My speedometer is reading incorrectly in my 65 mustangand i have not yet tested it next to a car with a good speedometer i know that it is not the wheels because they are the stock 14 inchers on it now any other ideas anyone ????????

 

first of all test next to a good known. or maybve someone has a navigation system that you can use to check your speed.
the following affects the speedo reading:
1. different transmission
2. diferent gear in transmission
3. different axle ratio
4. different wheel size (the full tyre diameter is the key point here, not the wheel size)

but i'd say first check next to good known car to see how much you're actually off

 

ok thanks a lot mayb the diameter is different ill check that out too. Someone else did the resteration so im not to sure about the trany so ill have to look at it. My guess is im about 10 mph off just from guessing.

 

Get yourself a stop watch or some thing with a second hand, jump on the freeway and get up to 65. At 65 you will be doing a mile a minute, compare your watch against your speedometer, any differences ether way and you will know. You can also use mile markers on the highway. Its not an exact science but it will get you close. If its off, Ford still sells trans gears of different teeth count to get your speedo close







68 Mustang
68Torino GT 390

 

60 mph is a mile per minute.

you have to use mile markers

if you go 60 indicated im almost certain it well read 1 mile (unless your speedo its self is off internally as in worn out...good test for that though) the odometer is timed off the speedometer so 60 indicated will still read 1 mile in 1 minute even if your actual speed is 30 mph

Happy hunting

-Gun

 

well my speedometer jumps all over and is realy real laggy like i can start at a stop lighti get up to at least 45 because im getting behind people that i know are doing at least the speed limit and the speedometer might read 40 miles an hour when im a mile from the stoplight and will stay there

 

Could be a bad cable or the speedo its self is worn out.

If the driven gear was off or the tire size was different or the trans had changed it would still work perfectly as in it would run nice and smooth and not jump around. The reading would be off but mechanical functionally would be fine.

If its jumping start with cable then the speedo its self..Could be damaged drive or driven gear as well.

-Gun

 

I agree with gun jam. Jack up your car and check your cable, it runs underneath into your tranny housing. Depending on the transmission there should be a bolt, where the wire goes in, which secure the gear in place. Unscrew it, and carefully check the wire, and gear. Look for any problems with the gear, chips, cracks, over use, also check if it is lubed.

Then you could take off your dash then remove the cluster and check the speedo itself. Check the insert where the cable goes in. Does it look like there could be any problems.

Also when checking the cable look for any sharp bends, or breaks in the cable. Follow it all the way up to your cluster.

 

also when you have the cable out from the trans as Dave mentioned give the gear on the cable a spin by hand it should spin very easily and be very smooth. if it binds during rotation then its probably the cable.

By smooth I mean imagine sticking a round toothpick in a cube of room temp butter and then twisting it in a circle....well okay maybe not quite that smooth but you get the idea

All easy checks and free of cost too!

happy hunting.

-Gun