Speedometer problem

[Robert Schaad]

Started driving my 72 From 7/11 the other night and speedometer started reading about 60 when I was driving about 35. I have already replaced a lot of things as a normal replacement objective. I then jumped on the Freeway and the 120 speedometer went crazy, pegging out, jumping from 80 to above 120. Pulled over and removed the speedometer cable so as not to destroy gauge. Ordered new Speedometer cable. Just another thing I wanted to replace any ways. Replaced, and did not help. Here is the funny point. My car came with a 150 speedometer gauge and when restoring it, I had a 120 that was in a little better condition and put it in. That 120 looked better but was going bad. I put the 150 back in now and works great. Also put new LED dash lights in while replacing Speedometer. Gives a great new look over the old ones.

 

[Nacho-RT74]

Speedo is gone... If you check on back of speedo face, will find a coil spring which is the needle return spring. This spring is tensioned by a lever hold by a teflon bushing which also keeps the needle shaft in place. The teflon bushing keeps some pressure over the lever which is also a spring by itself being melted into the speedo housing to keep the pressure over the tension lever. This section is the one what cracks on bushing and gets loosen the return spring.

It is fixable without dissasemble, but tricky

 

[Nacho-RT74]

Here is the fix with epoxy on back. I had to keep the bushing in place with a fork and rubber bands throught the shaft while the epoxy was curing to make the pressure over the tensioner spring lever

BUT I fixed ( fixed two actually but one of them was also broken into the input shaft assembly ) because it was a km speedo REALLY hard to find. Being in USA the best would be replace it for a good one

This is the other one I could fix. Note the high beam indicator is an horizontal slot underneath the 120 mark, not the vertical slot like the previous pic which would be in place of the 120 mark

Then recalibrate it using a drill. 1000 RPMs equals to 60 mph. Made maths to km and using a 550 RPMs drill ( the 1000 RPMs I have doesn't have reverse speed to make spin the speedo correctly )

With a chrono just checked after 5 minutes running the reading would be the correct one between speedometer and distance

This was made maybe 30 times to be sure, adjusting more or less the lever tensioner spring to give a more accurate speed reading according with the total distance on a 5 minutes run ( couldn’t more time because the drill got hot )

Then also attached a decal on red line for better look

 

[493 Mike]

Nice repair! You have to think outside the box due to your location. I salute you sir!
Mike

 

[Nacho-RT74]

Well I must say all Chargers in Venezuela got actually standard cluster. Just in 74 some Coronets called locally Special Editions ( made to replace the New Yorker which on 73 was the last year being assemblied locally ) which are extremelly rare got Rallye clusters, of course in Km along with lot of luxury options. It took me 8 years to get one cluster from one of these being parted out. Two years later found the second one. Just was interested on the speedo because I already had Rallye cluster on my car bought on eBay.

so, that’s the reason I had to fix these.

two or three years later I became an extra 150 Miles speedo a friend sent me from USA for free ( it was stuck at the input shaft but could get it spin free ) with a healthy bushing into kilo speedo interchanging the odometer gears and the face. Rest is the same including calibration ( 150 miles is 240 km ) so that’s the one I will use when reassembling my car and storaged the one fixed on a box. Will also storage the 150 miles still on my car.

Being outside USA spare parts at hands is a must.

 

[Paul_G]

Nice job Nacho.

 

[Ron H]

Yeah Nacho is a genius. He guided me through some wiring for my console with nice-detailed info like he provided in this post.

 

[smithchargers]

Speedo is gone... If you check on back of speedo face, will find a coil spring which is the needle return spring. This spring is tensioned by a lever hold by a teflon bushing which also keeps the needle shaft in place. The teflon bushing keeps some pressure over the lever which is also a spring by itself being melted into the speedo housing to keep the pressure over the tension lever. This section is the one what cracks on bushing and gets loosen the return spring.

It is fixable without dissasemble, but tricky


View attachment 973387

This is an old thread but Nacho, do you have any better pics of the spring and lever positioning? I had to do this same repair to mine but the speedometer now won't go past 40 and is also way off below that speed

 

[Nacho-RT74]

Hi! There is not an specific position for the lever/spring. The final tension of the helicoidal spring to get the speed adjustment will tell you.

If the speedo doesn't go further than 40, there is another problem elsewhere

 

[HeavyFuel]

The speedo in my 68 Charger reads progressively higher as I go faster. At real 40 mph, the dial reads just a few mph more, but at about 75, the Speedo says about 95. And so on.

Spring getting weak? Slipped?

So if I understand how the Speedo works from your explainations, the spring can be adjusted to apply more tension, and thus, a more accurate reading.

But…disassembly of cluster/gauge is required?

I’ll probably just leave well enough alone.

 

[Nacho-RT74]

The speedo is a combo of a magnet spining along with an aluminum intertia wheel (dunno if thats the right name for it) and the return spring. The return spring is part of the adjustment of course. Asuming the magnet is still nice, right, giving more or less tension you can readjust the speedo accuracy.

This is of course if there is not another mechanical failure on the assembly

yes, speedo needs to be removed to reach the spring lever adjustment.

there is not a direct drive between speedo cable and speedo needle itself, just to the odometer. The needle moves thanks to the magnet spining and what the magnetic fields drags the intertia wheel. The needle is conected to this aluminum inertia wheel.

 

[blue69runner]

Just took a look at a new one. Man that is really high priced. But every thing for these car's are not cheap. Their might be some one that can fix it for you that would be less money out of pocket. Had mine fixed in the runner. The part's in it where shot. Non rally.

 

[HeavyFuel]

Mopar Action has a really nice article about this topic in the current issue....that's what got me thinking about the whole thing.

 

[vsj100]

Hola. Mine is a 68 coronet with 120 sweep speedo. It started making a loud hum as the speed increased. Then would only return back to 40. Then it would peg at 120 and now only returns to 70. I'll disconnect it. The cable is new. Thanks to all and merry Christmas.