Intermittent speedometer problem Freightliner cluster on a 6-speed Allison Transmission with speed control

[robertdube]

[Dwight Lindsey]

I had a speedometer issue and was helped by a fellow Monacoer who pointed to the speed sensor on the Allison transmission.

Look at this post:

 

[waterskier_1]

I'm not sure about a Freightliner or Dutch Star (this is a Monaco group), but Monacos of that Era got the speedo signal from the alternator. 

  - Rick N 

Colorado Springs,  CO 

[Ivan K]

Yes, alternator pulses can and are used for engine speed but for road speed it would need to take into account the current transmission gear. Mine 1999 Allison has output speed sensor.

[wamcneil]

A description of the problem would help…

I had a sketchy Allison transmission output speed speed sensor that would periodically drop to zero and immediately spring back up. Initially it would do that only towards the end of a long trip when everything got hot. 

That messed with the cruise control and made it feel like the engine was surging. 
The problem got worse over time. 
If that output speed sensor goes totally dead, the trans will throw an error and it won’t shift out of 1st

Edited June 18, 2023 by wamcneil

[waterskier_1]

2 hours ago, Ivan K said:

Yes, alternator pulses can and are used for engine speed but for road speed it would need to take into account the current transmission gear. Mine 1999 Allison has output speed sensor.

Opp, I was think of the Tach.  Sorry.

  -Rick N.

[dl_racing427]

21 hours ago, waterskier_1 said:

I'm not sure about a Freightliner or Dutch Star (this is a Monaco group), but Monacos of that Era got the speedo signal from the alternator. 

  - Rick N 

Colorado Springs,  CO 

That's for the tachometer.