I have a chevelle drag car that keeps cracking the bell housing all the way around the trans. I have installed solid motor mounts an did not help solve the problem. What will help cure this problem? Engine is a 406 with 350 turbo.
If you have solid motor mounts and a poly trans mount the trans is taking all the torsional diflection. Either solid mount the trans or put a mid plate in. I know the mids a pain in the ass but its the way to go. Why, because then if you have to pull motor or trans the other is still hanging there while stopping all the twist when racing you get benefits two fold.. Sounds like its making power if its cracking the bell are you spraying it, or all motor leaving on a trans brake????
IT is all motor and no trans brake, It has a poly trans mount. looks like we are going for the mid plate. Thanks for the info
If the block has been line bored, You may need to get the dowels checked for alignment problems. Basically the crank center may have changed. It can be fixed with offset dowels. alsokeep inmind if this is the problem a mid plate might mask the problem and cause main bearing wear....JOHN
put a stock RUBBER trans mount in it. Steel motor mounts should never be used with a steel or poly type rear mount. With solid mounts any chassis flex is directed to the weakest point, bell housing or tailshaft. Trust me, I been doing this for a while. No midplate is needed.
Like was mentioned earlier, check the driveshaft length. If it's too long it may be bottoming out in the transmission during launching. Also, check for bad bushings in the rear suspension for the same reason. Bad vibration in the driveshaft can possibly cause it too. I personally don't think motor plates are needed. Nor do I think using a poly trans mount with solid motor mounts have anything to do with it either. I have heard that it's very bad to put a TH350 in neutral at the end of a pass though and there are a few posts on it on other boards. I would do my best to find problem areas in the drivetrain first and then get an Ultrabell from J.W. Performance.
You should lay out the center line of the cars driveline , front to back , on a concrete floor to check there isn't a misalignment of the components. If you use a midplate that could cause a stress point which in turn is cracking your bell housing.Had it happen in a friends race car and it completely broke and the trans spun around three times stopped by the shifter cable. Hope it helps, Rob.
I am with Jay on this one, especially if you do put a mid plate in. You will then have the package mounted at three points and the stock chassis is not rigid enough to stop the twisting forces breaking the weakest point which in this case appears to be the bellhousing. If you do want to put a mid plate in, let the trans hang or just put a support under the mount to carry the static weight. A stock rubber mount would also work unless you have a very flexible car. Do you have solid sub frame bushes or are the originals worn out to the point where they let the front sub twist up excessively? Roo
If you install a midplate, space the convertor the same distance rearward as the thickness of the midplate.
Da Tinman is right. your solid frt or side? check trans to motor alignment and drive shaft if it's bent or u-joints aligned properly
Are you breaking/cracking the same case and welding the crack? A lot of th350 are very thin when you get past the lip. I weld aluminum angle all the way around the case, not front to back and it'll take a couple of strips to tye it all together. Tinman is right, use a rubber mount to let the tail flex. Midplate is a good thing, but you really need a complete cage so that it'll tye everything together. Just sticking a midplate in there to tabs mounted on the frame will just let the midplate flex right along with the frame and the engine/trans will support the midplate more than vise-versa. I assume you have a piece of a cage and what i'd really be looking at is to extend what you have out to the front frame to minmize the flex, thats your real problem. You didn't give year of chevelle and the 406 isn't strong enough to really flex the car so i bet it has been a drag car for a while and has had a big block and the front left frame where it is bent around just under the rear of the front fenderwell has been flexed/twisted/welded/and hacked on for 20 years. Have a look at that and see if it is weakened.
Da Tinman, and Roo are right on the money, my altered (an old Ken Cox chassis) has front, and mid plates, and uses support that's under the trans mount (but it is not bolted to the trans) to carry static weight, never had any trans, bellhousing breakage issues.
If this is a bracket car and you're seeking consistency to the nth degree, stay with solid mounts or plates. Good luck
My Dad used to put one steel motor mount at drivers side and rubber on other. Reduced vibration and passenger side compresses a little but you solve the problem of pulling at drivers mount. Oh, trans would be rubber too.
Motor plates, mid-mounts, rubber transmission mounts, chalk lines on the floor, etc, etc, will not correct a bent or a too-long drive shaft. Check for that first, seen it way too many times especially on GM cars...
Thanks for all of the info. This is a High School Vocational class project and all of your info will give us a place to start to look for the problem. This is a 72 chevelle it is on a stock frame with a six point cage. The engine is a 406 with 12.5 to one pistons. Trying to keep these young people of the streets and get them interested in our dieing way of life. Thank for your help Auto shop
Seen a few old GM A-bodies run deep into the 12s and even 11s for years on end with nothing but a log chain on the driver side motor mount. No cage or special doodads either, and they never broke a bellhousing. Other guys did break bellhousings, usually from a driveshaft problem, wheelhop, broken mounts, etc.
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