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Remove speedo drive from m45 and transplant into non-speedo drive m47?

B

bugjam1999

Member
Joined
Aug 18, 2015
Hi all,

I?m assuming this is madness, but could the speedo drive assembly be removed from an m45 4-speed and be transplanted into a later m47, one that doesn?t have a speedo drive as it was from a car with the electrical diff pickup for the speedo?

A friend is going to turbo his 1978 245 and so either we make a hybrid speedo with a later speedo hiding in the back of an earlier set of clocks (seen it done, a different friend did it) and transplant a later axle into the car (or come up with a different way of creating the signal).

Or we put an m47 in it that we?ve butchered to accept a speedo drive since the chances of finding an m47 with a speedo drive fitted are pretty low.

Or... any other options? I suppose it wouldn?t be too difficult to put a pickup on the propshaft that ran a stepper motor running the original clocks, but that sounds faff-tastic.

Suggestions please.

Cheers
 
Everything is possible, even converting an M47 II to have speedo output. But that requires a new and completely different tail casting, machining the output flange and who knows what else...

Considering this will go in a turbo car, why not just get a proper iron housing earlier (1979-1986) M46 which is longer lasting and already has the speedo output?
 
petiww said:
Everything is possible, even converting an M47 II to have speedo output. But that requires a new and completely different tail casting, machining the output flange and who knows what else...

Considering this will go in a turbo car, why not just get a proper iron housing earlier (1979-1986) M46 which is longer lasting and already has the speedo output?
Click to expand...

Or swap a later model rear end and cluster in.
 
Ok thanks all, as suspected... madness. This would only be the solution if it was somehow an easy bolt together option.

The m46 wasn?t sold in vast numbers here and isn?t easy to find now, so turbo engine, m90 and some solution for the speedo signal it is... guess we?ll see how much a complete axle will be before attempting a custom approach to the speedo signal.

Cheers :)
 
bugjam1999 said:
Ok thanks all, as suspected... madness. This would only be the solution if it was somehow an easy bolt together option.

The m46 wasn’t sold in vast numbers here and isn’t easy to find now, so turbo engine, m90 and some solution for the speedo signal it is... guess we’ll see how much a complete axle will be before attempting a custom approach to the speedo signal.

Cheers :)
Click to expand...

The M46 back cover is a Brit-ish Laycock De Normanvillan thing and has absolutely nothing to do with an M47.
 
Speedometers are overrated, I use a $98 GPS in my 242, it doesn't work in the tunnel of course and have had it go a little flaky on super cloudy days. I just kind of keep up with traffic, until someone makes me pass them.
 
VB242 said:
Speedometers are overrated
Click to expand...

I agree. I drove the same setup the OP wants, a '78 with a M47, without a speedo for a year and a half. Never got a speeding ticket. You just kinda keep up with traffic, or go what feels right. A speedo is nice though.


You could also swap in ABS struts and use one of those sensors for your speedo feed. You'd have to convert the signal, though to the right signal frequency with some sort of circuit to work with a stock electronic speedo. Possibly just grind some teeth off the tone ring or make a new one? Or... swap to a GT style cluster and use a aftermarket speedo with calibration function.
 
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