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06-09-2009, 10:31:18 PM
What could cause a crack in the bellhousing in a TH30 auto. Its almost cracked all the way around about 75% of the bellhousing and its cracked all the way through. I did it at the track in the 1/8 mile. I have a 3500rpm stall converter and the car ran slow. It launched good and I got told last time I had a tranny leak. Climbed under the car and found the crack in the bellhousing.
I have polyurethane engine mounts and tranny mount.

06-09-2009, 10:39:14 PM
Prolly that poly trans mount. They've been known to break trans mounts and bellhousings due to no 'give' in the driveline under Tq.

Stock trans bushings work well for any street/strip car.

06-10-2009, 09:40:40 AM
th350 casings are very weak and prone to cracking

poly mounts don't help but I don't believe they are completely to blame. If its gonna break than its gonna break.

I have run a solid mount on mine for the past 6 years without any problems (knock on wood) on a stock case

06-10-2009, 01:20:16 PM
Any drive line shock can split the bell housing on a TH350 if a solid trans mount is used. I'm not sure about the poly mounts but it may not be flexable enough which could break the bell housing. We always use the old origianal rubber trans mounts for that reason.

As for the broken bell, replace it with the JW Perfomance SFI approved bell housing ( http://www.jegs.com/i/J+W+Performance/564/92452/10002/-1 ).

06-10-2009, 01:22:34 PM
I would venture out to say that in front of the crack it is trying to twist more or less than the trans behind the track. Could be broken or weak motor mounts or similar issue with the trans mount.

06-13-2009, 02:43:00 AM
Well All the mounts were replaced at the same time. Energy suspension engine mounts clamshell style and trans mount. All are less than a 2 years old and if they have 4000 miles on them I would be suprised.

I do have a spare trans case that I can swap internals from this one to other. I will swap the poly trans mount for a new rubber one and use a limit strap to keep the strain of the trans case.

I might install the new bellhousing from jegs.

02-18-2010, 07:13:32 AM
Not sure if I mentioned before but the crack is about 3/4 of the way around the bellhousing. No wonder it makes noise at about 3000rpm. at least it works well enought to get the car on the trailer.

Well I got my new Th350 trans from Jakeshoe. Now all i need to do is get it installed. I will take some pics of the cracked beelhousing and put them on photobucket when I get the cracked case out.
And yes i will be changing the poly mount to a stock rubber one.

I did start removing the trans on superbowl sunday but was interupted when i slipped and my finger caught on of those scres on the driver side firewall. Sliced the finger open and had to go and get some stiches. All better now. All I need to do is get the trans swapped out and I can drive the car again.

02-18-2010, 10:45:41 AM

I would look more at the engine moving. I ran with slicks with poly poly before going with solid motor mounts.
Maybe even use elephant ears for track only outings. I ran 10.20's with a 350 and never cracked anything,
but I clamped down the engine.


02-18-2010, 12:58:37 PM
I've seen a few broken over the years. I have one in the back yard right now.

02-19-2010, 07:08:12 AM
Here is the photobucket link to the pics. check them all out.

there are 16 of them. the crack extends from driver side along bellhousing and then there is one by the driver side bolt holes that mount trans to engine.
I could bend the big part to separate the crack. Inside the bellhousing too. At least it held long enought for me to get it on the trailer. Cracked in like 6 places.
Putting the Jakeshoe TH350 manual special in tomorrow!!!

02-20-2010, 03:52:47 PM
well the trans is in dam torque converter would not seat last night. I work nights and fell asleep under the car. I had been up from 10 am thursday and it was 2pm friday aftenoon. But its in. I need to flush the lines and trans cooler and then put header back on and the starter. what a pita!!!!

But the hard part is done, pulled my back and I am all sore. Im 41 this month and dam out of shape. Need some gym time to drop some weight so I can pick up these heavy car parts. I had to pick it up by hand to get the floor jack under the trans. Car was not high enough with only jack stands. But its in. I am spending the say with my son so tomorrow I will get it finished then its off to fix my truck that I bleww the V6 in last week. Only vehicle I have left is the ZX14 and its to cold to be riding but I have to go to work.

02-20-2010, 04:14:43 PM
Links to the cracked case



02-20-2010, 05:21:37 PM
I have ran mine for years with a poly mount on the tranny.Like Mr. Dragster said,you need to control engine movement.I run a solid mount on the drivers side,and a stock mount on the passenger side.The tranny has the poly mount on it, and has never given me a problem.

02-22-2010, 12:15:30 PM
The engine does not move and it has energy suspension clamshell poly mounts. I think the engine has 2000 miles on it since it has been back in the car. How are people running stock rubber mounts and have less trouble than I am having? I will be easy on it until I get my truck back together. I dont want to have to ride the ZX14 in the 30 degree weather again.

This is the last automatic I ever hope to put in anything. I want to go back to standards.

02-22-2010, 02:45:03 PM

That is something I haven't heard of in a long long time.
I never did it, but once in a while I would see or hear about one solid motor mount.
That's a good tip, and you can share a pack with a buddy. We were cheap & poor, we used chain or flat stock.

Just because it doesn't move when revving in the pits, doesn't mean it doesn't move under load, especially at the track.
Yes some engines jump when you touch it, so people might think that's how you check.


02-22-2010, 05:34:39 PM
Well the trans is in and it works fine while up on jack stands. Problem is the knocking I heard was not the broken trans but the the engine. I cannot win. So the engine is toast. So it will be down for a while. Going back with good stuff this time. I allready have Dart heads so I will save my money and lay out a plan.

02-22-2010, 11:25:02 PM

Check competition products. They have a very easy to use web site,
and you can gather a lot of information for your project.
Even if you buy somewhere else, it helps remember all the little things, and ~pricing.


02-25-2010, 02:47:07 AM

Check competition products. They have a very easy to use web site,
and you can gather a lot of information for your project.
Even if you buy somewhere else, it helps remember all the little things, and ~pricing.


I have thier catalog, they seem to have good prices. I know I want forged pistons, good rods at least a cast steel crank (prefer forged) But i need to decide if I want to run natural or forced induction. blown/turbo 9.0:1. natural will only be about 9.5:1. with a 64cc chamber head.