MackR797-W45Holmes

my trick for that is to leave it in high and go from 4 high to 5 high, then put it in direct and rev slightly so it engages into 5 direct, it works for me and when you get the hang of it, it won't grind anymore

i hope that makes sense...

Yes this works for me also.

Steve.

I've had that happen a few times. Usually it's a combination of two things.

1) The plungers & cams in the power divider are getting worn.

2) Mismatched tires from front to back on the tandems.

The clunking is the result of the pins & cams "jumping over" 1 notch every so often trying to compensate for tires of slightly different diameters on the drives.

Measure the circumference of each of the 8 drive tires. Put the 4 largest ones on the right side, & put the 4 smallest ones on the left side.

With a Mack power divider NEVER put all 4 larger tires on one drive axle & all 4 smaller tires on the other drive axle, as this causes the power divider to work constantly to compensate.

"Brand X" trucks with a conventional inter axle differential are not sensitive to mismatched tire as they are a regular spider gear type setup.

If you match up all the tires as I stated previously & it still clunks, then it's time for a power divider rebuild.

superdog, no o/d , 12speed direct air shift.

Tires could be the problem,do you have an OD transmission?

no overdrive. 12speed direct air shift.

I have a clunk type noise ocassionally maybe once or twice per mile not consitent could this be coming from the power divider section ? does mismatched tyres cause this ?