Speedometer Issue

[440gtx1967]

The speedometer on my GTX is slightly off by 3-4 mph compared to a few different speedometer apps I have installed on my phone. But what seems to be the greater issue is that once the speedo hits 70mph it sits there and doesn't seem to go any higher, it'll float and stutter around the 70mph mark...any suggestions

THanks

 

[kiwigtx]

The speedometer on my GTX is slightly off by 3-4 mph compared to a few different speedometer apps I have installed on my phone. But what seems to be the greater issue is that once the speedo hits 70mph it sits there and doesn't seem to go any higher, it'll float and stutter around the 70mph mark...any suggestions

THanks

Possibly dirt or a stray hair caught up in the speedometer mechanism behind the dash fascia.

Or, it could need a little lubrication on the cable.

 

[wagonman]

Or some trans fluid wicking up the cable to the speedo head. They are like a clutch and need to be dry. I lubed the head in one of my cars about 5yrs ago and it is just now starting to get back to normal. A shot of contact cleaner might help if you can get to it. Deoxit come to mind or QC cleaner from Oreilly's. When I was starting out in the auto repair field my boss's dad had an old LaSalle and every year he brought it in for a LOF. That thing must of had 50 Zerck fittings and one on the speedo cable. The old man would not let me use the air grease gun on that but a handgun and just a small squirt. Old Italian guy, Atsa enougha ansonia Georgio. The stories He had OMG.

 

[tak419]

LOL new cars are off by that. No speedometer especially an old one is going to be accurate. 3-4 mph off isn't too bad actually.