why do i keep breaking th350 tranny's ?

[Torrance]

i have a sbc, th350 and 203/205 doubled transfer case. in my toyota. trannys keeps cracking the case at the tail. motor mounts are solid, 1st
t-case mount/crossmember is solid and second t-case is using the factory style setup. thought i had all the bugs worked out of my mounts till i broke this trans.

 

[TreeClimber]

You have too much weight hanging off that tailshaft.
Also, mounts shouldn't be solid, as you need the ability of absorbing some of the vibrations.
And... make sure everything is true and straight, i.e., that the motor mounts are correctly aligned with the trans mount, and that there is no binding therein.

There is a thread on Pirate, which talks about double t-case mounts tearing out the transmissions. I'll see if I can find a link.

Can't find the thread, but the concept was; by clamping the t-case in front and in back, it becomes immoveable.

With the torque and vibration of the engine/trans wanting to twist the front of the tcase, and the torque and vibration of the driveshafts trying to twist the rear of the tcase, you are essentially setting up a 'bind' which needs to find someplace to release it's energy. That cracks the transmission output, which is the weakest aluminum casting location.

The basic solution, was to allow the engine, trans, tcase to have a little flex built in.

So then, why do drag racers solid mount the drivetrain? Because they're releasing the bind every time the tires break traction and do a burnout.

However we've built our rigs to prevent the tires from breaking traction, thereby capturing that inherent energy.

Dunno if that's correct, that's just how I remember reading it.

 

[Bunk1]

Are the dual rear mounts fighting each other?

 

[Torrance]

im pretty sure the dual rear mounts are not fighting each other.

 

[Torrance]

thanks for the great imput. was looking on ORD's webside. they have alot of good info on there too. looks like ill be redoing all my mounts again.

 

[Gibby1]

I have the identical setup that you do. All my mounts have bushings.

There is a good write up here.

http://www.pirate4x4.com/forum/showthread.php?t=317741

 

[leadfoot067]

the only thing not mentioned here is the frame flex that happens when you twist up the suspension,if you have everything solid mounted to the frame,the frame moves..thus breaking at the weak point...ive been runnning a SBC 4 speed to a 203/205 for several years in a K5,and everything is rubber or poly mounted,motor,and both t-cases..have only broke 2 adapters,1 was my fault..the other was just a crack and i replaced it..everything needs to move a bit...not much but some..

 

[zukkev]

Patches on here had the same issue when he put his buggy together, and the fix was IIRC to run a single mount in the center under the dual cases...solved breaking trans cases....and he beat the poor thing.

 

[Torrance]

Thanks for the great link Gibby. thats exactly the style of crossmember i was thinking about doing? do you think 1.5" 120 dom tubing will work well? i have some left over from my exo cage.