Author Topic: More 6.9 throttle linkage shenanigans  (Read 1143 times)

daantjie

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More 6.9 throttle linkage shenanigans
« on: 04 December 2019, 08:20 AM »
Hi guys

Rather than tack onto old threads, I thought to start a new one here, mostly as a "PSA" of sorts.  Dave and I have compared some notes as he had recently taken a hard look at his throttle linkage setup as well, and we both think that this is an area that many owners probably neglect.  I myself am embarrassed to not have checked this sooner, not only was it filthy, but look what I found on the "bell crank" linkage at the fire wall:

Surely this is not right, and the rod needs to be parallel to the rest of the unit ???

Any other folks care to chime in?  If this is indeed not correct, then my throttle movement has been sub - optimal all along, bugger :o
« Last Edit: 04 December 2019, 08:32 AM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

rumb

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Re: More 6.9 throttle linkage shenanigans
« Reply #1 on: 04 December 2019, 08:34 AM »
yes, that is suppose to be straight.  :o
'68 250S, '77 6.9 euro, '91 300SE, '98 SL500 '14 CLS550

daantjie

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Re: More 6.9 throttle linkage shenanigans
« Reply #2 on: 04 December 2019, 09:00 AM »
Thanks Robert, yup it was a real WTF moment for me ;D  I guess if you really mash the pedal repeatedly this could happen, but still I am guessing due to other wrongness in the linkage setup this was the weakest spot and gave up?
Daniel
1977 450 SEL 6.9 - Astralsilber

raueda1

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Re: More 6.9 throttle linkage shenanigans
« Reply #3 on: 04 December 2019, 09:05 AM »
To add to the above, note the bent arm on the this shaft.  The small shaft on top should be parallel to the long shaft.  The ball on the firewall was missing too, just like Daniel. 

I wonder how common these issues are?  They aren't easy to spot unless you look hard or take it all apart.  I'm guessing the answer is "very."  The car will still seem to run fine and all you might feel is play in the gas pedal,  but shifting will be wrong and WOT may not actually be WOT at all.  Last but not least, is the bushing on the tranny end of the shift rod still intact?  It's hard to see unless you really look.  If not then the throttle movement wont be correctly transferred to the transmission.  This all falls into the "something isn't quite right but I can't figure out what" category.  Everybody should run out to their cars right now to checK!  ;D
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

UTn_boy

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Re: More 6.9 throttle linkage shenanigans
« Reply #4 on: 04 December 2019, 09:42 AM »
I think maybe all of these bent issues could happen if the engine/transmission mounts completely collapse.  Collapsed mounts will definitely affect the geometry of the linkages, but I'm not sure to what extent.  I've gotten to where if I have to raise or lower the engine/transmission I always disconnect linkages and remove or loosen the fan shroud on the radiator to prevent damage to anything.  (Years ago I broke a fan shroud on a W108 trying to raise the engine because the shroud was still connected to the radiator.....I learned the hard way).  I can only speculate as to why these pieces of linkage are bent.  I'll have to admit I've never seen this problem, but here it is in the flesh!  I've seen a lot of bent linkages on mechanically fuel injected W108/W109 and W113 cars, but that's usually due to inexperienced shops trying to correct another underlying issue.  The issues here are a mystery! 
1966 250se coupe`, black/dark green leather
1970 600 midnight blue/parchment leather
1971 300sel 6.3, papyrus white/dark red leather
1973 300sel 4.5, silver blue metallic/blue leather
1976 280s astral silver/blue MB Tex
1978 450sel 6.9 Euro, Anthr/velour

raueda1

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Re: More 6.9 throttle linkage shenanigans
« Reply #5 on: 04 December 2019, 11:57 AM »
I think maybe all of these bent issues could happen if the engine/transmission mounts completely collapse.  Collapsed mounts will definitely affect the geometry of the linkages, but I'm not sure to what extent.  I've gotten to where if I have to raise or lower the engine/transmission I always disconnect linkages and remove or loosen the fan shroud on the radiator to prevent damage to anything.  (Years ago I broke a fan shroud on a W108 trying to raise the engine because the shroud was still connected to the radiator.....I learned the hard way).  I can only speculate as to why these pieces of linkage are bent.  I'll have to admit I've never seen this problem, but here it is in the flesh!  I've seen a lot of bent linkages on mechanically fuel injected W108/W109 and W113 cars, but that's usually due to inexperienced shops trying to correct another underlying issue.  The issues here are a mystery!
yeah, mysterious indeed.  I like the engine mount theory but in my case I'm quite sure that wasn't the problem.  My mounts were fine when I pulled the engine.

Another possibility:  tilting the engine to pull the transmission.  That might also destroy that ball.  I doubt it's coincidence that Daniel and I both had broken balls. ::)
-Dave
Now:  '76 6.9 Euro
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

TJ 450

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Re: More 6.9 throttle linkage shenanigans
« Reply #6 on: 04 December 2019, 09:57 PM »
I'd say that's from previous engine removal or lowering the trans as you say. It's not likely to happen by itself.

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

oversize

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Re: More 6.9 throttle linkage shenanigans
« Reply #7 on: 05 December 2019, 12:28 AM »
Definitely bent!  The linkages are often overlooked and are the cause of stiff-throttle-frustration that many people experience when driving an old Benz.  Make sure every joint & pivot is well lubricated with engine oil.  I even like to use a smear of moly grease in the sockets for added insurance.  Throttle balls are a serious danger to safety and can cause the throttle to jam.  Make sure yours has the late design that is made from black nylon (not the old clear/yellow) and incorporates the metal insert for added protection.  Ensure the whole linkage isn't binding on anything and check that full throttle can be achieved with the help of a friend and the engine (obviously) switched off.

Personally I still find the mechanical throttle way to stiff and it may benefit from a weaker return spring for added enjoyment and spirited driving...
1979 6.9 #5541 (Red Bull)
1978 6.9 #4248 (Skye)
1979 6.9 #3686 (Moby Dick)
1978 6.9 #1776 (Dora)
1977 450SEL #7010 white -P
1975 450SEL #8414 gold -P

daantjie

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Re: More 6.9 throttle linkage shenanigans
« Reply #8 on: 05 December 2019, 05:20 AM »
Thanks all yup I am attempting to straighten it out on the bench.  Of course most parts are NLA, especially the small white shaft bushings which is quite disappointing :'(
« Last Edit: 07 December 2019, 09:51 PM by daantjie »
Daniel
1977 450 SEL 6.9 - Astralsilber

Randys01

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Re: More 6.9 throttle linkage shenanigans
« Reply #9 on: 07 December 2019, 06:39 PM »

try the rh drive variant. another 3 foot of linkage entrails!