Hey all,

I recently bought a used 1995 mustang GT and as we're goin down highway 77 we figure out that our speedometer is 30 miles per hour ahead. so when the speedometer says 90mph we're really goin 60 mph. I was wonderin if any of you have run into this problem and know what could have caused this problem and how to fix it. thanx!


P.S. although the tac runs accurate. trip meter and odometer is also off,
James

 

 

The car has had gears put in it without the speedo being adjusted.

Use this link and it will tell you what gears are in the car

GEAR CALCULATOR

Having lower gears (numerically higher) will cause the speedometer to read that you are goind faster than you really are, and in turn cause your odometer to accumulate miles more quickly than it actually should.

 

Hey,

Joker, I just wanna say thanx a bunch, you were right. the gears were changed by the previous owner and are set at 4.10, no wonder it felt so fast, haha. Does anyone know what the stock gears were set at for a 95 mustang GT (five speed). I was also wonderin if anyone knew if posi-traction came on that car stock, cause it also turns out that my car has that too, so just wonderin if that came stock or was added.

And does anybody know how to change the speedometer to make it correct?

 

No problem man, glad I could help you.

Posi track came stock on all gt's since at least 88 that I know if, possibly before that.

Stock gears on a 95 I believe were 2.73's, if not then 3.08's.

To correct the speedo on a 95, I believe all you have to do is change the speedo gear that goes in the tranny ( you might want to consult a better source on that though). After 95, you have to buy a speed adjuster thingy (yet another technical term there ) because after 95 they went to some sort of electric setup.

 

Hey thanx for the help. My Grandpa, the mechanic (my other topic about Goodrich tires in the subject has more about him) will check and see if he can do the speedo adjusting himself. i was also wonderin if changing the gears to 4.10 has any affect on horsepower, does that add any?

 

No gears do not add any hp. Gears simply cause the rear end to turn more frequently per engine rpm. They will make your rpms go up quicker, thus putting the car into the power band faster than stock gears.

 

alright, but i am lookin to get something to add horsepower. i always hear nitrous is the biggest "bang for your buck" although, my car couldn't handle it with that low of gears, just wonderin, i know a kit cost around $500 (some cheaper) plus switches are about 75 dollars, but do you konw how much a refill is? cause it all goes at once so.....you'd have to refill it each time u use it. but i don't plan on getting that anyway, just wondering. But what do you think would add the most horsepower without buying a new engine or spending thousands of dollars?

 

No, you dont have to refill it each time you use it. typically a 10lb bottle of nitrous will last you one or two good times to the drag strip. Refills here are right around $3.30 per pound. Which makes it around $35 per refill.

 

I know this is a dead topic, but what about tire sizes?

I had a friend who got pulled over for speeding. She claimed she was going 50.....cop said 60. The cop's explanation was that changing the tire size affected the speedometer.

So the larger tires would make the speedometer slower, her milage slowed(it's electronic), but fuel economy better(since she's driving at a lower RPM).

 

Yes taller tires do effect your final drive. I may not be correct on this but from my understanding, taller tires will make you run less rpms at higher speeds. Basically they have the same effect as putting higher hears (numerically lower) in the car. You will notice in the gear calculator it should ask you for your tire size.

 

so if you put larger tires on would that slow up your acceleration at all?