Hello forum, I bought a 71 convertible a few months ago & having issues with my speedometer. Speedo did work before but was about 5 to 6 mph off. I took it to a shop to add a cruise control & now it doesn't work at all. They blamed it on the gear, which is blue, but even though it is less than a $20 part, they didn't change it. Ridicolous! So I paid $600 for the CC & they charged me $500 to install it but doesn't work.
I was told my rear end gear is 3.31, tires are 235/60/15 & the current gear is blue & has 20 teeth on it. My Vet is at a 3rd shop now & I am dropping off a blue gear I just got.
Is the blue gear supposed to spin freely or is there supposed to be any resistance? I'm not sure replacing the gear will fix the issue or not. Wanted to check & see what you guys recommend from here? Does the gear inside the trans (M22) go bad & need to be changed?
What else can I check?
The first shop also converted carburetor to Holley Sniper 2 EFI with Hyperspark ignition & I bought the 5" display module. It comes with a GPS but it doesn't work either. Says looking for GPS signal or acquiring Sat but won't connect. Holley says all you have to do is plug in the magnetic antenna & that's it. Anyone else have an issue with GPS on this unit?


Thank you to all!
Have a great day!

 

Welcome to the Forum. Yes the plastic gear will and go bad. There is a company that sell replacement gears that allows you to put in the variables on your car so you know the correct gear to purchase based on your tire size, rear end, and transmission. I had the gear replaced in my 73 manual, it stripped out before I made it home. The tranny had to be rebuilt. These cars are old and not every shop should / can work on them. I am confident that other members will chime in with info on the EFI. When systems/ parts are change out on these old cars all types of issues will and do happen. Google is your best friend for obtaining information. I suggest you find a local Corvette Club and ask some of the members for competent shops in your area. Many shops and mechanics are more than willing to take your money and unfortunately are not familiar with our old cars. Good Luck. Also, when you post be sure to give ALL the pertinent information, tranny type, engine, carb and etc.

 

There is no 3.31 gear, closest is 3.36.
The 20 tooth gear is correct for the stock size tire but yours is 1" less in diameter so the 22 tooth might be a better choice.