I cracked the bell housing on my built Allison 6spd and took a chunk out of the adapter plate on the back of the lbz so I picked up a 5spd Allison and LLY cheap and now am just wondering a couple things. Will the 5spds bell housing bolt onto my 6spd no problem? Cause my 6 spd is built do I need to swap the oil pump from it into the good bell housing? If so how? And will I need anything special to pull off the rear adapter plate off the engine? Do I need to replace oil pan gaskets and rear main seal to do it? Thanks in advance for any help.
Cracked bell housing and adapter
- Thread starter drmatt
- Start date
The bell housing should go onto your six speed with no problems. Since the transmission is built, you will either need to swap the pump or move the modified pump valves/springs/shims/whatever your builder did from the old pump to the new one. It's easier to just swap the whole pump/separator plate assembly. Remove all the bolts inside the bell housing, and the pump will drop out of the bell housing.
I'll tell you right now, it's going to be a PITA to change that rear adapter plate with the engine in the truck. It's made to go on before the oil pan and has dowel pins that line it up to the back of the block and the upper oil pan. You will need to remove the lower oil pan to get out 4 bolts that go through the upper oil pan into the flywheel housing (3 go through the inside and one is on the outside). You also have to remove the flywheel bolts (very tight!). You will need to remove the turbo drain nuts and studs (this will allow you to leave the turbo in place). The coolant elbow that goes from the oil cooler to the flywheel housing will also need to be removed. If you pull the rear main seal, it will probably get you a little more room to work as the flywheel housing is coming out. To get it out, you will have to pry the top loose first. Once you get it back far enough to clear the dowel pins in the back of the block, you can pry it up to clear the dowel pins in the oil pan. Once you get it off, you'll need to pull the little metal sleeve off the crank that is part of the rear main seal. With the new housing on, you'll need a tool to install the new seal. Good luck with it.
I'll tell you right now, it's going to be a PITA to change that rear adapter plate with the engine in the truck. It's made to go on before the oil pan and has dowel pins that line it up to the back of the block and the upper oil pan. You will need to remove the lower oil pan to get out 4 bolts that go through the upper oil pan into the flywheel housing (3 go through the inside and one is on the outside). You also have to remove the flywheel bolts (very tight!). You will need to remove the turbo drain nuts and studs (this will allow you to leave the turbo in place). The coolant elbow that goes from the oil cooler to the flywheel housing will also need to be removed. If you pull the rear main seal, it will probably get you a little more room to work as the flywheel housing is coming out. To get it out, you will have to pry the top loose first. Once you get it back far enough to clear the dowel pins in the back of the block, you can pry it up to clear the dowel pins in the oil pan. Once you get it off, you'll need to pull the little metal sleeve off the crank that is part of the rear main seal. With the new housing on, you'll need a tool to install the new seal. Good luck with it.
It happens more than you know. They make a brace that helps keep it from happening. The weight of the transfer case combined with torque=broken trans case/bell housing. I've heard of the case splitting also.
The only thing that brace helps is; if you shatter your TC, it will keep the broken pieces from falling to the ground during drag racing. It will NOT save your extension housing from breaking or your rear engine plate.
Most common cause of tail housing cracking is bad ujoints or driveline vibration. Most common causes of bell housing breakage is no dowl pins in back of block or bad motor mounts.
I've had all the above. 
Except one being dropped. I've had cracked rear cover, bellhousing and multiple rear housings before I found a warped driveshaft. I'm still not real sure why the bell & rear cover cracked. Had dowels and mounts were fine.
Except one being dropped. I've had cracked rear cover, bellhousing and multiple rear housings before I found a warped driveshaft. I'm still not real sure why the bell & rear cover cracked. Had dowels and mounts were fine.