[GORDON HUMMEL]

John,
It's an Allison 740
You can use the switch to downshift & or to hold in a lower gear.
the switch accuates an air solonoid, as oppossed to cable shifters that were popular in the day.
The newer pad type shifters are for an electronic version of the Allisonn not yours.
My 1989 Eagle bus had an electronic Allison 748R & was build 2 years prior to our Newell. Not sure why we don't have the later trans other than someone got a good deal
Mechanical & electrical shift controls are not interchangeable; also that new key pad is very priecy, not to mention the computer it goes to.
You should be able to feel the Jake working! I hear my the most when there is a cement center divider close by.
2 stroke Detroits do not have the best jakes compared to a 4 stroke. Valve adjustment has been know to help jake performance.