Automatic to Manual Gearbox

[Benzowner]

A question for the techies, and possibly not MB based but could be.

If you change from an auto box to a manual box, does anything need to be "adjusted" with the ECU?

I will explain, my son has a car to which the above was carried out prior to him purchasing the car, but for some reason at high revs and in particular high gears, it is impossible to change up until the revs drop below about 3000rpm and needless to say all the speed scrubs off. H e knew this at the time of purchase, now a few years ago and cannot remember what needed to be done, he has had no need of the high rev gear change, not been on a track, but now comes time for sale and this is one of the things he needs to sort out. Any help would be appreciated.

 

[carat 3.6]

What's the car?

 

[Benzowner]

Toyota Supra with a 4litre V8 engine. The engine was originally with an auto box, now manual.

 

[DieselPete]

You could try speaking to a profesional mapping company they may be able to turn off certain parts of the software on the ecu and map the car to each gear on the dyno. Thats what id do first anyway. You may need to travel to find a guy who knows your type of car backwards

 

[Benzowner]

I thought that, thanks. Any suggestions?

 

[carat 3.6]

As far as I'm aware the supra was never sold with the 4.0 engine, so I'm going to assume that the car has the 1uzfe v8 from the lexus ls400? In which case the ecu needs no mods for a conversion from auto to manual.

What is it that stops him changing up? Does the engine die, or can he not get it in gear?

 

[Benzowner]

He can't get in gear until the revs drop to about 3000

 

[pembssurf]

He can't get in gear until the revs drop to about 3000

synchro-mesh issue?

 

[Benzowner]

No, I don't think so, there is no problem going down the box, where synchro would be worse I would think.

 

[edc]

How often does he change down gear at over 3k rpm with the next gear spinning at 3k+ ?

 

[carat 3.6]

If he cant get it in gear, the box needs looking at.

 

[Benzowner]

I think this old un will have to have a try in the car and see if the double de clutch works. Maybe it is the gearbox, he has been told it was the ecu, but I had my doubts. Thanks for all the info guys

 

[grober]

Sounds as if the car has suffered from " clutch drag" which means the clutch fails to disengage fully relying on the gearbox synchromesh to adjust speeds.
Clutch Drag Kills Synchros! ? Jacks Transmissions
quote :-
Question: Why do you need to rev the engine so high to check for clutch drag?

Answer: Clutches can drag if they are subjected to excessive engine harmonics and crankshaft torsional whip. In order to increase the engine harmonics, to test for drag, the engine RPMs need to be up high. Most engines don’t develop severe harmonics through the clutch until 5k RPM or higher.

that reference also details how to test for clutch drag.

 

[Bellow]

Clutch would be my first suspicion also (all synchros failing simultaneously is unlikely).
I would expect a dragging clutch to hinder selection of first and reverse gears at standstill though. There may be a reason for the clutch not clearing at higher rpm that is in its operating/release mechanism.

 

[grober]

The entire flywheel clutch mechanism needs close scrutiny. If poorly implemented in this particular conversion it may have damaged the gearbox over time.

 

[Bellow]

I'm wondering if the gearbox is one for this V8 or another with an adaptor plate.
Very difficult I'm told, to make an adaptor plate and retain 'absolute centres'.
Wondering if at higher rpm the friction plate (or a part of it) isn't being flung into contact with the flywheel or pressure plate and dragging (even locking) until the revs subside.

 

[carat 3.6]

I'll bet the clutch slave cylinder doesn't have enough travel to fully disengage the clutch, a manual box on that engine requires a substantial adapter plate which the slave cylinder probably isn't positioned to compensate for.

 

[Benzowner]

If a slave cylinder change would possibly do the trick, which would be the best to use? As you are probably aware, neither me or my son know too much about this type of mod.

 

[grober]

Installing the 6spd Transmission | MKIV.com
THIS ANY GOOD? CLEARANCES AND ADJUSTMENTS
V160 Clutch Replacement | MKIV.com

FROM
93-95 repair | MKIV.com


ps:- Feel free to ignore all this if it doesn't refer to your particular engine/clutch/gearbox

pps:- there is no easy answer to your question. insufficient effective travel could be down to many things = adjustment , slave cylinder position, or master/slave cylinder mismatch etc

 

[Benzowner]

Hi Carat,


Thanks for your reply and advice so far.

It is indeed a 1UZ, the car was built by Thor but I cannot find their website anymore so not even sure if they're trading.... I was told when I bought the car (owner talking now, my old man is Geoff) that it has a clutch from a Celica but cannot verify this. The clutch does need changing.... It's got a R154 gearbox.

However, when the gear change is made above 3k revs, the loss of power picks up as soon as it hits 3k revs, so this is why I'm thinking it's some kind of mapping issue, or that the car is in some kind of "limp mode" because something on the mapping isn't correct.

Think I need to find somewhere that can read the ECU and see if there's a fault anywhere but any/all advice is very much appreciated. There's a few places I could take it but if I could find someone or somewhere in the Bristol area, then without there being too much cost, I can find out what I need to do and how much.

Thanks, Simon