Puch Speedometer Rebuild

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Puch Speedometer Rebuild

Postby RebelRider.Mike » Sun Nov 03, 2013 5:33 am

I have a couple of Speedometers for Puch mopeds that I'm refurbishing.
A 40mph one by VDO, and a brandless 30mph one.
I'm using parts from a defunct Puch brand 30mph gauge to repair the two.

The pictures I have come from all three, but I've arranged them so they look to be from a single process.
I hope that's not too confusing.
Really, the only parts with significant differences are the gauge face, and the flat spring.
You can't even tell the difference between the flat springs.
They're just calibrated different for the different capacity gauges.

Well, here is a familiar face to all Puch riders.
This one has been stored indoors almost all its life, so its in pretty good condition.

I've already removed the light fixture (it just pulls strait out) and the cable from the back.
The center nut holds a bracket in place.

The bracket holds the gauge body inside the housing.

With the bracket removed, the gauge body can be pushed out the top of the housing.
The inside metal ring will be left behind.
The outside ring may, or may not stick to the gauge body instead of the housing.

In my case, the outer metal ring stuck to the gauge body.
So I was left with the outer plastic shell, a rubber vibration damper, an inner plastic... round thing, and the inside metal ring.

The speedometer gauge body has a rubber gasket between the outer metal ring and the gauge cover.

With all three gauges, I found the rubber to be in good shape.
Even the water damaged parts gauge.
Carefully removing it has allowed me to reuse them later.

The cover is crimped onto the gauge cup, so the only way I know of to get it off is to pry it.

I don't know if there is a better tool out there for this, but I used a small screwdriver.

I pushed back just a little at a time, like a can opener.
A couple of trips around had it loose enough to remove.

The cover comes apart as the the outside part with a rubber gasket inside, the glass, and an inside bezel.

Here is the uncovered gauge face.
Take note of the odometer reading so it can be matched later.

The gauge needle is held in place by friction. It just sits on the end of a shaft.
Its very delicate though (both the needle and the shaft tip) so care must be taken while removing.
The metal one on the 40mph gauge came of easily by pulling strait up with my fingers.
The two 30mph gauges have plastic needles and were much tougher.
I used an old pair of computer chip tweezers.

With the needle removed, the face comes right off.

Now the guts need to be removed from the cup.

On the back of the cup, there are two screws.
Removing them will allow the innards to come out.

The top of the assembly has the flat spring and a shaft attached to a metal cup.
It also has the odometer number wheels and movement sprockets.
The bottom of the assembly has gears to drive the odometer wheels, and a magnet that spins inside the metal cup.
So, the speedometer cable is physically attached to the odometer, but only magnetically attached to the speedometer.
Neat, eh?

Anyway, removing the nylon bushing from the end of the odometer number wheel shaft gives access to the place where the shaft and the white number wheel are connected.
This is a good place to put some kind of oil.
The black number wheels spin freely on the shaft, but the white one is "driven" by the shaft and is a tight fit.

Removing the two screws on top of the assembly allows it to separate into the top and bottom halves.
It also allows the removal of the red plastic worm screw shaft (or whatever its called).

I haven't figured out yet how to get the bottom half of the assembly apart.
Fortunately, I've not had any problems with one yet.
The sprocket end of the odometer number wheel shaft can now be carefully removed.
This will be difficult until its completely pulled out of the white number wheel.
The black number wheels will slide right off, so some care is needed there too.

In the case of the 40mph gauge, the left-most nylon sprocket (controlling the 10,000's place wheel) was missing a tooth.

These movement control sprockets have narrow teeth, which hold the number wheels in place most of the time.
They also have wide teeth, which move each wheel at the appropriate time.
So every time a preceding wheel goes a full rotation, a small "U" indent in the side of the wheel grabs hold of the next sprocket in line and uses it to move the next wheel in line 1 digit forward.
Now, this took me a while to wrap my brain around.
I also assembled it wrong a couple times before I finally figured it out.

Here is an example of the "U" indent I mentioned earlier.
Though in this case, the "U" is broken and has been repaired with a small metal pin.

To remove the sprocket shaft, I had to file down one end. (Both ends are crimped.)
I got a replacement sprocket from the defunct speedometer, and cleaned them all with Pine Sol and water. A set of tweezers and a small brush really help.
Careful though; these little sprockets like to snap out of the tweezers and go flying across the room!

I found that a fuel funnel with a strainer at the bottom helps to rinse small parts without loosing them down the drain.

So here they are all cleaned up and looking good as new.

Now the black number wheels can be reinstalled, along with the odometer's wheel shaft.
The order of the wheels and number placement is not important.
So long as you get the numbers in the right direction.
The white number wheel goes on last and should be quite snug.
Also, the nylon bushing at the very end of the shaft gets reinstalled under the retaining spring.

Next the movement control sprockets go on along with their shaft.
As each one gets placed, it will "lock" the wheel to its left in whatever position that wheel is in.
Make sure the number that will be facing up through the gauge face is the same as it was before it all got taken apart!

With all that done, the red plastic screw shaft and the two halves of the assembly can be reassembled, and placed back in the gauge cup.

At some point, the steel rings can be cleaned and polished.
Here I've got one of them ready.

The bulb and light fixture can also be installed.
This speedometer will be used on an upgraded 12V system.
So I've replaced the old 6V incandescent for a 12V green LED.
If you do this, remember, LEDs only let power go in 1 direction.

Here the face, needle, and cover is reassembled and put back on the gauge.
The cover is not crimped yet though.
I used a small Phillips screwdriver to turn the speedometer shaft clockwise, to verify that the needle and odometer work.

Its also hooked up to a 12V source of power.
This way I can make sure the new bulb is actually lighting up the gauge face.
One of the three bezels sits so low on the gauge face that it blocks the light.

Everything is working, so I've crimped the cover down.
The rubber gasket, metal rings and housing parts are all put back on.
Everything is held in place with the nut and bracket in the back.

And now I have a shiny "new" 40mph speedometer for my Puch!
(I'll finish the 30mph one later...)

1979 Puch Free Spirit
1987 Honda Rebel
2014 Ural M70
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re: Puch Speedometer Rebuild

Postby John » Sun Nov 03, 2013 8:10 am

Great how too write up with pics, thanks. Now why didn't you just zero the gauge for the restoration.

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re: Puch Speedometer Rebuild

Postby mopedlar » Sun Nov 03, 2013 12:59 pm

I've restored my share of Puch speedos over the years and most of the time, it was 30+ year old hardened grease that kept the gears from turning. After cleaning off all the old hard grease with WD-40 and a very fine pick, I used White Lithium Grease on the gears to keep them rolling smoothly. WD-40 is good for freeing them up, but not as a long term lubricant.
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