65' 230 SL Automatic Transmission Question

[jfkb2]

Good afternoon,

As I was taking my Pagoda out for a drive this past weekend the automatic transmission started to downshift hard when stopping. I believe it would be going from 3rd to 2nd and at the same time the engine would rev up, the car would lurch forward and it would be difficult for the brakes to keep the car stopped. If I let go the brakes the car would just continue to accelerate.

Any suggestions/help would be greatly appreciated.

jfkb2
 

[teahead]

https://www.sl113.org/wiki/Automatic/Start

[DaveinOC]

Lots of good information in that link to the transmission and adjustments. As Joe Alexander noted the throttle venturi switch can get out of adjustment and cause harsh downshifting while coasting to a stop. I had that problem a few years ago.

Another related item to check is the throttle position solenoid. It's the round item that holds the throttle linkage open slightly when the transmission is in a forward or reverse setting. Manual transmissions have a dashpot there and no solenoid. They seem to get magnetized over time and will stick and hold the linkage slightly open. If you need to kick the throttle to idle down in P or N that's an indication the solenoid is sticking and the throttle is being held slightly open. I got a new one from the Classic Center a couple of years ago and they are about $1400, but it cured my throttle sticking and a high idle when parking. If it is set too high it can also mess with the throttle venturi switch setting; as IIRC with no pressure on the throttle the venturi switch creates a closed circuit and line pressure is reduced allowing a softer downshift.

I don't know what condition your linkage balls are in but if any of them are worn the linkage won't function properly. I think there are several sources for the ball ends, and if you need to replace them the linkage tour goes into great detail on how to adjust them all for proper operation.

Short answer, it's probably (hopefully?) just some adjustment issue.

[Ed Riefstahl]

Hi Jfkb2,

Sounds to me like your linkage may be sticking somewhere.
I've recently gone through some automatic transmission issues. The harsh shifting on the early SL's can break the slip joint / yoke in the differential. Ask me how I know this. The later 60's SL's got a beefier slip joint. So, avoid driving it until you can check it out.

My first thought is to thoroughly check all the linkage and ESPECIALLY THE SOLENOID on the the top of the transmission. It's not visible from under the car and often gets missed while lubing the linkage. The solenoid and linkage should be accessible through a small cover under the carpet, on the passengers side of the transmission tunnel very near where the passengers food would rest. This solenoid releases the hydraulic pressure while the car is coming to a stop. If the pressure is not released, the transmission will down shift very harshly, especially from 3rd to 2nd.

I'd check, clean and lube (a drop of ATF works great) all the linkage while your at it, but I wouldn't change any adjustments.

Just my 2 cents and it's a place to start. Good luck, hope it helps.

Ed Riefstahl
Erie, PA

1966 230SL (Ms Magoo)
1970 280S (Miss Daisy)
1989 300SE (Majestic)
1999 BMW Z3 5 speed
1991 BMW 318I 5 Speed
1997 Toyota Paseo Convertible - Red 5 speed (have you ever seen one?)
1997 Ford Ranger step side (Mater)
2023 Mazda CX 5

[jfkb2]

Thank you all so much I will have to try to get a look at the linkages and the solenoid.

jfkb2

[ja17]

Yes good reply from Ed. I would start by checking the linkage.

[jfkb2]

Hello all,
I was finally able to get some time to take a look at the auto trans linkage through the access in the passenger foot well. The linkage moved freely but I lubricated it anyway. Then I took it for a drive. I still have the same problem. If I leave the car in second without touching the accelerator the car will rev up to 3400 rpm and 25 mph. If I then put the car into third the revs will go down to normal and I would have to press the accelerator for speed. If I again put the car into second just driving along the car down shifts as it should but the revs jump up and the car starts speeding up to 25 mph again without touching the accelerator. I am unsure how to test the solenoid. Any other suggestions I would greatly appreciate.

PS. I hope everyone has a great Independence Day!

[BobH]

Hello, i'm no expert but from what i've read you need to go through the linkage tour, not the transmission linkage, the linkages under the bonnet/hood.  This needs to be correctly adjusted before you look any further.  Your problems may be cured with a simple adjustment of the intake venturi, seems a good place to start

Have a read through this:

https://www.sl113.org/wiki/Restricted/Linkage-tour

[jfkb2]

I have read through it a long time ago. It looks like I will have to go through it again and give it a go. Thanks.

[WRe]

Hi,
I would check the throttle switch, unmount and clean it: https://www.sl113.org/wiki/Automatic/Start#RoughShifting.
Rough downshifting (3rd to 2nd) is often caused by incorrect rev adjustment.
"The Throttle Switch operates below a speed of 1200 rpm a soft shifting and prevents a strong shift shock,when the transmission shifts back to 2nd gear. If this happens anyway, you should increase the switching range on the Throttle Switch to 1400-1500 rpm by turning and use of a test lamp."
I don't know why this increases the speed, maybe a side effect.
...WRe

[jfkb2]

Hi All,
Again thanks for the help.

I have gone through the linkage and adjusted it as necessary, tested the voltage at the venturi switch (both wires have voltage when the throttle is closed and only one has voltage with the throttle open) and had my wife watch the transmission linkage with ignition on (number four fuse removed) with the car in gear the linkage moved aft, it moved forward one step with the throttle depressed half way and it moved forward again when the kick down switch was activated. I have not taken it for a test drive as it is raining here at present, maybe tomorrow. Any further suggestions would be much appreciated.

jfkb2

[jfkb2]

I was finally able to take the car out for a test drive yesterday, after making all the adjustments suggested here, on a beautiful Independence Day in Southeast Michigan. The car performed beautifully, the transmission had proper smooth up and down shifts without any lurching down shifting from 3rd to 2nd for a stop. And when the car was stopped in gear the rpm's were 900. Very happy!

Thanks for all the help.

Jfkb2

[rwmastel]

That's great!  Congratulations.  For future readers, what would you say the problem was?  Engine linkage, transmission linkage, reseating fuse #4, combination of these, something else?  Did this problem begin suddenly, or start with minor shifting issue and grow more pronounced over time?  Again, for future reference.  Thanks.

[jfkb2]

I believe it was the engine linkage with throttle slightly open and a bit dirty, I adjusted the linkage and cleaned the throttle. I also lubricated the transmission linkage although it did not seem to be bound up at all. I am not sure whether reseating fuse 4 had any effect or not. I did video the transmission linkage while I was driving so I could see how it moved during the drive with the gear selector in different positions however, the engine noise was too great to hear my narration so, I am not sure how much it would help to publish it.

The downshifting problem occurred not to long after I received the car from its extensive restoration but it eventually rectified itself and ran fine for a couple of years although it has not been driven very much. The problem all of a sudden resurfaced when I was driving the car earlier in June about half way through an hour long drive on suburban streets it became apparent again. That is when I started researching the forum and started this thread.

Again, thanks for everyone's help.

jfkb2

[Ed Riefstahl]

Hi Jfkb2,
I've been wondering about your transmission issue. I just finally got the re-manufactured transmission installed in my 66 230SL a few days ago and got to thinking about yours.

It's been 11 months since my last cruise in our SL when it had it's last harsh shift that broke the slip joint / yoke in the rear differential. After rebuilding my rear axle over the winter, I discovered I may have a transmission issue. The transmission had a very loud clatter internally after I got it running again.

I contacted Sun Valley Mercedes Transmission in CA and had a couple lengthy discussions with Mark. He explained that the early SL's had problems with the torque converters. Something inside can come apart. Long story short, the harsh shift in the transmission broke the differential in my SL and I wasn't even driving it hard. So, consequently I had to rebuild both the rear differential and transmission.Not a real surprise to discover the later 60's SL's were built with a beefier slip joint.

So, I'm just checking to see if your car is still shifting normal. I wouldn't want this to happen to you. It didn't sound like you actually found any real cause to your harsh shift problem, so I'm a little concerned. It was a very long, time consuming and expensive failure.

Good luck,

Ed Riefstahl
Erie, PA

1966 230SL (Ms Magoo)
1970 280S (Miss Daisy)
1989 300SE (Majestic) Sold it last week
1999 BMW Z3 5 speed
1991 BMW 318I 5 Speed
1997 Toyota Paseo Convertible - Red 5 speed (have you ever seen one?)
1997 Ford Ranger step side (Mater)
2023 Mazda CX 5

[jfkb2]

Ed thank you for the concern.

I do think that the combination of the processes I went through with your and others help really has fixed the issue. The next time I drive it will tell as the car has been sitting for about two weeks now. It has been to rainy and wet to take it out.

jfkb2