Bellhousing Breakage
 

I found this past weekend on my '70 Olds 442 D/SA that I've got a crack in the bellhousing. This is the second one in the last two years. Transmissions are TH-350 behind a real torquey Olds 455 that runs high tens. I use stock motor and transmission mounts, and have a turnbuckle mounted from the frame to the LH cylinder head. Over 25 years of racing this car, I have only broken a few bellhousings, but now have broken two in two years. A machinist friend suggested that the transmission cases probably get fatigued after so many years of racing. We both think that I should add a brace to the RH side of the transmission case that some guys are using that joins the bosses at the front and rear of the case. Thoughts? Experiences?

Re: Bellhousing Breakage
 

At the beginning of the year I broke two in a row. Because I couldnt find anything wrong I replaced every bolt in the engine mounts including the ones that bolt in from the frame and all new bolts in the crossmember. I also shortened the yoke on the transmission 1/8 inch to make sure the driveshaft wasnt banging the trans and I also machined .085' off the converter pads to loosen up the flywheel to converter and to put the converter pilot into the crank a little more. So far so good.

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.

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.

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.

Re: Bellhousing Breakage
 

Tony, if you dropped me from that height ONCE, I'd crack - and you've done it a couple times. :eek:

Re: Bellhousing Breakage
 

As regards to the BOP trans case, try to find a unit that was used on an Olds 350 Diesel powered car. The cases are beefier and also heavier; it also applies to the TH-200 used on Diesel applications.

Re: Bellhousing Breakage
 

After breaking two TH-200 cases I made up a crude brace, will try to post photo below. Also, like others, put a torque strap from left cyl head to frame, and bought a cast aluminum deep oil pan from Turbo Action for extra support for the case. We do use the steel mounts front and the stock transmission mount on the rear crossmember. There have been no further case problems since these changes.
There's another thread on here "M200 breakage" showing a photo of the brace, not pretty but seems to be working so far....

Grant Eldridge
E/SA 6650
National Record Holder 2011

Re: Bellhousing Breakage
 

I also broke several cases behind my olds motor. Tried several things with no luck. I installed the jw bellhousing about 7 yrs ago no problems since.

Re: Bellhousing Breakage
 

Do you have solid body mounts or does your roll bar limit the amount of frame flex on your car?

When you jack up the front of your car where do you put the jack stands?

Even with rubber mounts they only have so much give.