My speedo was reading 10 - 15 mph under true speed. So when the speedo read 65 mph I was really going 75+. This was verified with the GPS . At 40 mph, both speedo and GPS were close; the faster I went, the greater the error.


Last week the speedo was sent to North Hollywood Speedometer for calibration. Today they called and said he speedo works fine and requires no adjustment. They suggest that the problem is related to the cable. I had borrowed a second speedo from a member here and tested it while mine was at NHS. The tests with the loaner were good, a small error due to tire size. It read about 4 - 5 mph faster than actual at 65 mph.

I'm thinking the speedometer cable is slipping causing the gauge to under read at speed....????


I was wondering whether any one else has experienced this.

***Update: NHS opened up the speedo and found The jewel support which secures the speedcup to which the pointer attaches was worn

I haven't heard of that happening but I'm sure it's possible, or maybe winding up somehow? If your tire is 10% smaller it seems you would be off by 1 MPH at 10 MPH, 4 MPH at 40MPH AND 8MPH at 80 MPH?

Just got the speedo back from NHS; did a test run @ 60 run down Pacific Coast Hwy. It still under stating speed by 10 mph at 50 - 60. At 10, 20, 30 it's dead on.

The gauge face on my speedo is custom painted tan, so swapping over to the borrowed speedo is gonna require having the faces changed and the milage reset

Jim,

1. Do you have an EGR counter? I've heard they can be an issue. It would be under your passenger foot rest.

2. Is there any squealing or noise coming from the cable? Usually there is noise and the speedo needle is very wobbly if the cable is stretched or bad.

Wonder if it's your angle drive at the trans...

Bypased the EGR years ago.
No noise, speedo needle steady
Cable relatively new...

Since the back up speedo works good, albeit over reads slightly, I'msending both speedos to NHS. Basically they will switch dial faces and reset the milage.

Just heard back from NHS, the problem was The jewel support which secures the speedcup to which the pointer attaches worn

Just heard back from NHS, the problem was The jewel support which secures the speedcup to which the pointer attaches worn