Modulator schematic?

[Soaringcook]

Hi, does anyone have the wiring schematics for the electric modulator on a mt643/dt466e?


Also does anyone knows where the relay is?

2000 international 3800

Any help apreciated.

[cadillackid]

ill have to look for the schematic but ultimately theres just 2 wires going to the modulator a Plus and minus.



the relay will be up on the firewwall under the hood.. theres a bank of 3 or 4 relays. I think the panel they sit on is labelled.



the ECM controls the coil to the relay (and does a poor job of it). the only way I was able to test the circuit was to set up a light that I could see from in the cab and drive the bus.. only then would the ECM command on the modulator circuit (when the engine is under heavy load).. if you have servicemaxx software you can command that output on for testing as well.



if you put 12 volts to the modulator itself you should get a good solid "clack". I think the pins on it are labelled + and - on it.. I gave away the new one I had so I cant look.



that darn modulator failing was the demise of the AT545 in that bus!

[Booyah45828]

Like christopher said,

The modulator relay is in a group of them on the firewall above the engine.

I don't believe a failed modulator would prevent your bus's torque converter from locking up. It should still lock up, just at a much lower speed/rpm.

Or did we find the cause of your calculated - realized speed discrepancy? And you've now got another problem?

[cadillackid]

Originally Posted by Booyah45828

Like christopher said,

The modulator relay is in a group of them on the firewall above the engine.

I don't believe a failed modulator would prevent your bus's torque converter from locking up. It should still lock up, just at a much lower speed/rpm.

Or did we find the cause of your calculated - realized speed discrepancy? And you've now got another problem?

theres so ,many 643 threads all the sudden. . I thinkl this is the OP where when he let off the gas pedal at highway speed his RPMs dropped out really quick vs slowly dropping with speed..



that seems like a failed lockup.. but ive gotten some of these threads mixed up lately.

[Soaringcook]

I do have servicemaxx and nexiq. How can i use it to command the output put for the modulator/relay? And do i plug a light ti the modulator or relay for testing?

[Booyah45828]

Originally Posted by Soaringcook

I do have servicemaxx and nexiq. How can i use it to command the output put for the modulator/relay? And do i plug a light ti the modulator or relay for testing?

It depends on how the modulator is wired or controlled. Some are by ecm, some are by a switch on the throttle pedal. We went through this a year or so ago with simplicity and his bus. IIRC, the modulator didn't effect the tcc working or not, just what rpm it engaged at (lower then normal)

Search the forum for the thread(s) and read through them.

In the shop we always tested them during the annual. With koeo, we'd push the accelerator pedal to the floor and someone underneath would check plunger movement. No plunger movement meant troubleshooting was done to fix the problem.

Search cadillackid's posts too. IIRC again, he did some testing and found the ecm control of the modulator was erratic, and the engine had to be running, which lead me to believe our buses had the "fix" of a switch on the pedal assembly.

[cadillackid]

Originally Posted by Booyah45828

It depends on how the modulator is wired or controlled. Some are by ecm, some are by a switch on the throttle pedal. We went through this a year or so ago with simplicity and his bus. IIRC, the modulator didn't effect the tcc working or not, just what rpm it engaged at (lower then normal)

Search the forum for the thread(s) and read through them.

In the shop we always tested them during the annual. With koeo, we'd push the accelerator pedal to the floor and someone underneath would check plunger movement. No plunger movement meant troubleshooting was done to fix the problem.

Search cadillackid's posts too. IIRC again, he did some testing and found the ecm control of the modulator was erratic, and the engine had to be running, which lead me to believe our buses had the "fix" of a switch on the pedal assembly.

thast pedal fix was really common on Ohio busses.. from what I understand WW Williams in columbus originally developed it and then built kits thast went to their locations all over the country.. its easy to spot.. if you look at your gas pedal you will see a little skinny medal paddle with a couple wires connected to the switch that are not part of the main 5 wire gas oedal coinnector.. when you press down about 1/2 to 3/4 of the way youll see the pedal press that paddle and the switch 'clicks'.. the fix also left the ECM in the mix so either could call for the modulator.. my red bus still has the switch on it.. i never took it off when I swapped transmissions..

[Soaringcook]

Does anyone know the part number for the switch?

[cadillackid]

I don’t . It was a WW Williams fix up . They are an allison master dealer, there’s no IH part number for it. I can take pics of mine when I’m over at that bus again. I can probably pull it off prettt easy

[Soaringcook]

That wouod be great , so did International ever fixed the signal issue?

[cadillackid]

Originally Posted by Soaringcook

That wouod be great , so did International ever fixed the signal issue?

they may have.. I updated my ECM but that was after I had installed my allison 1000 .. so I dont know if that update fixed the issue or not

[Soaringcook]

Does anyone know about how much fluid comes out when i take the modulator off the tranny? Estimate

[Booyah45828]

IDK. We did it in the middle of service, so the pan was empty and very little fluid came out.

A catch pan underneath should be more then adequate. It won't be on the order of gallons coming out.

[cadillackid]

if it was 1/2 a quart id be surprised.. I had a small pan underneath and held up when I pulled the modulator out..