'Feel Good' Speedo

Interesting. You must have the wrong speedo drive gear on your ZF. Another way to test the speedo is using the gear calculator on this page http://www.panteraplace.com/page32.htm . Just enter the tire diameter and differential ratio (default is 4.22) and the RPM you want to check. My 71 car speedo is very close to the actual speed.

Mike

I calculate the 275/55 at 26.91" (of course the reality may be a little different) so it's not the tyres.

I agree it's probably the drive gear. It could be the speedo. I don't think I have a right-angle gear behind the speedo, so it isn't that.

The first owner may have had a replacement, incorrect, drive gear fitted. Or maybe it's always been wrong

I don't want to pull the drive gear out of the ZF - I think I read that bad things can happen if you try.

20% is not too hard to calculate in your head, or a 'post it' note next to the speedo might be a good temporary fix!

Mine is a 72 and the speedo on it is off also. On the interstate I run it up to 90 and I just keep up with most traffic. I figure I am actually doing around 80. I wonder if the odometer is off then too?

Glad to see this thread is about speedometer accuracy... I was scared to click on a link named 'Feel Good' Speedo

btw, most gps systems will give speed accurate to around 0.25 mph.

Carbo,
Um yes I see what you mean . i hadn't thought of that.
I guess I should have put 'speedometer' to avoid confusion.

Rapier,

Pulling the speedo cable angle drive from the gearbox is a cinch, just undo the large nut that holds it on. The 'don't want to do' you refer to is the 10mm bolt below the angle drive, which you should not undo as it allows the internal speedo drive shaft to drop inside the ZF.

I've just been through this, #9178 was reading 60mph when I was traveliing 75! Sure Officer but I was only doing 60 is not a valid excuse apparently .

There are two types of ZF angle drives Veglia-Borletti and VDO each with different ratios 1:1 and 1.1:1 (4 choices). Also the speedo internal ratios depend on whether it as Euro (kph) speedo or US mph speedo. The speedo is marked on the back either '1610 giro' revs per mile or '1210 giro' revolutions per mile. The 1210 is for the Euro speedo and goes with the 1.1:1 angle drive. You have to find the right combination. My car was a Euro import and converted from km/h to a mph face, I changed the ZF angle drive and it now reads accurate to within 4 mph at 80 mph.

Good luck
Julian

I found mine to be 10% out. 100mph on the clock reads 90 on the sat nav. This has been the case with every car I have put the sat nav in so far.
My car has 335,35,17.

Johnny

just for Andy

ewww. didn't need to see that.

George, send eye-bleach. quickly.

George,

You are a single guy right? This is the second time in a week you have posted a dubious half naked male photo. You need to get back to the hot tub girls pronto, before I start to worry.....LOL

Julian

sorry Julian

quote:

sorry Julian

Now that's a speedo that is right on the mark!

My speedo was way fast even with 27" tires. Yet the odometer appeared to be accurate? Go figure. My new electronic AutoMeter speedo is right on the button! I love it. Same for the new AutoMeter tach. The new speedo does have one quirk that I will have to look into. The trip odometer sometimes loses ground after shutting the engine off and re-starting.

quote:

Originally posted by Joules5:
...Now that's a speedo that is right on the mark...

This model caught my eye, she has amazingly pretty "smiling eyes".

Okay, okay, any lady in a swimsuit, with a swimsuit worthy figure, catches my eye.

By the way......

When a speedometer is off by the same amount at any speed, that is called a zero error.

When a speedometer is off by the same percentage at any speed, that is an error in span, or multiplication.

It is quite common for the error of a speedometer to be a combination of both zero and span.

It is also common for auto manufacturers to err on the side of the law, in other words, any error in reading should be on the high side.

Because of the way the needle of the speedometer is coupled to the drive mechanism, a mechanical speedometer is inherently worthless at low speeds. That is why the minimum reading is usually 10, 15, even 20 mph.

To check a speedo, it needs to be compared to a known reliable standard (your GPS in this case) at 3 different speeds, mid-scale, and either side of mid-scale. Since mid-scale on the Pantera speedometer is 100 mph, it would need to be checked at say 50 mph, 100 mph & 150 mph.

Any error that can't be explained by zero and span, a non-linear error, indicates a problem with the instrument beyond simply calibration error.

Most problems with speedometers in older cars can be remedied by cleaning & re-greasing the speedo cable. Don't use a thick grease, like that for wheel bearings, use a synthetic general purpose grease.

cowboy from hell
Instrument Society of America
certified control systems technician, level III

Thanks Joules for the advice and thanks George for the picture of the girl with the pretty eyes.

I may tackle this one. More likely I will leave some notes for the next owner.

Sadly I just don't have money to do what I want to do with the Pantera.

It will be for sale next month. I will use the money to get my other projects finished (my '46 Hillman Minx and fuel injected '68 Sunbeam).

quote:

Sadly I just don't have money to do what I want to do with the Pantera.

It will be for sale next month. I will use the money to get my other projects finished (my '46 Hillman Minx and fuel injected '68 Sunbeam).

Rapier, What? We've jumped from fixing the speedo to selling the car..... I I must have misread right, you are selling the Hillman and Sunbeam to do the Pantera...CORRECT! It's a rare beast, even more so in the UK.

Julian

What a bunch of whiney crybabies. Complaining cause your spedometer is a few miles off. Heck mine only reads Kilometers and I always haveto just guess how fast I am going. Be a real man and drive blind folded so you don't know how fast you are going and then see if you complain about ten miles an hour after that. :P

Detom,
I did that in my last car (Supercharged Vehicross) and it had to go the grave yard!
These days I'm trying to keep at least one eye open!
Tim

Use the force Tim, use the force.

she's dorky but I'd bump uglies wither'. Now I'm wondering about my speedo(meter). This post bringing back bad memories of swim team puberty and a speedo that mom got on sale that I would "grow into". I never quite lived down the "pitch a tent!" I heard for years after. Been driving loud brash muscle cars ever since.