extension housing on 1997 dodge ram 4x4 manual trany was replaced last month due to a crack. Now, the new housing is cracked. I would like input as to the cause and remedy.

 

If they didn't get the extension centered properly (concentric to the crank) then it can be subjected to enough stress to do damage.

May not be the case in your particular situation but I have seen this happen before in older Dodge manual trans-equipped trucks. There are offset locating pins on the back of the block that are used for aligning the bell housing concentric to the crank. This is how the input shaft of the trans is properly aligned to the pilot bushing and keeps the clutch from orbiting on the flywheel face.

Disclaimer - this is my experience based on older trucks - it may not hold for the newer style extensions. I would be interested in knowing for sure if the same mechanism is used on the manual diesels - or if they are aligned via a different mechanism.

 

One of my drag race partners trans mount was broken,causing excess movement and a crack. To fix the broken mount he weld up a new one out of solid steel,thinking he would "fix that sucker for good", ! 2 tailshafts later he put back the correct soft mount. All this was on a Dart, but you might check your mount John?

 

I was looking to see what came up on this one. Might check a couple of other things also. Not much chance of the shaft being too long, but you might check the U bolts on the rear axle, it could shift foreward on acceleration and drive the shaft into the tail housing. My guess would also be the mount, some kind of a problem there.

 

[glow=red,2,300]DOH!!!![/glow]

I was thinking bell housing when I replied earlier - must have been late at night.

Like the others I would suspect a mis-alignment problem due to something else being shot - maybe the rear trans mount bushing has gone soft and is allowing excessive movement under load.

You could also look to see if there is excessive play in the slip-joint fit between the output OD and driveshaft slip-yoke ID (provided that is the configuration instead of a fixed u-joint saddle on the trans output). If the bushing is worn and letting the slip-yoke drop down (mis-align itself) when stopped then re-align under load it can create an orbit to the slip-yoke rotation that can chew up the extension housing. I have seen this happen on other vehicles but it is not very common.