Auto Trans Skipping a "Gear"

[KevinC]

I have found that, intermittently, my car will so from 2nd to 4th skipping 3rd gear altogether. It seems to only do this at about half throttle, as it shifts ok with a very easy take off, as well it does when you "floor it" to hold first. When I shift manually from 2nd to 3rd then 4th, no issues...it shifts fine, too.

Any thoughts? :?:

Kevin Caputo
Boca Raton, FL
1967 230 SL Automatic
670 Light Ivory
113 Bronze/Brown MB Tex

[Shvegel]

Lukily there is no need to get excited. What has happened is the external linkage that controls kickdown and neutral shift pressures has gotten a little sticky. either take it apart and grease it up or just mash the gas a few times to the floor which should shake it loose.

What is happening is that the linkage is getting stuck in the idle position and the shift are happening at much lower speeds than normal.

The upper end of the linkage is accessable through an access plate under the carpet on the passenger side of the transmission tunnel.

[rwmastel]

Kevin,
My 230 automatic (VIN #018381, what's yours?) does that sometimes, too.  I figured out when.  The transmission is allowed to shift into 4th around 50 kmph (31 mph).  If you hold 2nd gear until that speed, then let up, it will skip 3rd and take 4th.  If you accelerate really easily, you will get 3rd before that magic speed for 4th.  If you accelerate briskly and hold 2nd until over 60 kmph (37 mph), then you should get 3rd gear (and some power & RPMs) and then 4th when you let up.

Shvegel,
Knowing these details, do you still think it's a linkage issue or could it be a vacuum issue or something else?  My car has low compression (120 psi), so I assume low vacuum.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[hands_aus]

Is this more likely to be a cold season problem?

My 250 was doing this slip during winter but recently has been back to normal.

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto

[Shvegel]

Rodd,
My understanding of the system is that the three way solenoid adjusts the transmission control pressure based on condition. at idle(sensed by a switch on the throttle body) the pressure is dropped so the transmission will not create undue drag on the engine, At cruise the soleniod is not powered and normal pressure is applied and at full throttle(sensed by a switch under the pedal in my 280) the pressure is raised which raises the shift points accordingly. All of this works in concert with the vacuum modulator of course.

Even though there is a vacuum modulator I doubt that low vacuum would play a part since the vacuum range for an engine at cruise or part throttle is fairly low anyway.  All I know is whenever my tranmission starts to act funny I pop it in neutral and stab the gas to the floor 5 or 6 times and it straightens out. I used to pull the linkage and re-grease it(I even tried some Dupont Krytox teflon based wammy jammy NASA stuff but in a couple of months it would still get funny.

I just sent my 1970 280SL up to my friend Rick Ollah in Duluth Minnesota for some metal work(he is the best metal man I know).  Rick ended up driving the car from Cleveland and he called me from the road to tell me the transmission was slipping etc. I had him stab the gas a few times and he was on his way.