Speedometer jumping around help

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dan0340

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Hey I have a 73 duster I’m working on with my son. Have been asking a lot of questions lately as this car needs a lot of work. It has a 360la with a 904 automatic tranny. My question is the speedometer jumps all around gets a bit more stable at higher speed but not by much. It got worse after I picked it up from transmission place for a rebuild, but it was bad before I took it to them too. Can someone point me in the right direction. Do I need to find a new cable or is it something where it attaches to the transmission??anyone have experience with something similar? Thanks!
 
Try greasing the cable. Friction is grabbing it and the end/ends that are squared off that drive the cable/speedometer are skipping in their prospective sockets. If that don’t work new cable and drive sockets, as in new Speedo and gear.
 
ch1ll said:
Try greasing the cable. Friction is grabbing it and the end/ends that are squared off that drive the cable/speedometer are skipping in their prospective sockets. If that don’t work new cable and drive sockets, as in new Speedo and gear.
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how would I go about that procedure and what do you use to grease it?
 
Make sure it’s all the way in the gauge and well greased. Does it make noise too?
 
dan0340 said:
Do you have a link of where I could get a new one?
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New Old Stock Mopar.
Brewer's Performance - Mopar A833 4-Speed Transmission and Component Specialists

Imported replacements will be available for much less through your parts house of choice.
Pioneer CA3002 at O'Reilly's, AutoZone, Summit, Rock Auto...

NAPA and Advance look like they may have something that'll work, but other choices look better.

Layson's has an American made reproduction. Part number IS-663. You'll have to get through their website on your own.

OER reproduction. Probably an import. I have no idea if it's any good.
1973 PLYMOUTH DUSTER OER 3592360 OER Speedometer Cables | Summit Racing
 
dan0340 said:
how would I go about that procedure and what do you use to grease it?
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Its been a while since I have done this, but you need to remove your cable to grease or replace, either way. What I can’t remember is if the cable itself can be pulled through the casing once it is removed due to the squared off ends. If it does come through, don’t pull it all the way out. Pull it out a bit, grease cable and push it back in. Repeat process each time pulling it out a bit further grease and push it back in till the cable rotates freely in the casing.
 
dan0340 said:
Hey I have a 73 duster I’m working on with my son. Have been asking a lot of questions lately as this car needs a lot of work. It has a 360la with a 904 automatic tranny. My question is the speedometer jumps all around gets a bit more stable at higher speed but not by much. It got worse after I picked it up from transmission place for a rebuild, but it was bad before I took it to them too. Can someone point me in the right direction. Do I need to find a new cable or is it something where it attaches to the transmission??anyone have experience with something similar? Thanks!
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Yes it has been my experience in the past that when it jumps all over the cable has gone bad.
 
mine does the same, and occasionally I get a horrendous noise from the speedometer itself, but it is very intermittent. the other things I've observed:

1) I don't see any jerkiness of the motion of the odometer, it is smooth in operation
2) the Odometer reads about 3% low. on a trip last weekend, I observed the odometer and compared it to the mile markers on the interstate. 33 miles on the interstate registered 32 miles on the odometer.
3) the Speedometer reads a little more than 10% high. comparing to a GPS app on my phone, 60mph indicated in the car registers 54 mph on the GPS app, 67-68 in the car is 60mph road speed according to the GPS app, 80MPH in the car is 71-72 according to GPS, etc....

I could understand if the speedometer and odometer were off by the same amount (both 10% high, both 3% low), since they aren't, I'm assuming the issue isn't the cable, but the speedometer itself. does anyone have any advice on how to lube/correct the speedo to remedy this?
 
michiganpat said:
mine does the same, and occasionally I get a horrendous noise from the speedometer itself, but it is very intermittent. the other things I've observed:

1) I don't see any jerkiness of the motion of the odometer, it is smooth in operation
2) the Odometer reads about 3% low. on a trip last weekend, I observed the odometer and compared it to the mile markers on the interstate. 33 miles on the interstate registered 32 miles on the odometer.
3) the Speedometer reads a little more than 10% high. comparing to a GPS app on my phone, 60mph indicated in the car registers 54 mph on the GPS app, 67-68 in the car is 60mph road speed according to the GPS app, 80MPH in the car is 71-72 according to GPS, etc....

I could understand if the speedometer and odometer were off by the same amount (both 10% high, both 3% low), since they aren't, I'm assuming the issue isn't the cable, but the speedometer itself. does anyone have any advice on how to lube/correct the speedo to remedy this?
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I can't answer all of your questions, but I can give you something to go on.

Before trying to make any corrections to the speedometer or odometer, be sure you're running the size tires you want. If your plans include a taller or shorter rear tire, any corrective measures you take will be undone when you change sizes.

Speedos can be lubed. That might take care of your noise, but the problem could be terminal. I believe you have a later car, and I'm only familiar with Rallye dashes, so use the search function to get specifics on how to lube your speedo.

Your speedo reading high problem can probably be addressed by changing the speedometer pinion gear to one with one or two more teeth. Take yours out, count the teeth, and put up a "Wanted" ad here for one with more teeth. You'll probably get a response pretty quickly. If not, there are Ebay sellers and reproductions available. Again, be sure you have the tires you want on the car before doing this.

Unless you're rallying and must use the odometer in the car, I wouldn't worry unless it's off by a lot. To me it's more important to have an accurate speedometer.
 
yeah, car is a '76, standard dash. tires are a little bigger than stock out back and brand new (originally came with D78-14, 25.5" tall, went to 225/70R14, 26.4" tall), so I'd expect it to be a bit low (like the odometer is acting)

if I change the speedo pinion gear to get that "correct", then I assume it will throw the odometer off even worse, since they're both driven off that gear. any advice on what to lube the speedometer with?
 
michiganpat said:
yeah, car is a '76, standard dash. tires are a little bigger than stock out back and brand new (originally came with D78-14, 25.5" tall, went to 225/70R14, 26.4" tall), so I'd expect it to be a bit low (like the odometer is acting)

if I change the speedo pinion gear to get that "correct", then I assume it will throw the odometer off even worse, since they're both driven off that gear. any advice on what to lube the speedometer with?
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Your odometer is probably fine. It works on a simple gear driven system. So if it works at all, there's not much to go wrong. On the other hand, the speedometer works by a magnetic field produced by spinning magnets. These fail, and need repairing or replacement. So much so that reproductions are available. Since yours has made that noise, I suspect it's badly wounded or terminal.

There are a couple avenues to take. The least expensive is to remove the speedo, inspect the drum (post pictures here on FABO for input) lube and reinstall. Lube can be a very small amount of light oil on the bushing or graphite lube. You'll find opinions differ on which to use. Move the needle on it's spindle to correct the MPH reading. Get the correct pinion gear for your tire size and rear gear ratio. See chart below.

You can try disassembly, repair, and reassembly yourself. Unless you start buying expensive parts, you're still on the inexpensive side. This would normally take some experience and expertise, but you may be able to find repair info.

You can send it out to a speedo repair shop. Start a thread asking for recommendations as to where to send it.

Buy a reproduction or NOS. Maybe the most expensive. The repops are close to $400.

Speedometer Pinion Gear Chart.png
 
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