140 MPH Speedo Conversion

[focodave]

Does anyone know if a 140 MPH speedo is a direct bolt-in replacement for the 85 MPH speedo in a 1980?
Do I need a different speedo gear down at the tranny to make the 140 MPH read properly?

[azruss]

I replaced mine with a 140 mph speedo and it required a different fitting on the cable. The 1980 had a plastic clip type, where the early speedo had a threaded fitting. Its my understanding that transmission gearing is the same over the models and it is rear end ratios that change. If this is the case, then the speedo drive would need to match the rear end ratio. Something makes me think way, way, way back in the day, i tried to change speedo drives as i had one that was leaking and mating gear varied by one tooth making me stick with the original leaking one. This is all speculation. Curious to see what others say.

[bradartigue]

There is no difference in the input - e.g. you can use either gauge with any transmission as they all spin the wire to the gauge at the same rate. As noted the fitting on the gauges is different, but I can tell you I've used the clip-on-cable on the threaded bases without them slipping off many times.

[vandor]

All the shallow faced speedos, ie. late 1977 and newer, use the clip-on cable.
So for a direct bolt-in, you need a Speedo from a late 1977 to 1979 Spider. Only the 1979 will have km/h markings, the earlier ones are MPH only, which I like for the cleaner look.

The pre-1977 speedos have a deeper sitting face, so it would not match your tach, and the screw-on cables are shorter, so it would be a pain to install.

[focodave]

Thanks, guys, for your quick replies.
Very helpful -- as always !!

[Turbofiat124]

This is probably old news but I installed a 140 mph speedometer from a 1970 model in my 1980 model. And also the matching 1970 tachometer (the needle on the original one was bouncing around like mad).

Here is how I made mine work. Sounds dodgy but it has worked fine for years.

Get an earlier model cable and lay both cables together, remove the cables and cut the sleeves in the same location. File any burrs off so that the ends are flush and straight.

Take about a 3" piece of 5/16" copper tubing and slide it over the sleeves then butt each end together.

Using one of those "cheap" cable wire strippers like the one below, use the 10/12 AWG crimping portion and crimp both ends. Then wrap it up with black electrical tape.



On a side note. Something is really screwed up on my car. I must have the wrong speedometer gear drive or something. I'm also running 14" 60 series 185 tires and a 4.10:1 axle also from the same 1970 Spider.

Speedometer / Actual

80 / 55
90 / 65
100 / 70

I checked the speeds with my GPS. I'm not sure what the deal is.

I thought about just making a new faceplate with the correct numbers rather than buying a speedometer correction drive.

The odd thing was even before I installed this axle (just because the pinion on the original one broke) the speedometer was just as inaccurate. At 60 mph, the speedometer was pegged out!