Installing the 5sp transmission into a '98-'02

[hoser]

Discuss:

Is it possible to install the later '03+ A750F 5speed transmission into an earlier 100 (98-02)? I see two possible 5sp transmissions on car-parts.com for $1k and $1.5k

One would also need the transmission ECU and the interior trim pieces. What else? Compatibility issues? Possible or is it a pipe dream?

 

[Greg B]

I also wondered about this on when we were discussing going from 4.10 to 4.30 gears in an '03+ to lower the gearing when running 33's. That's the biggest regret I have for buying the '01, but I got a deal I couldn't pass up. For those of us running 33's this would be ideal vs re-gearing to 4.88's (overkill).

 

[100 TD]

Physically it should not be a problem, the only thing I can think of as a real concern would be the interface between the Transmission ECU and the engine and or body ecu. One would have to look at the pre and post 2002 diagrams and see what the real differences are. The communications between the ECUs could be a problem, of course the codes thrown by the 5 speed tranny would be different and there are more of them, I'm just not sure how the engine and body ecus would see these codes and report them. If anybody can lay there hands on some tech info on the way the comms system works, and can see that they would still communicate then you may be home and hosed.

 

[100 TD]

Not sure if the bloke in the previous post is correct, the transmission ecu may be part of the engine ecu and this will complicate things with the connectors and wiring, the connectors changed in 2003 on the OZ spec so maybe the US did as well. The connectors are available somewhere as Dtronic get them to make their chips work, so maybe you could get the later ecu and some connectors and do a painfull task of pulling the connectors of the existing harness and then hooking up the new connectors to the old harness and plug it all in. You could of course solder wires to the ecu and join them to other connectors and solder other connectors in parallel to your existing harness and plug in that way. Then you would be able to go back if for some reason it didn't work.

 

[Jim_Chow]

My '03 LX electrical FSM shows an ECT solenoid (on the tranny) that connects to the engine ECU (actually 5 ECUs together in that block behind the glovebox) via 14 wires. Then there is a park position neutral switch, accelerator position sensor, stop-light switch, shift lock control ECU connecting to the main ECUs. Also, there is an ECT pattern select switch (power and 2nd gear start) that connect to the ECU (but not directly to the solenoid).

Okay, this is what the system outline says:
"Previous automatic transmissions have selected each gear shift using mechnically controlled throttle hydraulic pressure, governor dydraluic pressure and lock-up hydraulic pressure. The electronically controlled transmission, however, electrically controls the line pressure, throttle presure, lock-up pressure and accumulator pressure, etc. through the solenoid valve. The electronically controlled transmission is a system which precisely controls gear shift timing and lock-up timing in response to the vehicle's driving conditions and the engine condition detected by various sensors. It makes smooth driving possible by shift selection for each gear which is the most appropriate to the driving conditions at that time, and by preventing downing, sqat and gear shock when starting off."

The rest of the page describes how the gear shift control, line hydraulic pressure control, high response gear shifting control, clutch hydraulic pressure control, lock-up and flexible lock-up control, stop light switch control, Ai-shift control, ECT pattern select switch circuit, and transfer shift operation work.

So it appears the ECU behind the glove box tells the solenoid what to do, as the solenoid is physically attached to the transmission housing. The park/neutral position switch and shift lock connect ECU interact with each other a little, but all the other parts feed directly into the main ECU's (I'm looking at the schematic). This leads me to believe the ECU is different altogether. If you have a 4spd schematic, you could at least compare the pin numbers and wire coloring.

I have seen a LX that had a 5spd manual swapped in, but for that, you probably replace the entire ECU bank since none of the stuff (ECT solenoid, park/neutral switch, lock-up ECU are used).

 

[Jim_Chow]

I examined the additional text about the 5spd tranny operation and it's the main ECU that tells it when to shift (depends on speed, TPS, APS sensor values), what gear to shift into, etc. The tranny itself just has a dumb solenoid on it that accomplishes the shift, lock/unlock functions, no dedicated tranny ECU. It's the main ECU behind the glove box that's the brains behind all of it. So if you want to run the 5spd tranny in a 98-02 LC, you'd also need the '03+ ECU, and whether that can be integrated seemlessly into a 98-02 isn't obvious to me.

 

[100 TD]

Thought it wasn't seperate

 

[hoser]

Well, thanks for entertaining the idea, fellas.

 

[100 TD]

Well I did correct myself 5 hours after I first posted and said I may be incorrect. This was before you reposted. I got to thinking what I had read up on them and the change in the connectors between 02 and 03 DTRONIC units for the diesels. As I say, the connectors are available, maybe Cdan can get them, then it would be a case of fitting off a new connector on your harness and plugging it in to the ECU. You would have to make a loom up for the tranny but that wouldn't be to hard. It is cheap for a 5 speed and a cheap regear and the advantage of an extra gear. I reckon go for it. The ratios are as follows (errors and omissions excepted)

5 speed & 4.3 diff from 4 speed vehicles
1st 3.520/15.14
2nd 2.042/8.78
3rd 1.40/6.02
4th1 .00/4.3
5th 0.716/3.08
Rev 3.244/13.95

4 speed & 4.3 diff
1st 2.804/12.06
2nd 1.531/6.58
3rd 1.000/4.30
4th 0.753/3.24
Rev 2.393/10.29

5 speed & 4.1 diff
1st 3.520/14.43
2nd 2.042/8.37
3rd 1.40/5.74
4th 1.00/4.1
5th 0.716/2.94
Rev 3.244/13.30
So this does better than the standard 5 speed for regearing use.

5 speed and 3.909 diff(current turbo diesel in OZ)
1st 3.520/13.76
2nd 2.042/7.98
3rd 1.40/5.47
4th 1.00/3.91
5th 0.716/2.80
Rev 3.244/12.68
I typed all this in Word without 4 speed ratios and then went looking for 4 speed ratios and found Hoser has done similar to this before!

You will have to multiply it out for 4.88 or whatever, I couldn't be bothered, just want to see a 5 speed fitted up where a 4 speed was.