Mack quantum with 18 speed Eaton has by itself split down in top gear

[Gorilla]

Driving along at 100km/hr, went over some bumps and the trucks revs went high and i realized the truck by itself had split down a gear, i tried to move the splitter switch back and forward and nothing happend so i pulled over and checked if any lines had come lose or anything like that but nope all seemed good.  So i took off and all went well and about 15-20 minutes down the road it did exactly the same thing.  Again i stopped and went through the gears and all went well after that for the next 20 minutes and i got to my destination (new location to finish working on the truck before i put it in service) Does anybody know where i should start with my investigation?

I know i have some air leaks which i will address before i drive it again but pressure seems to be keeping up on the gauge and i am not getting any low pressure errors. 

[Adkat]

Has it got a spin on air filter up in the rail somewhere behind the gearbox? The air line that runs into the filter/reg at the top rh rear of the box should come from the spin on if it has one. You can also pull the bottom off the filter reg and give it a clean out.

[Gorilla]

47 minutes ago, Adkat said:

Has it got a spin on air filter up in the rail somewhere behind the gearbox? The air line that runs into the filter/reg at the top rh rear of the box should come from the spin on if it has one. You can also pull the bottom off the filter reg and give it a clean out.

Im heading to the truck right now, will check it out what you said and take some pics too.  Come to mind i have a pretty big air leak that i am next to address on a spin on air filter approximately 1 meter behind the gearbox, could this have something to do with it?

 

[Adkat]

Yeah most have the spin on filter in the supply line to the gearbox, unless it has been deleted. Should look something like this

 

Unless you have an air dryer mounted back there. Some pics will soon tell.

[Joey Mack]

Nice go.  Adkat... I dont know these trucks, but i feel like you are tuned in..  i was thinking about a shuttle valve if it is a manual transmission... But..... I watching..  🍺

[Adkat]

Should have an 18spd Eaton in it. Funny how all the fluid filters get changed, but that little air filter gets forgotten about. Had a 15yr old truck come through that still had the paint on it from factory 🤦🏻‍♂️.

Sounds like it's lost pressure and kicked itself out of high split? Shuttle valve would play havoc with the range shift not the splitter, I think?

Joey, you'd be all over these trucks, Etech CCRS roadranger, mostly meritor drives on hendrickson air. Only real headaches are the cab and electronics, being Renault. And that they're now 20 odd years old.

[Gorilla]

6 hours ago, Adkat said:

Should have an 18spd Eaton in it. Funny how all the fluid filters get changed, but that little air filter gets forgotten about. Had a 15yr old truck come through that still had the paint on it from factory 🤦🏻‍♂️.

Sounds like it's lost pressure and kicked itself out of high split? Shuttle valve would play havoc with the range shift not the splitter, I think?

Joey, you'd be all over these trucks, Etech CCRS roadranger, mostly meritor drives on hendrickson air. Only real headaches are the cab and electronics, being Renault. And that they're now 20 odd years old.

Gonna go trough the whole air system with a fine tooth comb, being reasonably new to working on trucks im still learning how the air systems work but im 100% anti push on air fitting, they all suck, they suck and they are all gonna be swapped for brass ones that bolt together that dont suck

 

Cab is fine, and its eaton diffs on hendrickson hair...only problem i have had was the 24v to 12v converter which was giving out a very "special" 20v!!! so i replaced it with a high end chinese one for $100 vs the original one for over 2k!!! and vualla all is perfect.

 

Edited February 21 by Gorilla

[Gorilla]

On 2/21/2025 at 11:16 AM, Adkat said:

 

Sounds like it's lost pressure and kicked itself out of high split? Shuttle valve would play havoc with the range shift not the splitter, I think?

 

how would i test the shuttle valve?

[fjh]

make sure your Air pressure is above  cut in pressure  90 or so ! Put the stick in a gear if when you pull the stick into neutral the air shift operate the  shuttle is not the issue! it also sounds as thou the split is the issue ! Im not positive on this but on the older thirteen speeds there was an insert valve on the piston maybe check to see if this has the same if so its an easy change! 

[other dog]

On 2/20/2025 at 7:16 PM, Adkat said:

Should have an 18spd Eaton in it. Funny how all the fluid filters get changed, but that little air filter gets forgotten about. Had a 15yr old truck come through that still had the paint on it from factory 🤦🏻‍♂️.

Sounds like it's lost pressure and kicked itself out of high split? Shuttle valve would play havoc with the range shift not the splitter, I think?

Joey, you'd be all over these trucks, Etech CCRS roadranger, mostly meritor drives on hendrickson air. Only real headaches are the cab and electronics, being Renault. And that they're now 20 odd years old.

I've driven 4 different trucks with 18 speeds in them, many with 13 speeds, and I never knew there was an air filter on them. Of course I never claimed to be a mechanic, and not much of a truck driver 🤣 

[Adkat]

3 hours ago, other dog said:

I've driven 4 different trucks with 18 speeds in them, many with 13 speeds, and I never knew there was an air filter on them. Of course I never claimed to be a mechanic, and not much of a truck driver 🤣 

Most roadrangers run a filter regulator, sort of like your shop air compressor filter reg. Mack usually run an additional spin on chassis mounted air filter.

 

[Adkat]

6 hours ago, fjh said:

make sure your Air pressure is above  cut in pressure  90 or so ! Put the stick in a gear if when you pull the stick into neutral the air shift operate the  shuttle is not the issue! it also sounds as thou the split is the issue ! Im not positive on this but on the older thirteen speeds there was an insert valve on the piston maybe check to see if this has the same if so its an easy change! 

Shuttle valve only allows activation of range cylinder when stick goes to neutral.

The splitter gets an air feed straight from the reg, and a signal feed from the shifter.  Splitter will shift as long as there is no load on gearing.

Breakdown of splitter cylinder 

[Geoff Weeks]

26 minutes ago, Adkat said:

Shuttle valve only allows activation of range cylinder when stick goes to neutral.

The splitter gets an air feed straight from the reg, and a signal feed from the shifter.  Splitter will shift as long as there is no load on gearing.

Breakdown of splitter cylinder 

I thought/think he is refering to the "peanut valve" in the splitter cover. I don't know if they still use it, but it could be part of the problem. B11 in your picture

[Adkat]

5 minutes ago, Geoff Weeks said:

I thought/think he is refering to the "peanut valve" in the splitter cover. I don't know if they still use it, but it could be part of the problem. B11 in your picture

Yeah I reckon that's what fjh was referring to. I'm thinking he probably has the updated design though.

[other dog]

9 hours ago, fjh said:

make sure your Air pressure is above  cut in pressure  90 or so ! Put the stick in a gear if when you pull the stick into neutral the air shift operate the  shuttle is not the issue! it also sounds as thou the split is the issue ! Im not positive on this but on the older thirteen speeds there was an insert valve on the piston maybe check to see if this has the same if so its an easy change! 

Is that why on the older 13 speeds they recommended shifting it like a 2 speed axle, that you shift to the next higher gear first then move the splitter button back to direct, then the later ones they said it was OK to preselect the splitter?