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Solid transmission mount?

Jon B.

Jon B.

Retired three times; still working.
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I’m thinking about removing the rubber mount that bolts between the Novak adapter and the crossmember, raising the xmember, and bolting the adapter directly to the crossmember. I can gain about two inches of clearance by doing this.

Is it a dumb idea? It’s not like the extra vibration would be noticeable.

I had to shim the crossmember down from the frame to keep the SM465 lower than the floor, and to improve the rear driveshaft angle.

Jon B.
 
This is one reason I went with the AA adapter. Best idea I had for the Novak was to bolt a bracket to the adapter and mount the isolator off the bracket onto the crossmember.
 
I just finished building my flat belly plate and needed a new cross member for the SM420 for the same reason you are wanting a different one, ground clearance. I used a piece of 1/2” thick flat stock, added a couple of bends and welded to DOM tubing with poly bushings that attaches to the frame with tabs. Bushings came from Barnes 4WD, and are cheap.

IMG_3286 by Rick , on Flickr

The new cross member is bolted directly to my Novak adapter, but as noted by others, you need something at the frame as an isolator if you are eliminating the stock rubber mount. For the transfer case, I cut a piece of pipe on angle and slipped it between the Dana 18 torque mount and the 1/2” bar, welded it in place and bolted it solid. I’m now set for sliding over rocks.

IMG_3302 by Rick , on Flickr

I have a lot of design pictures in my build thread if you would like to see the details on how I built the new cross member and flat skid.
 
I have used poly body mount bushings as insulators. Seemed to work ok. Rubber would be better. You definitely don’t want metal on metal or bolt threads will start to be pulled out to flex of components.
 
All the mounts need to have the same range of flex so the entire mass of the drivetrain isn’t limited by one component.

I’ve tried this three times with three different designs, and two failed over time. One tore out the threads like nickmil mentioned, and the other broke the adapter plate AND the side tab on the D18. The two designs that failed, I was inspired by a Ford Ranger crossmember that has large, soft isolators out by the frame rails. My design was similar to what cj2atruck posted.

The first failure was quick with a loud bang. I realized that the flex in the soft Buick motor mounts was a lot more than the crossmember would allow, and the whole drivetrain was being locked in place by the solid mounts. The rubber crossmember mounts were too far apart to have enough flex in the center. I believe the t-case mount went first, then tore the adaptor in half.

Instead of seeing that problem at the time, my adolescent mind just repaired the broken pieces and tensioned the motor mounts down with straps. If soft motor mounts caused it, lock them in place! This worked for about a year of abuse, and I loved how it made the jeep feel (lots of vibrations, but firm and responsive), but it eventually destroyed the adapter again. I concluded that it was mostly from frame flex this time. Mounting bolts kept shearing off and eventually ruined the threads beyond repair; they were completely egged out.

The one that hasn’t broke, it’s a bit of a hybrid. I moved the isolators in beside the adapter rather than out by the frame. It retains the ground clearance by just bolting solidly to the adapter, but keeps the flexy bits in close to where they need to be. I also designed the motor mounts to have the same flex, so one isn’t overcompensating for the other. The cage on that one is built to act as a ladder support for the frame, so there is zero flame flex from bumper to bumper. That setup is on my 3b and has been abused in that iteration for about 23 years.
 
Well, now I’m concerned a little.

I posted a picture of my transmission mount that’s made from 1/2” steel bar, so it won’t flex, and the poly bushings are mounted on tabs welded to the frame. The v6 uses the exact same poly bushings mounted to the frame the same way in the same orientation. I had read about what you are referencing, namely that the motor and transmission mounts need be in “phase” or they will fight each other and cause failures. This is the reason I ditched the stock rubber mount, as I reasoned that the rubber mount would have more flex than the poly bushings on the motor.

So, with your failure experience, does it sound like my transmission and engine mounts are in phase so they won’t fight each other? I have an extra Novak adapter on the shelf, but I would like it to stay on the shelf…
 
cj2atruck said:
Well, now I’m concerned a little.

I posted a picture of my transmission mount that’s made from 1/2” steel bar, so it won’t flex, and the poly bushings are mounted on tabs welded to the frame. The v6 uses the exact same poly bushings mounted to the frame the same way in the same orientation. I had read about what you are referencing, namely that the motor and transmission mounts need be in “phase” or they will fight each other and cause failures. This is the reason I ditched the stock rubber mount, as I reasoned that the rubber mount would have more flex than the poly bushings on the motor.

So, with your failure experience, does it sound like my transmission and engine mounts are in phase so they won’t fight each other? I have an extra Novak adapter on the shelf, but I would like it to stay on the shelf…
Click to expand...

As solidly as yours is mounted, I’d be inclined to say it’ll probably be ok, but keep an eye out for cracks around the mounts. With everything mounted so rigidly, your drivetrain could be limiting frame flex, causing high stress points at the edges of the mounts.

Honestly, you have the room, there wouldn’t be any harm in fitting an isolator between the trans mount and crossmember. Frame flex holds a lot of leverage, and it’s likely trying to twist your drivetrain like a corkscrew.
 
Hmmm… The engine mounts on mine are poly bushings, similar to spring bushings, with 5/8” bolts through the centers. There’s not much flex to those, I think.

I’ll have to study this over the summer season and see if I can find my engineering hat over the next winter.

Maybe I should just add a bigger, better skid plate ‘til then.

Thank you, guys, for the comments!

Jon B.
 
cj2atruck said:
Well, now I’m concerned a little.

I posted a picture of my transmission mount that’s made from 1/2” steel bar, so it won’t flex, and the poly bushings are mounted on tabs welded to the frame. The v6 uses the exact same poly bushings mounted to the frame the same way in the same orientation. I had read about what you are referencing, namely that the motor and transmission mounts need be in “phase” or they will fight each other and cause failures. This is the reason I ditched the stock rubber mount, as I reasoned that the rubber mount would have more flex than the poly bushings on the motor.

So, with your failure experience, does it sound like my transmission and engine mounts are in phase so they won’t fight each other? I have an extra Novak adapter on the shelf, but I would like it to stay on the shelf…
Click to expand...
This is the same as what I did. Wheeled it for 10 years on 35” and later 40”. Never had the replace the poly bushings. The guy I sold it two years ago is still cruising.
 
ITLKSEZ said:
As solidly as yours is mounted, I’d be inclined to say it’ll probably be ok, but keep an eye out for cracks around the mounts. With everything mounted so rigidly, your drivetrain could be limiting frame flex, causing high stress points at the edges of the mounts.

Honestly, you have the room, there wouldn’t be any harm in fitting an isolator between the trans mount and crossmember. Frame flex holds a lot of leverage, and it’s likely trying to twist your drivetrain like a corkscrew.
Click to expand...
Good idea on the isolator between the trans cross member and the adapter. Easy change to make…
 
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