Hello all! I am new to this message board. I work at a fire department in Maine. we have an International fire truck chasis with an Allison mt647 transmission and this is one of the few forums where i have found posts about this same transmission. we are experiencing an issue that i believe is related to the transmission and am looking for help. we have a key that powers everything up on the chasis.....then a push button that starts the truck. the problem we are having is after the truck sits awhile(a couple of days) and you push the start button nothing happens......if you hold the button in for upwards of ten seconds it sometimes starts. occasionally we have to push the button several times before the truck starts.....and there has been a couple of occasions where it doesnt start at all. with little diagnostic info available to us we ran a wire from the push button directly to the starter solenoid and the truck now starts every time. wondering if anyone has ever seen this problem....seems like something in the transmission or module not working correctly.....HELP! :question: :question: :question:
Allison mt647 delayed start
- Thread starter emtff105
- Start date
dbarton291
Senior Member
RE: Allison mt647 delayed start
The MT647 is hydromechanically controlled and so has no transmission control module. First, make sure the transmission shift linkage is adjusted correctly so the neutral position on the selector corresponds to neutral on the transmission linkage. This will make sure the neutral start switch is closed in neutral.
Another possibility is that the neutral start switch (that is threaded into the left side of the transmission) is faulty. When the selector is in neutral, the neutral start switch should be closed and have near zero resistance across its two wires.
Another possibility is the wiring to the neutral start swtich may have dirty/corroded or loose connections.
Those are the only transmission related issues that could affect the engagement of the starter. If there are other systems on the vehicle that are in the starter circuit, these should also be checked.
The mechanics tips booklet that covers adjustments on the MT-647 is available at www.allisontransmission.com
I hope this gets you on the right track to a more permanent fix.
The MT647 is hydromechanically controlled and so has no transmission control module. First, make sure the transmission shift linkage is adjusted correctly so the neutral position on the selector corresponds to neutral on the transmission linkage. This will make sure the neutral start switch is closed in neutral.
Another possibility is that the neutral start switch (that is threaded into the left side of the transmission) is faulty. When the selector is in neutral, the neutral start switch should be closed and have near zero resistance across its two wires.
Another possibility is the wiring to the neutral start swtich may have dirty/corroded or loose connections.
Those are the only transmission related issues that could affect the engagement of the starter. If there are other systems on the vehicle that are in the starter circuit, these should also be checked.
The mechanics tips booklet that covers adjustments on the MT-647 is available at www.allisontransmission.com
I hope this gets you on the right track to a more permanent fix.
dbarton291
Senior Member
RE: Allison mt647 delayed start
I forgot one thing. In running that wire directly from the starter switch to the starter solenoid, you have most likely bypassed the neutral start circuit. I would strongly recommend you fix it quickly. You don't want somebody to accidentally start the vehicle in gear and run through a garage door, or worse.
I forgot one thing. In running that wire directly from the starter switch to the starter solenoid, you have most likely bypassed the neutral start circuit. I would strongly recommend you fix it quickly. You don't want somebody to accidentally start the vehicle in gear and run through a garage door, or worse.
Re: Allison mt647 delayed start
wow...i feel kinda embarrassed here......thank you so much for your input, however as i was reading your reply i realized that i did not have a mt647....i have in fact have a md3060! i have no idea how i did this.......the md3060 is fully electronic...i realize my issue is probably a neutral safety issue...or prndl issue......i just have no experience with this transmissionand i am looking for assistance on how to test/adjust/replace such a thing on this unit.....or do i have to have a scan tool/pc to diagnose this?
thanks for your concern regarding the bypass.....but this is a fire truck and we need to be able to keep it in service..... :clown:
wow...i feel kinda embarrassed here......thank you so much for your input, however as i was reading your reply i realized that i did not have a mt647....i have in fact have a md3060! i have no idea how i did this.......the md3060 is fully electronic...i realize my issue is probably a neutral safety issue...or prndl issue......i just have no experience with this transmissionand i am looking for assistance on how to test/adjust/replace such a thing on this unit.....or do i have to have a scan tool/pc to diagnose this?
thanks for your concern regarding the bypass.....but this is a fire truck and we need to be able to keep it in service..... :clown:
dbarton291
Senior Member
Re: Allison mt647 delayed start
Now that we know it's a 3060, that completely changes the picture. If you have no experience, this one is best left to the pros.
That being said, it's wise to get a wiring schematic on the vehicle. That should be available from the body builder that turned it into a fire truck. No matter who works on it, that will save tons of time.
This could be the neutral start relay or its wiring, the selector, ECU, a vehicle ground or other things too numerous to list.
Now that we know it's a 3060, that completely changes the picture. If you have no experience, this one is best left to the pros.
That being said, it's wise to get a wiring schematic on the vehicle. That should be available from the body builder that turned it into a fire truck. No matter who works on it, that will save tons of time.
This could be the neutral start relay or its wiring, the selector, ECU, a vehicle ground or other things too numerous to list.
Re: Allison mt647 delayed start
prior to being a firefighter, i was an auto tech for twelve years.....i worked on lots of automatic transmissions.....my specialty was driveability/electronics. i did a lot of work with chrysler transmissions so i recognized a few things such as input/output speed sensors.....etc.....i guess i was kinda hoping that somebody could point me in the direction of some factory schematics for this unit so i could check out the neutral safety switch and circuit. as far as the aftermarket fire truck manufacturer, i have some of their schematics on the way and some already here. where is the switch located? is it inside the pan? accessable without completely disassembling the unit? i appreciate your patience and help on this one...the local dealer is dragging their feet....i think they're scared of it because it's 'lectronic!!! lol....
prior to being a firefighter, i was an auto tech for twelve years.....i worked on lots of automatic transmissions.....my specialty was driveability/electronics. i did a lot of work with chrysler transmissions so i recognized a few things such as input/output speed sensors.....etc.....i guess i was kinda hoping that somebody could point me in the direction of some factory schematics for this unit so i could check out the neutral safety switch and circuit. as far as the aftermarket fire truck manufacturer, i have some of their schematics on the way and some already here. where is the switch located? is it inside the pan? accessable without completely disassembling the unit? i appreciate your patience and help on this one...the local dealer is dragging their feet....i think they're scared of it because it's 'lectronic!!! lol....
dbarton291
Senior Member
Re: Allison mt647 delayed start
There is no neutral start switch on or in an MD3060. The neutral start circuitry that is used is provided by the body builder, not Allison. This is not like working on a car from that standpoint. An Allison schematic will not show you all the systems that are in that vehicle.
On seeing selector power, neutral selected, plus some other parameters, the transmission controller grounds a wire that goes to the neutral start relay. That provides power to the starter circuitry assuming there are no other systems in the vehicle that are a part of neutral start, which there may be.
The schematics Allison does provide, which are not OEM specific, are in the back of the troubleshooting manual for that transmission. One way to get a troubleshooting manual is off ebay or at www.allisontransmission.com
Assuming they're done correctly, the schematics from the body builder, should show the locations of the components that are in the starter circuit. Then you can make sure the neutral start signal from the trans controller is going to ground. Check the relay for proper functioning and good contacts. Check the other wires in the starter circuit for opens, shorts, shorts to grounds and intermittents.
That's a start, anyway.
There is no neutral start switch on or in an MD3060. The neutral start circuitry that is used is provided by the body builder, not Allison. This is not like working on a car from that standpoint. An Allison schematic will not show you all the systems that are in that vehicle.
On seeing selector power, neutral selected, plus some other parameters, the transmission controller grounds a wire that goes to the neutral start relay. That provides power to the starter circuitry assuming there are no other systems in the vehicle that are a part of neutral start, which there may be.
The schematics Allison does provide, which are not OEM specific, are in the back of the troubleshooting manual for that transmission. One way to get a troubleshooting manual is off ebay or at www.allisontransmission.com
Assuming they're done correctly, the schematics from the body builder, should show the locations of the components that are in the starter circuit. Then you can make sure the neutral start signal from the trans controller is going to ground. Check the relay for proper functioning and good contacts. Check the other wires in the starter circuit for opens, shorts, shorts to grounds and intermittents.
That's a start, anyway.
