Auto to manual diff?

[BristolE30]

Hey guys,

Planning on doing the old auto to manual swap on my 325i soon. Whats the consensus on changing/leaving the diff? I'd prefer to use my current one but understand ratios may be wrong going from 4speed to 5.

Help appreciated

[Brianmoooore]

There's about a 10% difference between the speed of an auto and a manual E30 for a given engine revs, when in top gear and with the same diff. ratio, so if you keep the same diff, your engine revs. will be about 10% higher for the same speed in top. This will give better acceleration, but higher fuel consumption when compared with a 'factory' manual car.
All depends what you want from the car, but there's no reason not to try the original diff. first and change it later if it feels under geared.

[BristolE30]

There's about a 10% difference between the speed of an auto and a manual E30 for a given engine revs, when in top gear and with the same diff. ratio, so if you keep the same diff, your engine revs. will be about 10% higher for the same speed in top. This will give better acceleration, but higher fuel consumption when compared with a 'factory' manual car.
All depends what you want from the car, but there's no reason not to try the original diff. first and change it later if it feels under geared.

Thanks Brian, good to know. Will give the stock diff a go at first!

[BristolE30]

Also I was wondering if doing the manual swap effects the running of the engine in anyway. I know the ECU controls the kickdown etc on the auto so what happens to that when you do the swap?

[Brianmoooore]

There is supposed to be minor differences in the software between ECUs for autos and manuals, but nothing that you will notice in practice.
Only the EH auto box uses a kickdown switch (and a throttle position sensor connected to the box). 'Ordinary' auto boxes just respond to the sudden surge in engine power. Purely mechanical.

[BristolE30]

There is supposed to be minor differences in the software between ECUs for autos and manuals, but nothing that you will notice in practice.
Only the EH auto box uses a kickdown switch (and a throttle position sensor connected to the box). 'Ordinary' auto boxes just respond to the sudden surge in engine power. Purely mechanical.

Oh okay what’s the EH auto box? I’ve got the one with the sport switch behind the handbrake. Does it complicate the switch at all?

Also am I right in thinking when doing the wiring you are effectively tricking the ecu into thinking car is in park always?

[Brianmoooore]

EH box is the one you have, but it makes no difference to the conversion. Your engine has a combined throttle position switch for the engine and a throttle position sensor for the gearbox, with extra wires in the engine loom and a connection to the gearbox loom, but it's all unplug and forget
For the starter, there's two black/yellow wires behind the top right of the glove box area, plugged into two plain black wires. Simply disconnect both of these and plug the two black/yellows together. The blacks and all the wiring associated with them can be removed.

[BristolE30]

EH box is the one you have, but it makes no difference to the conversion. Your engine has a combined throttle position switch for the engine and a throttle position sensor for the gearbox, with extra wires in the engine loom and a connection to the gearbox loom, but it's all unplug and forget
For the starter, there's two black/yellow wires behind the top right of the glove box area, plugged into two plain black wires. Simply disconnect both of these and plug the two black/yellows together. The blacks and all the wiring associated with them can be removed.

Nice good to know! Thanks

[Vez010]

How did you get on with your gearbox conversion? I am thinking of doing the same with my 325i sport but not quite sure where to start.

Where’s the best place to get a manual gearbox and what should I be looking for?

[BristolE30]

How did you get on with your gearbox conversion? I am thinking of doing the same with my 325i sport but not quite sure where to start.

Where’s the best place to get a manual gearbox and what should I be looking for?

Long ol’ road ahead of you mate. If your serious about it start collecting the parts otherwise you’ll never get it done.

Did mine about a year ago and haven’t looked back, best decision I ever made with the car!! It’s a completely different beast with manual box.

[Vez010]

How did you get on with your gearbox conversion? I am thinking of doing the same with my 325i sport but not quite sure where to start.

Where’s the best place to get a manual gearbox and what should I be looking for?

Long ol’ road ahead of you mate. If your serious about it start collecting the parts otherwise you’ll never get it done.

Did mine about a year ago and haven’t looked back, best decision I ever made with the car!! It’s a completely different beast with manual box.

How long did it take you and any pointers on where to get the parts? I’m guessing ebay but not sure whether that’s the best place.