larry perkins Posted April 16, 2009 Share Posted April 16, 2009 forum,i need help,i have a 1988 rw613 superliner with 12 speed,this thing is about to break me. when driving and when the maxibrake is engaged the tranny will come out of gear and make a terrible noise. in high fifth there is just a slight clunk that comes and goes away,but as you use the maxibrake down in the lower gears the clunk is magnified and you know the tranny came all the way out of that gear and is trying to re-engage. at that point one goes to survival mode to get the thing to netural . so far premier mack of louisville(kentuckiana mack) has replaced all the air cylinders ,valves and regulators and problem is getting worse. before i replace the tranny,would anyone have experienced a problem simular to this? its really hard for me to believe that with low miles(less than 300k) and the correct maintenance preformed that this tranny that shifts and runs so smooth could be bad. there is never a problem while under load,only when the engine is preforming the braking process. larry perkins,perkins scale corp lou ky Quote Link to comment Share on other sites More sharing options...
David Posted April 16, 2009 Share Posted April 16, 2009 Make sure all the bellhousing bolts are tight. Quote Link to comment Share on other sites More sharing options...
MACKS Posted April 16, 2009 Share Posted April 16, 2009 I know that this might sound crazy but are you sure the noise is coming from the trany and not one of the rears most likely the front rear.I once had a six speed that I thought was blown it made a heck of a racket but only when you let off or down shifted, turned out to be the front rear. Quote Link to comment Share on other sites More sharing options...
David Posted April 16, 2009 Share Posted April 16, 2009 I've had ring and pinion problems and the noise would carry through the transmission. You would swear it was coming from the trans. Quote Link to comment Share on other sites More sharing options...
MACKTRUCKS4 Posted April 17, 2009 Share Posted April 17, 2009 I too at one time had a front rear go bad and if I were a betting man, (which I am) I thought it was the trans. Turned out it was the rear. Also I had a problem with my 12 spd., it would only come out of high gear on the highway when you would find the spot of rpm's when you had no drag on the motor, it would slide out of gear but when you started pulling, it would go back in. It turned out when the shift rail was put in, the alignment bolt was not in the hole on the shift rail. It was off just enough to let it shift in lo with no problem but in hi, it would slide out. Does your problem happen in both hi and lo, or just one? Quote Live every day like it's your last, because one of these days, it will be. Link to comment Share on other sites More sharing options...
larry perkins Posted April 18, 2009 Author Share Posted April 18, 2009 ok ,thanks for the assist. all bolts tight on bellhousing this noise happens both in hi and low range. i put a air pressure gauge on the air supply(s) of gear lever air shifter and have 69 lb, i did adjust air regulator up to 90 psi, drove with no difference then adjusted it back to 70 psi. i can walk beside truck moving in yard and noise can be heard when driver ask for power and then lets off pedal with clutch out.just a big clunk and gear noise. it was suggested by power trane of louisville to lock power divider in with air sw on dash,drive to see if problem went away, driver did for about 10 miles from job,thought we has found it, then 1/2 mile from shop in 25MPH zone he is sorta coasting and heard the noise clunk,didnt come all way out, then started pulling again and all smooth. any help appreciated. larry perkins Quote Link to comment Share on other sites More sharing options...
fjh Posted April 19, 2009 Share Posted April 19, 2009 ok ,thanks for the assist.all bolts tight on bellhousingthis noise happens both in hi and low range.i put a air pressure gauge on the air supply(s) of gear lever air shifter and have 69 lb, i did adjust air regulator up to 90 psi, drove with no difference then adjusted it back to 70 psi.i can walk beside truck moving in yard and noise can be heard when driver ask for power and then lets off pedal with clutch out.just a big clunk and gear noise.it was suggested by power trane of louisville to lock power divider in with air sw on dash,drive to see if problem went away, driver did for about 10 miles from job,thought we has found it, then 1/2 mile from shop in 25MPH zone he is sorta coasting and heard the noise clunk,didnt come all way out, then started pulling again and all smooth.any help appreciated.larry perkinsDid you pull the drain plug and see of there are hunks coming out of it? Usually the first thing you need do on a 12 speed with noise problems!the next thing is pull the side covers on both diffs and check the drain plugs there as well!You have already locked the power divider out so thats confirmed!Before pulling the trans pull the side BIG pto cover and look inside check to see that the split is operating corectly and going all the way in! Quote Link to comment Share on other sites More sharing options...
HK Trucking Posted April 19, 2009 Share Posted April 19, 2009 Did you pull the drain plug and see of there are hunks coming out of it? Usually the first thing you need do on a 12 speed with noise problems!the next thing is pull the side covers on both diffs and check the drain plugs there as well!You have already locked the power divider out so thats confirmed!Before pulling the trans pull the side BIG pto cover and look inside check to see that the split is operating corectly and going all the way in!I'd also bet that there's something going on in one of the rear ends. Quote "If You Can't Shift It Smoothly, You Shouldn't Be Driving It" Link to comment Share on other sites More sharing options...
fjh Posted April 19, 2009 Share Posted April 19, 2009 I'd also bet that there's something going on in one of the rear ends.In most cases I''d tend to agree with you hk but if I read right ,its jumping out of gear as well ,a rear end problem would not cause it to do this. I have seen the tail shaft snap ring come off and cause the split not to work properly. Quote Link to comment Share on other sites More sharing options...
larry perkins Posted May 2, 2009 Author Share Posted May 2, 2009 follow up, turned out to be the tranny,slider gear was worn so bad it was comming out of gear with back pressure. i will try to get a better description ,but it was a gear with a tapper and the taper had opened up fron wear,going to have to retrain the drivers to shift again. thanks for the asssist, i did learn a lot. larry perkins lou ky Quote Link to comment Share on other sites More sharing options...
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