Author Topic: 6.9 Strut Leakage Line Replacement  (Read 333 times)

PosedgeClk

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6.9 Strut Leakage Line Replacement
« on: 05 July 2019, 09:25 PM »
I have a newly acquired '79 450SEL 6.9 with a few chaffed hoses. At some point, someone did service to the front left ram and might have installed it with the connector angled a few degrees too outward. I can tell where a hose had been routed before.



I am not sure what is going on here, but my big concern now is replacing the leakage line. I disconnected it and looked carefully and saw black crud in the center of an otherwise clean fitting, an obvious indicator that the tubing is compromised. How well is the tubing known? Tygon is used a lot in aviation for similar fluids, but it is generally softer. The leakage line is forty years old at this point, so perhaps it was softer when it was new. The tubing is connected with a barbed fitting, so the pressure cannot be all that great.
1979 450SEL 6.9

TJ 450

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Re: 6.9 Strut Leakage Line Replacement
« Reply #1 on: 05 July 2019, 11:01 PM »
That is a bit odd. The tubing from new is hard, although it may get brittle with age. The material is Tecalan. As all it does is allow excess fluid to bleed off, it’s not under pressure. These were available new from the Classic Center a few years back, although if you could source a used one, that wouldn’t be an issue.

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

daantjie

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Re: 6.9 Strut Leakage Line Replacement
« Reply #2 on: 06 July 2019, 01:14 AM »
Yes these were still available a while ago from the Classic Centre and from memory they were quite reasonably priced.
Daniel
1977 450 SEL 6.9 - Astralsilber

PosedgeClk

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Re: 6.9 Strut Leakage Line Replacement
« Reply #3 on: 06 July 2019, 09:46 AM »
Thank you for the replies. I also noticed that the top of the fender well has some abrasion, so there might have been an incident before where the left front suspension dropped severely and rubbed. If this is the case, it looks as though the car did not move far.

I looked on Classic Center and did not see this tubing assembly, but I may just not be apt at finding items on there. My go-to industrial supplier in the USA McMaster-Carr sells several lines of PTFE/PFA tubing for hydraulic fluid. They are rated around 55D or 60D. I have not measured the ID or OD yet, but 3mm ID line is about $3 or $4 per foot.

What I would be more interested in is finding a spare hard line and a photo of how the line is supposed to be routed. I looked under the fender on the other side of the car, and there is not symmetry in the routing. The hard line looks as though it may have been bent in the past. It almost looks as though the bracket should be around the fittings, but I do not know without seeing a photo or reading a thorough description. I am going to rebuild the hydraulic hoses and replace the accumulators, so now might be a good time to try to source that line.
1979 450SEL 6.9

rumb

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Re: 6.9 Strut Leakage Line Replacement
« Reply #4 on: 06 July 2019, 05:28 PM »
I dont even see the small hose in EPC. Would be interesting finding out what bulk hose can be used.
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

daantjie

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Re: 6.9 Strut Leakage Line Replacement
« Reply #5 on: 07 July 2019, 01:08 AM »
Front is 116 320 16 72
Rear is 116 320 88 72
Daniel
1977 450 SEL 6.9 - Astralsilber

tcj

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Re: 6.9 Strut Leakage Line Replacement
« Reply #6 on: 07 July 2019, 03:02 AM »
Hi,

we are selling refurbished leakage hoses on an exchange basis.
And check your high pressure hose. The one on the picture seems to be damaged. This hose
gehts 100bar++.

regards,
Thomas
« Last Edit: 07 July 2019, 07:14 AM by tcj »
112.021
116.028
116.036

rumb

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Re: 6.9 Strut Leakage Line Replacement
« Reply #7 on: 07 July 2019, 06:51 AM »
Front is 116 320 16 72
Rear is 116 320 88 72

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

raueda1

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Re: 6.9 Strut Leakage Line Replacement
« Reply #8 on: 07 July 2019, 08:40 AM »
I recently replaced my power steering high pressure hose with this in 3/8" (9.5mm):
https://www.gates.com/us/en/search?text=6m2t

It seems to be perfectly suited to the strut hoses and fits perfectly in the hose fittings.   It's overkill, in fact - 2 steel braids and rated to 5000psi/344bar.   I'd use it for struts without hesitation.  Unless damaged somehow, the fittings are very easy to reuse.  This is a case where paying somebody for "refurbishment" doesn't make sense IMO.  I suggest cutting the hose using an angle grinder with a thin cut-off disk.  A hacksaw will mangle it. 

As for the return hose, Tecalan is a company, not a material per se.  I'm 99.99% sure that these tubes are nylon 12.  Given stiffness, temperature range, fluid resistance, etc etc nylon is really the only material that fits the application profile, especially back in the mid 70's.  And we all know how much MB loves nylon tubing.  Any nylon tubing of the right size and rated for low pressure hydraulic applications should be fine. ::)

I've gotten stuff like this at a local industrial hose distributor fabricator focused on construction and agricultural applications.  Any decent size city should have such a place.  Good Luck.

-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

PosedgeClk

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Re: 6.9 Strut Leakage Line Replacement
« Reply #9 on: 07 July 2019, 10:04 AM »
It seems to be perfectly suited to the strut hoses and fits perfectly in the hose fittings.   It's overkill, in fact - 2 steel braids and rated to 5000psi/344bar.   I'd use it for struts without hesitation.  Unless damaged somehow, the fittings are very easy to reuse.  This is a case where paying somebody for "refurbishment" doesn't make sense IMO.  I suggest cutting the hose using an angle grinder with a thin cut-off disk.  A hacksaw will mangle it. 

As for the return hose, Tecalan is a company, not a material per se.  I'm 99.99% sure that these tubes are nylon 12.  Given stiffness, temperature range, fluid resistance, etc etc nylon is really the only material that fits the application profile, especially back in the mid 70's.  And we all know how much MB loves nylon tubing.  Any nylon tubing of the right size and rated for low pressure hydraulic applications should be fine. ::)

My initial plan was to rebuild the hydraulic hoses, but I am short on time for this project and went ahead and ordered new ones. I need to have a 6.9 ready to drive non-stop from New York to Los Angeles by the end of this month or so. The leakage line tubing indeed looks and feels like Nylon, and that would be period for the car. I was surprised to see clean, white PTFE in the rebuild photos of the hydraulic rams. I have a little Teflon tubing floating around and may pick up some more of each to see which works better.
1979 450SEL 6.9

PosedgeClk

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Re: 6.9 Strut Leakage Line Replacement
« Reply #10 on: 12 July 2019, 09:20 PM »
I ordered several sizes of FEP tubing from McMaster-Carr, and the best one seems to be the 4mm x 6mm OD FEP by Altaflo, LLC. This is McMaster-Carr part no. 2129T25. At $18.30 for 10 feet, it is hard to go wrong. I am presuming that FEP has similar chemical resistance as PTFE and PFA (plastics with which I have been utterly amazed). The temperature range far exceeds that of Nylon. The bend radius looks good, and the plastic is quite clearer than Nylon or PTFE. The next step up, 3/16" ID tubing by the same company, and also sold by McMaster with part no. 2129T13, was far too loose. I had taken measurements with some good Mitutoyo calipers before ordering and thought that the 4mm x 6mm tubing was the best bet; the calipers did not fail me.

After soaking the old "probably Nylon 12" tubing, I declared the non-strut end to be melted and burned. The kerosene took the mm or so of grime off the plastic, and there is quite a nice black mark that did not come off. Whatever happened to the high pressure hose with what I suspect to be a tire incident likely affected the leakage line.

I removed the Nylon tubing with a pocket knife but should have probably used a heat gun to soften the plastic until it was easier to work. I scratched the brass with the knife. Not that it really matters, but it goes against good engineering practice, and I am in a hurry to have the car in good working order. On the larger non-strut end, I had difficulty pushing the tubing all the way to the end, and there is probably a trick to this. (Does anyone know the trick?) The barbs look identical on the smaller fitting, and I was able to push the tubing to the end with several minutes of effort. I might have to redo this line as I kinked it by putting much hand pressure on the larger fitting.

These are just a few hints in case the supply of these parts completely dries up and someone stumbles across this post in 2037 or so.

By the way, I contacted McMaster-Carr, and all of the similar tubing that they sell is Nylon 6. 6 vs. 12 is a debate going back many decades, but I got an ear full from an eighty-year-old several years ago about how they prefer Nylon 12 in the carpet industry as a far superior material. So I decided to go with PFA. ;)
« Last Edit: 12 July 2019, 09:38 PM by PosedgeClk »
1979 450SEL 6.9

PosedgeClk

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Re: 6.9 Strut Leakage Line Replacement
« Reply #11 on: 12 July 2019, 09:29 PM »
FEP tubing on the smaller fitting
1979 450SEL 6.9