Changing the Speedo
 

I want to buy the reverse glow guages, change the speedo to go up to 140mph (instead of 85mph) and get a 3:73 gear all at the same time. So what would I need to do to make sure the speedo reads correctly?

Get the correct speedo gear for the tranny.

but wouldnt that effect your ODOMETER? if the gear in the speedo hasnt changed, then when you're going 80 with the new speedo it's be like you were going 40 or so ... just guessing.. so technicaly you'd be putting less miles then you expected... ok, that's not so bad I guess.. but it'd still be "wrong"
=as

Any time you change out the rear end gears, you will need to buy a new speedo gear. They color cordnate them so you know which one to get. If your just changing the gauge itself, then you will not have to mess with the speedo gear. Just unplug the speedo cable fromt the back or the old one and plug it in the back of the new one.

Here is a chart to help you determine the correct speedo for your car.

http://ddperformance.com/speedo_gear_chart.htm

I guess I read that differently... I assumed that the new GLOW gauge things he wanted were an OVERLAY to the gauges that are in the dash.... if he replaces the whole mechanism then it's cool.. if he just replaces the overlay for the 85 with a 140 it'll be all messed up

OK, I will try to make this easier to understand. The gauges I want overlay the original ones, so if I just change the gauges when I'm going 85 it will say I'm going 140. So I would need to get a different speedo gear to fix that. OK so I go get that speedo gear and everythings fine. Now I want to put in a 373 rear gear. Now the speedo if off again so I will need totaly different speedo gear. My question is, what will be the final speedo gear I need to skip buying the first one.

You will need to buy a new gauge itself. You can go to a junk yard and pull one off of a stock 5.0. The stock 5.0's came with 140mph gauges and the police packaged stangs came with 160mph ones. If you replace the entire gauge, you will not have to worry about the speedo gear. The gauge itself is calabrated to show the correct speed at the correct location on the face.

When your ready to get your 3.73's installed, then you'll need to get a new speedo gear (it's located in the tranny so you won't have to mess with your gauges again)

I know how fun messing with the gauges are. I installed a custome gauge cluster filled with Autometer gauges in my stang. Hope this helps you out. :D

Well my car came with a 85mph gauge stock, but thanks for the help.

Thats strange, I thought only the 4 banggers came with the 85mph speedometers. :confused: You might want to look into getting one from an "newer" 5.0

Instead of getting a whole new gauge cluster, can't I just by the gear?

You are going to go though hell trying to find a gear (if one will even work) to make the 85mph gauge work with the new face. Then you will have to go though it all over again. Your going to tear your cluster apart anyways, so why not do it the right way and buy the speedometer gauge.