CH600 speedometer

[west illini]

I wasn’t sure forum group this should be under .

The speedometer in my 1993 Ch600 Doesn’t always work right … meaning , when I’m going 55, it may only show 30 .  And some  days  in row it’ll work just fine .  And then it won’t for a while .    I had the sender unit replaced, and it still behaves like this 

Where should I check next ? 

[mechohaulic]

not tooo knowledgeable of these new units; BUT I would consider the speedo head if a new sender didn't resolve the issue, I am not a believer in (expensive) parts changing  hit or miss.  not much else in electronic system.

[Mackpro]

If a Mack Transmission then check the  yoke bolt on the back. A lot of the time our trucks come in with the bolt and washer missing. This bolt holds the yoke on and also holds the tone wheel tight. The speedometer sensor reads off this tone wheel. A Fuller transmission can have the same problem but is a really common problem with the Mack trans 

Edited October 16, 2022 by Mackpro

[Onyx610]

11 minutes ago, Mackpro said:

If a Mack Transmission then check the  yoke bolt on the back. A lot of the time our trucks come in with the bolt and washer missing. This bolt holds the yoke on and also holds the tone wheel tight. The speedometer sensor reads off this tone wheel. A Fuller transmission can have the same problem but is a really common problem with the Mack trans 

Where do you live that these things just come loose…..??? We typically need heat and a one inch gun to get the nut loose and then have broken pullers trying to get these yokes off. Def needs to be a north east flat rate book. Add 8+ hours to the standard time. 

[mechohaulic]

I would think someone changing the sensor would ????should notice a loose nut (not the driver ) . and if it were loose enough to create a faulty speedo reading:: would it not also create a road vibration. ???? jus t wondering.

[Joey Mack]

was the sender installed correctly?   all the way in, til it touches, then 1 full turn out and lock it down??  yes a loose yoke will cause this issue as well..  have you looked at the plug on the back of the speedo to see if it hasnt vibrated loose?   not common, but possible..   

[Onyx610]

Just now, mechohaulic said:

I would think someone changing the sensor would ????should notice a loose nut (not the driver ) . and if it were loose enough to create a faulty speedo reading:: would it not also create a road vibration. ???? jus t wondering.

I think it would throw a code/derate. Other thing would be a big vibration like you said. 

[mechohaulic]

4 minutes ago, Joey Mack said:

was the sender installed correctly?   all the way in, til it touches, then 1 full turn out and lock it down??  yes a loose yoke will cause this issue as well..  have you looked at the plug on the back of the speedo to see if it hasnt vibrated loose?   not common, but possible..   

based on older units;to back off enough 1- the sender has to spin around a few turns; the attaching wires usually prevent a sender from making complete turns.2- original text states speedo is erratic 55mph it reads 35mph. even a bad wire harness would be speedo/ no speedo . 

[Joey Mack]

I don't recall a v-mac 1+2 to derarate..  for a speedo, just messed up operation..  the speedo head has dip switches...    

[mechohaulic]

I'll buy the beer if we receive an update with the actual cause  after repair was made based on forum advise. 😄

[mechohaulic]

it's a wrap for me. have been home for 1 :45; haven't showered yet and early start tomorrow on trailer (hopeful)finish.

[Onyx610]

The only other way I see these nuts coming loose is if they were re used like they weren’t supposed to be or torqued incorrectly. 

[Onyx610]

3 minutes ago, mechohaulic said:

I'll buy the beer if we receive an update with the actual cause  after repair was made based on forum advise. 😄

Can you make a 40oz?

[west illini]

Thanks for all the suggestions ,  I’ll follow up on them, and give an update when we find something out 

[Joey Mack]

There is more to this one..  the speedo system on a '93 is simple compared to V-Mac 3...  My guess is a poor connection, if the sensor is not out of adjustment.. 

[Onyx610]

I agree. 

[Joey Mack]

Mech...  Get cleaned up and sleep well..   it will be here tomorrow..  jojo

[mechohaulic]

2 minutes ago, Onyx610 said:

The only other way I see these nuts coming loose is if they were re used like they weren’t supposed to be or torqued incorrectly. 

now you have to be more specific : "these nuts coming loose"THERE ARE TOOOOO MANY NUTS COMING LOOSE TODAY"The yoke nuts coming loose is correct, . ;;;THANK YOU lol   lol