Breaking bell housings
 

1977 Chevy Malibu,stock rear supspension with urethane control arm bushings.
Small block running 13:60/13:80's(1/4 mile)
4:11 gear.
turbo 350.
leaves nice.
Rubber trans mount.
Solid motor mounts.
Car does not twist when it leaves(not enough power).
No vibrations, car feels smooth.
I have not checked the pinoin angle yet.
Why would this thing break the bell housing????
Any ideas would be great.

Re: Breaking bell housings
 

How long have you owned the transmission? Possibly was cracked in another application?

Re: Breaking bell housings
 

Get rid of the rubber mount. cut the broken bell housing off and put an ultra bell on your trans.

Re: Breaking bell housings
 

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.

Re: Breaking bell housings
 

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.

Re: Breaking bell housings
 

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.

Re: Breaking bell housings
 

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

Re: Breaking bell housings
 

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

Re: Breaking bell housings
 

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.

Re: Breaking bell housings
 

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.

Re: Breaking bell housings
 

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.

Re: Breaking bell housings
 

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.

Re: Breaking bell housings
 

All of these suggestions sound logical to me.....let me just throw something else out there, in case these suggestions don't fix the problem. I have seen where the back of the blocks were crooked, therefore requiring shims to be sure the bell housing aligns "straight"..
"back in the day", it was common to break 4 speed transmission housings......after dial indicator and shims, I never broke another. Good Luck

Re: Breaking bell housings
 

big difference between 8000 RPM and your boulevard cruiser at 1500-2500 RPM MAX--do a dial indicator first see what you come up with then go from there--- those mounts probably are aggravating the situation too-- my 2 cents

Re: Breaking bell housings
 

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

Re: Breaking bell housings
 

Great thread!
The reasoning for not using solid engine mounts to avoid this problem may be a good bandaid for the real problem: Chassis Flex.

When building my cars spent a lot of time making the floor pan stiff welding all seams top and bottom with the car level then locating roll bar mounts with chassis stiffness the intent within the rules. A lot of hard dirty work but makes stock chassis cars stiff and lets the suspension work.
Rubber body mounts on A and G bodies replaced with solid steel or aluminum helps a lot.
Even though this is a 13 second car doesn't mean there is no flex. Get rid of it and pick up some ET.

Good Luck!

Re: Breaking bell housings
 

Been running street/bracket cars for years with solid motor mounts and rubber trans mounts at various power levels...never cracked a housing yet. We must just be lucky.

Re: Breaking bell housings
 

About the solid side motor mounts:
If you run a production block (Bow Tie blocks didn't exist when I was showed this.)
Bare block, with something soft below the test cylinder, put an inside mic in the cylinder above the soft pad, front-to-rear, up top, barely tight enough to stay in place. A healthy guy with hand above & below the mic, press hard & fast together and watch the mic fall to the pad. The old guy-machinist that showed me this about 50 years ago was no body builder either.
Think about your ring seal during launch in the cylinders next to those solid motor mounts. I would use a torque strap with stock mounts myself.

Re: Breaking bell housings
 

jbt352… Mount the body solid to chassis by welding flat bar between frame and body mount reinforcement pads (helps reduce chassis flex). Check to see if your rear upper and lower control arm bushings are in good shape, worn bushings can change pinion angle on acceleration. I'd add a aluminum convertor cover off a mid 80's GM 4x4 to act as a case girdle in the bell housing area. You have lots of positive feedback from your post. Good Luck…Maurice.

Re: Breaking bell housings
 

I remember reading years ago that Bob Glidden built engines on the floor so that the cylinder walls would'nt distort. That made me think some, and that usually hurts!

Re: Breaking bell housings
 

I agree 100% solid motor mounts and a poly trans mount is the best way to go

Re: Breaking bell housings
 

jb,
When I first built my bracket Camaro many years ago, I broke two TH400 bellhousings in less than two months :( My trans guy told me to get a driveshaft made. That took care of the problem. Put over 2000 passes on the car after that and never had a single trans problem. I never felt any type of vibration at 7200 rpm's but the old driveshaft must have been out of balance or out of phase or something.

By the way, I had the same setup as you, solid engine mounts with a rubber trans mount. The car was a full chassis with cage so there was not a lot of flex.

Re: Breaking bell housings
 

One trick that Alfe Weibe shared with me was to use "Hockey Puck's" in place of Body Mounts on GM "A" and "G" body (full-frame) cars where aftermarket mounts are unavailable! Just drill holes in them & replace the worn and sometimes deteriorated body mounts!

Reasoning is that you are "making the body part of the chassis" by adding stiffer body bushings, it will "decrease"the flex that the "factory rubber bushings" offer in absorbing vibrations, body twist, and ride comfort that "stock body mounts" are supposed to do!

More often you will also find with "stock body mounts" the body lines will move as body bushings wear out, signs that the body is actually twisting.

Just make sure that "during installation", you tighten the body mounts with the weight of the body on the chassis and suspension, "NOT ON A LIFT OR JACK STANDS! This will bind the chassis (found out the hard way) and in "Stick Applications" "buckle the rear quarters"
I final tighten them on an open car trailer.

Alfe's way of telling me to "Go Puck Myself" LOL

Re: Breaking bell housings
 

One odd thing to check, the passenger side motor mount to the frame. Many moons ago I kept breaking TH400 bells, car had solid mounts, turn buckle on drivers side, rubbery trans mount. Finally one day while I was doing dry hops in the drive way with the hood off, everything looked great until I backed up and the engine raised up about 20* off the frame. I found out the original motor mounts on the frame had torn off the welds under the mounts. I had checked all the attaching bolts first for being tight but the frame metal was torn out of the crossmember on the passenger side. After replated the frame and adding turn buckle never had another trans issue.

Good luck finding your problem