Bellhousing Breakage

ss3011 · 08-06-2012, 11:58 AM

It is good that you have a production style transmount. Two things, first, have you trimmed off the ears to make it easier to install the trans past the headers ? That metal is in a critical place for stiffness of the bellhousing, and trimming it away just weakens it. Second is, there were no Heavy Duty 350 THM cases for Buick, Olds, Pontiac (BOP), but you may be able to find a Composite Case, which has both the BOP and Chevy bolt patterns, that bellhousing has more meat and may last longer. One last thought, is to make sure you don't have a worn out case extension bushing, the one that rides on the driveshaft yoke. Too much clearance could cause extra vibration that works on the bellhousing. If the crack starts at the dowel pin, and spirals back, it could be the bell bolts have worked loose, make sure they are torqued to specs, about 35 ft lbs.

Tom Goldman · 08-06-2012, 12:36 PM

I see way more BOP cases with cracked bells than Chevys, so either the case is weaker or the big BOP's just have too much torque.
I'd start with a fresh case and go with an Ultrabell. Stronger ,safer and a lot easier to get than the multifit cases.
I'd definitly check the driveline alignment and the mount either way.

Run to Rund · 08-06-2012, 01:11 PM

Manual trans guys are used to checking bell housing alignment and installing offset dowels. I just wonder how much is the bell and how much is the placement of the dowels in the block. I don't know if you can use an empty T350 case and check its alignment to the crank centerline, but I'd try something to verify it.

Also, you might look into motor mounts with restricted flex (or steel mounts) with the stock type trans mount.

08-06-2012, 11:58 AM	#1
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 909 Likes: 70 Liked 239 Times in 114 Posts	Re: Bellhousing Breakage It is good that you have a production style transmount. Two things, first, have you trimmed off the ears to make it easier to install the trans past the headers ? That metal is in a critical place for stiffness of the bellhousing, and trimming it away just weakens it. Second is, there were no Heavy Duty 350 THM cases for Buick, Olds, Pontiac (BOP), but you may be able to find a Composite Case, which has both the BOP and Chevy bolt patterns, that bellhousing has more meat and may last longer. One last thought, is to make sure you don't have a worn out case extension bushing, the one that rides on the driveshaft yoke. Too much clearance could cause extra vibration that works on the bellhousing. If the crack starts at the dowel pin, and spirals back, it could be the bell bolts have worked loose, make sure they are torqued to specs, about 35 ft lbs.

08-06-2012, 12:36 PM	#2
Tom Goldman VIP Member Join Date: Jan 2003 Location: Allentown,PA Posts: 2,477 Likes: 892 Liked 883 Times in 237 Posts	Re: Bellhousing Breakage I see way more BOP cases with cracked bells than Chevys, so either the case is weaker or the big BOP's just have too much torque. I'd start with a fresh case and go with an Ultrabell. Stronger ,safer and a lot easier to get than the multifit cases. I'd definitly check the driveline alignment and the mount either way. __________________ Tom Goldman 1500 SG , 1506 STK

08-06-2012, 01:11 PM	#3
Run to Rund Senior Member Join Date: Sep 2007 Location: Henderson, NV Posts: 583 Likes: 8 Liked 54 Times in 27 Posts	Re: Bellhousing Breakage Manual trans guys are used to checking bell housing alignment and installing offset dowels. I just wonder how much is the bell and how much is the placement of the dowels in the block. I don't know if you can use an empty T350 case and check its alignment to the crank centerline, but I'd try something to verify it. Also, you might look into motor mounts with restricted flex (or steel mounts) with the stock type trans mount.