Author Topic: Rebuilding 6.9 struts  (Read 331 times)

raueda1

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Rebuilding 6.9 struts
« on: 19 February 2021, 02:49 PM »
Robert (aka rumb) persuaded me to tackle this, and so I am.  The plan is to carefully refurbish a set of spares and swap them with existing struts when spring arrives.  I'm reasonably confident that I'll be able to rebuild the struts themselves.  I've still got a few questions so any direction would be terrific.

1.  Rubber strut mounts:  My impression is that they're NLA.  I'm trying the Classic Center but not confident - but if they're available I'll report back with the happy news.  The parts themselves are as follows, best I can tell:

      Strut mounting ring, rear      116 327 1481
      Strut mount, front      116 327 1881

Can anybody confirm availability and source?  New would be ideal but I'm assuming failure and having to reuse the old ones.  For each corner I'll have 2 to choose from and obviously take the best.  But can anybody comment on the impact of tired mounts or have experience in just reusing the old ones?

2.  Strut ball joints:  I have a front set that I picked up somewhere along the way.  Again, my impression is that rears are NLA.  This might force into the same situation as the mounts, taking the best of what I have.  Assuming no obvious play and good boot is there any major downside to reusing?

3.  Front bumper/stop:  They have all turned into greasy putty.  I can't find them in the parts catalog.  Anybody know if they're available someplace?   

Any help, advice or encouragement would be great.  Thanks in advance and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: Rebuilding 6.9 struts
« Reply #1 on: 19 February 2021, 04:20 PM »
Dave yes to my knowledge the top mounts for both front and rear are NLA.  They pop up very occasionally on ebay but they are usually quite dear.

Rear ball joints are NLA yes.  Front you can get decent aftermarket.

Bump stops are not available separate AFAIK.
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: Rebuilding 6.9 struts
« Reply #2 on: 19 February 2021, 05:04 PM »
Bump stops are not available separate AFAIK.
I was afraid of all that.  So what do you do about decomposed bump-stops?  Just do without?
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

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Re: Rebuilding 6.9 struts
« Reply #3 on: 19 February 2021, 05:26 PM »
I thought tcj has made the bumpers.

'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

raueda1

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Re: Rebuilding 6.9 struts
« Reply #4 on: 21 February 2021, 12:26 PM »
I thought tcj has made the bumpers.
Thanks Robert, that is indeed the case.  We've been in contact.  I didn't realize how the bumper was designed.  The rubber is actually molded onto the strut end cap.  I assumed that it was simply snapped in place or something like that.  Anyway, there are 2 options as I understand it:

1.  A whole new part, which includes a replacement end cap and bumper (6 month backlog on that!)
2.  Send your end cap and they mold a new bumper onto it.

So I'm going with option 2.  Now on to the task of getting everything apart.  Chers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: Rebuilding 6.9 struts
« Reply #5 on: 21 February 2021, 03:48 PM »
How about a pictorial :D?
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: Rebuilding 6.9 struts
« Reply #6 on: 21 February 2021, 05:23 PM »
How about a pictorial :D?
Others have done it: https://forum.w116.org/mechanicals/6-9-strut-overhaul-the-story-so-far/msg96018/#msg96018

Regardless, I'll document carefully and see if there's anything of value to add.  There may be some details or clarifications when I get into it.
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

raueda1

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Re: Rebuilding 6.9 struts
« Reply #7 on: 23 February 2021, 08:17 AM »
Further update: 

As we all know, the upper front strut mounts are NLA through the usual channels.  Anybody thinking about rebuilding the struts will likely discover that the mounts are compressed and deteriorated.  TCJ (on this board) tells me he has, or can produce, these mounts as well as refurbish old ones.  It is not cheap.  But as I always tell my friends, "Your strut is no better than your mount."   ;D

You can PM him through this board.  I'm looking forward to nice, refurbished struts for more summer 6.9 driving adventures.  Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

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Re: Rebuilding 6.9 struts
« Reply #8 on: 23 February 2021, 11:32 AM »

This is one of several parts that annoys the hell out of me that MB doesnt make them anymore.  They sell new struts but not the mounts.  Genius.  :-\
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

Rolo

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Re: Rebuilding 6.9 struts
« Reply #9 on: 25 February 2021, 10:50 AM »
Martin replaces the front bump stops when he rebuilds.

raueda1

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Re: Rebuilding 6.9 struts
« Reply #10 on: 25 February 2021, 05:02 PM »
Today, to my surprise and delight, I got the first strut apart.  It was actually pretty easy thanks to whoever discovered the need for heat.  I used a heat gun.  The caps actually came off quite easily when they hit 110C or so (using IR gun).  Rumb's thin cap wrench made cup removal very easy!  Hardest was getting all the crap off them first. 

Anyway, I could use some advice on the significance of the piston condition.  It was immediately obvious that there was a distinct pattern of linear polishing on the piston (first picture).  Presumably this corresponds to the normal piston travel (??).  Why the polishing would be in lines like this I have no idea.  Second, the polishing shows 2 distinct patterns.  Picture 2 is the opposite side of the piston.  Note that the lines extend higher up on the cylinder, so whatever wears the piston isn't uniform.  The piston was very smooth - couldn't feel anything whatever by the "fingernail smoothness test".  The pix make them look scratched.  They aren't, that's a trace oil coating that the camera somehow picked up.  Additionally, per picture 3 there is some substantial scoring on the top of the piston above the ring.  But the ring isn't scored, just the area above it.

So, I'm not sure what this means, if anything.  The strut was from a relatively low mileage (82,000 miles) donor car.  There didn't seem to be much leakage, if any, and struts did seem too work.  The car seemed to rise fine though ride was rock hard cause of bad accumulators.  The owner dumped it after getting a US$15000 estimate to fix it.  Any comments welcome!  Thanks and cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

daantjie

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Re: Rebuilding 6.9 struts
« Reply #11 on: 25 February 2021, 05:23 PM »
Might not be a bad idea to take these to a specialist hydraulic shop and have them take a gander.  I am thinking shops doing work on earth moving equipment and such like Komatsu and Caterpillar.  I highly doubt these struts are unique in their design and function and thus largely one can assume that the same logic should apply in various applications?
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: Rebuilding 6.9 struts
« Reply #12 on: 25 February 2021, 05:27 PM »
Might not be a bad idea to take these to a specialist hydraulic shop and have them take a gander.  I am thinking shops doing work on earth moving equipment and such like Komatsu and Caterpillar.  I highly doubt these struts are unique in their design and function and thus largely one can assume that the same logic should apply in various applications?
Excellent idea!  And I'm in an area where earth moving is a big deal - huge mining operations, etc.  There are certainly many such businesses here.  I'll report back.......            Thanks! 
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

rumb

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Re: Rebuilding 6.9 struts
« Reply #13 on: 26 February 2021, 06:28 AM »
There was a discussion on m100 about the surface condition of the inside  of the tube (an maybe the shaft).  a lot a back and forth with no real conclusion. Some stated that everything is hardened and the honing would be counter produtive. If you can find a real hydraulic shop to pontificate that would be great.

The lines on the shaft are from the nylon seal ring and would be micro-contaminants in the fluid and the constant rubbing back and forth. The more wear on one side suggests offset pressure perhaps from the front suspension always being pushed towards the back of the car and somehow translating to the wear?

The piston ring is the main seal against all the pressure just like a regular engine piston ring.  The nylon rings are doing cleanup duty as well as controlling alignment. My understanding is that some small amounts of fluid gets past the piston ring and the first nylon ring and then are "pumped" out via the small drain line.  The bottom ring is the last resort seal and when that wears you get leaking fluid out of the bottom of the strut.

I doubt there is significant wear on the piston ring but that would be a good question for the hydraulic specialist.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

raueda1

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Re: Rebuilding 6.9 struts
« Reply #14 on: 26 February 2021, 12:36 PM »
OK, I'm just back from the hydraulic shop.  These guys do every manner of hydraulic work from mining and oil patch equipment to the snow cats at the ski areas.  "We don't work on anything that travels on the road."  The strut created a lot of interest and there were soon 3 guys inspecting and commenting.  After about 5 seconds of explanation from me one guy took over and identified all the strut components and their function.  I was impressed.  Here's the gist of it:
  • The polishing on the cylinder (top picture above) is normal and not of concern IF you can't feel any scratching with your fingernail.  I couldn't and neither could they.  So that's good. A very light polishing with fine emery cloth would OK but optional.
  • They were unconcerned with the scoring above the upper sealing ring.  It doesn't reach the ring and may well be from offset pressure.  They agree with Robert, ring is fine.  However, on no account attempt to remove the ring.  it will almost certainly break.
  • They did note that the cylinder seems to be plain steel.  A VERY LIGHT HONING WAS RECOMMENDED.  A ball hone, or even a brake hone, is fine. 
The bottom line is that the strut is sound and should be good as new after new seals.  I guess if your struts are similar or better, then great.  Something I did notice is that my strut has a different piston ring design from that in WGB's excellent write-up.  https://forum.w116.org/mechanicals/6-9-hydraulic-strut-overhaul-take-2/msg96477/#msg96477
Compare my piston (picture above) with his (below).  It looks like WGB's piston has a giant ring above the smaller one on bottom.  Both part numbers are the same.  This suggests to me that making hybrid mix-and-match struts is probably a bad idea.

A final comment on the strut mounts.  As noted earlier, tcj (Thomas) can rebuild the front strut mounts.  Send him your old one and get it back with new rubber.  He is apparently prepared to run a batch of upper rear mounts but apparently has not done so cause he hasn't seen demand.  Price TBD.  So, anybody needed rear mounts - which is probably all of us! - should let him know your interest.  I hope he won't mind me posting this. 

Per Daniel I probably will doing a write up when this is all done.  It's not like the info isn't out there, it's just all spread around and could use consolidation.  That's it for now, stay tuned..... ;)    Cheers,
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0