Jump to content

SCREAMING 12 Speed !!!


Fastduramax
 Share

Recommended Posts

Welp a good 20 hours plus of labor my rebuilt 12spd is in... Take it for a rip and its deafening in 10th and 12th gears under throttle in other words 4th and 5th hi, quiet in direct... Totally screwed because I bought this tranny 8 years ago for my previous RD that turned out to have a bad rear end so I kept this tranny for a backup confident that it was built by a life long highly regarded Mack technician that has since retired... Anyone have any input on the cause ? This is like the 5th 12spd I have owned and have to say none were ever quiet and none shift the same but this one is scary obnoxious ! Drive it till it grenades ? Not sure if it will last 1 load ,1 week, 1 month, 1 year or if it will just sing like Axle Rose forever !

  • Haha 1
Link to comment
Share on other sites

7 hours ago, Fastduramax said:

Thanks Paul, could you explain further ?

Well you need to think what is spinning in those gears that isnt in the others

The needle bearings in 4th and 5th dont spin if your in that gear 

So it maybe a needle bearing in one of the other gears 

Does the noise go away when you back off ?

 

Paul 

Link to comment
Share on other sites

9 hours ago, Fastduramax said:

FJH even if I was running a side mount it shouldn't scream when not engaged correct ?

The pto gear is still engaged to the counter shaft if set to tight it will will whine all the time! you don't have that problem with 99 percent pto! it runs off the center section (Main Box)

the only suggestion I have for you is to drain the oil remove the pto cover and look inside the back section and see if you can see anything odd!(shift fork rubbing the gear teeth or anything like that ) when the split is in hi! as paul said there are needle / roller bearings on the counter shafts however the sound would likley be there all the time They tend to whine somewhat in hi but not as bad as your describing!

Link to comment
Share on other sites

Ok thanks guys, yes Paul it does go away while rolling and even under Dynatard but screams under throttle even light throttle... I did a quick inspection of the tranny before installing it because it sat for so long the only concern I saw was a fairly sharp gear under the drivers side PTO cover not sure if that could be the culprit or not ? I do know it got a full bearing kit when it was rebuilt...

Link to comment
Share on other sites

High polish on the gears. Don't hate your rebuilder fellow, he likely did a good job. You need to replace the gears that are high end during overhaul. They become so polished you can shave your face looking into them. They don't teach you it at school, but when the high driving gears loose surface X-hatch they get a polished whine. It resounds under load, but not jaking, because you use the side of the gear that has X-hatch remaining.  We eventually made it standard procedure to replace top gear(s) on rebuilds if any polish, they are undersized to the mate gear so they wear fast due to RPM contact cycle being so high.

Turn up the radio, Buy your retiree Mack technician breakfast, it will run out fine.

  • Like 1
Link to comment
Share on other sites

Thank you MT you are obviously a very educated man and that was an explanation I was looking for, well sort of lol... And yes I will buy my man Billy breakfast if I get to see him again he's to grumpy to hate on... Guess I will crank up the Bluetooth and drive it like I stole it and hope for the best... If I may I'd like to run this by you, the 12 I pulled out had the upper right counter shaft push out through the cover plate (357K original miles) quietest and best shifting 12 I have ever had unfortunately I happen to be the third owner so I wasn't the pilot its entire life... Anyway I would like to oversee a complete rebuild of my original tranny for insurance on my very vocal one, I got a price on a complete Timken bearing kit for under $900 clams my local Mack dealer said $1500+ if that sounds correct... In your opinion is it worth the investment for the future ? Also as a side note I have a good Mack rear mount PTO on the shelf that I know is getting near impossible to find these days.

Link to comment
Share on other sites

2 hours ago, Fastduramax said:

 he's too grumpy to hate on...

LOL..You have to be ornery to enjoy rebuilding 12 speeds. Those Devils will make your SRT(standard repair time) look terrible at weeks end.

 

IMO- I'd stick the kit in it. It has no major failed parts, so definitely a prime candidate (assuming loose, plug-popper shaft didn't lose a set screw into gears)? Keep receipts and clean the cases with aluminum cleaner so they shine like the sun. Pics are cheap these days, get pictures of gears laid out for inspection of wear and catalog. Spray fog interior and moth ball.

If you eventually need to unload it you will find a buyer. BMT is a prime place to sell.....year ago I sent a carrier locker kit to Moscow, Russia for our man Vladislov.    

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...