Speedometer reads 10mph faster than should.

[Delorean3610]

Hey guys, I'm going to be driving to DCS and one of the only concerns I have is that my speedometer reads about 10mph faster than it should read. What should I do? Located in Pittsburgh, PA.

[Cory W]

Are your front tires the original size (195/60R 14)? The speedo runs off the left front wheel, so it you've increased or decreased circumference at all, you'll affect the speedo readout. I'm predicting you have narrower or lower profile tires up front than spec (so the wheel has to turn faster to keep up speed). This will artificially inflate your odometer reading as you drive, though.

Not the end of the world for sake of driving your car, so long as you keep your bearings as to how fast you're actually going. A dash mounted GPS will help keep you on track.

[DavidProehl]

Another thought: Do you have the original 85 mph speedometer gauge or a different one (I think 130 mph is the most common replacement)? If the graphic was updated but the gearing on your angle drive was not that would result in your reported speed being off quite a bit.

[Delorean3610]

I have the correct size tires in the front, and I have the 170 mph speedometer.

[DavidProehl]

I have the 170 mph speedometer.

There it is! That is it. Your gearing is wrong. Either in the binnacle or at the angle drive. Not sure which, but that is what is going on.

[Patrick C]

There it is! That is it. Your gearing is wrong. Either in the binnacle or at the angle drive. Not sure which, but that is what is going on.

Or the speedo needle needs to be removed and reseated, pointing a bit lower on the left.

[Jonathan]

Does it read 10 mph faster at all speeds? Or just in the centre of the gauge, for example? I'd assume it doesn't sit at 10 mph when you're parked, but have you compared it to a known speedometer (GPS as suggested) and documented what you find? You might benefit from a co-pilot doing your data recording though and leaving the driving up to you.

[content22207_2]

1:1 angle drive. OEM ratio is 8:9.

Bill Robertson
#5939

[David T]

1:1 angle drive. OEM ratio is 8:9.

Bill Robertson
#5939

The speedometer head needs to be removed and calibrated. At 60 MPH the cable should be turning 1,000 RPM's. Typically speedometers are calibrated at 60 MPH and checked across the band. The tolerance is + - 5%. If odometer is also reading fast the gearing is wrong. You can check it over a measured mile.

[content22207_2]

Wouldn't it be a lot easier just to put a proper ratio angle drive on the car?

Bill Robertson
#5939

[Elvis]

Where do you get a proper angle drive ?

back in the days when I had time - I recalibrated some speedos.

never touched the angle drive - just the magnet, spring and needle position
inside the speedo.

170mph speedo is too much, 140mph is better to adjust.

[content22207_2]

Where do you get a proper angle drive ?


Houston's units have the proper gear ratio (but there were some problems with their last production run in terms of spindle nut clearance). I believe Josh Bengston made a production run of proper ratio drives. And Grady, but that was a long time ago.

If I'm not mistaken Hervey's were the only 1:1 ratio drives.

Bill Robertson
#5939

[Elvis]

I never heard that anybody made any other angle drives than with stock gear ratio.

if yes - then the mile counter would be wrong !!!

[content22207_2]

Jaguar, MG, etc angle drives are all 1:1 too. They don't normally come with long spindle cables, but if a PO modified one to fit on the wheel it too would read about 10% off.

Bill Robertson
#5939

[DMCMW Dave]

If it's off 10 mph at any speed it's not the angle drive. Move the needle.

[Farrar]

For testing purposes, if you have a smartphone you can download a free GPS speedo app, go for a drive and compare.

[PJ Grady Inc.]

Houston's units have the proper gear ratio (but there were some problems with their last production run in terms of spindle nut clearance). I believe Josh Bengston made a production run of proper ratio drives. And Grady, but that was a long time ago.

If I'm not mistaken Hervey's were the only 1:1 ratio drives.

Bill Robertson
#5939

Actually we are offering rebuilt Smith's angle drives again and are considering remaking more "Hard core"gear sets. I recently checked out the DMCH unit and found it to have a 1:1 ratio (8 teeth on each gear).
Rob

[content22207_2]

That's a shame. I have an older Houston unit (the ones with a zerk fitting) and it definitely is 8:9.

British eBay is full of new manufacture 1:1 angle drives for MG and Jaguar speedometers. Houston may have gotten one of those manufacturers to make some with longer spindle cables (MG and Jaguar angle drives have stubby cables). If they did, unfortunately the gear ratios are wrong.

Bill Robertson
#5939

[Elvis]

Found this thread in the archieves, interesting.

http://dmctalk.org/archive/index.php/t-10687.html