Transmission Won't Shift to 4th Until Warmed - PeachParts Mercedes-Benz Forum

dataiv · #1 11-04-2005, 05:47 PM

Hey folks,

I've been searching to no avail. I am looking for reasons that my transmission on my 91 300D won't shift into 4th gear when it's cold.

The only time this happens is on a cold morning (like 5 degrees C), for the first 5-10 minutes or so of driving.

I can make it go into 4th if I pop it into Neutral and back into D at speed. Then it goes into 4th right away.

Could this be caused by having slightly too much transmission fluid, and once it warms up, it's fine? I have Mobil 1 Synthetic ATF in it. It is due for a change shortly.

Or, what else can this be caused by? All summer it was fine, but as the nights have gotten colder it has started doing this. Apart from this quirk everything else is fine.

Ideas on what causes this to happen only when it's cold and what it could be?

Thanks

mbonly · #2 11-04-2005, 11:36 PM

I would try TRANS-X on it first. It sounds like a fluid flow problem. If there's any gunk restricting the flow in the million and one places the fluid has to flow through then Trans-x will disolve it and allow fluid to flow even when cold.

compress ignite · #3 11-04-2005, 11:52 PM

Dativ,

In answer to your question... these trannys are VERY,VERY sensitive to fluid levels.
'Must be measured EXACTLY per factory instructions.
(I've used a hand pump to remove 6 Oz. of fluid on a '84 300SD to make the level correct.)
[only after checking the ambient air temperature and pressure]

If problem still rears it's ugly head

(LAST RESORT!!!)Do a search on "Trans-X". Your 722.41 may be sensitive to the AMOUNT of
Trans-X added ! (This is a POWERFUL solvent)

If you're already using Mobil 1 ATF (at least 10,000 miles) the chance of
any sludge in the system is slight...unless the P.O. did'nt change the atf
regularly and the M1 has broken loose some GOO.

mbonly · #4 11-04-2005, 11:59 PM

It did wonders on my tranny and POs regularly don't change the trans fluid anyway

dataiv · #5 11-05-2005, 09:31 AM

I was wondering about Trans-X.. but did want to leave that until I am positive that it's not something else.

The M1 ATF is due for a change.. before I put M1 ATF in last December I doubt the fluid had been changed in a while.

It never did this weird not shifting into 4th thing until 3 months or so after I put M1 ATF in. The first time was in April, then it never did it again until now that summer is over. For some reason it never did it during the cold months of Jan, Feb and March, but the car was always inside overnight. Right now I have the garage full of other stuff, so the car is outside.

I guess it's possible the M1 has dislodged some goo - but the real problem I had when changing the fluid last time was measuring the level. No matter what I did I was getting different readings on the dip-stick every time I pulled it out.

Do you think it's possible that slightly too much fluid could result in not shifting to 4th gear when cold?

So I'm wondering if next time I should just drain it and then put in the amount that is specified?

Should I still just try changing the fluid and see if that makes a difference? And then if not, maybe try Trans-X?

Thanks for the help.

Ken300D · #6 11-05-2005, 11:29 AM

If the Mobile Syn ATF in there now was your first change of the ATF, then there is some possibility it has dislodged a lot of gunk, varnish and the like - and clogged up the ATF filter. When this happens it can reduce your operating pump pressure inside the transmission and reduce the pressure that moves the valves around in the valve body within the case.

So, at a minimum, you should start with the cheap solutions first. Change the fluid AND filter again - continue to use Mobile Syn ATF.

Transmissions are an expensive thing not to follow the fluid/filter maintenance cycle, and I'll bet most people don't have it done often enough. Not to mention the MB maintenance cycle is a bit shorter than other cars.

Good luck - let us know how this works for you.

Ken300D

dataiv · #7 11-26-2005, 10:51 PM

Changed the fluid and filter and installed the K1 Spring Kit today. The transmissions shifts much more nicely now and there doesn't seem to be any 2-3 flare any more when cold. I made sure the level of the fluid is exactly right now and I also don't seem to have the 'hesitating to shift into 4th' problem any more. I think the fluid might have been slightly low.

There was no gunk at all in the filter.. I even took the filter apart to check for sure. So hopefully all is well now and it will stay this way.

Thanks for the help.

dataiv · #8 11-29-2005, 04:02 PM

Well... the first cold day since was a couple days ago, and it did the same thing again. For the first 5 minutes or so it doesn't go in to 4th gear.

I still have no idea why... any other ideas, other than trying something like Trans-X?

Could it be some cable that is sticking when cold, and if so what should I check?

Pete Burton · #9 11-29-2005, 04:06 PM

Try bringing your modulator pressure up just a little bit.

dataiv · #10 11-29-2005, 04:12 PM

Where on the transmission is the modulator adjustment? I found a how-to on how to adjust it, but it doesn't say where it is.

http://www.mercedesdismantlers.com/722.3and722.416_transmission_adjustments#722.3%20Series%20and%20722.416%20Transmission%20Adjustments

The how-to also says that adjusting the modulator adjusts shift quality, not when, so is there any reason why this would change the shift into 4th when the transmission is ice cold? It's just not shifting into 4th when cold, and afterwards, it works fine. The other shifts are always fine.

Pete Burton · #11 11-29-2005, 04:37 PM

Quote:

Originally Posted by dataiv

Where on the transmission is the modulator adjustment? I found a how-to on how to adjust it, but it doesn't say where it is.

http://www.mercedesdismantlers.com/722.3and722.416_transmission_adjustments#722.3%20Series%20and%20722.416%20Transmission%20Adjustments

The how-to also says that adjusting the modulator adjusts shift quality, not when, so is there any reason why this would change the shift into 4th when the transmission is ice cold? It's just not shifting into 4th when cold, and afterwards, it works fine. The other shifts are always fine.

As shown in the picture, the modulator is on the left side and has a vacuum line attached. I suspect the fluid is having trouble moving the spool valve in the valve body, and a little more modulating pressure may help.

dataiv · #12 12-06-2005, 11:10 AM

UPDATE: Adjusted the modulator slightly and it was a bit better as far as shifting into 4th while cold. It didn't take quite as long before it actually did shift. Then, checked the fluid level again, and drained about 200 cc's, now it appears to be just fine. If it doesn't stay this way then I will try adjusting the modulator slightly again.

dataiv · #13 12-11-2005, 10:44 AM

UPDATE: So far, so good. It's been about a week now since I drained the 200 cc's of fluid and adjusted the modulator. It goes in to fourth without any problems now. Also the K1 spring kit seems to be doing its job and there is no more 2-3 flare at all