig :



And it is then located into the start of its bore in the steering knuckle :



The whole lot is supported carefully in a hydraulic press such that the pressing forces are correctly located on the flat base of the knuckle immediately around the bore, and the installation tool presses only on the inner circumference of the joint's collar. 

It is important that the stub axle is not subjected to any forces in this operation.

The difficulty here is that the upper portion of the steering knuckle curves such that it obscures the vertical axis of the joint, prohibiting conventional pressing arrangements.  The self-made tool in these photos has an aperture on its rear side to fit around the upper part of the steering knuckle so that a proper coaxial pressing action is facilitated without contacting or putting force on the upper part of the steering knuckle. 

It takes 8 to 10 tons of force to press the joint into its bore in the steering knuckle.  It is crucial to do this slowly and continually inspect the work to ensure that no skewing happens. 


[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

The joint is fully installed when it protrudes from the underside of the knuckle by a consistent amount all around its circumference :





The horizontal link can then be reattached to the steering knuckle, and I then usually mask up and paint the assmembly in Standox etch primer and matted down 2K black.

The result of this is a reconditioned unit with a perfectly installed joint free of damage to the dust jacket. 



Note that in this photo, the paint must still be cleaned off the brake caliper mounting face. 





The unit can then be reinstalled in the car.  I usually then also clean out and repack the wheel bearing, and set it up for the proper end play using a dial gauge. 


[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

The complete job including - disassembly, cleaning, joint replacement, painting, reassembly, wheel bearing repacking takes about 6 hours per side. 


[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

WGB

Great stuff Sclass.

When I did my 6.9 front end I had the joints replaced by The Star Shop.

I also think the original boots are made of a much more durable flexible plastic material than the rubber boot fitted to the replacements and thought should be given to changing them over and re-using the old ones.

I would like to see more pictures of your special tool. (Maybe I should re-word that  ;D)

Bill

WGB


Big_Richard

Quote from: WGB on 09 September 2011, 06:44 PM
I assume this is the commercial version of your fabricated jig.



Wow, I wish i knew that thing existed when i did mine - i wouldnt of ended up paying a fortune for someone else to do it.

I think that tool fits into the "must have" category for serious w116 enthusiasts.

TJ 450

Congratulations for another excellent post! It couldn't be a clearer guide. 8)

Tim
1976 450SEL 6.9 1432
1969 300SEL 6.3 1394
2003 ML500

KenM

Excellent post S Class, valuable info, this sort of info should be in the wiki.

Which I still haven't learned to drive properly, getting there I hope.

WGB

#11
Here is a renewed 6.9 "Guide Joint" as was fitted on my car.

The 6.9 spindle is heavier and has an extra "titty" which makes a visual change from the standard one.



The extra titty is visible in this photo on the arm above the guide joint housing and is described in the workshop manual  in job 33-400 "Removal an replacement of steering knuckle".

The position of one of the brake backing plate bolt positioins in the knuckle was also moved after May 1979 and later models have brake backing plates with multiple bolt holes to allow for different positions.

Bill 

koan

Nice job s class, especially the fabricated tool, I'm a big fan of home fabrication to get the job done.

Next investment of mine will be a press, looked at a few cheap ones but they seem a bit flimsy.

koan
Boogity, Boogity, Boogity, Amen!

s class

Thanks guys - I must give credit to "69ltr" who posted up pics of a similar home-made insertion tool about 2 years back.  I made up mine following that inspiration, and it has held up well, I think I've done 8 steering knuckles now with it. 

koan, my press is a chinese type unit, but rated at 20 tons and it works well.  I paid around US$550 for it new, but you may get something similar for less, as we get hammered here on shipping costs. 


[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