How to use a BMW Getrag gearbox with a T5 motor.

I thought I'd share with you what I have done to get a BMW Getrag gearbox to work with my 850 T5 engine. With the gearbox options for creating RWD Volvo T5s becoming harder to come by and more expensive, this is an option for what could cost less than £500 and easily replaceable if goes bang!

My application is within a Mazda, however the process is pretty universal so can be used by all.

Parts required;
-Gearbox adaptor, mine is from the Swedish company KL racing, you can choose a variety of adaptors, I have the adaptor for the Getrag boxes from a 6 cyl 5series (e34). It costs £215 +postage from Sweden.

https://shop.klracing.se/sv/artiklar...an-getrag.html

-You will need a 240mm clutch plate found in most manual e30-e36 3 series using the 10 spline shaft. (See clutch note below). These cost around £120 for a kit or if you can find just the clutch plate you can save a few £)

- throwout bearing (you can get a longer bearing that makes up for the extra 10mm from the gearbox adaptor, or modify the clutch release arm by inserting 10mm spacers). £10

-Slave cylinder to suit your gearbox. £20

-custom made spigot bearing adaptor (see info below)

-BMw guibo to suit your gearbox (a getrag box from a 5 series uses the larger one from the m5) £25

-A custom prop shaft (you can make/adapt your own - however it will need balancing). £X

-You will need to modify the shifting mechanism, but this is fairly straightforward.

--The gearbox--

You can use a variety of the Getrag gearboxes, but ensure it fits your adaptor plate first. I went for the cheaper Getrag 260 gearbox, which is good for the power I want to achieve and can be found for about £50. If you're pushing 350ft/lb torque go for a G265/5, expensive but strong, expect to pay £600+

Get the gearbox from the e34 5 series as the bell housing is slightly shorter. If you use the e30 getrag box the flywheel needs to be spaced into the gearbox so the splines reach the clutch - however in sure this way will bring up even more challenges so get the shorter bell housing!

The bell housing needs to be modified.

-Firstly at the back of the engine where the water outlet sits above the crank sensor, a ~50mm deep x 100mm wide square needs to be removed from the bell housing.

-Secondly, a further ~50mm deep x 100mm wide section needs to be removed from where the Volvo starter motor sits. You can bolt the adaptor plate up to the bell housing to ensure you are removing the right amount in the right place.

- Finally, the clearance of the flywheels outer teeth is very very fine to the inside of the bell housing. To overcome this, it's safe to chamfer the lower inside edge of the bell housing slightly.

http://i682.photobucket.com/albums/v...829_095842.jpg

-- The clutch --

You can use the 850 T5 pressure plate (up to a point where power will be too much) but the clutch plate itself needs to be a clutch that has no damping springs (or very little). The issue that I found was that the damped clutch I was trying to use was quite wide and was not allowing the clutch pressure plate to be fully disengaged. This was obvious when I couldn't engage gears easily and on examination it was clear the springs were fouling on the pressure plate release fingers. (See the pic below).

You can get undamped clutches, just ensure that the plate is 240mm and has the correct spline for your gearbox (mines a 10 spline shaft which is the most common). Or I have seen that the dual mass flywheel has 4 small springs in and remains relitivley flat, this may be an option if you find the clutch too snatchy.

http://i682.photobucket.com/albums/v...583099030.jpeg

- a standard clutch release bearing can be used but you need to space it 10mm towards the clutch, I achieved this by welding two 10mm spacers on the clutch release arm which works great. Another option is to obtain a clutch release bearing that is longer, there is one available from Sachs, but I am unable to find the part number :-( .

-- Spigot bearing adaptor --

Funnily enough, no one has mentioned this one yet on any forum that I have read. The BMw gearbox input shaft doesn't reach the Volvo spigot bearing and if it did it isn't the correct bore anyway. The concern would be not having the shaft sit in the bearing would cause excess lateral forces on the gearbox input shaft bearing and cause premature wear. To over come this, I had a friend with a lathe make me up a very simple adaptor, which needed to be 25mm long, have an outside diameter of 15mm and an inside diameter of 12mm.
The picture below is my first attempt which the length was too long, but it gives a good idea of what it needs.

http://i682.photobucket.com/albums/v...1_145053_1.jpg

http://i682.photobucket.com/albums/v...02-WA0004.jpeg

--Master cylinder--

Luckily my Mazda has a hydraulic clutch anyway, however I still went ahead and modified the setup anyway, I bought a Wilwood high volume master cylinder (cheap for what it is!) You can get them from demon tweaks for £55, the slave uses a 3/4" piston. I have a brake/clutch hose manufacturer nearby which helps, thus cost £24.

http://i682.photobucket.com/albums/v...30-WA0002.jpeg

The rest is going to be custom to your application, such as prop shafts (luckily BMW do propshafts in halves, so get tge front half and have someone make you one up or give it a go yourself and get it balanced. ) Gearbox mounts (easy to make), gear linkages (modify the standard one) etc.

I hope this helps someone as theres little info available on it, I've had a lot of hurdles to overcome along the way!!

Excellent write-up, this should be pinned somewhere.

Makes me want an old estate!!!