18 speed problems

[mike5025]

I have a 2006 granite with mack 460, and mack 18 speed, have completely rebuilt tranny once, now rear synchros out again second time, third counting complete rebuild. truck has 250,000 miles. I have kenworths and petes with 750,000 miles on original fuller trannsmissions. Are these transmissions this bad? Where can I get parts to rebuild rear section high low range synchro.

[jakebrake86]

Welcome to the site! The newest Mack transmission I've owned was a 1982 two stick six speed which, in my opinion, was unbeatable. I haven't heard good things about the newer Mack transmissions, though.

[rick harper]

Make sure you or your driver is pre-selecting before going from low to high or vice verse. If no, it wont let the pack fully engage and after time it will burn up. Alot of updates thru the years. Be sure and get current parts thru Mack because of all the updates.

[rsb502]

You shouldn't have that kind of trouble with that trans they are pretty tough id bet it was not pre selected you have to make sure it he air pressure is on the solenoid before the shiftor you'll burn it up flip the switch to go to high as soon as you get power on 4th that gives it plenty of time same for down shift and don't flip it back and forth in neutral

[Superdog]

the transmission on my son's Rawhide went out at 485,000.I'm still fighting Mack over that.

[HK Trucking]

That's a disease with the Mack 9, 13 & 18 speed transmissions. The Hi range/lo range synchro starts acting up, causing a terrible grind on the first few shifts when the truck is cold, then it keeps getting progressively worse as time goes on, which leads to the teeth on the hi/lo shifter getting worn down to the point that the trans will jump out of gear when you put the power to it. As Rick said above, Mack has updated parts available that are supposed to cure this problem. Another way you can avoid the clashing on cold upshifts is to shift by going from 3rd lo range to high range on the button & lo on the stick, then shift up from there in hi range. This allows the range shift to take place at lower transmission rpm, hence less strain on the range shift synchros. I had one that started clashing when cold & I nursed it along for quite a while by shifting it that way until it warmed up.

[Challenger]

Mack did come out with updated lo, hi split and synchronizer parts this year. Get the Mack parts, the generic aftermarket parts wont last. There was also a service bulletin saying you have to replace the synchronizer fork pinch bolt. They say the bolt has a scotch lock on it and can only be used 1 time. Even if you use loctite and torque the bolt it can back out and cause synchronizer failure. Im sure there are alot of mechanics who reused that bolt and caused premature failures after their repair.

The main 2 Mack Granite trans failures I see are the pinch bolts coming loose around 60,000-70,000 miles. I assume this was a factory defect. And the other one is transmission cooler failure. The cooler fails and allows coolant to flow into the trans and basically wipes it all out.

The other reason are improper repairs. I just repaired 5 trans from one owner. He had a guy who knows Mack trans repair his trans. He did half ass repairs with aftermarket parts. 2 of the trans never made out of the garage.