Speedometer Bounce

marty in Ohio

marty in Ohio

Well-known member
My speedometer bounces from zero to 75 when I start up and then settles down to read the correct speed. This most often happens when the weather is hot or when the car gets hot. Last week I pulled the housing and took out the cable to lube it and noticed a small kink where the housing goes into the transmission. A friend gave me one from his "supply of stuff" and I put it in this morning. No change in the bounce! Now I'm thinking the problem is in the head. I'm wondering if the mainspring is too loose. Do I dare open the case and tighten the spring or am I looking for trouble? I'm sort of a novice at this.
Marty
 
I've had mine opened all disassambled, cleaned it, oiled it and put it back together. I didn't use any special tools. Just take your time and don't lose things.
 
Did you lube the new cable? When a speedo is taken apart, the magnetic field is interrupted and often will require being adjusted by a speedo repair shop, not always.
 
Use a hand electric drill with appropriate flat blade end to spin the head and see if you can recreate the bounce. If you can then it is most probably not the cable.
 
marty in Ohio said:
My speedometer bounces from zero to 75 when I start up and then settles down to read the correct speed. This most often happens when the weather is hot or when the car gets hot. Last week I pulled the housing and took out the cable to lube it and noticed a small kink where the housing goes into the transmission. A friend gave me one from his "supply of stuff" and I put it in this morning. No change in the bounce! Now I'm thinking the problem is in the head. I'm wondering if the mainspring is too loose. Do I dare open the case and tighten the spring or am I looking for trouble? I'm sort of a novice at this.
Marty
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There are two differant cables did you use the right one?
 
Yep, I used the right cable and I changed the housing also. I did lube the cable as I slid it into the housing.
Marty
 
It sounds to me like the main shaft inside the speedo is binding, so that the cable gets wound up like a spring until it overcomes the friction, then suddenly lets go causing the bounce you describe. I don't think it has anything to do with the clockspring inside the speedo.

Driving the speedo with an electric drill may not duplicate the problem since the drill has plenty of torque to overcome friction. See if you can find something to engage the shaft and try to spin it by hand. I had a Waltham round speedo that had a shaft binding problem due to hardened grease.
 
Just get in there and clean the old grease out. It will be nasty and hard I'm sure. What do you have to lose? Sounds like it needs a restoration anyway
 
As Tiny suggested, modelacarman and I took apart my speedometer today. It is a Stewart Warner oval unit and it still had the original lead seal on it. The crud that we dug out of it looked like a crumbled pencil eraser. We took it down to the main shaft but couldn't figure how to get the shaft out. We think you need a small spanner wrench through the bottom. Well, we soaked it for a couple hours in 3 in 1 oil and put it back together. It still has some bounce but it's better. I don't know where I'll go from here but thanks to all who helped.
Marty
 
Marty: The input end is a bushing and a bevel drive gear that screws into the frame. This takes a special wrench, and sometimes is quite tight. Once that is removed, you can clean the petrified grease out of the gears and soak the magnet shaft with oil. If that doesn't help, the shaft is tight in the bushings and will need to be loosened up, carefully. Go too far and it will be loose. 85 year old pot metal is fragile so go easy on it. If you need help, contact me, usually 1 day turn around on speedometer service jobs like this.

www.marksspeedometer.com
mark@marksspeedometer.com
 
Sure sounds like a bent cable, but if the main shaft was hard to turn, then that is probably your problem. Broken cables will follow.
To get the main shaft out is a lot of work. It has to come out to clean up the shaft and old lube. I have the procedure, but you could easily end up with a throw-away.
A lot of shafts have high friction, because that is about the only thing you can't take apart easily. They have been in there for 85 yrs.
 
Marty, I'm glad that worked out.
As others have stated lube your cable also. I like speedo cable lube. Your local parts house will have it
 
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