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Garage => Mechanicals => Topic started by: raueda1 on 19 February 2021, 05:49 PM

Title: Rebuilding 6.9 struts
Post by: raueda1 on 19 February 2021, 05:49 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,
Title: Re: Rebuilding 6.9 struts
Post by: daantjie on 19 February 2021, 07:20 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.
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 19 February 2021, 08:04 PM
Quote from: daantjie on 19 February 2021, 07:20 PMBump stops are not available separate AFAIK.
I was afraid of all that.  So what do you do about decomposed bump-stops?  Just do without?
Title: Re: Rebuilding 6.9 struts
Post by: rumb on 19 February 2021, 08:26 PM
I thought tcj has made the bumpers.

Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 21 February 2021, 03:26 PM
Quote from: rumb on 19 February 2021, 08:26 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,
Title: Re: Rebuilding 6.9 struts
Post by: daantjie on 21 February 2021, 06:48 PM
How about a pictorial :D?
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 21 February 2021, 08:23 PM
Quote from: daantjie on 21 February 2021, 06:48 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 (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.
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 23 February 2021, 11:17 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,
Title: Re: Rebuilding 6.9 struts
Post by: rumb on 23 February 2021, 02:32 PM

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.  :-\
Title: Re: Rebuilding 6.9 struts
Post by: Rolo on 25 February 2021, 01:50 PM
Martin replaces the front bump stops when he rebuilds.
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 25 February 2021, 08:02 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,
Title: Re: Rebuilding 6.9 struts
Post by: daantjie on 25 February 2021, 08:23 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?
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 25 February 2021, 08:27 PM
Quote from: daantjie on 25 February 2021, 08:23 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?
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! 
Title: Re: Rebuilding 6.9 struts
Post by: rumb on 26 February 2021, 09:28 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.
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 26 February 2021, 03:36 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 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 (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,
Title: Re: Rebuilding 6.9 struts
Post by: daantjie on 26 February 2021, 08:08 PM
Nice work Dave ;)
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 26 February 2021, 08:17 PM
Quote from: daantjie on 26 February 2021, 08:08 PM
Nice work Dave ;)
Thanks, but don't get too carried away quite yet.  Today I went 1 or 2 steps backwards.   >:(  The issues:

1.  Disassembly of first front strut went very smoothly.  I paid for that today.  Today's cup was in much worse shape, clogged with an enormous amount of dirt and very rusted.  Long story short, I had to cut it off, destroying completely.  :o  No loss, as it was terrible anyway.  Still, now I need another cup.  So, if anybody has a front strut cup just laying around I'd be very grateful for it.  I can probably get you a replacement when I get the struts off the car, though that wouldn't be for a couple months.  Anyway, please PM me if you can help.

2.  I just noticed that one of the rear struts has a weird part number.  One is 116 320 3613, as it should be.  The other is 116 320 2813.  They look identical.  Can anybody shed any light?

Thanks greatly for any help anybody can offer.  The adventure continues.......   Cheers,
Title: Re: Rebuilding 6.9 struts
Post by: daantjie on 26 February 2021, 09:35 PM
Dave, Martin/Thomas sell the new cups, I bought a set from them not too long ago,  top notch quality.
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 26 February 2021, 10:16 PM
Quote from: daantjie on 26 February 2021, 09:35 PM
Dave, Martin/Thomas sell the new cups, I bought a set from them not too long ago,  top notch quality.
Sweet!  I reached out to Thomas.  I'm saved!
Title: Re: Rebuilding 6.9 struts
Post by: tcj on 27 February 2021, 02:28 AM
regarding 2813 and 3613: 3613 replaces 2813, some internal changes/improvements. Both match your car.
Title: Re: Rebuilding 6.9 struts
Post by: raueda1 on 27 September 2021, 10:10 AM
Case closed, and with a very happy ending.  I thought it would be illuminating to share it.  I'm recently back from the long road trip that I feared - ~6500 miles from Utah to New England, NY etc and back again, about 5 weeks.  I may report on that elsewhere, this is about the struts.  Conclusion:  the rebuild resulted in a vast improvement!  Here are the details.

To hone or not to hone? As rumb noted, the topic seems to be controversial.  Following the advice of the hydraulic shop I used a small ball hone and managed to get a decent 45 deg crosshatching.  Cleanliness is everything, so after wiping clean I used an ultrasonic cleaner followed by progressive solvent rinses (water --> isopropanol --> carburetor cleaner).  The cylinders were VERY clean). 

Leaking:   I just had car on the lift for oil change and general inspection.  There's not the slightest trace of suspension fluid leaking, dripping or anything else.  That includes the hose fittings (all of which were rebuilt as described elsewhere).

Spheres:  The front and central spheres were replaced last summer with Febi units (if I remember right).  Rear units were replaced with MB units during this job.

Ride and handling:  This is really quite fascinating to me.  Before the rebuild the ride seemed great, though notably soft.  VERY soft in fact, truly the magic carpet ride, maybe too much so.  The car had a lot of body roll when cornering at moderate speed (e.g., highway ramps).  It could be disconcerting because the front had a tendency to dive and oversteer and rear somehow not quite coordinated.  Hard to describe.   But if somebody else was driving the car I'd warn them that hard cornering was a bit weird and not to do it.   The change after the rebuild was profound.  Ride became significantly firmer, still relatively soft but much more like what we'd think of as a "modern" feel.  Yet the isolation and softness over bumps, road expansion joints etc was still superb.  Amazingly cornering was greatly improved - less body roll, and cornering was just far better controlled somehow.  No more weird dive or transitioning to oversteer. 
      Could the spheres be contributing?  Well, the "wallowyness" was present when I got the car.  Changing the front and central spheres last summer didn't change it.  Would new rear spheres do something?  The old ones seemed to work fine, so I don't see how.  I can only conclude, maybe, that wear or maybe an earlier strut replacement on one of the axles caused the front and rear struts to have different properties somehow, and now they're all the same.

The bottom line:  I undertook this job mostly to get rid of the leaks and not worry about the struts again.  I never thought that struts could become tired over time.  I just figured that they'd work the same afterwards.  Well, apparently they DO become tired.  The new ones did NOT work the same, they worked a lot better.  If you have a nagging suspicion that your ride and handling aren't quite what they should be, I'd highy recommend this job, even if your suspension seems to be "working fine." 

Now off to rack up another 1500 miles on yet another road trip - Palm Springs California, Las Vegas (again!) Zion Nat'l Park.   What great cars these are!  Happy motoring and cheers,
Title: Re: Rebuilding 6.9 struts
Post by: Eyeman on 29 September 2021, 11:58 PM
Glad your suspension work as successful.  I finally got my car back from an over year long suspension overhaul.  Seems back to how my car always handled.  The only problem is the car now sits around two inches higher than before.  Is there some way to set our cars to have a certain ride height and my mechanic just set things high?  Or do you think my car will "settle" somewhat in time?
Title: Re: Rebuilding 6.9 struts
Post by: daantjie on 30 September 2021, 12:11 AM
Check if the H setting has not been activated (dash knob all the way out).  With knob fully pushed in this is the N (normal driving) position with selector disk on the height control valve fully against the stop.  Your arms on the leveling valves need to be level in this position, between "L" and "F".
Title: Re: Rebuilding 6.9 struts
Post by: rumb on 30 September 2021, 09:06 AM
There are adjusters on the leveling units.  Somewhere buried in forum is how high a 6.9 is suppose to be.  The official MB method used location points on the chassis and tools that dont exist.  Some ppl have come up with an actual measurement of wheel well heights.  Maybe someone can find this info.

Here is the first I found:
https://forum.w116.org/mechanicals/6-9-ride-height-7295/msg77911/#msg77911
Title: Re: Rebuilding 6.9 struts
Post by: rumb on 30 September 2021, 09:41 AM
Here it is:
https://www.m-100.co/content.aspx?page_id=2155&club_id=406485&item_id=828332&message_id=2113650&fs=1&sp=ride%20height&#req

One measure is from center of roof: Overall vehicle height (constant) is given as 55.5 inches

fender well to ground seems to be:Front 26" and Rear 25"
Title: Re: Rebuilding 6.9 struts
Post by: Eyeman on 30 September 2021, 09:45 AM
Thanks for the info that there are adjusters.  For sure my car is sitting too high.  This mechanic is weird, but it's getting hard to find anyone to even work on this type suspension anymore.