Air Shifted Mack Transmissions:

[Rob]

Do any of you guys that have either the air shifted six, 10, or 12 speed transmissions have any problems with rapid engagement of reverse from forward position? On my 10 speed, sometimes is readily slips into reverse, and sometimes I have to let the clutch out in neutral to release the gear bind before it will switch positions. Can be kind of annoying because when it jumps into reverse when the mainshaft is still turning, it really lurches. I usually wait about 3-5 seconds before switching after stabbing the clutch pedal to let the trans stop spinning, then let the clutch out gingerly and if not engaged, it goes right in. The clutch brake is shot so it is useless.

Last evening it was getting cold outside and it is the first time I've really had it out since the shift plate rebuild when cold. I don't have antifreeze in the cooling system yet so it can't stay outside.

Rob

[jeffbyrne]

Do any of you guys that have either the air shifted six, 10, or 12 speed transmissions have any problems with rapid engagement of reverse from forward position? On my 10 speed, sometimes is readily slips into reverse, and sometimes I have to let the clutch out in neutral to release the gear bind before it will switch positions. Can be kind of annoying because when it jumps into reverse when the mainshaft is still turning, it really lurches. I usually wait about 3-5 seconds before switching after stabbing the clutch pedal to let the trans stop spinning, then let the clutch out gingerly and if not engaged, it goes right in. The clutch brake is shot so it is useless.

Last evening it was getting cold outside and it is the first time I've really had it out since the shift plate rebuild when cold. I don't have antifreeze in the cooling system yet so it can't stay outside.

Rob

Hi Rob, I'm only just starting to play around with the ten speed, but an old guy at Mack in Sydney told me your 60 psi reducers are there to stop that, I think he was saying you dont need them but they stop the hard throw. Regards jeffro

[Rob]

Hi Rob, I'm only just starting to play around with the ten speed, but an old guy at Mack in Sydney told me your 60 psi reducers are there to stop that, I think he was saying you dont need them but they stop the hard throw. Regards jeffro

Hi Jeff, my regulators are all working correctly. The transmission does not shift from forward to reverse 100% of the time when the valve is flipped. What I meant with the clunking into gear is when the main is in neutral position and the flipper is selected to reverse, the trans does not always shift into reverse. I then have to put the main in gear, and engage the clutch to load the gearing, and mainshaft, then disengage the clutch and the gear slides, (usually). When it slides the mainshaft is still spinning and this reverse engagement is not at all smooth jerking the truck. Really don't want to destroy anything and this may be a "nature of the beast" but having no experience, figgered I'd ask. There are times though that the thing will not go into reverse for several iterations of this. I've moved the truck near five feet forward before it will shift to reverse a couple of times.

Certainly wouldn't want to butt the front bumper against a wall, and not be able to back out because reverse will not select.

Thanks,

Rob

[jeffbyrne]

Hi Jeff, my regulators are all working correctly. The transmission does not shift from forward to reverse 100% of the time when the valve is flipped. What I meant with the clunking into gear is when the main is in neutral position and the flipper is selected to reverse, the trans does not always shift into reverse. I then have to put the main in gear, and engage the clutch to load the gearing, and mainshaft, then disengage the clutch and the gear slides, (usually). When it slides the mainshaft is still spinning and this reverse engagement is not at all smooth jerking the truck. Really don't want to destroy anything and this may be a "nature of the beast" but having no experience, figgered I'd ask. There are times though that the thing will not go into reverse for several iterations of this. I've moved the truck near five feet forward before it will shift to reverse a couple of times.

Certainly wouldn't want to butt the front bumper against a wall, and not be able to back out because reverse will not select.

Thanks,

Rob

Hi Rob, I'm having trouble getting reverse in the truck I just purchased, I've only managed to select rev once, and that took alot of flipping in/out. When I'm in neutral on the button with lever in gear, I cant get neutral, so its in the shift knob or the airshift I spose. I spent 1/2 hr nudged up against the front gate then managed to get rev. With mine it is very quiet, can hardly hear the shifter. This is the 1st time I've had anything to do with airshift. Jeffro

[Kav]

Hi Rob, I'm having trouble getting reverse in the truck I just purchased, I've only managed to select rev once, and that took alot of flipping in/out. When I'm in neutral on the button with lever in gear, I cant get neutral, so its in the shift knob or the airshift I spose. I spent 1/2 hr nudged up against the front gate then managed to get rev. With mine it is very quiet, can hardly hear the shifter. This is the 1st time I've had anything to do with airshift. Jeffro

Hi Rob and Jeffro , I find that if you are using the truck every day they shift easier. Before I changed the regulators on the ten speed I had trouble getting it into reverse and also if it hasn't been used for a while you sometimes have to flick the little lever a few times. Sometimes it helps if you put a kit in the switch. You used to be able to get a Spicer kit with just the rubbers that you need. Buntines in the Northern Territory who had hundreds of Macks, apparently used to run higher pressure in them (maybe full supply pressure) but I once saw one of their twelve speeds with a broken reverse selector when it was traded in to Mack. Another thing - do you have anything that builds nests in the exhaust hose in the changer. We have wasps who seal the pipes with mud nests and that doesn't help the change. Best regards - Michael.

[Rob]

Hi Rob and Jeffro , I find that if you are using the truck every day they shift easier. Before I changed the regulators on the ten speed I had trouble getting it into reverse and also if it hasn't been used for a while you sometimes have to flick the little lever a few times. Sometimes it helps if you put a kit in the switch. You used to be able to get a Spicer kit with just the rubbers that you need. Buntines in the Northern Territory who had hundreds of Macks, apparently used to run higher pressure in them (maybe full supply pressure) but I once saw one of their twelve speeds with a broken reverse selector when it was traded in to Mack. Another thing - do you have anything that builds nests in the exhaust hose in the changer. We have wasps who seal the pipes with mud nests and that doesn't help the change. Best regards - Michael.

Hi Michael, thanks for your input and reccomendations. I have completely rebuilt my shift top cover, all shift cylinders, and checked regulator pressures to each one. Also rebuilt the valve in the cab. This truck had sat for nine years without being started prior to my ownership and my problem is most likely nothing more than lack of use. It is a "one finger" ordeal to slide the clutch gear when the top cover is off, and the engine is not running, and the shifting (when proper) is very quiet. I have no air leakage any longer that I've detected and the problem is much more pronounced when the truck is cold. At this point it is not totally reliable and I may up the pressure to that cylinder as the other functions work very well without delay.

Thanks,

Rob

[Rob]

Well this may be a lack of usage thing. Today I had the truck in front of the shop and went back and forth probably 50 times with the shift sequence hanging for the first few times. After about 1/2 dozen times, it never did bind, or hang again but rather slipped right from forward, to reverse, and back again readily. I didn't drive the truck on the road as the temp was well below freezing and there is no anti-freeze in the coolant system.

After letting the truck sit for a few hours I did the same thing a few times and all seems to be working well.

Appreciate all the input.

Thanks,

Rob