Hard mount questions... Please weigh in..

skipnrocks · May 30, 2014

So here is the question. I decided to hard mount the my motor-tranny-tcase. I built the mount like I normally would off of the skid cross member. Then I wondered if the deflection under a hard belly hit would crack my tranny. I have between the frame rails three cross members. The front and back are 2in .250 wall dom the middle is 1.75in .120 wall dom, and in between the front and middle and back and middle are 3 1.75 .120 wall dom cross-members. It is off of these cross members I was building my hard mounts. My question is with 1/2in alum plate and a hard hit am I at risk of cracking the transmission housing. In that case should I build an independent cross member so it would not ever be a concern?

Hope that paints a decent picture of what I have but it might be gibberish.

wont work · May 30, 2014

I hard mount all my offroad rigs and race trucks.

I always built the nounts to either hang from the top or side that way no matter what happens in the belly of the buggy it doesnt effect the drivetrain.

skipnrocks · May 30, 2014

That is kinda what I was thinking. It would take a crazy impact to deflect my skid but if it happens its 900 bucks at least out the window each time.

SB406 · Jun 4, 2014

Yep. Broke a tranny that way, and mine wasn't even hard mounted. My current belly is .25 wall 2x2 box with 3/8 steel plate over it. It still moved (5500# rig). I'm a big fan of poly mounting everything from above. The hard mounting both ends scares me after breaking that trans. It don't take much to crack an aluminum trans with a 205 hanging off the back. If you think your chassis doesn't flex you're fooling yourself.

wont work · Jun 4, 2014

SB406 said:
Yep. Broke a tranny that way, and mine wasn't even hard mounted. My current belly is .25 wall 2x2 box with 3/8 steel plate over it. It still moved (5500# rig). I'm a big fan of poly mounting everything from above. The hard mounting both ends scares me after breaking that trans. It don't take much to crack an aluminum trans with a 205 hanging off the back. If you think your chassis doesn't flex you're fooling yourself.

If a frame doesn't flex it breaks welds and tubing

Elliott · Jun 4, 2014

if your 205 is hanging off of your transmission that is what broke your case, hard mounting everything is the way to go but you have to have a lot of mounts ( engine, mid mounts, transmission mount, and 2 case mounts usually to be stout enough not to have any problems.

SB406 · Jun 5, 2014

My 205 isn't hanging off the trans. It has it's own set of mounts off the PTO cover and the 2 bolts on the side. What broke my trans was when the mounts went to the lower cross member. It pushed up and twisted the trans.

My point was that every chassis flexes. If it's more than your drivetrain can flex, something has to give. Either a mount has to flex or a case has to break. Solid mounts flex too... and sometimes crack from fatigue.
Everybody has their way of doing things. I just prefer the safety factor of poly bushings.