Another Skoolie with Allison 545 issues

[!eslie.brewer.me]

Does anyone out there know if I can and how to convert an electric modulator to vacuum? The modulators seem to be an ongoing issue on all of these 545s, among other things.

I want to see if I can convert the electric modulator to a vacuum. Any help would be great.

[cadillackid]

on a diesel.. VERY difficult since there is no source of vacuum that is related to engine load..



on the mechanical DT engines like my 360, the modulator is cable-driven and is connected to the accelerator's mechanical linkage.. on a 466E you would need to fashion something up that matched the original geometry and would physically tie to your accelerator pedal so as you press down it would pull out the cable like it does on the old engines..



Vacuum modulators are used only in gasoline engine applications.. gasoline engines create high levels of vacuum when they are under little to no load.. essentially you starve a gas engine for air when its idling or under no load.. thus its gaspin for air creating lots of suction (vacuum)... this deactivates the modulator pin (a vacuum modulator has a spring so when there is no vacuum the modulator is fully applied)...


on a gas engine when you put it under load.. ie pushing on the accelerator pedal it gets more of the air it desires so the vacuum level goes down.. this is also a way of telling the transmission.. hey this engine is under heavier load, we should shift later and firmer...



diesel engines are not starbed for air when they are under no load.. in fact being turbo charged they are always under Positive pressure.. there is never a vacuum on a turbo diesel in a normal operation... thus you cannot convert to a vaccum modulator..



the electric modulator navistar and others use was a piss poor device.. being either all-on or all-off it was essentially just a kick-down device... it was developed because on the 'E' engines there is no physical accelerator linkage.. the pedal on the floor just goes to the computer which tells the engine to run.. (drive by wire)...

[!eslie.brewer.me]

Wow! Thank you so much for the detailed information.

The modulator I had was leaking transmission fluid. I opened it up and sure enough the seal from the transmission fluid to the electrical components had failed. It was shorted out and not working.

I'm fairly electrically inclined.

If I were to dissect further and find the circuit board, I wonder if I could fix the short, apply silicone for a new seal and put back together.

Then I'm wondering if I can bypass the relay and install a monetary push button on my control panel in the cockpit.

Then essentially I would turn it into an electric manual transmission.

I would be able to shift when I push the button.

This is very rough Theory but needing to find a solution and that seems plausible.

What do you think?

[cadillackid]

the modulator itself doesnt have a circuit board in it.. though it might have a Flyback diode in it that couldve shorted.. if its a dead short the most likely culprit is the coil itself is dead.. fluid may have ate the insulation on the windings..



the ECM controls it based on engine load..



its not an absolute manual shift mechanism.. it is to raise line pressure (and shift point) when the engine is under load..



when power is applied the pin extends and raise pressure .. when power is off the pin pulls back and line pressure lowers..



a momentary switch would give you some sort of kickdown but would go right back uo when you let off the switch.. a much better way if you want to eliminate the computer is to put a switch on the acclerator pedal.. this is what was done to my red bus.. so when it reached 60-70% pedal the modulator came on and ran the trans in high pressure mode until you let off.. this also allowed the trans to run in modulated mode while the RPMs were up since the pedal is essentially and RPM setpoint.. when I tried hooking the ECM back in like it was factory.. it hunted all the time.. I hated it.. however when I got my bus my modulator was bad and that ultimately started my transmission down its death spiral till it died and I swapped it out for a better one.

[!eslie.brewer.me]

My dream transmission would be an Eaton 18 speed.

This is the first automatic I've ever had and the first diesel. A fish out of water.

I can't thank you enough for your advice!

I'm stuck in a place called Canadian Texas, with a busted transmission I had an Eaton 18 speed with the clutch and everything I needed to put a pedal and a shifter in. I can't seem to get ahold of the guy, now that I have the money for it.

So, I'm trying to decide if I should just keep on looking for another one like an Allison 643, Etc or if I should just fix this one and get another one when I get to my next destination which would be a bigger city with more options.

I'm out in the middle of nowhere and it's hard to find anything.

I pulled the governor out and it looks like the governor drive shaft is busted.

I called a few transmission shops but they said that only the rear end and or the Driveline would cause the governor drive shaft to bust, the way it did.

I'm trying to attach pictures so please let me know if they don't show up.

I know I need a modulator and Governor drive shaft but if I get those two and it starts shifting how do I know that it was the transmission and or the rear end, driveshaft? That was the ordinal issue.

I don't know ]w what I'm looking for on this bus.

There was a lot of vibration but I didn't know what was normal and what was not. I've never driven a bus either.

[!eslie.brewer.me]

I think I figured out how to post pics...

[!eslie.brewer.me]

One more pic ...

[cadillackid]

the drive gear still looks OK.. wheres the rest of the governer shaft? did you get it out or did it end up inside the transmission?


I dont think ive ever seen a governor driveshaft just bust in 2 by itself.. now i HAVE seen a weight fly off the governor and cause the shaft to break.. .. seen the plastic governor gear get ate more than once..



I think I still have a governor laying around for a 545... ill have to look and see if I tossed it or not.. it wouldve been for my DT360 which shifts close to what your 466 does..



I didnt even know you could get an 18 speed in an SAE2 bell.. I thought they were all SAE1 bell housing.. ive seen 13's in an SAE2... cool stuff if you have one!. that thing has to weigh enough youd need to fashion up a secondary mount.. I wouldnt let that hang from the bell..



driveline vibe can come from many different things.. most often it is worn out U-joints, out of balance driveshafts, out-of-phase driveshafts.. you can get vibe from rear end as well but that doesnt usually make it all the way up to the transmission...


a bad tailshaft bearing (rare) could allow the output shaft to wobble.. but id expect it to eat the plastic gear before I would break the governor.. wow thats a wierd one..

[!eslie.brewer.me]

I think I'm going to try to repair this 545 until I can get to a bigger city. I have no idea what I'm doing at all. I've never worked on Transmissions before. The governor itself is fine and the plastic piece on it is good too.

I'm having a heck of a time getting the bolt off of the emergency brake to get into the transmission shaft.

I wonder what caused it to bust the governor drive gear? If I can get the e-brake bolt off then I can dig in further. Any tricks?

Trying to find a new electric modulator seems expensive and tough to find. Any suggestions there?

[!eslie.brewer.me]

What kind of switch did you put on the accelerator pedal? And what transmission did you end up going with in the end?

[Booyah45828]

Pull the pan, you should be able to see the governor gear and it's drive gear on the main shaft from there. Post a picture of your governor too.

I've never seen a governor shaft snap. If the governor itself would seize, I'd think the nylon gear would give up before the shaft would. The only way I could see that braking is if the mainshaft was allowed to move around and shear it off. But you can check that by lifting up and down on the output yoke and checking for movement.

Unless you broke it trying to get it out. It has to slide straight out the case by a few inches before you can angle it.

The same electric modulator is used in both mt and at transmissions. Going vacuum won't gain you much, and going cable very little as well. Fixing what you have will be easiest solution. There seems to be a shortage of modulators for whatever reason, which is why the price has tripled in the last year. You might be able to find a used one cheap, just verify that it works by power testing it before installing it.

[cadillackid]

Originally Posted by Booyah45828

Pull the pan, you should be able to see the governor gear and it's drive gear on the main shaft from there. Post a picture of your governor too.

I've never seen a governor shaft snap. If the governor itself would seize, I'd think the nylon gear would give up before the shaft would. The only way I could see that braking is if the mainshaft was allowed to move around and shear it off. But you can check that by lifting up and down on the output yoke and checking for movement.

Unless you broke it trying to get it out. It has to slide straight out the case by a few inches before you can angle it.

The same electric modulator is used in both mt and at transmissions. Going vacuum won't gain you much, and going cable very little as well. Fixing what you have will be easiest solution. There seems to be a shortage of modulators for whatever reason, which is why the price has tripled in the last year. You might be able to find a used one cheap, just verify that it works by power testing it before installing it.

im guessing shortage because they are past the 15 years of required manufacture.. the last mechanical allison that used the electric modulators was in 2003.. they are likely not high on anyone's priority list to make..

[Booyah45828]

Eh, they'll make them if they can sell them. Yeah, they're 15+ years old by now, but there are still a bunch in use out there yet. The shortage is more to do with all the headaches of manufacturing in a post-lockdown world.

[sportyrick]

Went through that area on the way back from Skoolie Palooza, pretty stark. I think you'd be surprised who you could scare up if you start asking around. There is an old retired transmission guy out there somewhere. I wouldn't negotiate that job w/o some professional help. Salvage yards, school maintenance barns, car or truck dealers, car salesman, tow truck drivers, somebody knows a transmission guy, you can't be shy, u have to stick your hand out for a shake and ask everyone you see. Human nature is to help a stranger in need.

[cadillackid]

I think finding a used modulator is well within the scope of doable..



my guess is Mike and B sales in eastern ohio here can score one


I gave away the nearly new modulator I had to another forum member, but I do still have the governor.. it shifted out somewhere around 2600-2700 RPM under full throttle... it seems to be in good condition.. you could always move the springs and weights over from your broken one unless the head got torn up.. but my guess is it would probably work pretty good just dropped in.

[!eslie.brewer.me]

I got the bus started today!

Have a leak on one of the fittings but that should be an easy fix.

I got her to shift thru the gears!!!

Smooth as butter!!!


I probably looked like aa crazy person when that happened! I was laughing and crying, hysterically at the same time.

Thank u to everyone for their help and words of encouragement!!!

Been an Insane amount of super hard work but I did it.

*“You know the greatest danger facing us is ourselves, an irrational fear of the unknown. But there’s no such thing as the unknown — only things temporarily hidden, temporarily not understood.”

- Captain James T Kirk.