Ok.....Summit racing sent me a 18 tooth gear, they said this will correct my speedo in the new transmission I bought from them. Now at 70 mph my speedometer reads 100 mph.. Any suggestions? Summit seems unable to supply me the correct gear.

 

If I remember correctly, a 25 or 26 tooth gear was in the tranny when you got it and at 60 mph your speedo was reading 50 mph. You should have inserted a 22 or 23 tooth gear (3-4 less than you had) to get the speedo reading close.

Oh, and I guess you've figured out that aftermarket sales places don't have qualified tech/engineering folks to help you out anymore.

 

I installed a 22 tooth gear....and at 50 I was doing 60 actually...so 10mph off. Summit sent me a 18 tooth now when my actual speed is 70 my speedo reads 100mph. I was thinking i needed to go up with the amount of teeth. Seems like I must break down and pull the tailshaft and change the gear on the output shaft as it seems I can't seem to get a gear to lower my reading. It was just eaisier to pull the speedo gear and try to get the correct one than to remove the tailshaft with the tranny in the car. But it seems now that I really don't have a choice.

 

http://www.tciauto.com/Products/Tech...eedo_gears.asp

Don't guess, use a calculator and figure it out for sure.

 

I was thinking I need a 26 tooth.. 4 up from a 22 tooth

 

a smaller number of teeth causes your speedometer cable to spin faster. this confirms your symptoms.

with a 22 tooth gear, it was causing your cable to spin too slow and register 50.

you went too far in dropping the size to an 18 tooth gear. with a 18 tooth gear, your cable is spinning too fast. next step is to try out a 20 tooth gear and this will get you alot closer.

since they are cheap buy a 19, 20 and 21 and only pay shipping once. try each one, it is a easy swap out, and then choose the one that is closest. don't expect to get exact, but close.

i have fought with the same issue for 2 years and I even purchased a speedometer gear reduction attachment looking to get closer to exact. but mine is correct at 35 and about 5 MPH off at 70. leading me to think I have a incompatible drive gear in my tailhousing, or some have told me that my speedo housing itself is not magnetically 'zapped' correctly in order to get me a linear increase in my speedo dial comparable to my linear increase in my speedo cable speed. I have removed and replaced my speedometer 4 times trying new and rebuilt ones. lots of effort and it ain't happening again. Close counts in Horseshoes, and hand grenades, and speedometers!

do all your calculations with tooth count of both speedo drive gear and driven gear, rear end ratio, tire diameter, final drive ratio and determine what driven gear you need to force your cable to spin at 1000 rpm at 60 mph.

the hard part of calculating is finding your drive gear tooth count in your tranny tailshaft. There are different ones depending on tranny and age. this gear drives your replaceable driven gear. they are a much bigger effort to swap out.

if you don't want to determine exactly, then yes, just try a 20 tooth driven gear, this will get you alot closer