Auto Tranny Help

[scottb1982]

My girlfriend has a 92 525i euro spec (we're in Germany) with a terribly worn out auto tranny. Her mom just wrecked HER 95 320i (euro). How much would be involved in trying to put the tranny from the 3-series into the 5-series? Is it compatible at all? Thanks, and please don't flame me too bad, I'm new to BMWs.:(

[M Quick]

It should be bolt on! Both cars has the m50 engine so.
But you may have to take the auto DME from the 320i for it to work!

[scottb1982]

It should be bolt on! Both cars has the m50 engine so.
But you may have to take the auto DME from the 320i for it to work!


I know the 320i has the M52B20, and the 525i has the M50B25, so would that still be compatible? And please educate me in what the DME is

[jfj707]

M52 and M50 stuff do bolt up, I believe. Didn't know they were making the M52 in '95, might be a euro thing.

The DME is Bosch's engine control software/computer - the ECU would be a generic reference to it.

[whiskychaser]

You probably have the 5HP18 tranny in the 525i. But be aware there are about 12 variations. In September 1992 BMW changed the electrical socket at the tranny end. So a post Sep '92 wont even plug into a pre Sep '92, even if they are both from a 525i. eg I have replaced a tranny ending in 075 with an 073 and an 071 (the last one out of a 325i).
But I CANT replace it with an 083.

Best bet would be to get all the information off the plates on each tranny.
Then have a look at the German site below. If they list it as 'austauschbar' (exchangeable) you may be in with a chance. But I would certainly give them a call
http://www.harald-heller.de/catalog/product_info.php?cPath=66_101_207&products_id=336

[scottb1982]

Would it be easier to swap the whole motor, transmission and computer then? I would imagine the wiring harness might be a bit different too. The motor and transmission in the wrecked car are in a lot better shape than the 525. I know the 320 has a smaller motor, but it just needs to last till September.

[jfj707]

They made 520's, it would be slow, but work.

Wait a sec though... if it is an M52, is it not OBDII?

[whiskychaser]

Would it be easier to swap the whole motor, transmission and computer then? I would imagine the wiring harness might be a bit different too. The motor and transmission in the wrecked car are in a lot better shape than the 525. I know the 320 has a smaller motor, but it just needs to last till September.
If you use the 320's engine and gearbox with its own ECU and tranny EGS then it should obviously work. I wouldnt fancy changing the looms so I'd be having a close look at wiring diagrams before starting. Something else to consider is the diff ratios. That 2.0 litre might struggle if the 525i diff is too high. IIRC 2.0 and 2.5 diffs have different cases and cant be swapped.

[scottb1982]

If you use the 320's engine and gearbox with its own ECU and tranny EGS then it should obviously work. I wouldnt fancy changing the looms so I'd be having a close look at wiring diagrams before starting. Something else to consider is the diff ratios. That 2.0 litre might struggle if the 525i diff is too high. IIRC 2.0 and 2.5 diffs have different cases and cant be swapped.

Thanks for the help so far! Please keep it coming!

I did a little more "wiki searching" and discovered they COULD both be M50 series motors, which will hopefully be easier to swap. I'm deployed and can't see which motor it has until I get back. I know that the 5-series has the M50B25 motor of some variation (I worked on it some before I left) that was in pathetic shape, so the car was already slow. This is strictly home-to-work car, so it doesn't need to be quick. I'm hoping I can just swap the transmissions and call it good, as I see a lot less hassle by doing that. Hopefully, if nothing else, I'll have to swap out the transmission computer (by reading some inputs so far, the transmission is controlled by its own computer? Or is it merged with the engine computer?) I also know the gearing could be a little off as well, but hopefully for the better, since the 2.0 is weaker than a healthy 2.5. and the current 2.5 is not in tip top shape.

I know it seems like a lot of work, but again, we move back to the states in October, so the euro-spec car only has to last that long. Its too expensive to try to buy a used US spec car in Germany that is in decent shape. I'm trying to see if I can make something work with what I have, and if its even worth the hassle. I'm a pretty competent mechanic, but I'm used to GM/Ford/Japanese/VW cars, not these "Refined German" vehicles. I've always wanted to learn about them, I was just never offered the opportunity until now.