E36 TRANSMISSION & DIFFERENTIAL GUIDE
Updated: Jul 20, 2022
Something you don’t always think about when building your car is the gear ratios and how they play an important role. Depending on what type of transmission you have, and what final drive (differential), it can drastically change the acceleration and top speed of your car even with the same engine. Of course, there are many other factors that can be in play, like unsprung weight (wheels and tires), but for the sake of this blog, we are only going to be talking about E36 manual transmissions. And the end of the article I will give a quick overview of the automatic transmissions, but I assume most people reading this will only want to know the information on the manuals.
The E36 in the USA came with 4 different kinds of manual transmissions:
Getrag S5D 200G (1992-1995 318i)
Getrag S5D 250G (1996-1998 318i, All 323i/325i)
ZF S5D 310Z (USA 1995 M3)
ZF S5D 320Z (328i/1996-1999 M3)
Each one of these transmissions has different gear ratios per gear. Everyone is kind of familiar (even if you don’t know what it means), with rear-end differential gear ratios (3.73, 4.10, 3.25, etc). Each gear of the gearbox has a set of gears to give its own ratio as well. What this means is you can have shorter or longer gears depending on what your driving style is. Most of the time 1st gear is very short (high gear ratio number) and the last gear, sometimes called overdrive is a long gear (short gear ratio number). Here are the gear ratios of each gear in these transmissions.
As you can see, all of the transmissions feature a similar gear ratio, which is in design by the BMW engineers. What is different is the strength of the transmission. Since the Getrag transmissions came on the lower horsepower models (318,323,325) they were not built to hold as much power. The Getrag transmissions are also notorious for weak synchros and a 2nd gear. Does this mean they are bad transmissions? No, we have had Getrag S5D 250 G transmissions hold up to stock S52 power just fine on track, but I would not add more power, or drift with these transmissions. So obviously the coveted transmission is the ZF series of boxes which can be expensive to get, and also come with their own set of problems. These have been known to have detent issues, causing a lack of return to center on the shifter, and a 5th gear lean. Luckily this is an easy fix with the detent repair kit (link below).
Ok, now let's get into differentials. Since the gearing on the transmissions is relatively the same, the rear end is what’s going to make everything feel different depending on your driving style. Here are the differentials that came with each model.
*Many of these BMWs could be specially ordered with custom differentials by the customer, so always verify the metal tag on the differential when looking.
As you can see the final drive ratios are kind of all over the place. There are advantages and disadvantages of using a shorter or longer gear. Most of the automatic cars came with a shorter (bigger number) gear ratio resulting in faster acceleration. If you are doing a lot of highway driving, you may want to opt for a longer gear ratio (smaller number) to get the best top speed and lowest RPM.
All of this can be tricky and may take some trial and error to see what works best on track or the street. Keep in mind that although all of these transmissions can be swapped on any of the engines, the driveshafts and shifter linkages can not. You will need to source the correct driveshaft and shifter linkage when converting to a different transmission.
If you are looking to swap transmissions, all of these share the same bell housing bolt pattern. This means you can install any transmission onto any engine (4 or 6 cyl) without modification. The flywheel and clutch share the same spline and bolt pattern as well. The difference will come in the size of the flywheel.
Although not as popular for obvious reasons, the E36 did come with a few different types of automatic transmissions. Here are the gear ratios:
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