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mack ch613 bellhousing bolts loosening and snapping


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I have a 1999 mack ch613 daycab with a 427 engine and an eaton/fuller 10 speed trans. I am currently in the process of pulling the trans for the 5th time in a year because the bellhousing bolts keep loosening ans snapping off. The mounts at the trans are brand new and the one at the front of the motor seems to be fine. Why does this keep happening? I've used both the blue then the red loctite, yet this keeps happening. Is this a case of driver abuse or something else that I'm not seeing?

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Bell to block bell to trans gear up to high tire size change are the center of the clutch disc coming apart pilot shaft bearing then check the nut behind the wheel in the seat time for a road test dial indicate bell check grade of bolts.

Ed

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yes remachine all mating areas that were loose and then blue loc tight the bolts when reinstalled.

my college instructor built a tool to bolt to the flywheel and would recut the bell hsg. using the starter. for aluminum bells. it was quite simple apiece of 1x6flat bar that would reach across the flywheel plus 3in. then drill two holes to line up at say the 12 and 6 o clock positions of the clutch bolt mounting holes then drill and tap for 3/4 nf bolts then drill the 3/4 nf bolts to accept 3/8 bolts. the large bolts would set the height or stand off for the bell hsg. the small bolts would attach It to the fly wheel then drill and tap two holes on either side of the one mounting bolt that is on the off set end of the tool and install two bolts tighten evenly (this is to remove chatter from the tool) then take a piece of tool stock 1/4 or 3/8 sq. and sharpen a side then weld to a drilled and tapped piece of flatbar 1/4 thick then locate that onto the 1x6 bar ,drill holes and secure with 3/8 cap screws then bar eng. over until high points are found then in .010 increments crank the eng. over until bell housing surface "cleans". this has now trued the bell hsg.to the clutch face and should remove 2nd. spline clutch wear problem from imput shafts and allow trans to be securely attatched to the eng. NOTE YOU WILL STILL NEED TO REFACE THE TRANS, ADAPTOR.

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Most times the cause is from misalignment. A few thou. mismatch on the Trans to Bell or the Bell to Block will put a large amount of stress to loosen and then sheer the bolts. Check the bell for true order take it to a good machine shop and have a clean up mill on both sides. I'd do the trans flange also. I'd also use aircraft grade bolts which have a high sheer strength and tighten them to specs.

Might loosen the motor mounts on assemble to let the Engine and trans "Self Align" also. A belt and suspenders solution to cover the bases.

Paul

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"OPERTUNITY IS MISSED BY MOST PEOPLE BECAUSE IT IS DRESSED IN OVERALLS AND LOOKS LIKE WORK"  Thomas Edison

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when did this problem start? was it after a clutch replacement? did any thing else happen eng. trans. or with the rears? are you having problems keeping other components tight? does the driver complain of vibrations at certain road speed or given engine speeds?

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As far as I know it didn't start happening till after a motor swap. It may have been before that as I don't know the whole history of the truck. No vibration complaints from the driver. Like I said previously, a dealership we work with is having the same issue with no ideas why.

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well I wonder if the motor half of the bell housing is aluminum or cast iron if it is aluminum perhaps some time earlier in its life someone over tightened the bolts and streached the threads and now they keep coming loose no matter how hard they get tightened

Also a hightensile bolt is only strong when it is at the correct tension so once they are all tightened to the correct tension if they start to come loose just a little bit they wont work properly and shear and I guess once one bolt is gone it loads the rest up and then just snowballs

I guess if this is the problem the threads could be heli coiled

on sugar cane harvesters loctite wont work any good and araldite is used instead have to let it set over night or longer and the bolts wont come undone without help you need to heat the bolt and it softens the glue then comes undone ok

I dont think its the driver these bell housings will take a fair flogging with out giving any problems they handle a lot more power than the motor been used and to think that the problem only started with change of the motor should tell were the problem lies both surfaces have been machined so an alignment problem is unlikely

Anyway hope some of this waffle helps a bit

Paul

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They actually call the motor half a flywheel housing. Yes it's aluminum, been replaced with used ones on several occasions and been replaced with new at least once. As I said before, no motor issues, runs just fine. Plenty of power and no vibrations. Am currently replacing both the bell and flywheel housings. Mack doesn't make a steel flywheel housing, but we did find a steel bellhousing to replace the aluminum one. I don't think that is causing the problem because this has happened with two different trannys.the first one was a rockwell 10 speed, now has an eaton/fuller 10 speed. Both bolt up identical.

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Is the 427 a ETech or E7 engine? ETech are metric threads & some of the E7 engines had some american threads & some had metric threads. If motors have been changed ck out bolt threads. We replaced a engine bell housing on an E7 and it had metric threads but the new bell housing came in with american threads, it seem's like there was a bulletin on this but I can't find it.

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