W126 Strange trans behavior when cold! - PeachParts Mercedes-Benz Forum

LandYaghtLover · #1 01-24-2011, 07:59 PM

This is a weird one. So for the past few cold (very cold) starts the trans does not shift well at all. I get in and fire her up. Sometimes even let it warm up a while. No matter. When I take off the trans holds gears for dear life. Also the economy gauge stays further than normal to the right. Often there will be surging and overall the car feels sluggish.

However. If I pull over, kill the engine and immediately fire it up. All is normal. Car is more responsive and shifting is where it usually is.

The car will behave oddly well past warm up. Does not appear to be heat related since even when pretty cold yet a restart will "fix" things.

Any ideas?

Hit Man X · #2 01-26-2011, 04:26 PM

Does not sound trans related as the trans is all mechanical for shifting, maybe the car is not charging properly? CIS computer loose? Grounds?

LandYaghtLover · #3 01-26-2011, 08:16 PM

Well my alt squeaks badly. Figured just the bearing. But if I turn on one heated seat the headlight dim noticeably. So the alt is on my light of projects. Probably rebuilt it. The brushes on it are fine. I had removed them and cleaned all the contacts as well as cable ends. In fact I did any and every cable end in the engine bay I could find.

But if electrical, why would a "reboot" of the car fix it? And it certainly fires up nicely.

Hit Man X · #4 01-26-2011, 10:29 PM

Quote:

Originally Posted by LandYaghtLover

Well my alt squeaks badly. Figured just the bearing. But if I turn on one heated seat the headlight dim noticeably. So the alt is on my light of projects. Probably rebuilt it. The brushes on it are fine. I had removed them and cleaned all the contacts as well as cable ends. In fact I did any and every cable end in the engine bay I could find.

But if electrical, why would a "reboot" of the car fix it? And it certainly fires up nicely.

I have had vehicles restart and run better with issues. :shrug: Maybe lazy solder within the CIS computer?

Reboots seem to work on PC's running Windows.

Stock alt is, what, 80A? Last time I used my heated seats it could only keep two on low temp setting from memory.

LandYaghtLover · #5 01-27-2011, 12:26 AM

80 amp is what I have read also. I would like to go 120 if even possible. I can keep all four seats on high heat unless I have rear defrost and headlights on, then one or two will start blinking indicating there is low voltage. Or the defrost may blink also.

I will have to dig into it further. The odd thing is that its VERY consistent. It will always happen. So the past two cold starts I fired it up for only about 15 seconds. Then shut her down and started up again. No issue.

Whatever it is, its confusing. Wonder if its vacuum related instead.

Hirnbeiss · #6 01-27-2011, 07:18 AM

the tranny is vacuum controlled, and the economy gage is driven by vacuum, so there may be a connection. check the vacuum hose to the tranny, then check the vacuum modulator on the trans.

LandYaghtLover · #7 01-27-2011, 10:51 AM

Modulator and vac hose are new to trans. In fact, all the rubber on the engine is new. Either way, its the restart that is odd since it fixes the issue. Trying to think what vacuum part could do that trick and all I think of is the idle valve. But if that was open wide I would think rough/high idle.

London380sl · #8 01-27-2011, 11:03 AM

i've noticed that, with the cold temperatures, my transmission also is a bit sluggish to shift for the first mile or so. Once the oil gets warmed up a bit it shifts normally. This has been my experience with other cars so I'm not too worried about it at the moment.
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I could be wrong but I don't thinking idling the car to allow it to warm up will help warm up the transmission as the car is in park and there would little if any fluid flowing.

LandYaghtLover · #9 01-27-2011, 11:15 AM

Quote:

Originally Posted by London380sl

I could be wrong but I don't thinking idling the car to allow it to warm up will help warm up the transmission as the car is in park and there would little if any fluid flowing.

Unfortunately I wish you were right, but thats not the case here. Originally I may have suspected just that since it makes sense. But the problem I am having remains the same well after warm up as mentioned above. I usually let the car warm up for about 5 minutes every morning anyway. But if I do or not, same issue with the boggy engine and trans holding gear. And it will do it even after a half hour or more of driving. But if I restart the car, even after just starting it up with no warm up, it will shift fine. Its pretty much 100% predictable. And its the weirdest problem I have ever had with a car!

david s poole · #10 01-28-2011, 05:29 PM

the only thing i can think of is the kickdown solenoid that it might be sticking on causing the holding of lower gear.

LandYaghtLover · #11 01-29-2011, 01:51 AM

Good thought. But I already checked that. And I rarely ever press the pedal far enough to ever activate it.

However, your idea is a pretty close description to the issue. Maybe I will disconnect it and see what happens. The switch itself may be bad. Worth a shot.

Hirnbeiss · #12 01-29-2011, 09:21 AM

It's been a while since I had an analog museum piece, and even longer since I drove one in iceball country, but I have to think it is related to the throttle linkage. The control pressure cable, connected to the throttle linkage, is what determines the shift point. On my 201 and 124 I don't recall any cold-start mechanism that affected the linkage, but on yours maybe there is? Is there anything that performs a choke function when cold that pushes on the linkage, and is supposed to release when cold? Having an open throttle plate will lower your vacuum too, giving the poor economy reading.

LandYaghtLover · #13 01-29-2011, 11:42 AM

Beats me. Just odd that the problem remains until a restart, no matter how cold or warm the engine.