Speedo Drive help

[Euro Auto Thailand]

Dear First Fivers,

I have just installed a 90's 3 litre motronic with a five speed after removing the 3.2 auto unit.
Everything is running well but I have no speedo.
Can anyone suggest a suitable way to either:

A) Use the existing speedometer

B) Change the speedo for a later electronic unit

the gearbox has no speedo cable drive and the differential is standard so no sensor to drive an electronic unit - hense stumped.

I have another project underway putting an M60 manual into a '75 e12 which will need the same fix.

Thanks all.

[Odometergears]

I've been thinking about this for a while because it keeps coming up. If you used the tranny out of a 1982 and new E28, how could you use the newer electronic cluster? Most everything on a 1980-81 will be the same size as E28 stuff. To use the E28 cluster, you would have to use the E28 dash. Then to connect everything, you would have to salvage parts of the wire harness to make all the connections like turn signals, dash lights, speed sensor, etc.

Ok...

I just talked myself out of it. Use a tranny out of a 1981 or older or just insert the speedo gear in the tranny and call it good. Would be a world easier.

Jeff C

[Mike W.]

You can't use the original speedometer as there is no speedometer drive on the newer transmissions. To run an electronic, you would need to either install a later diff, which would require subframe modification, or come up with a way to mount a pulse wheel to send a signal to the speedo. And then install and wire up an electronic speedometer. It's possible, but not easy.

[Blaise]

I am not sure if the cost would be justified, but you may want to check with a speedometer rebuilding company. They would know what your options may be at the speedo end.

http://www.specmo.com/services/calNconv.aspx

[Euro Auto Thailand]

Some good ideas so far, thanks.

Do any of you know if on the later sensed diffs if the trigger wheel is going the same speed as the drve shaft?

I have an old set of clocks that i'll pull apart to see of the electronic clock can be fitted inside, the wiring doesnt seem too scary.

Sombody also PM'd me and mentioned GPS speedo which is a good idea if only to pass speed traps safely.

The option of fitting the drive gears to the box is out as this is an e34 box.

Regards,
Gavin

[Mike W.]

No, the trigger wheel runs at ring gear RPM. #2 in the illustration being the trigger wheel of course.

[Euro Auto Thailand]

Thanks Mike, so that would be the same speed as the propshaft?

[Blaise]

No, same speed as the ring gear.

[Mike W.]

The same speed as the axle halfshafts, not the driveshaft or propshaft. You could theoretically bolt something onto one of the CV joints, but I think they want it to stay clean.