Ticking sound from dash at highway speeds - speedo cable? Spark knock?

[MoPar~Man]

First time on the hiway today after complete front stub / front suspension R&R. And the car didn't fly apart or crash! I must have put most of the bolts and nuts back where they should be.

The last time I drove this car at 60+ MPH was probably in 1999. It was at Carlisle in 1997 !

Today I'm hearing a tick that seems to be coming from the dashboard, I'm thinking it's either the speedo or the speedo cable. I guess we know these cars aren't as quiet as modern cars on the highway, so with wind noise and road noise it's not that easy to isolate the tick. Speedo needle is stable, not jumpy. I'm guessing the cable turns at a much-reduced rpm vs engine rpm.

Ticking does seem to change, like go away, when engine is under more load (ie going up hill). Is a ticking cable a known phenomena in these cars?

 

[CBODY67]

Exh system "tick" will be more intense when the engine is working more, not less. Especially if it is an exh manifold bolt 1/8th turn loose.

Is the "tick" frequency proportional to vehicle speed, directly? Does it get louder as indicated speed increases?

Nothing in the instrument panel area that is directly related to engine speed.

Speedo cable turns about 1/3rd as fast as the transmission output shaft turns. Not engine speed, per se, as engine speed is variable in the lower gears.

HVAC fan?

Enjoy!
CBODY67

 

[MoPar~Man]

Exh system "tick" will be more intense when the engine is working more, not less. Especially if it is an exh manifold bolt 1/8th turn loose.

Is the "tick" frequency proportional to vehicle speed, directly? Does it get louder as indicated speed increases?

Nothing in the instrument panel area that is directly related to engine speed.

Speedo cable turns about 1/3rd as fast as the transmission output shaft turns. Not engine speed, per se, as engine speed is variable in the lower gears.

HVAC fan?

Enjoy!
CBODY67

I haven't driven anywhere for long enough at a constant low speed (like 30 or 40 mph) to notice the tick. The speedo needle might pulse a little at 20 - 25 mph. At 55 - 65 the tick didn't change pitch but I think the repetition rate does change so I think it's definately related to something turning, like the drive shaft. HVAC fan was not on during this.

Maybe this is related: The 215-75-14 tires that are now on the car are going to be smaller than the 8.25-14 that the car originally came with. I would have expected the speedo to read higher than my actual speed, as the smaller tires would be turning faster. I'm basing my actual speed on TomTom GPS/Map unit in the car with me. At 100 kph (62.5 mph) the speedo was showing 55 mph. At 50 mph the speedo showed 42. Speedo showing 84% - 88% of actual speed.

I need to do an analysis of the odo readings to see how they work out vs real distances.

 

[R&R]

Cable may be loose on either end. Easy enough to check transmission connection first. If it’s tight check speedo connection. It’s common. Usually gets worse over time as it gets looser. Not familiar with 8.25 tire size. Regardless, once you decide on final tire size, I believe you can easily calibrate the speedo by changing the gear on transmission side of cable. I imagine you need a larger diameter gear with higher tooth count.

 

[CBODY67]

Yes, use the odometer readings to calibrate the speedometer, as the odometer is driven directly from the speedo cable. Once that is better/closer, THEN worry about the speed calibration.

CBODY67

 

[mgm1986]

Yes, use the odometer readings to calibrate the speedometer, as the odometer is driven directly from the speedo cable. Once that is better/closer, THEN worry about the speed calibration.

CBODY67

I will confirm this is spot on. I thought changing the gear in my '68 would fix my speedometer reading but it actually made it worse. Since my trip meter doesn't work it has proven difficult to confirm if the odometer is correct but before you go and replace the gear in the transmission it is worth trying to do as @CBODY67 suggests.

 

[mgm1986]

Just thinking out loud here, possibly a bad idea but...

When you are driving and you hear the "tick", does it change if you put it in neutral? And further, if while coasting in Neutral, does it go away if you were to shut the car off (while coasting in neutral)?

 

[Big_John]

Ticking does seem to change, like go away, when engine is under more load (ie going up hill).

Exhaust manifold leaks will often sound like a tick and come and go with engine loading and temperature.

 

[R&R]

Exhaust manifold leaks will often sound like a tick and come and go with engine loading and temperature.

Also an exhaust leak can be heard at an idle. Especially when first started. The colder, the louder. Often goes away if it’s real small, or only heard in winter time till it warms up.

 

[MoPar~Man]

I had an observer in the car while I connected a cordless drill to the speedo cable under the car. The observer confirmed the ticking coming from instrument cluster when the speedo was registering a high speed (50 or 60 mph). Perhaps the tick gets louder with speed, I'm not sure. The odometer wheels were turning, so that mechanism was not stuck or inoperative.

I reconnected the cable to the transmission and disconnected it from the speedometer, and pulled the center wire out. I'll drive the car like that for now, I'll have a GPS to tell me my speed. I'll pull the cluster later, I have a spare, I'll try to determine the source of the ticking and correct it.

 

[R&R]

I had an observer in the car while I connected a cordless drill to the speedo cable under the car. The observer confirmed the ticking coming from instrument cluster when the speedo was registering a high speed (50 or 60 mph). Perhaps the tick gets louder with speed, I'm not sure. The odometer wheels were turning, so that mechanism was not stuck or inoperative.

I reconnected the cable to the transmission and disconnected it from the speedometer, and pulled the center wire out. I'll drive the car like that for now, I'll have a GPS to tell me my speed. I'll pull the cluster later, I have a spare, I'll try to determine the source of the ticking and correct it.

The cable itself is usually the culprit. Gets loose, worsens over time, eventually frays and breaks. If it wasn’t loose, I would rule it out before taking the speedo apart.