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1991 S Class (W126) 300 SEL - 15W-40 Valvoline Max Life Diesel Oil, Mann Filt. Zerex G-05 Coolant,
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Discussion Starter #1
All,

I recently had a new brake job (pads, rotors, brake bleed) on the 1991 300SEL. Is there any reason as part of that procedure the vacuum system in the car could go wonky. The tranny isn't working properly now.

Huge thanks,

Robert
 

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1985 300SD 1988 560SEC 822 1976 450SEL 1981 300SD
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1,075 Posts
There's a vac line to the modulator, at the rear of the motor - that could have been dislodged while the brakes were worked on. If you are having harsh part-throttle shifts, but smooth full-throttle shifts, then that's a good indicator of the above problem and solution.

Hope that helps, Chris.
 

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1991 S Class (W126) 300 SEL - 15W-40 Valvoline Max Life Diesel Oil, Mann Filt. Zerex G-05 Coolant,
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Discussion Starter #3
Chris,

Many thanks. yes there is some partial throttle issues, but most noticeable one is when I slow down and having it upshift from say 3rd to 2nd- CLUNK!

Any help with the exact location of that vac line. Accessable from the top or do I need to get it on a lift?

Huge thanks,

Robert
 

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1985 300SD 1988 560SEC 822 1976 450SEL 1981 300SD
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Easy to see in daylight or a flashlight from the top of the motor, no lift necessary.
Best seen from the drivers' side - you might have to feel for it at first.

And yes, that clunk as it upshifts pretty much decides you have a vac issue as described.

I went through both my 126s and did all the vac socks ( the rubber pieces that locate the hard lines). Cost, about 20.00 for each car. Solved a few vac related issues I can tell you....
 

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1991 S Class (W126) 300 SEL - 15W-40 Valvoline Max Life Diesel Oil, Mann Filt. Zerex G-05 Coolant,
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Discussion Starter #5
Chris - great info! I'll double check that hose. Regarding the socks - would you happen to have a parts #'s and a procurement source - web or otherwise.

Thanks again

Robert
 

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1985 300SD 1988 560SEC 822 1976 450SEL 1981 300SD
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I'll see if I can dig out the pn's - my friendly local dealer (shameless plug for 3-Point) had them in stock.

LMK how it goes, good to have a contact across the pond.

Care to take a look at a Euro SEC for me?

R, Chris.
 

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1991 S Class (W126) 300 SEL - 15W-40 Valvoline Max Life Diesel Oil, Mann Filt. Zerex G-05 Coolant,
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94 Posts
Discussion Starter #7
Thanks for the pn's. Sure I'll check out an SEC. Is it the one being discussed here in Van. in the thread just below. The white one?
 

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1990 300SE
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I have this problem with clunky partial throttle shifts and smooth as silk full throttle shifts. So the problem/solution is the vacuum line to a modulator? I'll have to keep an eye on this thread. :)
 

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1985 300SD 1988 560SEC 822 1976 450SEL 1981 300SD
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Vac line etc...

I have this problem with clunky partial throttle shifts and smooth as silk full throttle shifts. So the problem/solution is the vacuum line to a modulator? I'll have to keep an eye on this thread. :)
From my experience, it can be. Costs nothing to check on vac lines and connectors; if that isn't doing it, you will need to check that the modulator itself isn't crapping out. And you'll want a vac gauge to do that, procedure is here on the forum...hope it works for you.
 
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