Kevin in Atlanta

Son's 87 S4 automatic with 90k miles.

Symptoms when cold: No 3rd or 2nd. Car will shudder under load.

Symptoms disappear once the car is at running temperature.

What we have done: Changed fluid and replaced the filter. Nothing in the A/T pan and the the fluid looked great.

After we did the A/T service the symptoms disappeared for a couple of weeks before returning.

I am thinking we might have a seal or pump issue.

I have a quart of Transx additive on the shelf. Not sure that will help.

MainePorsche

Something to consider.
Rest of the doc is in the link.


TRANSMISSION SHIFT POINT DELAY
The 2nd to 3rd gear upshift on some models is delayed 60-80 seconds to enable catalytic converter to reach its operating temperature quicker. Shift point retard solenoid is energized by CIS-E control unit or air mass sensor control unit through transmission shift point (upshift) retard relay.
Governor pressure is lowered through hydraulic line which is bolted to governor pressure test port. See Fig. 3. Under certain operating conditions (coolant temperature, vehicle speed and time), solenoid valve is de-energized and governor pressure is dumped. The 2- 3 upshift is delayed only when coolant temperature is 0-140øF (0- 60øC). Operating time is dependent on coolant temperature when engine is started, and is longest when coolant temperature is 68-86øF (20- 30øC).
Fig. 3: Identifying Transmission Shift Point Delay Components Courtesy of Mercedes-Benz of North America.
LUBRICATION & ADJUSTMENTS
NOTE: See appropriate TRANSMISSION SERVICING - A/T article in TRANSMISSION SERVICING section.
TROUBLE SHOOTING
AUTO TRANS DIAGNOSIS - 722 SERIES Article Text (p. 7)
1996 Mercedes-Benz C220
Copyright © 1998 Mitchell Repair Information Company, LLC Wednesday, January 26, 2000 12:03PM
TRANSMISSION SLIPS IN ALL GEARS
Incorrect modulating pressure. Modulating pressure control valve or pressure relief valve is dirty or sticking. Vacuum line to transmission vacuum capsule clogged or leaking. Working pressure control valve dirty or sticking. Low working pressure. Defective primary pump.
Transmission Slips When Starting Off In 1st Or 2nd (Reverse Is Okay)
Band B-2 shift valve sticking. Band B-2 piston worn or
damaged. Band B-2 adjusted incorrectly or worn or damaged. Adjust brake band B-2 by installing a longer thrust pin (if necessary). If transmission operates properly with selector lever in "2", but not in "3" or "D" position, one-way clutch may be slipping.
Transmission Slips In 2nd Gear Or Shifts From 1st To 3rd Gear
Check control valve B-1 for ease of operation. Replace valve body (if necessary). Remove and install brake band piston B-1, check sealing ring and replace (if necessary). Replace brake band B-1 and thrust body for B-1. Command valve binding.
Transmission Slips During 2-3 Upshift Or Slips Initially, Then Grabs Hold
Check modulating pressure and adjust (if necessary). Check
for temperature throttle installation (if equipped). Valve body worn or damaged. Replace valve body (if necessary). Replace inner plates of clutch K-1 or recondition clutch (if necessary). Check front cover Teflon ring.

http://jenniskens.livedsl.nl/Technic...x%20akp722.pdf

GregBBRD

Porsches do not have that shift point delay to allow the catalytic converter to heat up. Some models have a shift retard feature where ignition timing is retarded to "cushion" the shift into 2nd, but I can't imagine that causing this.

The one thing that both 2nd and 3rd have in common is B2....which does have a history of piston failure....although B2 also is engaged in 1st gear....so that doesn't make complete sense. Sounds like perhaps B2 is slipping on the drum under higher gear ratio loads?

My guess is that you probably need to rebuild this transmission. I offer rebuilt exchanges (of two different "grades"), rebuilding of your own transmission, and still have brand new transmissions, from Porsche.