76 530i motor&5spd into a 74 Bavaria?

[canada karl]

Would this be a fairly straight forward swap besides converting the pedal setup? Also would the intake and carb setup bolt right up to the 530i block....same M30?

[Mike W.]

Yes the carbs would bolt up fine, but there may or may not be provisions on the later head for a mechanical fuel pump. Installing an electric fuel pump would be easy enough, but as cranky as those carbs were I'd just convert the car to FI.

The major stumbling block I see is the driveshaft, a Bav has a wheelbase ~2 inches longer than an E12. Sometimes auto and manual driveshafts will interchange, 3HP22 and G265/6 5 speeds will, but I suspect the Bav would have a BW65 A/T and I have no idea on how it compares, length wise, to a 3HP22. Nor do I know if the center bearing is in the same place. You would almost have to get under it and measure things to be sure. I suspect the guibo is the same or interchangeable, but I'm not sure, but you can look that up.

[canada karl]

Could a 2'' piece of billet steel be fabricated to act as a spacer between the driveshaft and the diff? Drill out bolt holes to match? Maybe have it balanced ? What were the major issues with the carbs? But you're probably right about going to FI.

[Mike W.]

Perhaps you could machine a spacer, my first thought would be aluminum, mostly for weight but also workability, but it might not be hard enough, I'm not enough of an engineer to really say. For reasons I know technically, but don't really understand, BMW driveshafts are very cranky about being shortened and even more so on lengthening. It has to do with them being fusion welded. But you really have to get down and measure everything, make sure the center bearing is in the right place. And it's possible, though unlikely the Bav driveshaft might work. Or the front of one and the back of another. You can mix and match driveshafts in spite of what the manuals say. But there's so little data left on them you're going to have to do much of the groundwork.

There used to be something of a forum for Bavs, but I can't find it anymore. Some links, but not what I remember. Might have been a newsgroup it was so old. Funny to read actually, very much a take no prisoners attitude.

The carbs. Arggg. I had a Bav, my first BMW, and I dealt with those things for over a decade before I got a 530i parts car and converted it to FI. MPG took a hit. Torque took a hit with the conversion, both much to my surprise. But oh my god, the thing just ran so much better. I could start it outside the car, no pump 3 times, but not 4 or else you'll flood it and it idled cold. Wow, what a revelation. And I could get 10 or 15K out of plugs instead of maybe 5K. The carbs either had a flat spot, which I could tweak out of it, but only for a day or two when it wouldn't idle. Or I could get it to idle most of the time for a while, but with a flat spot at any time in any gear. Parking lots were an adventure with the flat spot and on off acceleration, hard to just kind of feather it just above idle. I got so I could pull the top of the carbs off, pull the jets out, shoot them out with carb cleaner and button everything back up in maybe half an hour. Kind of a quick carb rebuild for a pair of carbs. I did try different main jets, it would change things somewhat, but not really make an improvement, just different. Trust me, you really don't want to go there.

[canada karl]

Well after reading your adventures with those carbs I see that FI would be the way to go. I think installing the FI wiring might be a challenge for me. Now I know why the owner wants to sell the car. He's actually in another province than I am so just communicating with him by email. He says he has rebuilt the carbs but I don't think he solved the because he says he is having issues with the motor? Were those carbs Solex? In the pictures of the car the body looks solid and the interior is in excellent shape so it has potential for a swap. I'm just at the "what if"stage right now. Thanks for the info. Karl

[Mike W.]

Zenith carbs.

[Mike W.]

I think installing the FI wiring might be a challenge for me.

When I did it in the early 90s there was very little documentation out there, pre internet. Now it should be no big deal. Hardest part wiring wise was wiring up the fuel pump in back and running the wires to it.

One problem with a D/S spacer is the end of the shaft is supposed to locate on the pin at the end of the tranny. That helps keep it centered and is also a safety factor in case the guibo comes apart.

[tlake]

Yes the carbs would bolt up fine, but there may or may not be provisions on the later head for a mechanical fuel pump. Installing an electric fuel pump would be easy enough, but as cranky as those carbs were I'd just convert the car to FI.

The major stumbling block I see is the driveshaft, a Bav has a wheelbase ~2 inches longer than an E12. Sometimes auto and manual driveshafts will interchange, 3HP22 and G265/6 5 speeds will, but I suspect the Bav would have a BW65 A/T and I have no idea on how it compares, length wise, to a 3HP22. Nor do I know if the center bearing is in the same place. You would almost have to get under it and measure things to be sure. I suspect the guibo is the same or interchangeable, but I'm not sure, but you can look that up.

Until the middle of 1976 model year, the 530i auto used the BW65 A/T. That might help

[528i-1981]

Karl, I don't think this will be a cheap solution to do safely. My 2 cents, fwiw - there are people that know way more than me, but these would be my concerns.

Having just replaced the CSB and removing the D/S, I was surprised at the size of the balancing weights welded to the driveshaft. They weren't big at all. I knew that the driveshafts were spin-balanced as an assembly at the factory. As Mike explains, everything that comes between the transmission flange and the diff has to be balanced. Small variations in balance translate to large lateral torque.

If you're lucky, the two missing inches all appear on one side, but if not I would be inclined to use two spacers, one at each end, to preserve the CSB mount where it is. Moving that adds another layer of complexity and introduces geometric changes that could be hard to compensate for. If one side of the replacement shaft is too long, then you won't have this option and will have to move the CSB. This will require its relocation with three degrees of precision, which is not a simple undertaking. I personally would need expert help to do this.

I think a machine shop should be able to make spacers and even machine in a centering pin solution. I think the bigger issue is that any spacer will experience a ton of torque. Longer bolts will mean more flex in the assembly and ultimately could lead to cracking (particularly around the bolt holes) and disintegration under load. What bolt torque would you use, and how would the compression affect the alloy? I don't have to tell you that shards of metal ejected from a spinning assembly at several thousand RPM would be dangerous. So, selection of the alloy will be critical. Some billet is very hard and, while strong, could grenade due to brittleness. You also have issues with metal fatigue over time as your solution is heated, cooled, stressed, relaxed and some alloys really do poorly here. And everything must be in balance - any variation will induce cyclic vibrational stresses. You'll need expert help here. You also have to worry about road debris bouncing up and dead-eyeing one of your custom spacers, which could cause instant shattering. More ductile steel alloys will be heavy, perhaps much heavier than the design of either the transmission or the diff were intended to accommodate.

You would also want to test the rotational balance of anything you put in the drive line and preferably the entire assembly. It would suck to go through all of this only to have the driveline vibrate at the top of every gear.

This could be a fun engineering project, and who knows, it might be easy to select the correct alloy and the driveline geometry breaks in your favor. They do more involved things on some TV shows I've seen, but they never give you a 10,000 mile update on those shows.

[canada karl]

Well what kind of steel is the rear flange made of? I have extra drive shafts that I could cut the rear driveshaft flanges from and weld those to the existing shaft to make up the 2'' difference at the diff end. Use a strong grade of bolt. Of course the unit would have to be be balanced at a shop that specializes in such things.

[Mike W.]

The more I think about it the worse the idea of a spacer or the like sounds to me. You really need to get under the Bav and measure things. You have some fudge room, to lengthen the shaft a bit, but not a whole lot, so it doesn't have to be perfect.

Looking at some records I've gotten from Realoem, it appears the 265/6 D/S is the shortest of the 5 speed shafts. And looking there again, I'm seeing the '74 Bav shaft as 38MM longer than an E28 shaft. I can find nothing on E12 lengths but they're probably close, maybe the same as E28, and the lengths listed don't correspond to where I measure things. So you might get lucky, real lucky, or just be able to have it shortened. Now even that isn't all that easy since shortening BMW driveshafts isn't easy and very few places will do it. And you can adjust the length a little bit depending on which guibo you use, the flanged one or the rounded one.

Now I'm crazy hands on, including welding, but doing a D/S is definitely something for the shops. Literally, if it comes apart it could kill you. Driveshaft failures at the front are extremely dangerous and can get really ugly. At the rear it's usually no big deal, but at the front it is.

[Lock]

For what it's worth you can mix and match Dorman driveshafts halves. When I took out my 3HP22 auto and put in the e34 260/6 manual transmission the replacement Dorman driveshaft I got was too short by about an inch or two on the rear half, there wasn't enough spline engagement, so I talked to Dorman support and ended up buying an e28 533i driveshaft and using the rear half as it was slightly longer to solve the issue. The splines are the same so it connected right up, and each half is balanced independently so no issues with balance. I think the model numbers I used are in my manual transmission post.

[canada karl]

Thanks for the info to all those who responded.

[Harv]

Karl, my M30b30 will be available soon with all the injection and ecu.

John.

[528i-1981]

each half is balanced independently so no issues with balance.

First off, great new avatar pic of your E12 in the snow. Interesting about the drive shaft halves. Everything I read about separating the halves stressed the importance of marking the orientation to preserve balance. I was pretty paranoid about that. Here you've Frankensteined two halves and preserved overall balance. I wonder what's up with that?