I am thinking about redesiging the trans/t-case mount on my Pup and I came to realize the material of the mount is only half the battle as to how stiff it ends up working out. Isn't it also a matter of how far apart from the center the bushings are mounted? If the drivetrain is vibrating on an axis it would seem that the same mounts moved further apart would dampen vibrations less than if they were closer together or one central mount.

I am using a bellhousing off a 4cylinder truck to bolt a v6 engine to a 5speed and dual cases. The bellhousing (gm 60-degree pattern-) only bolts to the top of the engine (not all the way around like imports). The starter pocket was on the wrong side so I cut out 2" of the flange, then cut a 1.5" dia hole in the top of the bell to set up the clutch. It is a thin casting with no webs. My engine is about 225 peak ft/lbs. Not a v8 but definetly more power than went through this bellhousing in stock form.

In short I am concerned about the strength of the bell. It is very thin with thin end flanges. What if it blows up/ Is that possible? My current transfercase mount is a rear mounted front range offroad mount. IF a bellhousing breaks will the front of the drivetrain drop down if it is only mounted at the rear of the second case? Or will the input shaft keep the drivetrain intact?

I have a couple potential fixes if you guys think the bell should be strenghtened. I could build a plate and put bolts through the remaining holes, or do like some inline 6s do and build a lower bellhousing brace. Or I could build a transmission mount to go along with the t-case mount.

Now you guys who are engineers, can you predict how mounts can add stress to a bellhousing? If you have a stiff rear mount that allows 0movement but rubber engine mounts does that put more stress on the bellhousing? If the engine is 225 ft.lbs max than that would mean the max torque on the bell would be 225 right? Seems like thats not much to worry about but this bell is very thin even compared to a 4cyl toyota bell.

My current t-case mount is pictured below. I have to redesign it because it is practically impossible to remove the drivetrain without moving the cab. I think it will be worthwhile to also change the mounts to rubber and move them closer to the centerline of the trans.


Bellhousing before I cut a hole in the top and clearanced it for the starter.


Starter clearance:



T-case mount that I want to redo---- If I can get the thing down out of there... (built it when cab was off)


The mount is making nasty vibrations against the cab...

It's really stuffed up there high...




So what should I do? Strengthen the bell somehow, add another mount for the transmission? I think I have to redo the transfer case mount no matter what. Someone pointed out to me that at the very least I should smooth out the hole I made as the new starter pocket for strength.

[edit] Nevermind... I just took a good look at your set-up and what I was thinking doesn't really apply.

I was elsewhere last week <img src="/forums/images/graemlins/pfft.gif" alt="" /> We talked about how most folks match the engine mount and tranny mount materials (rubber/rubber, poly/poly or solid/solid but not rubber/solid). I think it certainly makes sense to consider length-of-lever-arm in the equation, but few folks do. Based on the relative lengths of your lever arms, I think you'll be fine.

The hold in the tub and the bellhousing looks a little rough, but I figured you were still building and testing. When you get to polishing, it makes sense to smooth the starter hole in the bell and maybe fab a little cover to minimized the chance of grit getting in the starter or bell.

You could also build a 'powertain cage' to connect the motor side of your motor mounts to the beam section of your tranny mount -- I don't think it is really necessary, but it may give peace of mind. Remember that swappers running FJ40s have used this sort of bolts-to-the-back-of-the-transfer-case mount with outboarded rubber bushings for decades, some with TH350 autos that use a half-style bell. I recommend that you just run it...

If you are still nervous about it, run rubber donuts in place of the poly donuts you currently have (I might be interested in purchasing the poly ones at some point).

Randii

Thanks for your advice randii I read your other comments as well.