calibrating the old speedometer

[DukeGnarley]

Alright, so I've upgraded gear ratios to a 3.55 and i need to get this speedometer reading properly.

i've been everywhere i can think of. transmission shops, parts stores, and even a couple of ford dealerships. the only thing i could find is a 20 tooth speedometer gear (my old one was an 18) for my C4. I installed it, knowing it wouldn't be right, but would probably be closer. My speedometer seems to read about 20% higher than the actual speed of the car. so, going off of that it would seem that i need a 24 tooth speedometer gear. I'm not sure where to find one, or if it will even fit.

So, does anyone know if a 24 tooth speedometer gear will fit in the stock C4? Where should i try to find one?
Any other suggestions?

 

[Ronstang]

It think the white gear is 24 tooth and should be available from any Ford dealer but ones that handle FRPP would be your best bet.

 

[66HertzClone]

This one is close, http://store.summitracing.com/partdetail.asp?autofilter=1&part=TCI-881004&N=115&autoview=sku I made the same gear change as you did and used this gear, since there are so many teeth they end up being very thin and will wear out as a result. When I removed the gear as I installed the GV overdrive to my car, I notice the teeth were almost paprer thin, no dobt it would have failed in a very short time. I think it was in use for about 1K miles, not a very long life at all.

 

[mudbilly]

i have the same set up and i think that the best i could find was 22 i don't remember the exact count

anyway my speedo is 5 mph fast.......

 

[DukeGnarley]

Is anyone using a ratio adapter (little gear box thing)?

 

[68RCodeConv]

Best you are going to find is a 23 tooth gear. Most Mustang vendors do NOT have them but Ford Motorsports sells them as well as some transmission places. As for the speedometer gear reducer, good luck. They only came on cars with 3.91 or 4.30 rears and are very hard to find and sell for big $$$$ when they show up on ebay. I've heard of aftermarket gear reducers but I have yet to see one that is a bolt-on deal. A 23 tooth should get you close. I have 3.89 rear gears and with a 23 tooth gear I'm only 5% fast.