speedometer reads too high
08-08-2010, 10:16 PM
#1
Racer
Thread Starter
speedometer reads too high
about a week ago on my 69 the speedometer started reading 10 mph too high with the needle not returning to zero. the car has a 350 with a 700r4 trans. i put the trans in about 8 years ago and it has always read about 3 mph too high. the ten mph high is a new problem.
i put in a new speedometer. took a test drive and had exactly the same problem except the speedometer now returns to zero when stopped. still 10 mph too high.
i couldn't think of a reason why the cable would make the speedometer read too high but i replaced it anyway. still have the problem. still 10 mph too high.
does anyone have a possible reason for this? i am out of ideas.
i put in a new speedometer. took a test drive and had exactly the same problem except the speedometer now returns to zero when stopped. still 10 mph too high.
i couldn't think of a reason why the cable would make the speedometer read too high but i replaced it anyway. still have the problem. still 10 mph too high.
does anyone have a possible reason for this? i am out of ideas.
08-08-2010, 11:11 PM
#2
Team Owner
The speedometer drive gear in the 700r4 tranny was not the correct one for your rear axle and tires.
08-09-2010, 07:54 PM
#3
Racer
Thread Starter
having the incorrect gear would account for the initial 3 mph error, but the 10 mph error just started a couple of weeks ago. the gear has not been changed.
08-09-2010, 08:21 PM
#4
Team Owner
What is your point of reference, trust NOTHING but a GPS....I happen to use a Garmin...all else for what EVER reason...is a LIE....
the speed is what it is, and you will be amazed how all over the map speedos and tachs are.....
BTDT, and some posts of what I thought by the tach must have been 150 mph...turns out it's all rong....
I believe Garmin....
screw the tach....
the speed is what it is, and you will be amazed how all over the map speedos and tachs are.....
BTDT, and some posts of what I thought by the tach must have been 150 mph...turns out it's all rong....
I believe Garmin....
screw the tach....
08-09-2010, 10:22 PM
#5
Racer
Thread Starter
my reference is the radar speed limit signs we have here in town. i go by two of them going to and from work. they both read the same. if the speedo says forty the sign says thirty. before this started there was only the 3 mph difference. i am stumped on this problem. maybe a gps would be a good way to go. seems a little inconvenient though.
08-09-2010, 10:34 PM
#6
Team Owner
In your original post, you noted that there were problems with the speedo cable. That being the case, you have no good reference to what the speedo would have read with the cable problem solved. I suspect that it would have read 10 mph faster. But, that's just a guess...
08-10-2010, 11:34 AM
#8
Team Owner
