Tach/Speedo Cluster Issues...

[sharkstiva]

OK, my donor car is a 1992 Ford Festiva L. This car had the Tach/Speedo cluster. I decided to swap my single speedo cluster. Hooked up, and works properly...

The issue:
My speed is exactly 5 mph faster on the gauge than what I'm actually running. (checked by clocking the car at a constant flat speed of 60 from mile marker to mile marker).


Is this an issue that is common?

My donor festy's speedo cable is exactly 2 inches shorter than my current one; Would this affect the proper speed being shown?

I thought if they were exact year/submodel, the transmissions would have the same gear ratio? Would they differ festy to festy?

I'd appreciate any knowledge.
Thanks!!!

[getnpsi]

Speculation, but maybe the 4 speeds or autos had a different speedo gear setup and the cluster is out of the 88 or 89? I don't see you having a smaller size tire the whole time and never noticing before.

[Pu241]

I would suspect the mile marker testing protocol.
Mile markers are not as accurate as I once thought.
Borrow a GPS for a more accurate speed reading.

The length of the speedo cable has nothing to do with the speedo or odo reading.

I know of no differences in speedo/tach clusters vs speedo clusters.
Believe they all use the same gear and are interchangeable from 4 to 5spd and from tach cluster to non-tach clusters.

[FestYboy]

^correct, everything is interchangeable. your actual speed will be off if you're still running the 12" tires.

[FB71]

correct. in the 70's and 80's especially, manufacturers built in a significant error into the speedo. They consistently show 5%-10% faster than actual speed. This trick was used to bump fuel economy numbers for the feds.

[sharkstiva]

Oh, and I'm running 14" AR Estrellas, with 185/55/r14 Federal rubbers. So versus, stock tires I'm about 2% bigger diameter wise than stock wheels, so wouldnt that have negated a 5mph speed hike?

[FB71]

yup, at least reduced it.

[Bert]

I completed the tach cluster swap into a Festy last week (the reverse of what your did) On a regular car the speedo cable runs through the steering column bracket whereas on the retrofit (or perhaps in your case) the cable has to be run beside that bracket. I had an Aspire speedo cable on hand with a 'fewer revolutions per mile' nylon gear. The cable was 2 inches longer than the Festy setup but alas the gear wheel and length of the transmission drop-down was incompatible.

[sharkstiva]

You guys are absolutely amazing! I appreciate all the help, but unfortunately I think she's(the speedo) right. I passed a Police Speed Radar going 45, and that's what the speedo read. So, i'm assuming I'm doing exactly what my dash says? i hope so. don't wanna get a speeding ticket for thinking it was off a bit.