Speedometer reading slow

[J Persons]

To compute what speedometer gears you need -

Driven gear tooth count = Drive gear tooth count X Axle ratio X Tire revs per mile, divided by 1000

All T5 and Tremac trans have a replaceable drive gear. But it's a PITA to get to, the tailshaft housing requires removal to get to the gear. The good news is: Aftermarket T5 and Tremacs use a 7 tooth drive and don't normally require replacement. Most '90 through '95 OEM T5's use a 8 tooth gear, and it should be replaced with a 7 tooth drive gear.

There is a chart in most all Ford motorsport catalogs that list all the available drive and driven gears and what rear ratios they apply to.

Don't be tempted to use a 23 tooth driven gear to get the correct reading. These are not Ford spec gears, the pitch is wrong and sooner or later they will fail.

[HI Cobra]

When I got my CR with the T-5Z going it read high. I down sized twice before
I nailed it and in my case it was just a matter of disconnecting the speedo
cable on the side of the trans and swapping the gears, took longer to jack
the car up than to change it.

[Juggernaut]

Originally Posted by J Persons

To compute what speedometer gears you need -

Driven gear tooth count = Drive gear tooth count X Axle ratio X Tire revs per mile, divided by 1000

All T5 and Tremac trans have a replaceable drive gear. But it's a PITA to get to, the tailshaft housing requires removal to get to the gear. The good news is: Aftermarket T5 and Tremacs use a 7 tooth drive and don't normally require replacement. Most '90 through '95 OEM T5's use a 8 tooth gear, and it should be replaced with a 7 tooth drive gear.

There is a chart in most all Ford motorsport catalogs that list all the available drive and driven gears and what rear ratios they apply to.

Don't be tempted to use a 23 tooth driven gear to get the correct reading. These are not Ford spec gears, the pitch is wrong and sooner or later they will fail.

Thanks guys, I ran the numbers, looks I need a 17 tooth gear, right now there's a 16 tooth installed.

Just so there's no confusion, I'm not the original poster for this thread, my speedo is reading too fast, not too slow.