ok so i have an 86 bird. originally equipped with a t5. had an electric sending unit for speedo and had an 85mph speedo. i swapped in a newer 700r4 with electric speedo. at the same time i swapped in a 140mpg speedo. now 20mph is 140mph! you should watch the odometer turn! how do i fix my problem???

 

I believe there is a speedo box under the passenger side dash that translates the signal from the tranny. I know that signal has changed a bunch of times over the years. Do a search along those lines and you will probably find what you are looking for. Sorry I don't know more.

 

Hey boss, got a number for you to check this guy out! He helped me with

my Richmond 6spd, and now this new Magium T-56 I have now...

His name is Roger, the place is Speedo Service.....# 414-463-6660...

Maybe he can tell you where to look....knows his speed-O's

good luck

 

cool thanks!

 

i spoke with roger. he said to pull off tail housing and cut off wheel and replace with speedo gear and new sending unit. sounds like a pain in the ***.. and not the cheapest. i think im gonna try something different that will cost me like 5 bucks. im gonna grab a 92ish vss buffer box and hook it up in between the speedo and sending unit. then i can put a dip switch in it and change for rear end gears and tires easily. is an 86 speedo a direct swap with something newer like a 92? if so i see no reason why this would not work. i had a 96 pickup someone scrapped the computer in and carbed it and it had no speedo. i grabbed a vss buffer off a 94 put it in and it worked great

 

I'm late to the game here but I had the exact same problem. I put in a new 700r4 that came with the metal 40 tooth relucter wheel on the output shaft. That is for a newer vehicle that has anti-lock braking and puts out abot 10 times as many pulses per revolution. I could have done what you suggested and beat the 40 tooth wheel off and install the plastic gear with matching sending unit but instead i removed the tail housing and ground down 36 of the metal ridges leaving 4 equal spaced ridges. That worked out to be pretty close for my tire size and rear gears. From there you can change the calibration if you have the ability to get it dead on, but mine was only a couple mph's off. You need to do the do the math to figure out drive shaft rpm's in a mile versus the speedometer rpm's in a mile, usually either 1000 or 4000.

 

The newer vss does work btw

 

Wow! Long time between posts but glad you got it all figured out. Does the speedo work properly? Did you have to take the tailshaft out? I think in '91 the buffer box was incorporated into the ECM, or that is what I have read. Give us a little more information on your fix.