'86 Carrera Speedometer Calibration??
 

Hi All,

The other day I used my GPS to check my true speed and to no surprise my speedometer is showing about 4-6 MPH higher. This is in the range of 55-75 MPH.

I did a search on the board and saw some posts regarding an adjustment of the trim pot. in the speedo.

I looked all over the small circut board but sure didn't see one.

One edge of the circut board had a "brownish" look to it and also had that hot or burnt electrical smell to it. The odometer works fine, just the speed reading is too high.

BTW..it is an '86 and the tires are the original size.

Any ideas how I can calibrate my speedo ??

Thanks in advance! J.R.

I heard there is a pot in the speedo that you can adj. I did mine the easy way, I sent it to N. Holleywood Speedo. It is very accurate now.

JR...it's in there..itty bitty screw..may be size of an eyeglass screw..and you will have the flexability of different tire diameter for the same size with different tire mfgs..................Ron

Blown - what did N. Hollywood speedo charge to do that?

Ron - Have you tweeked the calibration screw before?

yeah Matt..works pretty good..didn't use a GPS..had the bride do 30mph and 60mph in cruse control in her Honda...and I confirmed it on the big ride on interstates..when you know the new sedan/tourist/out of state old driver is doing the speed limit at 70mph in cruse control..had to drill a hole in speedo case to get at the itty bitty screw to adjust..then covered hole with slice of electrical tape...I unscrewed plastic wire attaching mount on speedo/moved it to the side, then looked in for screw, then figured where I had to drill hole to acess screw...and the speedo shops get around $100..PIA looking for screw...let me know if you will try it...............................Ron

Thanks Ron! I'll give a try later this week, once I get done with my other projects.

Ron.....I'm still not clear on where you are saying the trim screw is.

On the circut board or the speedo head??

J.R.

JR/Matt...just took a pic..in center of the white is the hole for screw driver. so the driver goes straight into the screw..which I hope makes it easier to find.................Ron

http://forums.pelicanparts.com/uploads/PA080055.JPG

Thanks Ron! SmileWavy

Like Ron said N. Holleywood charged me @ $100. They also put a new lense on.

Hey Dean
 

Dean..N. H. is a class act/no question..and my needle could use some new florescence..but the drift was there to be, some what, wrench independent..and some say that adjusting at 60mph will not lead to acurate 30mph readings..maybe so, but I didn't find that to be the situation with my speedo..anyway, nothing to lose by giving it a shot ......................Ron

Ron....Thanks for the pic, I'll pull mine again and take a closer look.

I cleaned my scratched lens with some plastic cleaner/scratch remover and it worked GREAT! Nice clear lens now.

BTW...Does anyone know if there is an adjustment (+ or- ) for the clock??

JR/Matt..forgot to mention..like a clock, a change from the 12 o'clock to 1 o'clock may be a change of 5-10 mph..and I believe clockwise increases speedo speed...and JR, thanks for trggering some neurons..................Ron

Thanks Ron. I was going to ask that question. I just want mine to be acurate at 70-75 MPH. Right now it says I'm doing 85-90 mph when I'm in 5th gear @ 3000 rpms.

If the speedometer is 10% high, would the odometer be off also and show more than actual miles?

The odometer is not affected by an inaccurate speedo. At least that is true on my 83 SC. My speedo reads 8-10 mph high at 65 but my odometer was right on with the highway markers for 5 miles.

On my 1986, my speedo reads exactly 10% too high at all speeds, according to my GPS. However, the odometer is under 1% high (I forget exactly, maybe it was 2%) per the GPS. I don't understand that one.

Both my speedo and odo where 10% high. After N.H. calibrated the speedo the speed is very close at all speeds but the odo is still high.

NH Speedo advised me that I would have to tell them exactly how much my speedo was off and then they would adjust according to what I told them. This approach does not seem to scientific. Is there a speedo place anywhere in San Diego?

different mfg tires have different diameters/slightly.. some speedo shops have a chassis dyno.. it may be N H or Palo Alto Speedo..
when I adjusted my speedo's itty bitty adjusting screw I followed the bride in her new Accord, set with the cruse on at 30 and 60 mph on a straight level road..