900 series bell housing bolts

[lew]

Last week I noticed some broken bolts laying on my crossmember (the one directly below where the trans and the engine join) on my M925. This truck is a recent gov rebuild and it looks as if they might have used the wrong grade of bolts. They installed grade 5 and it has been suggested to me that grade 8 would be ideal. I'm not certain of the actual cause of the failure yet, but for now the important part is extracting the broken pieces.
Is there an access panel in the floor in front of the shifter maybe? Do I have to lower the allison (big job)? I can drill and easy-out the lower ones easy enough, but can't get access to the top bolts.
Any ideas would be appreciated

thanks
Lew

 

[Warthog]

Your type of truck is a M939 series. There is no 900 series

 

[lew]

Copy, It's been a long day. Thanks for the correction
Lew

 

[rangereter]

In 1985 I signed for 4 each (brand new) M936's. Within the first year of using these trucks, I noticed that the transmissions were working loose from the engine flywheel housings... (because AM General used mild steel lock tabs for engine trans marriage bolts/screws.) Way before there was a PM magazine notice published discussing the fix for this problem, we removed the marriage bolts and lock tabs and installed new bolts with "lock" washers.
When you move the trans selector lever from 1-5 to reverse, there is a tremendous amount of torque (clockwise and counterclockwise) put between these two housings. If the trans to engine flywheel bolts are not torqued enough, the engine will tend to want to start "shucking" the trans assy. housing and eventually will work the 3/8-NC screws loose to the point that the screws will shear. The bottom line is this, if you have more than three broken marriage bolts (25%), you really should drop the transmission and extract the (suspect) broken hardware and reinstall the trans with new. Make sure that you put an ink pen or whatever else into the trans bolt holes to verify that you do indeed have broken screws in the engine flywheel housing adapter plate.
Regards, Bob

 

[wreckerman893]

When I was at Fort Benning in the 80's we had two M932A1's that had that issue. We turned them into 3rd Shop for a MWO and when we went to pick them up the mechanic that did the MWO said one truck had four bolts sheared off and the other had three. The ones on the top of the transmission seemed to be the most likely to fail. Made it very hard for them to be found. Usually you could tell because the transmission would make a banging noise when shifting up or down.

 

[autoshopteacher]

Not necessarrily a solution, but in the mid 80's there was a worldwide flood of substandard improperly graded bolts from China that found their way into US manufacturing and repair parts supply systems. I was an Ordnance Officer in !st Armored Division and we deadlined nearly all of our new 939 series trucks for stretched (broken) transmission to engine bolts. So, Lew, the wrong grade of bolt is a likely culprit. I can't help you with the replacement procedure, though. Sorry and good luck with your repair.
As an aside, we had soldiers going to the Caterpillar dealer in Nurenburg and buying those replacement bolts out of their own pockets to get their trucks off deadline. A very expensive purchace for a Private in Germany at that time.