1987 International Speedometer problem

[Twonkelman]

Hi, I got a 1987 International 7.3L IDI 5speed manual with the following problem:
The speedometer works “kind of”. It goes normal up and down but when I turn of the bus the needle stay at “10” and does not go down to “0”. I took of the cover and if I put the needle to “0” she stays but “jumps” around when I put the cover back on. I got it staying at “0” and then started the bus. All looked normal but when turned off needle rested again at “10”
Did anyone had a similar problem?
Where should I start troubleshooting? Cluster? Sensor (it looks like an electrical sensor for the speedometer, tachometer is a cable).

[Twigg]

Check the calibration against a GPS. If it's accurate forget it and move onto something more interesting

[Twonkelman]

Originally Posted by Twigg

Check the calibration against a GPS. If it's accurate forget it and move onto something more interesting

But I would like to know my rpms accurately for all kinds of reasons including shifting [emoji3]

[dan-fox]

Oh, more than one gauge? All of them? Maybe you need to check out how well your instrument panel is grounded, or spray some contact cleaner into a plug or two, or as a last resort reflow the solder joints on the back.

[Coamack1]

A lot of the commercial truck style gauges do not rest at 0 with the ignition off. They will stay up some. With the gauge bouncing around check the sensor for metal shavings or other contamination as well as grounds in and around the gauge cluster as dan-fox suggested.

[Twonkelman]

Thanks! I will check those items. It was not bouncing around with the engine running. So I will start with the grounds and connections.
I was concerned that with the needle not starting at 0 I was always running +1000 rpm more than indicated... But sounds that’s not the case. Is there a way to check rpm with a tool to check/calibrate speedometer?

[Coamack1]

I have used a non contact photo tachometer in the past, but have never compared them to a dash gauge. They use a reflective tape attached to the crank pulley. Amazon has several for $20. It is basically a hand held meter with a laser pick up to sense the reflective tape.
Mack

[Coamack1]

Also with the tachometer you have being cable driven, the cable can cause some binding internally. I did not see that the tach was cable driven. I have disconnected the cable and sprayed lubricant into the both end of the cable. Once reconnected and running the lubricant will be distributed into the cable. This can free up the cable internally, they can get corroded or dirty inside and cause some erratic behavior in the tachometer.
Mack

[Twonkelman]

Originally Posted by Coamack1

I have used a non contact photo tachometer in the past, but have never compared them to a dash gauge. They use a reflective tape attached to the crank pulley. Amazon has several for $20. It is basically a hand held meter with a laser pick up to sense the reflective tape.
Mack

ThanksMack!

[Twonkelman]

Originally Posted by Coamack1

Also with the tachometer you have being cable driven, the cable can cause some binding internally. I did not see that the tach was cable driven. I have disconnected the cable and sprayed lubricant into the both end of the cable. Once reconnected and running the lubricant will be distributed into the cable. This can free up the cable internally, they can get corroded or dirty inside and cause some erratic behavior in the tachometer.
Mack

Great Tip! Thank you!!

[Twigg]

Originally Posted by Twonkelman

But I would like to know my rpms accurately for all kinds of reasons including shifting [emoji3]

Well you said speedometer.

Pretty much all of the Tachos fail to return to zero. That's just how they are. They can easily be checked with a laser tacho on the crankshaft pully.

Mine was off, a lot. It was easily fixed with the calibration screw.

[Twonkelman]

Originally Posted by Twigg

Well you said speedometer.



Pretty much all of the Tachos fail to return to zero. That's just how they are. They can easily be checked with a laser tacho on the crankshaft pully.



Mine was off, a lot. It was easily fixed with the calibration screw.

Sorry, my mistake. I am from Germany and we call the thing which measures speed “Tacho” and the one who measures rpm “Drehzahlmesser” [emoji12] So I got confused.

Where is this calibration screw?
Thanks for the help and tips!!!

[Twigg]

Originally Posted by Twonkelman

Sorry, my mistake. I am from Germany and we call the thing which measures speed “Tacho” and the one who measures rpm “Drehzahlmesser” [emoji12] So I got confused.

Where is this calibration screw?
Thanks for the help and tips!!!

Usually they are on the back of the meter.

The same RPM meters were fitted to many buses, with many different engine configurations so the instruments have adjustments on the rear. They may also have a calibration screw for fine adjustment.