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  #1  
Old 02-08-2017, 09:05 PM
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1986 560sel transmission jerking between gears

The car shifts fine for the most part but if im going like 45mph and accelerate its shifts quite aggressively and jerks the car. Its only between that gear. I changed the filter+fluid and it seems to happen less but still occurs. Im not a professional mechanic but know my way around a little. any advice on a possible fix? Thank you in advance.

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  #2  
Old 02-08-2017, 10:06 PM
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The transmission got a so called modulator, they can be adjusted to make shifts firmer, I guess people have had problems with them, MB have redesigned them servers times, the new one is green and has a thin stick thing inside to make adjustments easier and external.
You can also buy a superior shift kit(some springs for mounting inside the trans) they solve issues with flaring and hard shifts, and can serve as an upgrade too.

Don't know if that helps ya
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  #3  
Old 02-08-2017, 10:25 PM
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Before getting carried away adjusting things, start checking for vacuum leaks. The modulator is vacuum based and vacuum leaks are VERY common! If you have no history of the rubber vacuum line fittings being replaced, now's a good time.
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  #4  
Old 02-08-2017, 10:31 PM
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Yeah, easiest way to check if you have a leak is where to economy meter is at idle. It should be at left all times with no throttle
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  #5  
Old 02-09-2017, 10:04 AM
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It seems all of you have mentioned the vacuum leaks to this modulator. Does this consist of the entire system and just check any and every line i can find or is there a specific set of lines to this modulator i should focus on? This modulator the adjustments are internal of the transmission? Does it have a name so i could try and do research on it or just transmission modulator? I appreciate all the help from you guys.

Edit: I also just went out and let it idle for 5minutes or so and the economy gauge stayed all the way to the left it seemed like it worked it way from the pin on 1 side up like 1/16 of an inch then sat there for the duration without moving again.

Last edited by qweasdzxc; 02-09-2017 at 10:21 AM.
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  #6  
Old 02-09-2017, 10:09 AM
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Steve Brotherton has some of the best write ups on transmission adjustments and diagnosis (with pictures). Google his name + transmission and you should get a PDF. Can't drop the link here at it forboten to BW.
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  #7  
Old 02-09-2017, 10:15 AM
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To test the vac modulator, reach under the hood and disconnect the plastic line going from the VAV to the vac modulator. Plug a Mityvac into that plastic line and pump it up. See if it holds a vac. If not the vac modulator is leaking.
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  #8  
Old 02-09-2017, 10:51 AM
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Quote:
Originally Posted by qweasdzxc View Post
It seems all of you have mentioned the vacuum leaks to this modulator. Does this consist of the entire system and just check any and every line i can find or is there a specific set of lines to this modulator i should focus on? This modulator the adjustments are internal of the transmission? Does it have a name so i could try and do research on it or just transmission modulator? I appreciate all the help from you guys.

Edit: I also just went out and let it idle for 5minutes or so and the economy gauge stayed all the way to the left it seemed like it worked it way from the pin on 1 side up like 1/16 of an inch then sat there for the duration without moving again.
If the economy gauge isn't sitting on the peg at low idle and in gear (600 RPM or so), you have a vacuum leak somewhere. The further off the peg it sits, the bigger the leak.

Look around under the hood for some of the rubber fittings on the vacuum lines where they connect to various things and see if they're spongy and "alligatored" in appearance. They should be fairly hard and smooth. If you have soft or rough vacuum fittings, just start replacing. It isn't worth the time to find WHICH one is leaking, because they likely all are to some extent and those that aren't now will in the very near future.

For what it's worth, I went through a lot of this in my own SL. My economy gauge was about 1/3 of the way across the dial in D and my shifts were pretty harsh. Replacing the vacuum fittings got it down to where the needle is resting on the peg in D or just off it (too small to measure). Still a slight leak somewhere, but it improved things dramatically - especially how the engine runs.
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  #9  
Old 02-09-2017, 01:44 PM
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I went to check the PSI on my modulator and was moving the incoming vacuum line to it around and it came lose the coupling on the end is all torn apart. My problem now is i cant find exactly where it went into. The only place i can see without having to take the carb+manifold off would be to a curved metal pipe(maybe 5 inches long) that leads into another plastic line that goes to some sort of sensor by the ABS system in the front? Would i be right in thinking the coupling went into the pipe?

Edit: Not sure how i didnt find it before but there is a banjo bolt off the back on the passenger side of the manifold with a peg for a vacuum line so that seems like the most logical place it could of gone. Also with how easy it came off and how bad the coupling was i think that may be my problem. Im going to fix that and check if not ill replace the modulator and also maybe a "k1 spring kit" i found is a problem for some going from gear 2 to 3. Thanks again to everyone who helped me and hopefully you wont hear anymore from me about this problem .

Last edited by qweasdzxc; 02-09-2017 at 03:42 PM.
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  #10  
Old 02-09-2017, 06:53 PM
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Vacuum issues are very common sources of transmission troubles in the older Mercedes. If the rubber connector was rotten, start looking, you'll find LOTS more! Other very common places to find vacuum leaks are in the HVAC actuators behind the dash and on the thermo-time "switches" under the air cleaner. On my SL there's 2 little red plastic looking things threaded into the left head up under the air cleaner. Both of the little plastic pegs had broken off, causing a big vacuum leak. Since one of them is also common with the vacuum feed to the WUR, it was throwing off the fuel mixture badly as well. Replacing them both and putting new vacuum fittings on made a tremendous difference in how the car ran.

The K1 accumulator spring is supposed to help with the lousy 2-3 shifting. My SDL has this issue and I'm planning on changing the spring this spring. Fingers crossed it solves that irritating issue!
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  #11  
Old 02-09-2017, 08:36 PM
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2-3 cold shifting issue

Quote:
Originally Posted by Diseasel300 View Post
The K1 accumulator spring is supposed to help with the lousy 2-3 shifting. My SDL has this issue and I'm planning on changing the spring this spring. Fingers crossed it solves that irritating issue!
The lousy 2-3 shift happens with my 91 560SEC only with cold engine and trans. I have to let up on the accelerator to cheat it to shift up to 3rd or it will shift a bit late. After warming only slightly 1 to 2 mins. max it's fine thereafter.
Do you have the same problem if so is that k1 piston and spring the one that's replaceable without removing the transmission, externally ?
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  #12  
Old 02-09-2017, 08:39 PM
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If it happens only when cold, it's probably just due to the fluid being slightly more viscous from the car being cold.

If you have issues with the K1 accumulator spring, you will have constant problems with 2-3 regardless of temperature. Usually flaring when changing gears or really sloppy engagement. The spring is replaced with the trans in the car and the oil pan removed, assuming the gas transmissions are the same as the diesel ones.
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  #13  
Old 02-09-2017, 09:55 PM
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That's a relief. Thanks for the quick response.

Gogs.
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  #14  
Old 02-09-2017, 10:52 PM
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Quote:
Originally Posted by Gogi View Post
The lousy 2-3 shift happens with my 91 560SEC only with cold engine and trans. I have to let up on the accelerator to cheat it to shift up to 3rd or it will shift a bit late. After warming only slightly 1 to 2 mins. max it's fine thereafter.
Do you have the same problem if so is that k1 piston and spring the one that's replaceable without removing the transmission, externally ?
G:
The delayed shifting when cold is deliberate; it is programmed into the controls to enhance the rate of catalytic converter heating.
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  #15  
Old 02-09-2017, 11:09 PM
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Ok, that makes perfect sense. Better cleaner exhaust emissions. Glad to know its normal. My wife's toyota had that back in the mid 90's. They probably stole the idea from MB.

Gogs.

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