blown 346

iTrader: (25)

I pulled my SBC 406 out of my 91 Camaro due to a blown intake gasket. After removal I noticed the bellhousing on the TH 400 has a hairline crack right at the top peak of it. The crack goes down towards the rear of the tranny about 6 inches.

I am going to have this welded to fix the problem, what would cause this??

Gilbert@Ace Racing

What sort of H/P does your engine make?

g

blown 346

iTrader: (25)

Never had it dynoed, I bought it already built. My guess would be a little over 400HP. The new motor will be making double that without spray. Thats the main reason Im curious to know what can cause the housing to crack. I dont want it to happen again with a larger HP motor.

Gilbert@Ace Racing

Well certainly improper installation can cause fractures in a case. Make sure that all of the available bellhousing bolts are installed and tightened using lockwashers.

That being said, if you are stepping up to ~800 h/p I would encourage you to seriously consider an Ultra Bell and a Safety Shield.

They are an added expense of course, but at that power level the case can be overpowered. Also, if the Intermediate drum were to explode at high rpm you would not be protected. The shrapnel can and will come through the case and floor pan and then into the passengers compartment.

g

blown 346

iTrader: (25)

The housing bolts did have lockwashers and were tight upon removal. Im looking at around 600 on motor and then I'll be spraying it 150 to 200. I'll look into the ultra bell housing and the safety shield.

Gilbert@Ace Racing

That's good to know. We always take a flat file to the case flange on each unit we have out. It simply ensures a solid mount. It we see any high spots we take the down with the file. Just an FYI for future reference.

Then let's say the mounting surfaces are flat and the unit was secured to the engine properly. What caused the crack?

Here are some more potential causes....

Loose motor mounts causing irregular stresses on the case.

Polyurethane engine and transmission mounts.

Solid engine mounts and a poly tranny mount.

Broken tranny mount.

Excessive power.

g

blown 346

iTrader: (25)

Both motor mounts were tight. It has to be the poly engine and trans mount.


Once the bell housing is fixed, should I remove the poly tranny mount and go stock?

Gilbert@Ace Racing

You know, most of the time that I see a broke case... broken anywhere... it is because the powertrain is mounted too rigidly. If it were mine I would definitely install a factory style rubber mount.

g

blown 346

iTrader: (25)

I will replace the poly mount with a stocker.

9000th01ss

iTrader: (10)

A driveshaft thats too long will take out a case.
During a launch or even regular street driving it can cause the yoke to hammer into the trans.

blown 346

iTrader: (25)

The crack isnt that far back. The crack starts where the bellhousing meets the back of the block. The driveshaft is the correct length.

9000th01ss

iTrader: (10)

If the DS is too long it won't neccesarily break at the back, in fact the few I've seen broke at the bellhousing. But I guess thats not the problem anyway.

blown 346

iTrader: (25)

I got the trans out tonight. Its getting fixed in the morning. Everyone I have spoken to has led to the trans being cracked when it was put in. Since I didnt install it myself who knows.

Gilbert@Ace Racing

The crack is in an odd place. I agree. After the repairs to the case take a straight edge to the flange to make sure it is flat. Do the same with he block before you install it.

But, I'm going to refer to my original recommendation for the Ultra Bell for the H/P you are planning down the road.. now would be the tie to do that upgrade!

Good Luck with the project!

g