Wolfmaniser

My first post! ahem,

does anyone make any sort of upgrade kit for the 4 speed auto? I've heard they are only reliable to about 400hp, and if I say, wanted a stroker kit, nitrous or a supercharger,
1. would the stock hold up, or
2. are there any higher friction plates, stronger servo pistons, etc. available, in case it couldn't? the last transmission I rebuilt was a ford c6, and although I'm sure that there won't be that kind of wealth of aftermarket parts, is there anything?

Mark

Wolf -
Welcome to RENNLIST!

Do a search of the archives...I think the general consesus is that the A/T is pretty much 'bullet-proof' up to ~600HP!

Jim Nowak

Mercedes made these trannys really well!

Rich9928p

OK, let me describe how Porsche keeps the ATs alive in the GTS.

From 1988 to 1991 (before the 928 GTS), all of the AT cars had less HP than the GT engine. Why? the AT COULD NOT RELIABLY take the GT engine HP/torque during shifting. So I disagree that the ATs are bullet-proof up to 600 HP unless something "special" is done.

The GTS has a special feature. When the A/T transmission shifts gears from 1 - 2 and 2 - 3, the EZK spark control module retards the spark advance to effectively reduce power to a level where the A/T is NOT DAMAGED by the high torque of the engine. You can feel the power reduce during shifts.

So, I do not recommend trying to shove excess HP and torque through the 928 AT unlesss you have a GTS with the torque reduction capability. Sorry.

Rich

KBlair

Wolfman - do a search here for the modification to the kick-down switch if you haven't already. Allows for 1st gear take-offs without going WOT.

Jim Nowak

Rich,

The GTS tranny wasn't special. All Mercedes with this transmission had that feature from 1991 until they discontinued the vacuum modulated transmission. They did this for smoother shifts as well as decreased wear and tear.

Wolfmaniser

Hmmm...
So, if necessary, how easy would it be to add this EZK spark control to an 84s? I was thinking about upgrading my ignition anyway, so if it's a bolt in sort of thing, again hmmm...

Steve Cattaneo

You can add more friction to the drums by changing the thicker steels to thin ones. To increase shift quality Mercedes Benz has two updated servos for the b1 and b2 bands. There are no high energy clutches or blue plates for the Mercedes Benz transmission.

Jim is right,
The automatic transmission protective circuit was first introduced in Mercedes transmissions. The protective circuit in 928’s was first used in the 1987 s4’s. At wide open throttle, above 4000 RPMs, during the 2 – 3 up shift and down shifts the EZK retards the timing by 16 degrees for 350 Ms. Every S4, GT and GTS has this feature.

Wolfmaniser,

If you want to increase the holding capacity of the transmission, install a new modulator, change the transmission oil and filter, use synthetic oil, adjust the TV cable for later shifts, update both servos. Because of the design of this transmission; having the power flow thru the planetary gears first it can handle over 600HP.

Wolfmaniser

Thanks a lot for the info, I feel a little better about my crazy ideas not blowing my car up, at least not the tranny.

Weissach1982

What about the 3 speed auto? Are there any upgrades other than a ''kickdown'' switch? I'm thinking about installing a rear mounted auto trans cooler, praying to get rid of that mushy feel.
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Cory Johnt

Weissach

Forget the slush box and put in a 5-speed. Problem solved.....

Wolfmaniser

Two feet, three pedals...huh?

Weissach

What, confused or to much to handle for you?? Same thing my girlfriend said....

Steve Cattaneo

Cory,

There are no updated servos for the A22, 3speed transmission, change the vacuum modulator it controls shift feel. it can also be adjusted, just squeeze the two steel pins together and remove the plastic cover; turning the t handle CW will make the transmission shift harder, do not forget to put the cover back on, also take out all of the slack on the throttle cable (gas pedal) then take the slack out of the TV cable on the linkage. That should make the transmission hold the gears longer. You must have at least 14lbs of vacuum at the modulator. If the Trans still shifts mushy have it diagnosed.

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byrdman454

Found this old thread and resurrected it since I am looking into an auto tranny rebuild.

Does anyone know the part numbers of the updated servos that Steve Cattaneo was discussing on post #8? Does anyone know a source for these and cost? What other updates are out there for the '91 S4 Mercedes auto transmission?

Thanks