E34 Tranny Swap

[Blackhallsun]

I’m ‘ new born baby’new in this community. Looking to buy a 1995 BMW 525i that’s been taken care of but the automatic transmission is on its way out and need to swap for a Standard manual. Which transmissions would work, any corks or warnings I should take into account before doing the job. Basically everything to worry about when it comes to doing that kind of job. Thank you.

[shogun]

Easiest would be to repair the automatic transmission, maybe just a valve body overhaul, transmission filter and ATF change will help. But for that we need more details about the trouble the trans has.
Changing to manual transmission involves more cost for parts and work, as not only the manual transmission has to be purchased, maybe also a new driveshaft and other parts.
Probably even buying a reman automatic trans will be cheaper and less troublesome.

[moroza]

Hello and welcome! I just recently did a manual swap on a 525i as well. Yes, repairing the existing transmission will be easier, and probably cheaper, but a manual will make it a much better car to drive. I'm a bit south of you and have the auto trans I pulled, in perfect working order, if that's the route you want to take.

Besides the trans itself, you'll need a driveshaft, a diff, shifter linkage, clutch and flywheel, pedals, clutch hydraulics, and some miscellaney.

Without an adapter plate, you can use any transmission that came with any M5x or S5x gasoline engine (M51 and M57 diesels may or may not work). You can also use M20 or some M47 (diesel) transmissions, but they're clocked 10 degrees off and will require crossmember and shifter modifications. I don't have definitive information on whether an N52 transmission will work; best knowledge is that it can be kludged to fit but not nicely. N54 I believe will not work at all.

Trans choices in no particular order:
1. S6S-420G-S50 out of a Euro (not US) E36 M3, or S6S-420G-S54 out of an E46 M3. The S6S 420G out of a V8 car will not work. The SMG version can be made to work with a ~$300 machine shop bill. This one requires a custom driveshaft and crossmember. Shift linkage from a US E36 M3 apparently happens to fit.
2. GS6-37BZ-M54 out of a >=3/03 E46 330i, <3/05 E60 525i and 530i (all M54 engines). E90 (N52 engine) transmissions have the same basic "37BZ" name but a different boltpattern. Crossmember has to be custom, driveshaft is E34 530iA depending on diff, shifter is either custom or E31 850 (works on paper, but nobody's tried it AFAIK). This is what I have.
3. GS6-37BZ-S54 out of a Z4M. Identical to No.2 except for a longer input shaft (see below).
4. S5D-310Z or -320Z out of most E39, E46, some E36 including M3, and E34 525i M50 <6/92. Because this came on early E34 525i, it fits natively if used with the correct shifter, crossmember, and driveshaft.
5. S5D-250G out of >6/92 E34 525i, some E36, and possibly some E46 and E39. Same deal with native fitment. Shifter, driveshaft, and possibly crossmember are different from No.3.
6. Getrag 260/5 out of an M20 car. Clocked 10 degrees off, but has native driveshaft fitment for your car and has the best gear spread.
7. Diesel transmissions. Have to come from abroad unless someone imported it (E28 524td was sold here, but I think all US models were automatic), have wide and sometimes weird gearing spreads, will also be clocked 10 degrees off.

1-3 and some 7 are overdrive 6-speeds; 4, 5 and some 7 are direct-drive 5-speeds; 6 is an overdrive 5-speed. 1-5 are semi-close-ratio, while 6 is a comfortable even spread. I find the 0.85 overdrive on the 37BZ too close to fifth; the 0.83 on a 420G is a bit better, but the 0.81 of the 260/5 is best IMO. In theory, the GS6-45DZ used on certain newer diesels could probably be made to work, and that's a double-overdrive box with an uneven spread.

Pedals are common to all E34, E31, and E32. Clutch master and most clutch piping are common as well, except the M5 which uses all 12mm fittings (others use 10mm). The best solution for pedals is to buy a brand new clutch pedal 35311155691 (~$40 on a slow boat from Deutschland), brake pedal 35211155686 (~$30), and bolt them into your pedal bracket. There are a few other details, but the upshot is: the $300-600 pedal assemblies you see on eBay are total ripoffs.

Diff depends on transmission and personal preference, but you're unlikely to be happy with the gearing if you keep the 4.10 currently in the car (except possibly the 45DZ). Factory gearing for an E34 525iM is 3.23 with a direct-drive fifth. This is much too short IMO; to match auto gearing you'd use 2.95 (closest available is 2.93), still a bit short. I use a 3.07 and it's reasonable with the 0.85 overdrive, equivalent to a direct-drive with 2.61 diff (closest available is 2.65). That said, I like tall gearing; opinions will vary.

Driveshaft depends mostly on transmission, also on diff.

Flywheel and clutch depend on transmission. Except for the 37BZ-M54, most of these can use any M/S5x flywheel. An M20 flywheel will also work, may require machining it or the rear main seal housing. M10 and M30 flywheels will work if the starter ring gear is swapped (or possibly use an M10/M30 starter). There may have been some changes in M20 ring gears sometime in the 80's.

The 37BZ-M54, however, has a shorter input shaft and expects a pilot bearing mounted further aft, in the flywheel. This means either an M54 6-speed flywheel, or an adapter to use one of the others. The rare 37BZ-S54 has a normal input shaft to use a normal M/S5x flywheel.

Clutch has to fit the trans and flywheel. Most of these are 240mm 10-spline disks. All versions of the 37BZ use 22 spline clutches. A 37BZ-M54 clutch/flywheel kit will work, but the pedal will be extremely light, possibly to an unusable degree. Adding a return spring makes it reasonably weighted but numb. This is a recent/ongoing issue for me, and the solution may be another pressure plate.

Apart from fitment minutae, your basic choices are: dual-mass flywheel with solid clutch (most BMW clutches since 1990 or so), or single-mass flywheel with sprung clutch. The former are smooth, heavy, the flywheel wears out, and the transmission will shift better. The latter are often lightweight flywheels, with more vibrations and noises, faster engine response, only the clutch wears, and shifting isn't quite as crisp. Costs are roughly equivalent; a brand new 37BZ factory clutch/flywheel setup is ~$650, which is about what a cheap single-mass kit costs.

The swap can be done for as little as $500 or so, if you buy a parts car or cannibalize a junkyard example, and use a used clutch (or find a good deal on an unused one). Typical cost is in the neighborhood of $2000, not including labor. I spent about $2200, some of which was lucky deals, some inordinate amounts of labor to save a few bucks, and some optional expenses. You may be interested in this.

It's a big job that's probably the single best modification you can make to your car.

[MeDerrty4]

I have a gearbox from a E46 m3 trying to use on my 95 e34 m50.My question is will I be able to shift thru the gears without any sort of shifter rebuild? Including getting to 6th gear

[moroza]

Yes, though it'll take some effort.

[MeDerrty4]

Such as?Well it's actually in the vehicle and I'm having a drive shaft made.My question is do I need to make any modifications for it to be able to shift thru the gears?

[moroza]

Physical effort to get it in gear and out, since you won't have the multiplying effect of the shift lever. If the transmission is a true manual, you're good to go. If it's an SMG, I think you can shift into all the gears but there won't be any detents. The modification to solve that is well-documented elsewhere.

[sliverdream]

Hi i am looking for help with a E34 engine swap my project car is a 95 auto 520i saloon which had a cable throttle the doner car is a estate 95 tds which has electric throttle can i keep the rear loom in my project car the tds engine out of doner is moving over along with dash pedals & steering column.Both cars are E34 if needed i will move rear Loom.

I will have too do a bit of hacking to the estate wiring loom if i have to move it over. Thanks,

[GoGetTheSlipper]

Finally, an updated thread on manual swapping the e34 🤙🏾

- - - Updated - - -

But nah serious question. I’ve been dragging my ass with the build, what’s a preferred diff? I have a Getrag 250 with a Luk clutch.

[moroza]

What engine and what purpose? If M50 and anything other than a dedicated track/drift car, I recommend 2.93, maybe 3.07.

[Mark185]

What engine and what purpose? If M50 and anything other than a dedicated track/drift car, I recommend 2.93, maybe 3.07.

I agree with this for a street driven E34. I have a 3.23 LSD out of a 92 525i manual on my 95 E34 Touring with manual trans swap and it revs a little higher than I would like at typical highway cruising speeds. Another option if you can find it is 3:15 differential out of E34 530i. I have one that was rebuilt as a LSD by on old member of this forum, Benjammin. I bought it years ago and have not installed it yet. Divorce and job change kept me from completing some planned work on my E34. I am just starting to get it back on the road now. S52 engine I installed in it years ago failed due to failed lower end bearings. Lesson learned - never install a salvage yard engine without inspecting lower end bearings first. I lost several thousand dollars. I replaced it with an M52B28 that is very tired and needs some TLC or another engine swap.

[moroza]

I agree with this for a street driven E34. I have a 3.23 LSD out of a 92 525i manual on my 95 E34 Touring with manual trans swap and it revs a little higher than I would like at typical highway cruising speeds. Another option if you can find it is 3:15 differential out of E34 530i. I have one that was rebuilt as a LSD by on old member of this forum, Benjammin. I bought it years ago and have not installed it yet. Divorce and job change kept me from completing some planned work on my E34. I am just starting to get it back on the road now.

3.15 vs 3.23 is a 2.5% difference, hardly enough to notice.

S52 engine I installed in it years ago failed due to failed lower end bearings. Lesson learned - never install a salvage yard engine without inspecting lower end bearings first. I lost several thousand dollars. I replaced it with an M52B28 that is very tired and needs some TLC or another engine swap.

I usually sneak in an ATV battery or one of those fancy pocket-sized battery booster packs and a compression tester, wait til there's ambient noise and nobody who cares is looking, and use them. My car's current engine is a $350 PicknPull M52B28. It tested over 180 after sitting a week, and has been doing great in my car for the last few thousand miles. I can imagine bad bearings sneaking by that test, but it seems unlikely. Couldn't hurt to check WIT, I suppose.