VDO Speedometer

[celcius232]

I am looking for a VDO speedometer to add to my 72 Six Days and was wondering what model was used adn where can I find one.  Was it the same model as used on some Bultacos?  What is the correct ratio for the Sachs motor and does anyone know a speedo shop that can change ratios? Thanks

Brian S. Goodman

[Doug Wilford]

Brian;
Your Penton should have a front wheel drive speedo ratio 1:42  120mph or 140mph VDO speedo. Cannot say about Bultacos.  ratios can be changed at United Speedometer Service 2431 University Ave.  Riverside, CA 92507

 

[celcius232]

Thanks Doug:  When you refer to the "front wheel" are you referring to the drive ratio as the speedo drives off of the countershaft on the right side of the engine--correct? I do not have anyway to drive it off of the front hub.  Brian

Brian S. Goodman

[Doug Wilford]

Brian,  Sorry but I do not remember the ratio when the speedo was driven off the counter shaft.  That was very inaccurate so we went with a front wheel drive unit in our enduro kits.  I am sure by 1971. In the fog of memories the first drive units may have been from the Husky Sportsman.

 

[Mick Milakovic]

Brian,
I have three VDO's at home.  Two are off Husky's from the late 70's and one from a Penton of the same era.  I can't remember the MPH rating, so I'll check tonight and respond tomorrow here.  Also, I have drives that work off the front wheel and cables, too.  What I'm not sure about is which ones work!  Because of that I'd be pretty negotiable about price.  Let me know if you're interested.

Mick Milakovic
Delphi, IN
765-268-2570

[Mark Annan]

VDO Speedometers and Drive Ratios (Revised 11-14-02)

 

I have been messing around with VDO Enduro speedometers in an effort to fit one to my Penton. I have figured out a few things that may be of interest to others trying to fit a Speedometer-Odometer to their motorcycle.

1. The speedometer "ratio" refers to the number of revolutions of the speedometer / odometer input drive required to register one (1) mile. Or conversely the RPM needed to indicate 60 MPH.

For example:

1.15 = 1150 revolutions make 1 mile, or 1150 RPM is indicated as 60 MPH

1.42 = 1420 rev/mile

1.6 = 1600 rev/mile

2.15 = 2150 rev/mile

(yes, I actually spun and counted to figure this out. Too much time on my hands or just nuts, you make the call)

The ratio is usually marked (stamped) on the housing as W1.15, W1.95, etc.

2. In order to get an accurate speed or mileage reading (assuming that the speedometer / odometer units are accurate, I don't know if they actually are) it is necessary to get a speedometer that coordinates with the drive mechanism built into the motorcycle, or fit an external accessory drive unit. How do you determine this? Let me try to explain how I did it.

3. First I figured out how many revolutions my wheel makes in a mile. I measured the circumference of the tire mounted on its wheel. In this case 3.00x21 = 87 inches. One mile is 5280 feet or 63,360 inches.

63,360 divided by 87 = 728 revolutions per mile

4. Next I determined the drive ratio of the speedometer drive mechanism built into the front wheel hub. I had easy access to the drive gears so I just counted them. The drive gear has 13 teeth and the driven gear has 7 teeth. 13/7 = 1.857. For every revolution of the wheel the drive output will spin 1.87 times.

5. Now just a little math and you will know what ratio of speedometer you need. (revolutions of the wheel per mile) x (drive ratio of speedometer drive) = the revolutions of your speedometer drive per mile, which divided by 1000 gives you the desired speedometer ratio.

Ex.1 728 x 1.857 = 1352 / 1000 = 1.35 (W1.35)

Ex.2 728 x 1.57 = 1143 / 1000 = 1.14 (W1.14)

 

If you don't have easy access, or just don't want to take your front end apart, you can spin the wheel and count the revolutions of the drive output. To make it easier elevate the front wheel. Then put a stripe of tape across the tire. Make an indicator to fit into the cable drive. I used a small (1/8"diameter) piece of wood dowel rod whittled to a square taper with a piece of tape as a flag. Spin the wheel 10 (or better 100) times and count the number of times the flag on your indicator goes around. In my case 100 revolutions of the wheel make 187.5 revolutions of the flag. All of this spinning and counting goes much easier with two people. One to count the spinning wheel, one to count the spinning output.

If you don't have, or can not get, a speedometer/odometer of the correct ratio there is a solution. A speedometer repair facility should be able to make up a gear ratio correction drive box. It is a small gear set (available in many ratios) installed in the drive cable. They are typically used to correct for changes in tire size or rear end gear ratios in cars and trucks. To find a speedometer shop in your area look in the yellow pages under speedometer, drive train, transmission, or look for a shop that services over the road trucks. Often they can also make up and/or repair drive cables. Some of these sources may also be able to change the internal ratio of your speedometer.

6. Another option is to use an external drive unit. These can be hard to come by. You may get lucky and find a complete kit (speedo, cable, and drive) intended for another bike and adapt it to your bike. I currently have a kit for early Yamaha's that I will use if I can't find a 1.35 speedo.

7. Some motorcycles use an external drive mechanism to drive the speedometer. These typically fit between the wheel hub and the fork leg and fit over (or replace) one of the axel spacers. The housing for these is typically allowed to float (it is not anchored to the fork) and the drive cable prevents the whole assembly from turning with the wheel. A tang or pin on either the wheel or in the drive unit slips into a corresponding slot or hole in the other part. This pin or slot arrangement then links the gear in the drive unit to the wheel hub.

8. When the speedometer is driven by the counter shaft (as on Sachs engines), if you change the gearing to something other than stock you will need to compensate for the change. A correction box can handy for this also.


PS.  The above info is also in the files section of the Yahoo group.  

Mark

 

[Paul Danik]

Brian,
The 72 Six-Day speedo was driven off of the front wheel.  The speedo drive unit fits on the right side of the hub and drives off of two small holes in the hub. The speedo and drive unit were not installed on the bikes when shipped, but came as part of an Enduro Kit. A spacer is removed to install the drive unit to the hub. You do not want to run the speedo off of the countershaft sprocket, just as Doug said.  Speedos, cables and drive units are around, but are getting harder to find. I am assuming that you are correct in the year of your machine, if it has a fiberglass gastank, not a metal tank, then you have a 72 or later and the above info is correct.

 

[Mick Milakovic]

Brian, I have a VDO complete with drive cable and external hub.  I do not have the external drive unit for the wheel.  It is a 120 MPH unit with a W rating of 1.42.  It will need restoration by a professional as it looks like it has seen plenty of action.  Let me know if you are interested.

Mick Milakovic
Delphi, IN
765-268-2570