Best Clutch, Flywheel & Gearbox Combos for BMW E30 M52 M50 Swap Build | Transmission Options | 046

Best Clutch, Flywheel & Gearbox Combos for BMW E30 M52 M50 Swap Build | Transmission Options | 046

In this video, I discuss the best transmission options for a BMW E30 with an M52 or an M50 engine conversion. I also touch on the prop shaft (driveshaft) and differential I intend to use.

Here's what I used in this video:
Blue Loctite: https://ebay.us/2SHbDd
Red Loctite: https://ebay.us/H37Y0G
Torx Socket Set Minus E15: https://ebay.us/IZZPvf

If you're working on a BMW E30 M52 Swap like I am, you've got a selection of good options when it comes to transmissions. By transmission, I don't just mean the gearbox either, because we'll need to be carefully considering our options for a flywheel, a clutch, a prop shaft and a diff too.

Starting with the gearbox. My E30 316i came with a Getrag 240 (g240) gearbox from factory. This is a manual 5-speed transmission found in 318i and 318i.

BMW did everyone a favour when they standardised their gearbox bell housings, making many interchangeable. Due to this, you will find that any of the manual gearboxes that came on E30s as standard will happily bolt up to an M52 or M50 6-pot 24v engine.

This gives us some good options for a gearbox. However, if your E30 was an M20 equipped 325i for example, your car will have come with the Getrag 260 gearbox if a manual. While this box bolts up to an M5X just fine, the gear shift will be on a bad angle due to the lean angle on the M20 being quite different to an M5X. Some people have simply bent the gear lever and gotten away with it, but I'd recommend against that.

The Getrag 240 found on the 4-pot cars don't have this issue. Thus, I was planning to use the g240 that came with my 316i. However, the issue came with this when I was working out which prop shaft I was going to need to make it work.

Unfortunately, as the M52 6-cylinder is a longer engine than the M40 4-cylinder, it sits as far back in the engine bay as possible. This knocks on to the gearbox pushing it back further into the transmission tunnel. Due to this, using the original 316i driveshaft is not an option without shortening it and rebalancing.

In fact, to use the base Getrag 240 with an M52 swap is not very well documented at all, some say you can use a pre-facelift manual 320i prop shaft and it will work. But it's somewhat unclear whether that's the case or not. Additionally finding this specific prop shaft is very difficult to do to even find out.

Luckily for me, a 318is gearbox came up for sale at a good price locally. The E30 318is also uses a Getrag 240 transmission but with some altered gear ratios and a longer output shaft. This longer shaft means you can use a much more common E30 325i driveshaft. It's very well documented that this combination will work, so I decided to purchase the gearbox and a 325i prop shaft and go with that.

As a side note, I'm planning to run with the small case 4.27 differential that came on the car at first. I'm anticipating this to rev far too high at motorway cruising speeds, and I'm a bit concerned that I'll blow up a small case diff, but I think to get the car moving it will be just fine, and I can select my limited slip diff ratio carefully down the line.

With the combination of gearbox, prop and diff decided on. It's time to talk about what will go between. The clutch and flywheel.

No matter which gearbox you select, even if you're using the ZF 5-speed transmission that would have come on a manual E36 328i for example, you'll probably want to use the same clutch and flywheel.

The clutch and flywheel I'm talking about is the single-mass one from an M20 engine. This will bolt directly up to the M52 engine, but does require some machining of the rear face of the flywheel. I believe I had around 7mm machined from mine. Once this is done the flywheel will clear the sump and block with no issue.

My lightened m20 flywheel weighs in at 7.7kg, which is a considerable amount lighter than the E36 dual mass flywheel. The M20 flywheel is a common performance upgrade for E36 enthusiasts due to this.

Fitting the gearbox is pretty straight forward with the inverse torx bolts. The only sticking point is the elusive E15 Torx socket which seems impossible to buy. Other than this, I made a DIY clutch disc alignment tool with a socket and an extension and the combination all bolted up perfectly.

For more helpful how-to guides and restorations: https://www.spannerrash.com/

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