I have a 06 mack that when you put the pto in and let out on the clutch it grinds like hell. Also while driving down the road it actas like it slips into neutrul and if i let off the fuel it goes back in but if i keep on the gas it goes nowhere. ony help will be greatly appreciated. thanks guys.

sincros in your trany are gone.

Call your local dealer (mack) and explain to them.This is a very common problem with mack trans.

Yea. All mack says is awe yea just bring it in and well fix er up for ya. If it the sincros then will it do it in every gear.

My guess if it does it in PTO, then it also slips when the tranny is in high range.  It the high range syncro in the back of the transmission.

Better check and keep an eye on the Stiebel box. 

Check the air operated switchblock on top of the Stiebel box and make sure it is properly switching in and out of PTO and it is not leaking.  Pretty common place for a line to break at the joint around here since it perfect for grease/oil to accumulate and break down the lines.  Give the air lines a good once over.

Also, check the fluid level in the box.  If I remember correctly, if it is low on fluid, it won't properly switch in and out.  I had this problem once on a 42m. 

I don't think it's the tranny Lo/Hi synchro because usually when it goes, it won't let you shift from Lo to Hi or vice-versa...but it will stay in gear.

You said that it is noisy when you engage the PTO and let off the clutch. I am assuming that when the PTO is not engaged and you let off the clutch that the noise is not there?

The air operated switchblock on your PTO case that 52putz is talking about can also leak air pressure internally as well. This can be determined by building air pressure then engage PTO as if you are preparing to pump, then turn off engine, switch key back on but do not start and roll underneath and listen for air leaking from vent on top of PTO case. When you are driving down the road and it seems to go into neutral, do you hear the same grinding sounds that you hear in PTO?

I know whats going had mine go out last winter if it slips out of gear driving,,  then your shift fork is bad, its in your lower stebiel box on mine the chattering noise was in the upper stebiel the rear coupling and the main pump shaft had stripped, that fork is made out of brass , had to replace the gear that slids from drive line to the pump those parts were over 3,000.00 top and bottom .

hi-lo synchro take it to mack where you get some warranty with it , it want be your last issues with it I promise.

 Not Likely a syncro if slipping possibly a clutch problem if you find it to be a tranny problem i suggest putting in a eaton 8LL trany and get rid of the mack trans little bit of figuring out the right mounts and shift linkage but a lot better trans and cheaper and better to get serviced and parts

It sounds to me you switching fork and slide gear in your pto are not meshing properly theres a ball and spring inside the slide gear if the gear is worn out and is only grabbing a very little teeth it will pop out of gear and grind when putting in pto if this in fact true you dont have much time drain the pto and check for steel or brass coming out of drain hole

ouch biged.

sorry big ed i guess i should have read all of the post saw it earlier today didnt have time to respond well antway what he said

Your tranny is going bad. I have a 06. Lost tranny,Get it checked

I hate to say this but me and pumpit are right on target tranny is not the problem, mack trannys are a problem but not worth the trouble and time to change it out drain your stebiel box and check for brass filings mine didnt show any ,but my fork had melted  to the gear slot and it will let you down pretty fast, if you fix it your self don't take the whole box out take the banana pump off the front then remove the front cover, that case alumium box cost about 10,000 so the less you remove the better, to bad and inspection plate wasn't built into this box.

if you decide to take just the front cover off be patient putting it back on the bearings on the topp swivel if there not straight it wont go on and big ed is right it breaks easy

either way let us know what you find

Where the noise grinding is coming from is the slider gear trying to stay in the drive side also when you are getting ready to pump at what air pressure do you switch from drive to pump at ,I was told to be sure you build air pressure to 120 PSI for the shift, my gear that slides forward and backward was really ok but it got changed anyway and is still good if you want it , just pay for shipping and its yours that will save you 450.00.  My advice get it fixed now cause it will let you down on the side of the road and being that big of pump it must have twin steer tow rigs hate those tows.

I drove a gravel truck that gave me a similar problem and it turned out that the nut that holds the yolk onto the output shaft of the tranny had backed off and allowed the output shaft to move inside the tranny and kick it out of gear. It was also an 06 Mack, the wrench you need is a 1" 5/16. Not saying this is defintely it but worth a quick check. Good luck.

AS BEFORE, OUCH biged.  it sucks ass but operator abuse also sucks the big one.  pay the bill, get er fixed and i hope the operator learnt their lesson.  if not, god has a 12 gauge for a reason and a system of appeal.

I'm with big ed. it's the shift fork. same scenario happen to me with the same issues. Shift fork is the weakest. Drain the oil for starters. You should see some clues at that point.

A clue,it's one of the 7 senses

Now there's at least 6' between the 2,trans and stieble