1948 Chrysler speedometer not working

[HCD]

I have a 1948 Chrysler New Yorker that Ive changed the speedo cable and speedometer is still not working. have also lubed the port near cable to cluster. Before it wasnt working at all, now it pegs to 100 when moving. I have a good shop manual but it doesnt have any info regarding speedometer. Im pretty sure the cluster itself will have to be rebuilt or replaced. Anyone had similar problems? any input appreciated.

[soth122003]

How long has the oil had time to soak in? Going from not working to pegging at 100 says it needed lube, but it might need more time to completely lube all the parts in the speedo. Granted it will probably need a rebuild, but you might want to give it a little more time to soak in and maybe it will work as needed, but probably not accurate. It might also help to slowly exercise it by using a low speed drill to turn the cable and work the speedo at a low speed.

 

Joe Lee

[Sam Buchanan]

It's possible the little clock spring that controls the needle has broken or come loose. So the needle "sees" the magnet spinning and has no spring to keep it from hitting the century mark.

[HCD]

replacing the speedometer cable was a real pain to replace, especially at the transmission. I was hoping that would have fixed the problem, if adding more lube doesnt work, Im afraid the cluster will need replacing or rebuilt.

[Eneto-55]

When I tore down the speedometer on my P15 (intending to just refresh the reflective paint) I found that what I guess to be white lithium grease was completely hardened. There was a lot of it right in the 'clock spring', so it wasn't able to perform normally.  I had to use a small jeweler's screw driver to carefully chip that stuff off of the spring. (Maybe not the problem with yours, if it was working correctly, then started doing as you described - my car had sat already for at least 40 years by the time I opened the speedo.  Plenty of time for that grease to harden like that.)

[HCD]

On 1/28/2025 at 1:17 PM, soth122003 said:

How long has the oil had time to soak in? Going from not working to pegging at 100 says it needed lube, but it might need more time to completely lube all the parts in the speedo. Granted it will probably need a rebuild, but you might want to give it a little more time to soak in and maybe it will work as needed, but probably not accurate. It might also help to slowly exercise it by using a low speed drill to turn the cable and work the speedo at a low speed.

 

Joe Lee

[HCD]

I was able to get a wd 40 straw into the lube pipe behind the speedo cluster a week ago and get more lubrication in there. Hopefu;;y if all it needed was more lubrication this may get it working again.

[Los_Control]

Thanks for the follow up .... I also need to work on my speedometer and was interested in others opinions on how they disassembled it and if any surprises?

My main concern is removing the needle without damage ... if there are any tips?

 

I have 2 different speedometers for my truck and there may be some differences but I assume they will be built similar as a car.

1rst speedometer on the bench with cable and drill, does nothing .... no movement of the needle at all.

2nd one it just jumps from 0-20 ... mostly just sits on 0 and jumps sometimes while the needle does vibrate when not moving.

 

I expect the 2nd one may have the same issue as @Eneto-55 describes and what I hope to find ... just open it up and give it a good cleaning.

I'm expecting to find something broken in the first speedo ... will be a experience opening them up. and then see if parts are available.

[Los_Control]

For anyone interested what they look like inside .... not what I was expecting .... this is a truck speedometer .... no idea if cars are built the same way.

The 2 round pieces go together and there is a teeny tiny long shaft that connect everything together.

I'm pretty sure my shaft was broke and this is why this speedometer did not move at all.

On the round silver piece you can barely see a tiny shaft sticking out in the center. Because it broke where it goes into the other piece on the left .... I'm able to split it apart.

 

 

 

See if this makes more sense, the shaft is permanently mounted to the upper piece and about 4" long.

You would remove the needle and my shaft broke off inside the needle ... so the shaft is shorter.

then remove a brass C clip on top of the spring to slide the shaft out from that point .... In the end, I should have a 4" shaft coming out of the top piece in order to separate these 2 pieces. ..... Because mine was broke, I did not need to take things apart in order to split it open.

 

I do not pretend to understand how things work ... it all seems direct drive to me .... the spring would dampen and slow down and maintain tension on the needle ... seems like there would be a clutch of sorts to allow slippage .... I really do not understand how the clutch works on mine.

Just seems to me the clutch would prevent the needle from pegging out at 100 mph and read correct mph.

 

[Eneto-55]

Here's a photo I saved from here on the forum at some time in the past - courtesy of Don Coatney. (I have photos of my own, but not sure where they are right now.) Don had lots of photo stored on some outside service, with just links to them on the forum. So those links are all now non-functional.

 

 

Edited February 13 by Eneto-55

[Los_Control]

53 minutes ago, Eneto-55 said:

Here's a photo I saved from here on the forum at some time in the past

Glad you saved the photo .... I imagine the difference between a car and truck .... different but similar in internals.

 

In the last photo I shared, on the silver cap at about 7:00 0'clock is a tang punched out in the cap.

That tang corresponds with a brass arm under the bracket below the clock spring.

So the silver cap can rotate 1 full revolution before the tang hits the arm and is stopped ... corresponds with the needle, full revolution then stops.

 

I imagine when the spring is installed, possibly it needs to be wound then locked in place?  .... like a lawn mower when installing a new rope?

Still seems like there needs to be some sort of clutch to allow slippage, or eventually the spring will just wind until broke.

 

I might spend some time tomorrow to see if I can learn anything .... I have little hope of ever fixing this speedometer and installing a new shaft and needle.

I may start looking for a aftermarket that fits in the hole .... is a repair that suits this truck.

[Eneto-55]

42 minutes ago, Los_Control said:

Glad you saved the photo .... I imagine the difference between a car and truck .... different but similar in internals.

 

In the last photo I shared, on the silver cap at about 7:00 0'clock is a tang punched out in the cap.

That tang corresponds with a brass arm under the bracket below the clock spring.

So the silver cap can rotate 1 full revolution before the tang hits the arm and is stopped ... corresponds with the needle, full revolution then stops.

 

I imagine when the spring is installed, possibly it needs to be wound then locked in place?  .... like a lawn mower when installing a new rope?

Still seems like there needs to be some sort of clutch to allow slippage, or eventually the spring will just wind until broke.

 

I might spend some time tomorrow to see if I can learn anything .... I have little hope of ever fixing this speedometer and installing a new shaft and needle.

I may start looking for a aftermarket that fits in the hole .... is a repair that suits this truck.

I have 3 other photos I copied from Don Coatney, but didn't want to load down the forum, especially if they are still on here somewhere. I also cannot figure out where my own pictures are. I thought I'd put them up here, but I think I found the thread where I talked about the caked white stuff that was all over the 'clock spring' on mine.  [That was in this thread: 

 

[Los_Control]

That is a good read ... It confirmed my broken shaft is now a parts donor .... my other speedometer the needle does still kinda move ... possibly it has a good shaft.

So between the 2 of them, I might be able to get 1 working.

 

What bothers me is the removing the needle part ... the shaft broke off inside the needle on my first attempt.

I do not want to break the shaft again on my other speedometer.

 

I watched a few videos and saw them using 2 kitchen spoons to pry up equally on both sides ... seems to work well for others. Just not for me.

So I might give it a 1/2 hearted try and see if the needle will come off without breaking.

I have lubed it pretty good and still a chance if I start driving that it may just come around and start working.

Although I would be happier if I can take it apart and clean and lube everything myself .....

 

Building headlight wiring on the bench today, will see if I can resist temptation to take it apart  

[Eneto-55]

That round drum sort of deal - the part that sits inside of it - Is that a magnet?  I looked at mine this morning (still disassembled) and I know that there is some 'slippage' in that area, some resistance to just peg the speed arrow/hand over all the way.

 

EDIT: If I can find the posts from Don Coatney that I got the photo above from, I would like to create a thread just about speedometer repair, and then either put in links to what he said about the photos he had linked to (and that I had copied), and also any other information about this subject that I can find. I don't know if it would work, but I think I'd ask people to not go off of the topic.  (Don was a great 'Post Bomber' - like a 'photo bomber', but purposely trying to drag a discussion off-topic. Maybe he wasn't doing it on purpose, but it sure seemed like it to me.  It really bugged the living daylights out of me, until I managed to do it to him once.... Maybe he never noticed, I don't know.)

Edited February 13 by Eneto-55
additional comment

[Los_Control]

12 minutes ago, Eneto-55 said:

That round drum sort of deal - the part that sits inside of it - Is that a magnet?

Mine is, but it is really weak .... I used a tiny screwdriver and it almost was strong enough to hold the screwdriver but it did slowly slide off.

 

@Sniper said, the magnetism only affects the needle, the odometer is directly gear driven ..... In the other thread.

 

So more food for thought .... does the tiny shaft only work the odometer gear and the spinning magnet creates a magnetic field of sorts that operates the needle?

Just boggles my mind trying to decipher how many beers it will take, to learn this new technology.

 

[soth122003]

9 minutes ago, Los_Control said:

So more food for thought .... does the tiny shaft only work the odometer gear and the spinning magnet creates a magnetic field of sorts that operates the needle?

To my understanding YES. The speddo cable drives the magnet, which creates a field that drives the needle. The spring is the dampening or breaking action that keeps the needle from going to 100mph or max on the speedo meter. So the faster you drive the more magnetic action the more needle pushes against the spring and shows relative speed. That's why it's so hard to get these cars up to 90-100mph. It is that speedo spring. LOL

 

18 hours ago, Los_Control said:

imagine when the spring is installed, possibly it needs to be wound then locked in place?  .... like a lawn mower when installing a new rope?

I don't think the spring is wound. It creates tension when the needle pushes against it. Then the tension pushes the needle back to 0 when stopped. I guess the engineers that thought this up were pretty sharp. If you really want to blow your minds, think about how different tranny gears or size wheels affect the speedo accuracy. 

 

Well that's my theory and I'm sticking to it. Now my brain hurts.

 

Joe Lee

 

 

[Los_Control]

I think this guy explains it pretty good. .... I bet he listens to @soth122003 

 

Now I need to understand more about the magnetic field .... more importantly, how strong does the magnet need to be?

I have heard others talk about having it re magnetized to add new life to the speedometer .... so if mine is pretty weak, is that normal?

Or should it be a nice strong magnet to make it work .... Off to the internets

[soth122003]

Thanks for the vid Los, now I feel pretty doggoned smart. Before you posted about the magnet, I thought the speedo might be gear driven somehow. But when you said magnet my feeble mind went what if? My head felt a little warm as the 2 brain cells I have started rubbing together to make a thought and presto.. my previous post was born.

 

Next thought....Faster than light travel. Wish me luck

 

Joe Lee

[Eneto-55]

Yes, I had intended to mention that the odometer is driven by a worm gear on the shaft you see along the side. My speedometer is like the one on the right in Don Coatney's photo. (Since I didn't save the text from the post where he put up that photo, I don't know what that other one is out of.)

 

(About the transmission gear, I think I recall that you could easily switch it out for a different size, to match the other variables.  So I suppose then that if you installed a transmission in a 46 P15 out of a 48 model, your speedometer (and odometer) would be off.  Or were the 15" tires on the later P15s the same diameter as the 16" tires on the early P15s?)

Edited Thursday at 10:22 PM by Eneto-55