hey guys, another question while i am working on this turbo... It is an '83 and has the 85 mph speedo in the cluster... is it possible to switch this to the 120mph style for the cable driven models? I'd much rather have the higher one, but if not oh well.. does anyone know if this works? Thanks.

The speedo is driven by a gear in the tranny at the tailshaft (I think) which in turn drives the cable.

So to read a reasonably accurate speed there has to be a number of things "in balance".

Rear tire size, which determines revolutions per mile of the rear axles.

Differential gear ratio. "X" tire revs means "Y" drive shaft revs.

Tranny gear, which translates driveshaft revs into cable speed.

Speedo mechanism, which translates cable revs into needle position and also has a gear-driven mechanism to turn the odometer. Trip odo drives main odo.

So changing to the much-desired 120 mph speedo is not impossible, but would require more than just changing the speedo unit.

What I can't tell you is whether or not a 120 mpg speedo tranny gear can be installed and then mesh properly with the 85 mph cable. If yes, then the installation of the 120 mph speedo AND tranny drive gear might be all that's needed.

I had a 1983 245GL with that 85 mph speedo, and did not like it. Rumor has it that the Feds, in their infinite wisdom, determined that drivers like to drive with the needle vertical. So setting it up with the desired (by the feds) 55mph at the vertical point was inportant, more so than having the resulting max reading of 85 mph. Of course, it should be much easier to "Peg it out" if your brick will go over 85 mph!

Good Luck,

Bob

:>)

hmm i see, I wasnt sure if the speedo was just geared differently so it would work with the existing cable and gear so they didnt have to work with all new parts... thanks for the info tho!

The driven gear at the transmission (or OD) tailshaft has to be correct for the rear axle ratio, not the speedometer. I think this is the source of a lot of speedometer/odometer inaccuracy. Someone puts a tranny from a car with one ratio into a car with a different ratio and doesn't change out the gear.
The only difference in cables is length, not fit. M45 cable is 1735mm, M46 cable is 2000mm and AT cable is 1875mm. Well, maybe the AT cable hooks up different. I've never had one so I could be wrong. But your existing cable should work just fine.
The thing you have to avoid is using a sedan speedometer in a wagon or vice versa. As long as the rev number on the faceplate is the same you're okay. The wagon speedometer should bear the number r0,960. If your donor unit has the same number, use it.
I put the 130 mph unit from a '79 into my '80 which originally had the 85 mph unit. Both bear the number r0,980, which is correct for the sedan of that era. I have checked the 130 mph unit at various speeds after installing it in the newer car and it is accurate.
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'80 DL 2 door, '89 DL Wagon

>>As long as the rev number on the faceplate is the same you're okay. The wagon speedometer should bear the number r0,960. If your donor unit has the same number, use it.
I put the 130 mph unit from a '79 into my '80 which originally had the 85 mph unit. Both bear the number r0,980, which is correct for the sedan of that era. I have checked the 130 mph unit at various speeds after installing it in the newer car and it is accurate.<<

Exactly...I dropped an "r0,980" 120mph speedo in the '81 turbo to replace the "r0,980" 85mph unit, it works perfectly.

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don '89 740ti, '81 242t,