E34 M50 37BZ swap complete

[moroza]

This, my 10,000th post, isn't meant to be a how-to guide (revision pending). Some steps took an appalling amount of time and effort, headache and despair, and I'd recommend doing them as I'd recommend drowning. That said, they ended up working, and this is meant to document how. I installed a GS6-37BZ-M54 6-speed manual transmission from an 08/03 E46 330iM sedan into a 1/94 E34 525iT originally equipped with an A4S 310R (GM 4L30E) automatic. This is also meant to organize some technical data of the swap so that someone else's gets a head start, hopefully with better solutions than the timesucking black holes some of my subprojects became.

Shout-out to Singing6, who pioneered this swap, helped mine specifically, and has generally been cool to deal with.

Summary:
* Replaced everything between the inner hub flanges and the rear main seal.
* Trans out of an E46 or early E60 with M54. N52 trans is different, may or may not fit an M5x.
* Clutch/flywheel for an M54 6-speed. I went with a Valeo single-mass conversion and customized it further. It works but not the best.
* Custom shifter, though there may be OE solutions (see below).
* Custom trans crossmember, though there's an aftermarket option.
* Driveshaft 26101227870 from a <10/93 530iA, with M3 giubo 26112226527.
* E34 or E32 188mm (medium-case) diff with 86mm PCD flange. I used the 3.07 out of a 530iM.
* (>=10/93 530iA driveshaft, and the same diffs with 80mm flange, should work also.)
* Axles to match diff. 188mm diffs can use either 86mm PCD axles or 94mm. I used 94mm 540iM axles, changed hub flanges to match.
* The result is faster, dramatically more fun to drive, gained ~20% fuel economy (from 20-21 mixed/25 highway to 23-25 mixed/30 highway), and has minor NVH issues.

Part I. Transmission

I waffled between the S6S-420G and GS6-37BZ-M54 for a while, then a 37BZ fell in my lap and settled the matter. A 08/03 330iM (not ZHP) sedan sat in a self-serve yard in New Mexico for two months before I just happened to go on a 3000-mile errands run and grabbed it.

Transmission choices, in a nutshell:
1. Getrag (pronounced ge-TRAG, not GET-rag) S6S 420G-S54 (not to be confused with 420G-M6x, the V8 version): very strong; quiet, apart from low-RPM LWFW rattle; good gearing spread for a close-ratio box; lots of FW/clutch options; not the friendliest synchros, especially cold.

2. ZF GS6-37BZ-M54 (not to be confused with 37BZ-N52, the N52 version): very friendly synchros, shifts great; strong and quiet, but neither quite like 420G (mine whines a little); few clutch/FW options; generally cheaper; gearing a bit too tight.

They weigh about the same ~42kg, use the same 94mm 6xM12 giubo pattern. Both also have versions with output flanges to use 105mm giubos. The 310R automatic is 735mm long from giubo mounting surface to engineblock mounting surface. The 37BZ-M54 is 635mm. Those numbers are from measurements at multiple points using straightedges, and should be accurate to +/- 0.5mm.

Of all the E-Torx bolts holding the trans to the engine, only two are necessary - the M12 lower block corners. The rest were replaced by plain ol' class 10.9 M8, M10, and M12 hex bolts.



The starter mounting on early M5x is a disaster, a perfect example of something worth heaving through BMW headquarters' glass front door with a note taped around it, "So nicht, meine Herrschaften." I corrected the design by screwing the flanges of two flanged nuts to the front side of the starter flange, the nuts trimmed to fit around the cast gussets.

The transmission rear mount is a bolt-on brace, much too low and wide for an E34.



There are aftermarket braces that keep the stock auto crossmember, but I made my own. Cut a plate of 1/2" aluminum, drilled to bolt to the trans. Cut the E46 brace in half, each half later bolted to the plate after the trans and driveshaft were installed. Fabrication was lengthy and tedious with my tools (angle grinder, handheld drill), but should be quick for a machine shop.







Before removing the slushbox, I took some dozen measurements of driveshaft position. After bolting in the manual trans and resting it on a threaded jackstand, I partially installed the driveshaft and moved the trans to get it at the same position. To verify, I also measured the gap between the flange yokes and the giubo to make sure the driveshaft and trans were square.

Next step was to fabricate extension platforms on the stock 525iA crossmember. This gave the cast brace halves clearance with the giubo, and spaced the trans mounts further apart to better stabilize the trans.

Not my finest welding, but it works. Painted in a couple layers of bedliner.





I bought 23701141614 mounts, and used both them and the old center trans mounts 24701138435 (in good shape and stiffer), mostly settled on 614 for now.

A note about mounts: E34 M50 motor mounts are well ahead of the engine center of gravity, further than most. This means that the trans mounts are holding up not only the trans, but a good part of the engine's weight as well, and in this loaded state transmit more engine vibrations. I imagine the center trans mounts reduce this, but until I build a custom brace, I don't have a way to mount them. While four mounts worked fine on my M62/420G setup before, I think six for an M5x setup is a good idea.

The exhaust brace made a big difference in engine noise as well. With the exhaust brace on the transmission and the stiffer mounts, the whole car resonated at certain RPM and the engine note was a lot louder. It sounded properly good, but too droney. With two soft mounts and no exhaust brace, it still vibrates slightly more than the original auto setup, not bad.

Part II. Clutch and Flywheel

There aren't many options for a 37BZ flywheel, at least not directly. Choices are: OE DMF (approx. 11kg/25lb flywheel weight), Valeo SMF conversion (12.3kg/27lb, measured, and with a heavier clutch and pressure plate, not measured), a rare and expensive Dinan lightweight DMF, JBR SMF with unclear clutch options (4.5kg/10lb), a UUC piece (also 4.5kg/10lb?), and a JBR adapter to use a normal M5x flywheel. From what I'd read and heard, 10lb is excessively light for a street M5x while 25ish is lethargic stock. I found an unused Valeo kit for $375 and had the flywheel modified (was supposed to be $100, ended up $240 and irritated).

I made a 3D model of the flywheel and fiddled with a few ideas to lighten it without removing anything important, before it occurred to me that a lot of metal on it was just to support the starter ring gear. Well, the flexplate does that just as well, weighs very little, and I already had one I could sandwich between the crankshaft and flywheel. A machine shop removed the starter gear and its supporting metal, then machined the back of the flywheel by the thickness of the flexplate (3.1mm) to retain starter function and stock clutch stack height, and balanced it. This took a 27lb flywheel down to 16lb, and could've gone to perhaps 13lb. I was aiming for a fuzzy-numbers weight (because weight, mass, and moment of inertia are all different things) of 18lb, and this was close enough when added to the ~3lb flexplate.









It works, has imperfections. The weight is about perfect for a stock M50, but the ECU hangs the revs unless the IACV is disconnected or restricted. For trans oil, I used one quart each of Redline 75W-140 and D4 ATF, per UUC's recommendation. Oddly enough, there's no rattle at idle but a moderate diesel-like rattle up to 2300rpm or so, when fully warmed up. It's worth mentioning that I have one weak cylinder, so I wouldn't expect engine power pulses to be as even as they should be.

Something about the E46 pedal geometry makes their pressure plates a lot softer. People putting E36 pressure plates (compatible with E34) into E46 complain about how heavy they feel, and the reverse - an E46 plate in an E34 (or 36) - means a clutch pedal so light, that the assist spring can sometimes hold it to the floor. With the spring removed, the pedal is still extremely light, barely/unusable. I put the spring back, and added the clockspring from a brake pedal to the clutch pedal. The result is a light-reasonable weight but a numb feel.



I used TheStigg's clutch spring bracket. Well-made, works great.



Part III. Differential

I find most BMW excessively short-legged in their gearing. E34 525iA has a 2.95 top gear that feels ok, a bit high. The 525iM has 3.23, and is screaming for another gear. I not only used an overdrive transmission, but also a taller diff: the 3.07 out of a 530iM. It's a good compromise ratio, but most of you would probably want a 3.15 or the original 3.23.

The 188mm (medium-case) diff can use either smaller axles or larger ones. I used the larger ones off a 540iM, and had to change the inner hub flange to match. Note that stock 525i sedan (not wagon) trailing arms won't accept the larger hub flanges.

Part IV. Driveshaft

An E34 530iA driveshaft is 8mm short of ideal for a 37BZ, or 3mm short if used with an E36/E46 M3 giubo 26112226527 (5mm thicker than stock, same 96mm PCD). At first, I had 3mm washers stuck between the driveshaft yoke and giubo, but later removed them, decreased driveline vibrations, and the CV joint seems to have no trouble with the extension.

530iA up to 10/93 used driveshaft 26101227870 that fits an 86mm diff CV. From 10/93, they used 26101227754 shaft that fits 80mm CV. The CV are not interchangeable; they have different tooth counts. The corresponding diff flanges are different lengths, the later smaller one sitting 12mm further forward. The earlier 530iA driveshaft is 1480mm between the giubo mounting surface and the diff input flange mounting surface, with the CV at rest (it can plunge ~8mm either direction). The distance between the 37BZ-M54 output flange and 86mm diff input flange is 1518mm. The non-M giubo is 30mm thick, while the M3 one is 35mm. 1480 + 35 = 1515mm. The joint seems a bit tight taking up those extra 3mm, but doesn't bind or seem to have any problems in service.

This was by far the biggest timesuck of the subprojects, because I stubbornly chose to rebuild a used driveshaft myself. Let me be clear that I do not recommend this method, partly because it took so long, and partly because I'm not sure it worked.

In a nutshell - measured the depth of each U-joint cap, pressed the old joint out, pressed in new joint GMB 220-1670, lined up each cap with previous measurements... then got two independent knowledgeable sources advising me that the tolerance on that dimension is +/- 12 microns or so ("half a thou"), far tighter than my original measurements' +/- 200 microns. So I spent several clock-melting evenings building a runout test contraption, and adjusting that damn U-joint until runout of the driveshaft measured within that spec. Then I clamped the joint with thick washers and welded the washers to the yoke.



Then, for curiosity, I measured runout of a few other BMW parts (diff, trans, a couple of spare driveshafts), and found that only the 37BZ-M54 transmission output was even close to half a thou runout; most were about four or five times that. Anyway, I suspect the driveshaft is slightly out of balance despite being within runout. I'm going to replace it with a spare sometime soon.

Part Va. Shift linkage

I built my own out of a 37DZ shifter carrier arm 25117529067 (used from Latvia for $34 shipped), 16mm steel rod, 1/8" x 1.5" x 2.5" channel aluminum, some 1/8" x 1.5" x 3" channel when I ran out of 2.5, 10x13x10mm bronze bushings, 3/8" or 10mm spring pins, and an old bedframe. The distance C between the center points of the carrier front bushings and the shift lever ball joint is 218-221mm depending on whether you measure direct distance or horizontal offset. I believe the factory measurement is horizontal offset, so C=218. The carrier I got is C=197, so I cut it in half and joined the parts spaced further apart by 21mm. Like the driveshaft, this was fairly time-consuming. Unlike the driveshaft, the results are excellent.

After it was made and installed, I found out that the E31 manual uses a two-pin shifter C=215. They're available new for ~$110. The 3mm difference doesn't matter; even 10mm off should still work. That's all I know about this option.

The first attempt to join the halves was a dead end and a waste of time - a machined block of solid aluminum, from a chunk of the 1/2" plate used for the trans mount. It took forever and someone made me realize it was a fundamentally weak design.



The second attempt used channel alu, chosen to fit the rear carrier half tightly and securely. This took about as long to make, but feels a lot stronger. The rear piece is 3" only because I ran out of 2.5"; it'd've been a cleaner installation without the spacer plates.



I deliberately made the selector rod heavy, double-shear, and adjustable via the slot. Note the offset, required to clear the giubo. Selector rod length depends on what lever is used, since some are more angled than others. The distance S between the centers of the stock 330i selector rod ends is S=123. On the 37DZ shifter, approximately S=150. I made it adjustable to be able to fine-tune the angle. The finalized result is about S=172mm.



The 37BZ's two-pin shifter arrangement is inferior to the older transmissions' one-pin setup, IMO. Every such carrier arm I've seen had longitudinal slop in the bushings, which furthermore are oval and more compliant longitudinally even if held rigidly. Meanwhile, the pin arrangement reduces radial compliance, but that's not a problem to begin with.

The best solution is an idea I have that's outside the scope of this post. The second-best would be to convert to a single-pin arrangement like most stock E34 shifters. Third-best is to use tight-fitting polyurethane bushings (either expensive and apparently ill-fitting Powerflex, or cheap thick poly sheet that you cut to shape with a razor). Fourth-best, what I did, was mistakenly buy brand new 25117507695 bushings at $14 each, deplore that they're sloppy in the casting, and hammer a bunch of small nails in to take up the slop.

The shifter cup is factory 25111220600. The other three joints (swivel joint to transmission internal rod, external rod to swivel joint, lever to external rod) I replaced with 24mm spring pins inside doubled 10mm ID x 13mm OD x 10mm OAL oil-impregnated bronze bushings, which I installed in the swivel joint and shift lever after pressing out the factory delrin. The theory is that, spring-loaded, the spring pins will self-compensate for wear. One spring pin was a 10mm that took a lot of filing and fiddling. The other was a 3/8 that went much faster but ended up less round. The swivel joint pin was a 6x20mm that needed to be squished to fit.

(My camera ate my photos of the bushings)

It took a long time, and I still want to replace the front bushings (or redesign the whole thing to be single-jointed at the front), but apart from a bit of rubbery feeling going into gear (still tighter than stock), this shifter feels positively excellent. Notchy, but not stiff or grinding. Fairly heavy, very direct and precise.

I blocked off the hole in the transmission tunnel, where the auto cable used to be, with two aluminum sheets screwed to each other with RTV on each, sandwiching the unibody. Quick, easy, effective.



Part Vb. Interior shifter

For the knob, I special-ordered an aftermarket weighted shiftknob (Youstar) to come disassembled, and with a custom combination of (fake) wood and (real) leather. It just happened to have a transluscent silver emblem.



Acrylic amber-colored paint (took about a dozen tries to get the shade just right) on a piece of clear plastic, from a salad tub IIRC. An LED array glued to another piece of clear plastic, itself glued to the knob weight over a convenient reflective metal cavity in it. My grandfather put together the LED array and machined an aluminum ring on his lathe. All that glued together to form a weighted, (fake) wood and (real) leather, illuminated, non-M no-stripes 6-speed shiftknob.

For the shifter surround, I decided to make my own. Sparing the details of all the experimentation I did, here's a summary: 3/8 plywood carefully (read: slowly) trimmed with saws and files to be a tight and uniform press fit with the center console and factory outer shift boot, 12"x12" sheet of burl walnut veneer, Titebond Cold Press glue, a 20-ton H-frame press and some rigid aluminum plates, Keda wood dye, SprayMax 2k high-gloss clearcoat.







I find it too much wood, may change the shiftknob. I also find it too glossy; were I redoing all the trim from scratch, I'd use semigloss, satin, or even leave it open-grained with tung oil or somesuch. For this purpose, I wanted to match the factory trim. A lot went wrong, but the result exceeded expectations even if it's a bit too shiny and orangepeely.







Part VI: Electrics

Thankfully not much on the E34. My Check Control has long been disabled and deleted, so I didn't even bother grounding the one wire to cure TRANS PROG.

I changed the ECU to avoid the rev-hanging issue, but have it anyway unless the IACV is unplugged. The ECU was a silver-label EWS-equipped Bosch 413 with a cheap eBay chip. The chip bypasses EWS, such that my EWS module is unplugged and the car starts and runs.

Cruise control requires a little rewiring. The starter circuit requires the trans in P or N, but cruise shuts off if it sees P or N. The common solution of a jumper in the auto trans range switch disables cruise control. The solution is instead to jumper the starter relay so it doesn't go through the slushbox switch, then just ignore the switch and remove any jumpers in it.

In the case of a pre-EWS car, a simple factory jumper plug replaces the starter relay inside the fusebox. In the case of my 1/94 EWS1 525i, I could either power the immobilizer (located behind the driver's dead pedal) at X55/8 or X55/5 (the factory uses F17, ignition-hot), or bypass the starter immobilizer altogether by splicing X55/6 and /2 (two fat wires, both listed as black/yellow but one of mine was black/green). My eBay chip happens to delete EWS, so I bypassed the starter and ECU immobilizer completely.

ASC and ABS work fine if the trans computer is left in.

Total cost, including some waste: $2209

[m60power]

Awesome thread!! That shifter carrier "arm" looks so beefy haha. You are a brave man tackling the driveshaft build yourself, that sounds incredibly difficult. ANy reason you retained the u-joint bearing caps in the yoke by welding washers, versus using those 'c-clip' retainer things that come in various thicknesses?

Also, your custom made wood shift surround looks awesome. I ended up buying an OEM vinyl one for my manual swap car, but I'm not sure if I like it yet, so I've been thinking about making one with some high quality walnut burlwood veneer glued to either a plywood or aluminum backer plate, then applying varnish or clear poly resin to it.

[Singing6]

So much more time and effort in yours than mine! I cant thank you enough for all the help you gave me while refining my swap, i hope you feel the same about yours.

Im VERY interested in the photos of the brass shifter parts that you replaced so you may have to tear it apart to provide photos.

Im finalizing the LWFW setup in my car over the next month or two. And will report how it turns out.


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[moroza]

Awesome thread!! That shifter carrier "arm" looks so beefy haha. You are a brave man tackling the driveshaft build yourself, that sounds incredibly difficult. ANy reason you retained the u-joint bearing caps in the yoke by welding washers, versus using those 'c-clip' retainer things that come in various thicknesses?

Because the clips require machining the yoke to have a flat surface, and the precision of adjustment they allow is apparently less than specification. What I learned, however, is that runout specification does not guarantee a balanced driveshaft.

Also, your custom made wood shift surround looks awesome. I ended up buying an OEM vinyl one for my manual swap car, but I'm not sure if I like it yet, so I've been thinking about making one with some high quality walnut burlwood veneer glued to either a plywood or aluminum backer plate, then applying varnish or clear poly resin to it.

I've never worked with veneer before, and made a few mistakes others might learn from. The biggest one was not letting the veneer dry enough after flattening it (soaked in water for 5 minutes and clamped in the press with paper towels, changing them every 8 hours over a 24-hour period). This caused the veneer to shrink, crack, and bow the whole piece after gluing it to the plywood. Cost of materals, including the chemicals but excluding the press: about $60. The next one I make would cost $20 for the veneer and another $20 if I used the same fancy-pants spray clearcoat.

So much more time and effort in yours than mine! I cant thank you enough for all the help you gave me while refining my swap, i hope you feel the same about yours.

Im VERY interested in the photos of the brass shifter parts that you replaced so you may have to tear it apart to provide photos.

Im finalizing the LWFW setup in my car over the next month or two. And will report how it turns out.

I might take it apart at some point, but you'll have to make do with text and your imagination for now, or a 3D drawing sometime soon if I find the time.

[demetk]

Nice fabrication work! I too fabricate with basic tools and go through a number of iterations before I'm satisfied with the result. Well worth it though as you learn a lot along the way.

[polov8]

Interesting stuff! I have a brand new GS6 53BZ that i scored for a song here in the UK and the shifter mechanism is going to need modifying in the same way. It was meant for a Morgan Aero 8 and came with what might turn out to be a really useful rear bracket:

P1050212.jpgP1050214.jpgP1050216.jpgP1050215.jpgP1050217.jpg

Needs a little repair on the right hand side, but that looks pretty much like what you made! I did look into getting a replacement that wasn't broken from Morgan, but they build like 14 cars a week on average, so I'm guessing they're not massively stocked up on spares. Looks like it'd be easy enough to pattern up and fabricate in steel though.

I shall certainly be referencing this thread when it comes to the shifter install.

[moroza]

My rear brace design is a lot stronger than the Morgan's or Reboot Engineering. I've got a half-inch plate loaded in shear along its height (mostly) through short triangulated gusseted extensions, not a 1/4" cantilevered plate. I daresay mine was cheaper, too.

[Singing6]

Strength is not a major concern on the rear brace. The stock part is cast aluminum so the billet aluminum Reboot Engineering part is plenty strong as it is also well gusseted. The pros of the steel part you made are mostly its cheapness. As the reboot part is lighter and does the same job all day long.


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[moroza]

Bumping this with one substantial update regarding the driveshaft. I had it off when I had to replace the trans output seal, which started leaking a few months after the swap. I hadn't replaced it initially because I didn't have the right socket (deep 35mm or 1-3/8") and it wasn't leaking then. My error was in setting the lateral position of the transmission brace; apparently I had it off by about 10mm. The way I determined this was inspired by a post on BenzWorld where someone attached weights on strings at four points along a two-piece driveshaft. In their case, it was to measure vertical deflection alone, but in my case, I measured both vertical and horizontal. See pics for the test setup. Vertical deflection was determined by measuring the longitudinal offsets of the four strings when suspended straight from the middle of the driveshaft, then their heights off the floor, subtracting the differences in tube diameters (as it were, all four were the same 60mm at the yokes), and making a simple linear plot to check for deviation. Horizontal deflection was determined by suspending the strings from the side of the driveshaft, then lining up a long straightedge and measuring the distance from that. My verticals were within 1mm of where they wanted to be, but checking the horizontals, even before the straightedge my eyeballs quickly determined the front one was off. This wasn't apparent by looking at the driveshaft alone, no matter how hard I stared; the strings made all the difference.

I loosened and repositioned the trans brace to shift it over to center, and now all drivetrain issues are gone. No more thumping during hard launches, no more shudder at 40-60kph. Turns out I successfully rebuilt an original staked-joint BMW driveshaft using nothing more sophisticated than a dial indicator and a welder, though the effort was such that I would hesitate to do it again, rather farm the work out to a shop.
20210128_171805.jpg20210128_171450.jpg

[circuit.heart]

Just reading this now - you definitely put more work into it than even my 53BZ swap. The auto crossmember can just be spaced down 30mm and you would've avoided any risk to drivetrain alignment

[moroza]

The longitudinal position of the trans mounts was also significantly off, hence the extension bars.