Breaking bell housings

[Alan Roehrich]

I would never use a steel or solid mount on a transmission. I've put in dozens of race car transmissions.

I use an ordinary stock replacement mount, with two radiator hose clamps around it as a safety device. Or a urethane mount. In 30 years of working race cars, including a lot of years as the person in charge of race car work in a well respected transmission shop, I have never seen a properly installed rubber or urethane transmission mount cause a broken case. But I have stopped several cars from breaking cases by replacing a steel mount with a correctly installed rubber or urethane mount.

If I'm not using motor plates, I use urethane mounts, or one steel mount on the driver's side and a urethane mount on the passenger side.

You do have flex, a vibration, or a misalignment. You may not have it identified, but it is there.

Adding a bolt on bellhousing merely moves the weak point to the case behind the pump, and when it breaks there, it will dump fluid under your tires.

[Jim B]

Another item to check would be to make sure the driveshaft slip yoke is not bottoming out against the output shaft splines. (Manually move the driveshaft forwards and backwards from the rear u-joint and make sure the driveshaft is not too long or too short) Make sure there are no broken/damaged rear suspension components that would allow the rear to move forward or rotate on the leave. I also assume the shaft length to tubing diameter/wall thickness combination and straightness are not causing a harmonic whip. (mostly seen in an insufficient driveshaft length to tubing diameter relationship) Also any history of cracked flex plates? It wouldn't hurt to check the pinion angle.

[Jim Kaekel]

Personally, I would ditch the steel motor mounts and replace them with stock units. I believe either all steel, or all rubber mounts. Then, install a torque strap on the left front of the engine.

[Alan Nyhus]

Another culprit can be the bellhousing dowel pins, if they've been changed. Some of the after market extra length pins are a bit bigger i.d. than the factory ones, causing the case to be stressed when bolted to the block. -Al

[Jeff Niceswanger]

Rossler has told me many times, that too much pinion angle breaks transmissions more than anything. He must see a lot of that.....

[jbt352]

Originally Posted by Jeff Niceswanger

Rossler has told me many times, that too much pinion angle breaks transmissions more than anything. He must see a lot of that.....

Jeff I agree .


This is my sons car, I ran a full body 69 Chevelle with a big block and turbo 400. The car went 12:00-12:30 with stock suspension. The car would twist and pull both wheels,and I never broke a tranny in all the years I ran it.
It had solid mounts up front and rubber at the trans.
This car should not have an issue going mid to high 13's.
Talked to the old owner of this car and he had the same problem.
We put the tranny in 3 years ago.
We need to keep looking.

[Lee Valentine]

Broke 4 TH-200's in my son's 85 Camaro, had solid motor mounts and rubber trans mount. Tried different driveshafts ,solid trans mount,new renforced crossmember,different transmission, brace on case etc. Finally put all stock mounts on engine and trans and never broke another case in 7 years.

[Mike Jones]

I broke the bell in my 12 second bracket car, 355/ TH-350 Camaro.
It had factory urethane mounts on the front crossmember and steel mounts bolted to the block, like they came in 1979
The driver side motor mount was slightly bent and the engine was
cocked up on the drivers side, just a bit. Could hardly tell, if you weren`t looking for it.
Found the bent mount when I pulled the motor.
Had rubber trans mount as well
Check the motor mounts are the same and not bent.
Just a thought...
Good luck.

[Alan Roehrich]

If this car has the stock suspension, un-altered, other than urethane bushings, and the rear end housing has not been changed, damaged, or otherwise altered, if the frame is not bent or broken, then the pinion angle should be close to stock. Unless the ride height is significantly altered from stock.

Now, if it has traction bars, no hop bars, adjustable control arms, the housing has been swapped or altered, or the ride height has changed significantly, then the pinion angle could be off.

If the pinion angle was off enough to break something, there should be a vibration present. Of course, solid motor mounts bring about a vibration of their own, and that could mask any vibration brought about by another cause. <------- Another reason that I despise solid motor mounts.

If the dowel pins do not protrude into the case far enough that the chamfer on the pins is well past the chamfer on the case, so that the full diameter of the dowel pins is well into the holes in the case, that could cause the problem.

At static ride height, the slip yoke should be about 1" out from being fully bottomed in the extension housing.

I think the first thing I'd do is verify that there are no problems with the rear suspension or rear end housing, and that the driveshaft is correct, in length and in tubing diameter and thickness, as well as having good u-joints. After that, I'd put the mounts back to the stock configuration, either new high quality rubber mounts, or new urethane mounts, on the engine and transmission. If you want, you can fabricate a torque limiter of some sort. I'm betting at that point your case breakage problems will cease.

[jbt352]

Thanks for all the ideas.
I like the idea of going back to the factory front mounts,considering the power level we are talking.