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          So you've got some "dinkering around time" (as Jeff puts it) now that the days are shorter, eh? Well, find a warm spot and pull out a cookie sheet, some towels, and get a grip ... a steady hand that is! Jeff is going to walk you through a rebuild on the speedometer for the 1941-1947 1st series Chevy / GMC truck. He's got plenty of pictures and lots of details. And if you're uncertain, just drop him a note.

          Great job on the Tech Tip. On behalf of many ... thanks!

Speedometer rebuild for GM Art Deco Truck
By Jeff Erickson
Bolter # 10036
1947 GMC COE 1.5-Ton
1953 Chevrolet 3100
  October 20, 2008

You can do this:

<<< click on the images for a larger view >>>


Are you ready?

So you've got your gauge cluster out of the truck. (If not, go get it!)

One of the best pieces of advice is to get a large flat oven pan with the 1/2" tall sides to use as your work area. This way everything can be laid out and you don't have to worry about the little pieces falling off the table. So long as you have a little patience and a steady hand, it isn't to difficult.

Careful Disassembly

Flip the cluster over and you'll notice three screws which hold the speedometer casing in place. Pull those three screws and remove the speedometer assembly from the gauge cluster. There are two screws beside the speedometer cable connection that need to be removed so you can access the speedometer itself. Remove those and the two rubber washers, and gently pop the speedometer from its case. Give it a good look over and familiarize yourself with it.


Grigg Mullen suggested using a pair of flat head screw drivers for removing the needles off the shaft:

"I personally broke a needle shaft when attempting my very first speedometer repair. I successfully repaired my replacement. Hope others can learn from my mistake.

"I also learned a few tricks later on while in the machine shop at NN shipbuilding. I worked on a bunch of dial indicators and such, some of them pretty small and tricky. We had needle pullers just for that. When those would not fit or work, a pair of matched screwdrivers and some luck worked pretty good to get needles off.

~ Grigg

With a pair of small flat head screw drivers, very gently pop the needle off the shaft it rides on. Set it aside. Now remove the two tiny screws to either side of it to remove the face plate of the speedometer. There is a small metal piece that sits over the odometer and is held in with two screws. Remove these and set them aside. Notice on one side of the odometer, there is a gear; and the other side has a small brass shim stack. With a pair of pliers, very gently remove the shims. Now the odometer can be removed by sliding that side in, releasing the geared end which can be lifted up and slipped out.

This next part is of utter importance. DO NOT touch, blow on, sneeze, whatever, on the small spring directly below where the speedometer needle sits. There are two screws which hold this piece on. Remove them and use extreme caution to gently lift that piece out, while not letting the small round piece underneath the spring fall out of the bottom. I put a small piece of tape across the bottom to keep it all in place. Set this piece aside in a safe place. The spring has a small cup underneath it that is reactionary to a small magnetic piece that spins as the speedometer cable turns. The very small amount of magnetic tension causes the spring to turn. The faster the magnet spins, the more the spring coils and the speedometer needle reads higher and higher. Stop and the magnet stops and the spring coils back down, leaving the needle at its lowest point on the gauge.

Back to what's left of the assembly. You can now remove the small worm gear shaft that sits next to the magnetic base. Set those pieces aside.

On to the odometer

There is a small brass clip attached to both ends of the odometer shaft. Clean the shaft up and using extreme caution, hold the shaft with a pair of pliers at the non-geared end and try to wiggle the small clip off the other side, next to the gear. Be patient and persistent -- use a little oil or WD-40 as necessary to ease the clip off.

The rest of the odometer rebuild is termed as if you are facing the odometer, as in the left side wheel is the 100,000 place. Hence, the right side has the gear and the 1/10th of a mile brown wheel.

Once you have the odometer in hand, you can start to remove the gear first and then the odometer wheels. Make very good note of how they come apart.

On the brown wheel, on the left inside portion, you can see a very small ' 0 ' -- this is where the zero is centered on the wheels and the 1/10th indicator is the only wheel to have this marking on the left side. All other wheels have the ' 0 ' on the right side but still use this as the position for zero. You'll also notice that on the left side of every wheel, there are two teeth, while the right side of each wheel contains many teeth across the entire inner surface of the wheel. These are for a purpose and turn in a very tactical way so that as one number flips over, they continue down the line causing the odometer to turn over and read mileage properly.

In between the wheels are a small goofy looking piece (very important technical term!) which has one extremely small gear that sits in the lower portion of these as seen in the photos. One side of these gears has an extra set of teeth and these will face right and will fit into the two teeth on the left side of the wheels when reassembled. It doesn't matter where the left side teeth go, but if you are rebuilding, you may want to pay special attention so that you can have your odometer reset to zero or whatever number you want.

After mine was completely apart, I scrubbed the old painted numbers off and lightly sanded the face to give the new decals a better surface to stick to. I used Simple Green to remove most of the old dirt and grease and then dried. DO NOT stretch the decals as you reapply them. There should be very little to no overlap if done properly. They can be trimmed with a small x-acto knife. I also ran it around the edge of the wheels to make sure none of the decal protruded over the sides.

When reassembling (here is a drawing to show how the odometer wheels go back together), apply a very small amount of grease to the shaft and inside area of the gears and wheels. Don't use to much -- you don't want it seeping out later and spoiling all your hard work.

Once you're done, you can set it aside, sit back and breath a sigh of relief.

Starting back at the base of the speedometer assembly

If you look it over, you will notice a very small brass soft plug [ pix ] . I used a tiny screwdriver, inserted it in softly and gently turned it counter-clockwise and pulled the plug right out. Underneath it is a very small piece of felt which can be removed with tweezers or a needle. [ pix ] Apply one drop, maybe two at most, and give the speedometer a spin to make sure it's thoroughly lubricated. I cut a small piece of new felt (but the old one can be reused) [ pix ] and inserted it into the hole. Apply one more drop of oil and gently pop the brass soft plug back in place. Push gently but firmly so it's seated tight. [ pix ] Surprisingly enough, there was still wet oil inside when I pulled the plug out. Not bad after 60 years!

If you haven't already, it's a great time to clean up all the old gears and main body of the speedometer. Simple Green and a toothbrush worked great for me. I also used a bunch of Q-tips to clean the old grease out of all the crevices and a small needle pick to get in between all the gears and make this stuff spotless. Once you're done cleaning, you can add a little grease to the gears and give them a spin to make sure it gets into all the teeth. Insert the smaller worm gear into the main body. Now for the delicate part: gently remove the tape from the spring and housing making sure NOT to disrupt the spring and needle shaft. Two screws and it's back together.

Now time to add the odometer

DO NOT try and slide the geared end in first as seen in the picture -- this is wrong! Start with the end that holds the brass shims and slide it into the hole while aligning the small slits in between the odometer wheels onto the small raised lip of the spring / needle housing. Slide the geared end into the other side and install the brass shims to lock the shaft into place [ pix ] . Add a little grease to the worm gear on the odometer shaft and give a few more turns to lubricate the assembly.

All of the notches must align with the thin bar directly below the odometer. [ direct view / angled view ]

Add the small metal piece over the needle shaft carefully and install the two screws holding that on.

The speedometer face

Lightly sand the whole face [ pix ] making sure there are no bumps, pits or cracks in the facing. Sand until you're happy with how smooth the face is. If you don't, you can very easily gets voids when applying the new decal to the face. Apply the decal starting at the center and work outwards so as to not get any trapped air under the decal. You can now attach it to the speedometer body with the two screws. [ pix ] Don't worry if the decal twists a little when attaching the screws as that part will be hidden by the dash bezel or cluster body.

Installing the needle

Final thing is installing the needle. It takes a steady hand but I lightly sanded the needle and set it upside down on a pin. Then I painted the backside and gave it time to dry. Once done drying, gently push it onto the needle shaft.

You're almost done! What I did to finish the needle was to take a small sheet of paper and cut a single slit into a piece of paper. Then I slid it over the face and around the needle shaft. Repeat with another sheet of paper from the other side. This protects the face and body of the speedometer while painting and also leaves the needle free of any finger prints if you try and paint it before installing (don't ask how I know that!). Blast a light coat of red paint (GMC only) or beige paint (Chevrolet only) on the needle and Voila! Sit back and enjoy your master piece.
To make sure everything worked, I hooked a cordless drill to the back of the assembly and squeezed the trigger until I had a few tenths of a mile down.



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