Are all 3.2 Carrera Speedo's electrically the same?

[bemmett]

Here's a strange issue that I inherited from my 87 Carrera's previous owner.

Both the speedometer and odometer are running at 2x normal, up to about 50-60mph (actual), then it just bounces around randomly between 80-140. Then, at 80mph (actual) things get more stable again.

The previous owner had the the sender replaced, and based on the part number on the old invoice it appears to be the correct. I do not know, however, if it's an OEM or alternate manufacturer. I read some threads that seem to indicate that there may be differences in function depending on who makes the part.

Separately, the speedometer was also sent away and calibrated. Reviewing the work order on the calibration, it seems it was calibrated as an '86 speedo, not an '87. I'm wondering if that's the culprit? Are the electric internals in the '86 speedo different than the '87? It would seem to coincide with the transition from 915 to G50 transmissions.

Has anyone seen anything like this before? I'm taking my car (not just the speedo) up to PA Speedo to see they can get a gauge of what's going on, but any info from this group is great!

Thanks,
~B

[spuggy]

Originally Posted by bemmett

Separately, the speedometer was also sent away and calibrated. Reviewing the work order on the calibration, it seems it was calibrated as an '86 speedo, not an '87. I'm wondering if that's the culprit? Are the electric internals in the '86 speedo different than the '87? It would seem to coincide with the transition from 915 to G50 transmissions.

The 915 and G50 speedo senders both generate identical signals (5V square wave, IIRC); same number of magnets, same type of switch.

I've had multiple speedos in my '77, from the original (until the odo broke again), to a couple of different 3.2 ones (one got flakey) and a 180 MPH one. Apart from the one that was electrically dodgy (and eventually died altogether), they all behaved the same.

In fact, the 915 was swapped out for a G50 and it made no difference to the speedo

HTH.

[CCM911]

I know this is a stupid reply, but did you check your speedo connections in the back next to the gear coupler? Could it just be a chaffed wire or something simple like that?

If you said it was a few miles off, we could chalk it up to tire size, but double??!! That is a really high variance.

I look forward to hearing what PA Speedo have to say.

[bemmett]

Thanks for the info, Spuggy. Good to know.

CCM911, it's not a stupid reply at all, but yes I did check the connections by the gear coupler. Green to green, brown to brown - the wires looked correctly connected, and no obvious chafing anywhere.

It's definitely bizarre that it's running double. I can't make any sense of it. I'm on stock 15's right now, and that was the first thing that the guys at PA Speedo asked about, since the variance is so high. I'm trying to coordinate getting up there so they can take the car for a day, so hopefully some updates soon!