Speedo options for 85.5 944
 

Here's a challenge for the techo's out there. The 85.5 944 that I purchased originally came with the later style speedo, which uses an electronic speed sensor in the tranny, rather than the mechanical (IIRC) speedo fitting on one front wheel, used in earlier models. The PO had done a tranny swap, to add LS. However, the tranny case is from the early model car, without the threaded fitting for the speedo sensor.

So my question is: If I have the late model electronic speedo in the dash, and the speedo sensor wire tied up unused under the rear of the car, is there any alternative sensor solution I can use to pickup speedo info from either the halfshaft or wheel? AFAIK, I would need to remove and disassemble the tranny in order to tap the fitting for an OEM sensor and add other necessary parts; I'm trying to avoid doing that if possible.

Thanks for any insite or suggestions.

Somewhere, I've seen someone build a sensor ring that they bolted to the CV. I *THINK* it went under the bolts where the washers would go and not where the gasket would go on the output flange. Building a bracket for the sensor then just depends on what is in the vincinity that can be bolted/welded too. How many teeth does the factory ring have?

For a generic speed pickup (say for an aftermarket ECU), I've seen folks just sense the CV bolt heads.

If using anything mounted outside the tranny, wheelslip will affect it more than if mounted on the diff carrier (which is an average of the two wheel speeds).

If its just for a club racer, buy a datalogger (you'll want one eventually anyway). It will give you GPS speed. Less work;)

SMD

Racecars don't have speed.

Then my 944S must be a race car. It doesn't have any speed. :-)

:shock: This year! :roll:

Not sure, but I think common aftermarket speedo's can be wired to a magnetic pickup....hall effect sender I believe....that would presumably mount to the diff output shaft. This is the way all of the kart gauges used to function, but that was a solid axle and you had to program the tire diameter you were using. I'd guess most of these gauges would be electronic display with calibration settings. I agree with SMD, however, get a data logger before you spend a few hundred bucks (1/3 of the cost?) on just a speedometer. I lost the speedometer in my early car when I went to a solid spindle for strength, but I've never really missed it on track....but a logger will give me that info. back.

Thanks for the replies thus far. The car is tagged and will see occasional street duty, such as going to an autocross. I'm currently using an older portable GPS I have (is what allowed me to pass MD inspection, too). Eventually I do plan to get a data logger, for all the benefits of track analysis.

I was hoping to find a relatively inexpensive solution to use the stock guage. I'm finding lots of sending units/sensors out there, but not sure if signal is compatible with stock guage. While aftermarket dash speedos allow you to "adjust" the speed display relative to the signal coming from the sensor, I haven't found anything yet where the sensor signal can be tuned before it gets to the speedo display.

Right now, I'm accustomed to using the speedo as a realtime reference while on-track. I know you can use RPM's, but if you're trying different gears at a particular point, then the mental gymnastics detract from the experience. I also know you can judge changes by looking at results further down the track. When I finally get a chance to track the car, maybe I'll find the lack of speedo isn't such a problem after all...

Or I may simply give up on this until such time the tranny has to come out of the car........