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Gearbox information for 320/6 and 323i

Here's some information related to the gearboxes and final drive for the 320/6 and 323i.

About the 320/6
The 320/6 came standard with a 4-speed gearbox, the Getrag 242. A 5-speed gearbox was available as an option but is very rare (unless it has been converted to 5-speed afterwards).
The 320/6 has a 3.64:1 ratio on the differential.

About the 323i
The 323i also came standard with a 4-speed gearbox, however most 323i are equipped with a 5-speed overdrive gearbox. A dogleg close-ratio sport gearbox was available as an option.
The 323i has a 3.45:1 ratio on the differential. If fitted with a sport gearbox, the ratio was 3.25:1.

Gearbox ratios
As you can see below, all gearboxes have direct transmission on 4th gear, except for the sport box which has direct transmission on 5th gear.
Getrag240242245245 Sport
1st3.72:13.76:13.68:13.76:1
2nd2.02:12.04:12.00:12.32:1
3rd1.32:11.32:11.33:11.61:1
4th1.00:11.00:11.00:11.22:1
5th0.81:1 -0.81:11.00:1
R4.10:13.45:13.68:14.10:1

Notes about conversions
If you have a 4-speed, you will probably benefit a lot by swapping the gearbox for a 5-speed overdrive model. You will get a more fuel economic car, and when cruising at speed you will have reduced rpms which means less noise and less wear. However, the swap is not completely straightforward, because the 5-speed gearbox is a bit longer and requires a shorter driveshaft. The best to do the conversion is to have a 5-speed gearbox and matched driveshaft before starting work. Here's a picture that compares the two driveshafts.

Notes about E30 M20 gearboxes (By Arne from the late graymarket site)
There is an alternative to those hard to find six cylinder E21 gearboxes: use the five speed from a 528e or E30 325e/i. The ZF transmissions in those cars are easy to find (translate as more affordable), often have lower miles, they will bolt up to our small six engines, and the gear ratios are almost identical to the E21 overdrive box. But there are some issues to deal with, which is the point of this article. Let's look at those issues one at a time.
  • The E30 trannies don't have a speedometer drive on them. To have a working speedo when you're done, you need to use an electric speedo from another model (I've been told the early 528e or 325e units fit well, but need to be glued in place) with a 'chopper wheel' kit to provide the electric signal for it. (Metric Mechanic has supplied the chopper wheel kits for people I've heard from). I am not sure how accurate these setups will be, as I don't know how the later cars with electric speedos compensate for the rear axle ratios. It may be that speedometers from some models are more accurate than others, or maybe the chopper wheels are different.
  • The E30 transmission has a pair of rubber mounts at the rear rather than the single one of the E21. The solution to this one is simple - use the rear transmission crossmember from the E30 that goes with the transmission. You will need to slightly enlarge the mounting holes in the crossmember to bolt it up.
  • Shifter - use the shift plate that came with the E30 transmission. Assuming you are replacing a worn E21 5 speed, use the E21 shift lever as it gives a shorter throw. You can use the E30 lever if you don't have the E21 lever.
  • Driveshaft - The E30 transmission is a tad shorter than the E21 unit. This means the E21 driveshaft is too short. Or is it? There are multiple options for this one.
    • Option one - install your six cylinder E21 5 speed driveshaft, and loosen the 4 bolts that attach the differential to the rear crossmember. Place a jack under the middle of the crossmember to take a tiny bit of sag out of it, then pry the differential forward about 1/2" - 5/8". Then tighten it up.
    • Another choice is to use the slip-yoke driveshaft out of an '84 E30 318i. This driveshaft's center bearing mounts are in a different location though, and a bit of welding on the underside of the car will be required.
    • If you have a six cylinder E21 four speed driveshaft and the flex disc mounts are the same (6 hole vs. 8 hole), you can have a driveshaft shop shorten it by 3.1 inches. This could be done with four cylinder E21 shafts also, but I don't know how much shorter it would need to be.
These tips should get you on the road with your new E30 5 speed. Thanks again to all who sent this information to me, and if anyone has other tips or corrections to offer, feel free to send them to me.
 

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