bmwe21.net forums

A lot is written about 5-speed E30 gearboxes in E21's, but the thing I see most is that it cannot be done.


I want to inventorise the pro's and con's for it, what the difficulties are and what parts of a swap are easy.


- The dimensions of a 5-speed E30 are the same of a 5-speed E21, isn't it?
- A 5-speed gearbox is a bit longer than the 4-speed, so the driveshaft has also to be replaced. Also, the flange on the gearbox side is different. Is the differential side of the shaft the same?
- An E21 has a mechanical speedometer drive, an E30 is electrical.
- An E30 is a hell of a lot cheaper then an E21 5-speed.

The thing that comes first in mind, is to change the mechanical speedometer with the electrical from an E30.
- But how is the speedometer build up in an E30?
- How does the instrument panel work?

- Is the signal from the gearbox just something with a connector and a wire? Can just a wire with that signal let the speedometer work?

[Ignorant mode]
Then the only thing that's left, is to build the electrical speedometer in the housing of the mechanical.
[/Ignorant mode]

Speedo signal on e30 comes from the diff.

is there not some way of incorporating an e28 instrument panel into the e21 think i came across that somewhere??

No idea tbh. It might be possible to incorporate e30 speedo into an e21 binnacle but I guess it'd be pretty fiddly to do?

A an e30/e21 hybrid cluster has been made, you also need a speed sensor ashrad had one made for his car using a e30 chopper wheel an sensor.

http://www.bmw-e21.hostingsiteforfree.com/specials.htm

I was thinking about this the other day if you put a e36 small case lsd in a e21 case you could swap it over with the chopper wheel and there is also a good chance that the e36 rear diff cover should swap over, trim 10mm of the diameter of the chopper wheel and you have a speedo sender and an upgraded twin ear diff cover all in one

Jason

Jason_323i wrote:A an e30/e21 hybrid cluster has been made, you also need a speed sensor ashrad had one made for his car using a e30 chopper wheel an sensor.
http://www.bmw-e21.hostingsiteforfree.com/specials.htm
I was thinking about this the other day if you put a e36 small case lsd in a e21 case you could swap it over with the chopper wheel and there is also a good chance that the e36 rear diff cover should swap over, trim 10mm of the diameter of the chopper wheel and you have a speedo sender and an upgraded twin ear diff cover all in one
Jason

Interesting idea; I was thinking of swapping the whole loom from an E30 into The Luger (long-term project E21), as I would dearly love to chuck that POS E21 fuse box for an E30 one.

To conclude. If you:

- Use an E30's diff,
- The E30's gearbox,
- A proper driveshaft,

And you can make an E30 speedometer work in the E21's instrumentpannel, then you are the man to use a 5-speed for less money then using an original E21 gearbox.

no

you can use a 5 speed box with several options to run an electric speedo, the above is only one option

And if I'm not mistaken the E30 diff is not a straight fit, I think you need to modify both the subframe and the driveshafts. If it was all a straight swap people would have done it more often I guess.