Z3 Automatic transmission 4 vs 5 speed

[Z3 2.0]

Hi fellow Z's!

I just joined the forum after buying a 1999 Z3 2.0 automatic. And I love it! BMW's smallest inline six is very, very smooth, as is the transmission. I was thinking that the four speed suited a 1.9 better because it means lesser gear hunting but it turns out to be a relaxed combi with a six cilinder as well.

I'm pretty happy with the four speed till so far, probably due to the (very) high final drive that's been applied (4.44 ratio means more torque to the rear wheels). In Europe BMW equipped the four speed transmission with a sport mode switch in addition to A/M mode, which I use frequently because the S mode adapts to the whole gear program.

I'm intrigued by BMW's choice for the GM 4LE auto transmission. Why did they fitted this older - but solid- transmission in the 2.0, 2.3 and 2.8 and not the GM 5L40-E or ZF 5HP five speed that were also available in that period (1997-2000)?
Since 1991 a 325i or 328i e36 already had the five speed auto, so they should be suitable for the Z3. Only when new engines arrived (M54 2.2i 2.5i and 3.0i) and after 2000 a five speed became available for the Z3.

So I'm looking for answers here.. why did BMW initially choose the four speed in stead of a five speed in the M52 Z3's?

[rf900rkw]

Why BMW chose the 4L30 over the ZF4HP22E for the E36 era is a mystery. The transmission is an archaic and crude hack; rudimentary electric controls and a separate O/D grafted into a mid-1960s design. BMW did force many changes through before using it, everything from clutch material and number to gear ratios. But it's still a design that was meant to be governor and vacuum driven. Like the old mousetrap game, you flick the switch/solenoid, and set a series of valves, accumulators and orifices into motion, hoping the end result is satisfactory. There are no speed sensors beyond the driveshaft/output. No clutch to clutch hydraulic control. No closed loop feedback learning, and no integration with other sister systems. The move to the five speed was not so much about adding one gear, it was about moving forward 30 years in the technology base. As far as why they didn't toss the 5L40 into the M44/M52 cars. Time and money. It takes immense investment to develop and certify a powertrain combination. Plus the DMEs involved may not have been capable of the communications necessary, integration. For instance the 5L40 issues a torque reduction request to the DME during a shift. This requires a fast acting electric throttle.

This is why, ten years ago when my wife wanted an automatic coupe, I insisted on a M54 3.0. Not because of the engine, because of the transmission.

[Z3 2.0]

Thanks for sharing your thoughts, rf900rkw, certainly learned a few more things here! However, as far as I know, the GM5L40 was applied to e36 3 Series. Both m50 and m52, so DME wouldn't be an issue for the powertrain certification. Also, the throttle valve is electric on all m52TU engines, even the ZF5HP would work (e46m52TU 328i powertrain combination).

One day I hope to resolve the mystery :-) . One theory might be that BMW considered a four speed in combination with high final gears more suitable for a Z3 m52 and m52tu in stead of the five speed 5L40.
it's true that BMW never chose for the more modern ZF4HP22E in any model series for unknown, but good?, reasons. The only alternative left was the GM4L30. Only with the third gen Z3 six cilinder engines (M54) they offered the 5hp auto from zf, which was the better automatic ofcourse.)

[Z3 2.0]

Hi rf900rkw, in another thread you answered: 'The two common causes of not shifting to fourth on that unit are a bad range sensor, and incorrect tire diameters. The front tires HAVE to be the same diameter on DSC cars, or the transmission will not shift as expected. Mismatched wear, brands, or even pressures have caused shift problems.
Does this also count for my 2.0/ 4L30 with ASC combination? I was planning to replace the 225/50 front tyres for 205/55 (according to the manual this is an approved tyre size) in order to improve steering and handling.