Speedo Repair/Recalibration

Kelly, I have no answer for you discrepancy at speed (tire diameter difference?), but all Pantera speedos stay at 10 MPH at rest. If you look closly, there is a very small pin sticking out of the speedo face that stops the needle at that location.

The 10 MPH slow at 80 could be because of a different rear tire diameter than the original tires.

Yup....
Mine runs about 20 mph slower since going from 15" wheels to 17" wheels.
Honest officer, my speedo says I was only going 75, not 95....

You can have the speedo recalibrated at a tach and speed shop.

That's because there fast standing still.

[QUOTE]Originally posted by ParaPantera:all Pantera speedos stay at 10 MPH at rest.

quote:

Originally posted by ParaPantera:
Kelly, I have no answer for you discrepancy at speed (tire diameter difference?), but all Pantera speedos stay at 10 MPH at rest. If you look closly, there is a very small pin sticking out of the speedo face that stops the needle at that location.

I'll have to take another look but at least in my mind it was resting above the pin. It registers 70 mph in 5th at 3krpm. I have the stock 4.22 ring and pinion but have 345/30/19 rears. If you do the math that’s a 27.14” diameter wheel. They measure accordingly, slightly under with weight on wheel but I'd say rolling diameter is pretty close. A stock wheel was supposedly 26.5”. If I do the math through the gears I get I should be 81 mph at 3krpm with this tire. The speed calculator at Mike Dailey’s site predicts the same. The larger tire only accounts for 2 mph increase as 79 mph is predicted for a 26.5” tall tire.

I’d time it over distance but the snow is flying.

I’ve had the car back on the road for a couple months now and just noticed it. Don't pay much attention to the speedo. Eyes are on the tach and the country road ahead. If it’s really reading 10 mph slow at 70 my top end smile just got wider.

I suppose my tach could be off but I have a 6200 rpm chip in my rev limiter and have verified (repeatedly) that it’s right on the money as I’m bouncing off the rev limiter.

So good people of the PI Forum, my questions are:

What was stock tire diameter?
What’s your rpm at 70 mph?
Are the speedometers easily rebuildable or able to be calibrated?
Anyone done it or have a reference procedure?
Figure I’ll brighten up the instrument lights while I’m in there this winter. I found some good posts on that.

Kelly

I wish I could help but my speedo reads in KM/H so anything I do would be of no help at all. In fact I think of all of my gauges in the Pantera as approximations of values. Kind of friendly suggestions but in no way accurate indicators of actual conditions. All except for my clock which has been dead nuts accurate from the day I got it. It is the single most amazing piece of equipment on my car. If my whole car was up to the standards of my clock, everyone on this forum would be jealous of me.

Kelly,
Most good speedometer shops can check and recalibrate your speedo. I had mine done at North Hollywood Speedometer 17 years ago (they also rebuilt my tach to work with an electronic igition) and I have never had a problem. Just find someone like MHS, you can trust.
www.nhspeedometer.com

When I'm going 60 mph, my speedo shows 70 mph. I am going to take it to speedo shop in Phoenix to get it correctly calibrated. I am sure the tires & wheels are part of the issue.

I agree with Detom. My clock is Veglia and this incredible piece of Italian art never lost a second. My new style tach is awesome too. The 6200 limiter is right on. But my speedo is another story. It has been calibrated and modified - I even have interchageable gears in a reducer to to enable finite adjustments. And it's still so far off I have no idea how fast I'm going. I once did the calculation to find where 60 mph was in rpm in each gear - but my old mind can never remember. So I just grit my teeth and hope for the best whenever I see Smokey on the road.

Kelly,
My car does about 80 mph at 3000 rpm. The speedo indicates 90 mph. I have BFG 285/40-18's in back. I believe the tire is 27 or 27.1 inches in diameter. I have a 4.22 ring and pinon and the .642 taller than stock fifth gear.
I don't know how accurate my stock tach is? Your numbers of 81 mph at 3000 rpm seem high to me based on what I have witnessed with my car. My tach could be reading low but the 80 mph is gps verified. I understand that a speedo shop can install an in line gizmo that is adjustable so that you should be able to make your speedo accurate regardless of tire size.
Art

Interesting Art...
My tach reads 3000 and I'm doing 79 with the same ring & pinion but running 345x35x17's on the raer.
Speedo reads 60 mph.

Coz,
I don't think we are way off in what we are seeing. I think our tires could easily be within a half inch of each other in diameter. With just a little tach error in either or both of our gauges, I could be doing 2950 at 80mph and you could be doing 3050 at 80 mph. What is most interesting to me is that you see 60 and I see 90 mph when we are going the same speed. Another little tidbit, my odometer seems to be very accurate while my speedo is not, go figure.
Art

quote:

Originally posted by Coz:
Interesting Art...
My tach reads 3000 and I'm doing 79 with the same ring & pinion but running 345x35x17's on the raer.
Speedo reads 60 mph.

Coz.
Are you sure you have 345/35/17's? I could never find a 17" tire any larger than the 335/35/17.
Forest