Fsmoto

Hello group. I'm new to the 928 and eager to get started with my project. Some of you may despise me after reading this but be kind

Picked up an 84 928S auto roller. My business is automotive, but specializing in Japanese performance mainly with Toyota and the almighty 2JZ engine platform. So here comes the communities gasp.... I plan on transplanting one of these engines into my 928. Will be using a modern and powerful engine management system from AEM.

For now I plan on keeping the auto trans and from what I've found it's not computer controlled solenoid actuated trans, which might actually work well for me. The kickdown cable apparently is what controls the shifts during normal cruising, that and plenum vacuum running back to the modulator. At least that's what I believe to be true, if anyone with knowledge cares to give a detailed explanation then I'm all ears. I've also read of a kickdown switch at the gas pedal that when when actived by burying the gas pedal a relay gets a signal at a predetermined speed from the speedometer gauge telling the trans to not shift until the pedal is lifted or I'd guess at redline somehow or another......I'm not sure if my model years transmission is like this though since the info I've found on this seems to be for later year cars.

My question is this. How can I get the trans to shift normally under load? Will I absolutely have to hook the cable to my throttle body or is there a solenoid or even electric motor similar to today drive by wire throttle bodies I could retrofit onto it?
Also for the kickdown. My engine management can definitely be wired for an output with any number of programmable conditions similar to how a modern day automatic transmission would receive the signal to downshift whether it be throttle position, manifold pressure, speed, rpm, etc. Soooo....can the kickdown be simply controlled by me ems?

Next up, but touching more on the first question. How will I know when the trans wants to shift? Does it normally upshift by a combination of the cable and vacuum at the modulator? My concern is since I'll be installing a turbo charged motor I'll obviously want to know shift points so that under mid load/boost I can have my ems pull timing so not to tear up the transmission.

Sorry for the overload of questions. I'm sure I'll have many more! If anyone has great knowledge on this I'd love to hear from you. I'm also interested in reading up more on my specific transmission, so if there's any links you'd like to share that would be helpful as well.

If it helps I have the trans code. It's a 722.316 which I think designates it as an A28.01

ammonman

The Mercedes sourced transmissions in the 928 determines shift point based on throttle position and road speed as indicated by the centrifugal governor inside the transmission (attached to the output shaft.) Engine vacuum level only affects how "firm" the shifts are. You will need to make sure that the throttle position cable (aka "Bowden cable") has enough travel and is range-matched to move the control pressure valve inside the valve body from no throttle to full throttle position in time with the range of the actual throttle plate. The kickdown switch activates a relay that energizes a solenoid valve attached to the transmission that delays upshift until maximum RPM is reached (also, if rpm is below max the trans donwshifts.) By changing to the straight 6 engine this will be affected. What is the maximum rev limit of the powerplant you intend to use?

Mike

GT6ixer

Ha! I love this. The ubiquitous SBC swaps are boring as all get out. And I think you'll find the 928 community more non secular when it comes to mods. I can't help you with your questions but I am following along with great interest as a fellow '84 928S owner. But no doubt you'll get all the technical information you need here and then some. Post some pics of your car and work as it progresses. I'm betting this will be an epic thread!

Fsmoto

Thank you Mike. Definitely some good useful info. I may ruin into a problem with the Bowden cables length since the throttle body will be quite a bit further forward on the 2jz. I'll have to fab some type of linkage I suppose. Hmm not a huge hurdle. The knockdown switch I can activate by way if programmable output from the ems, so that'll be easily configured. I will be spinning the motor upwards of 7400rpm minimum, really depends on what my cam choice tells me to stop when tq starts dropping off. I'll have more questions regarding the strength of the trans but that's better left for another part topic I think.

hacker-pschorr

Todd has made some slight modifications to his transmission for the added power of his 87. At the strip he's shifting at 8k

https://rennlist.com/forums/928-foru...deo-added.html

https://rennlist.com/forums/928-foru...-a-veyron.html

https://rennlist.com/forums/928-foru...ip-update.html

He also upgraded the driveshaft:
https://rennlist.com/forums/928-foru...-the-back.html

77tony

LS/GM C6 6 spd auto: https://rennlist.com/forums/928-foru...ed-car-31.html
1GZ-FE V-12/GM C5 6spd manual: https://rennlist.com/forums/928-foru...spd-928-a.html

MainePorsche

I found this on a search of my old posts, and thought it would be helpful to you. Sounds like it could be a task to take advantage of this function.


'Transmission protection switch'

The overload protection switch or transmission protection switch has a two wire connector on the drivers side of the transmission just left of the vacuum modulator. The plug is a female connector which attaches to the 2pin counterpart which is screwed into the transmission with a but copper colored round-shaped nut.
The connector connects a wire to a three pin two wire connector inside the car in the spare tire well right front corner. It is supposed to see open in P and N , closed in drive . It feeds 12 volts from the EZK ecu to the switch which is then connected to ground by the switch. The pressure-switch closes when shifting 1-2 nd opens from 2 -3 and also closes when shifting down from 2 - 1st ....it momentarily retards ignition timing. The Ezk has an input that is used for this transmission protect feature. The Ezk retards briefly by 16 degrees to reduce the torque and allow the brake bands / friction disks to get a firm grip again when changing gears.

The signal path is this: Ezk pin 26 to CEB V12, from there to U22 of the CEB, then to T32 (in the spare tire room) and to the switch, from the switch to T32 and to GP IV which is chassis ground.'

From 928 Tech Tips at jenniskens - a transmission tech Forum - good one too.

hacker-pschorr

The engine he's using is easily capable of 1200+ hp which would twist that Corvette transmission into a pretzel.

The Corvettes running big power opt for 4L80E or Turbo 400 transmission which are larger than the stock C5/C6 units. Not sure how that will fit under a 928.

The shop which helps Todd with his 928 built this Supra:

James Bailey

You might go post on the Supra forums that you found a cool 4speed auto transaxle.....has a 1750 RPM stall speed designed for 300 hp and up shifts around 5,500..and has a 2:20 final drive just in case you want to go 250 mph....and you are going to swap it into your Supra

hlee96

Fsmoto: welcome to Rennlist. Is this my ex-84 black roller with almost perfect camel colored leather interior from Chadds Ford?

Sorry can't add anything regarding the auto transmission, but I am sure to follow this.

-Hoi