Yellow Box or Actual Speedo calibration?

[kenzinger]

Hi All,

Just drove my new (to me) 1983 911SC home 900 miles with no problems! The only thing that I noticed was that the speedo is off by about 12%, which is enough to drive me crazy. Running stock tire sizes, it is not the original speedo (which was replaced from the 85 to 150 mph speedo in 2000 when the original stopped working)

I'm going to do a run with a GPS app and try to confirm the % error but I have a few questions:

1) Do people prefer the yellow box*or do they prefer to send it away to NH for a full calibration?*
2) What would the approximate cost be for NH to just calibrate and not do any other work?*
3) Any other recommendations or any other Speedo shops I should consider?

​​​​​​​Thanks!

[stevie 77 930]

You can actually adjust your speedo without the yellow box , the speedometer has an adjustable potentiometer inside. its mounter to the circuit board.

Here are a couple of threads.....

Calibrate my Speedometer

Need Speedometer Calibration Help

[kenzinger]

Originally Posted by stevie 77 930

You can actually adjust your speedo without the yellow box , the speedometer has an adjustable potentiometer inside. its mounter to the circuit board.

Here are a couple of threads.....

Calibrate my Speedometer

Need Speedometer Calibration Help

Thanks for the prompt reply! I'd looked through those threads and was really hoping to avoid drilling a hole in the side of my speedometer

[stevie 77 930]

You may not need to drill a hole . Remove the plastic cover on the back of the speedometer.
Identify the potentiometer...you can get a small screwdriver angled in to make the adjustment.

Reattach the rear cover, put your speedo back in (no need to push it on completely) and take it for a test drive using your mobile GPS. Redo as needed. Small adjustments only. Unfortunately, i dont remember which direction in the adjustment increases or decreases the speed

[RedCoupe]

I'm so glad that this thread was started. Just a couple of days ago, the odometer on my 86 quit, so I'm about to pull the speedometer out and determine which odometer gear to order from Pelican to get it working again. But, I've been living with a speedometer error of around 10%, so it'll be great if I can also fix that or at least reduce the error while I'm fooling with the unit.

[7783911]

I attempted YellowBox but it was erratic at times (possible rf interferance was their response). Its easy to use but in the end, I sent to PaloAlto and they re-calibrated according the wheel size etc and it is spot on now (<1% error according to GPS). I was very impressed with Helmut and his service (in fact sent other gauges to him for calibration afterwards). Given the cost/age of these gauges, i went the safe route and it was money well spent. He also replaced any worn gears for odometer while he was in there).

[kenzinger]

Originally Posted by 7783911

I attempted YellowBox but it was erratic at times (possible rf interferance was their response). Its easy to use but in the end, I sent to PaloAlto and they re-calibrated according the wheel size etc and it is spot on now (<1% error according to GPS). I was very impressed with Helmut and his service (in fact sent other gauges to him for calibration afterwards). Given the cost/age of these gauges, i went the safe route and it was money well spent. He also replaced any worn gears for odometer while he was in there).

This is exactly the kind of feedback I was looking for. I have a tendency to try and do the right fix even if it is more expensive. If you don't mind sharing, how much was the speedo service from Palo Alto and what was the turn around time?

[7783911]

<400, but i had more repairs but Hartmut was great to deal with

[Lyle O]

FWIW, I have been using the YellowBox for probably 3 or 4 years, with 0 problems. I really like the flexibility, as I have different wheel/tire combinations I use (one with a smaller diameter overall than stock, which gives me a 10% lower gear ratio). If you are going to try different set-ups in the future, you will face a re-do again... Anyhow, enjoy the SC.

[7783911]

the yellow box design changed last year and is frankly not as simple to re-adjust..but thats one persons opinion (actually TB rep said the same thing to me)

[kenzinger]

Originally Posted by 7783911

<400, but i had more repairs but Hartmut was great to deal with

Just got a quote from NH for $245 for just a calibration, which doesn't seem so bad to have it done right.

[kenzinger]

Originally Posted by Lyle O

FWIW, I have been using the YellowBox for probably 3 or 4 years, with 0 problems. I really like the flexibility, as I have different wheel/tire combinations I use (one with a smaller diameter overall than stock, which gives me a 10% lower gear ratio).

This makes perfect sense, but I don't plan on running anything other than stock tire size. I'm a fan of trying to keep things as stock as I can.

If you are going to try different set-ups in the future, you will face a re-do again... Anyhow, enjoy the SC.

Thanks so much! I am having a blast

[76FJ55]

One thing to consider, is it just the speed calibration that is out, or is the odometer effected too? Yellow Box will effect both, so if the ODO is currently reading accurately, calibration of the speedo is probably the correct action. if they are both off, then Yellow Box or similar would be a reasonable choice. I personally installed (10 years ago now) a Speedohealer on one of my motorcycles with good success. I haven't looked in a while, but back them looked at YB and Speedohealer, and was limited to the SH as the YB didn't have the adjustment range I needed. Either should be more than ca[able of your 12% requirement.

[kenzinger]

Originally Posted by 76FJ55

One thing to consider, is it just the speed calibration that is out, or is the odometer effected too? Yellow Box will effect both, so if the ODO is currently reading accurately calibration of the speedo is probably the correct action. if they are both off, then Yellow Box or similar would be a reasonable choice. I personally installed (10 years ago now) a Speedohealer on one of my motorcycles with good success. I haven't looked in a while, but back them looked st YB and Speedohealer, and was limited to the SH as the YB didn't have the adjustment range I needed. EIther should be more than ca[able of your 12% requirement.

This is super helpful to think about. I'm heading out tomorrow with my wife to confirm the error on the speedo and I'll be sure to check odometer readings then as well. North Hollywood said they would calibrate speed by altering the PCB, which seems surprising to me...