Solid Tranny mount? Good, Bad, or indifferent - Off-Road Forums & Discussion Groups
Jeep-Short Wheelbase All discussion of short wheelbase Jeeps: CJ, TJ, YJ and JK

Reply
 
LinkBack Thread Tools Display Modes
post #1 of (permalink) Old 01-23-2004, 02:51 PM Thread Starter
Pooh-Bah
 
uglyjeepoffroad's Avatar
 
Join Date: Oct 2000
Location: Hickory, NC
Posts: 2,339
Thanks: 0
Thanked 0 Times in 0 Posts
 
Solid Tranny mount? Good, Bad, or indifferent

I have broken two tranny mounts for my t-18 in the Commando. I know there are poly mounts available, but if I am not worried about vibration, could I just build a solid mount?
I am thinking 2" box steel mounted to the tranny in the middle and extended about 6" on each side onto the skidplate. This could work as a torque arm too. It would be bolted to the skidplate and the plate would be reinforced.

What do you guys think?
Seems like it would be strong and easy to build. [img]images/graemlins/40BEER.gif[/img]
Attached Images
File Type: jpg 1251765-Tranny mount.jpg (12.9 KB, 9 views)
uglyjeepoffroad is offline  
Sponsored Links
Advertisement
 
post #2 of (permalink) Old 01-23-2004, 03:28 PM
Moderator
 
Jim_Lou's Avatar
 
Join Date: Dec 2001
Location: Belleville, Illinois
Posts: 11,487
Thanks: 15
Thanked 22 Times in 17 Posts
         
Re: Solid Tranny mount? Good, Bad, or indifferent

</font><blockquote><font class="small">In reply to:</font><hr />
What do you guys think?

[/ QUOTE ]

I think something's going to break, soon. Fatigue will eat that up like a bowl of Kibble.

My 258-T18 combo is 25 years old, and I've used up about 3 transmission mounts, and those were when I had to cut half of the back side away to clear the PTO. You've got to figure out why they're going bad.

And the stock torque link looked useless to me - there was so much slack in the bushings that the engine would have to rock about 45* before it would even come into play. I tossed it with the second motor mount, 20 years ago, and never put it back.
Jim_Lou is offline  
post #3 of (permalink) Old 01-23-2004, 03:35 PM Thread Starter
Pooh-Bah
 
uglyjeepoffroad's Avatar
 
Join Date: Oct 2000
Location: Hickory, NC
Posts: 2,339
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Solid Tranny mount? Good, Bad, or indifferent

I know I have some axle wrap that will be solved when I build a wrap bar, but I don't know why else it would be breaking them.
It is a Scout T-18/dana 300 combo and it was chained to the factory crossmember when I got the Jeep. I put in a CJ skidplate and a stock tranny mount, but it has never had a torque arm.
What would start breaking with my proposed setup?
I thought that if it was held in place tighter, it would flex less and not move in the mounts as much. I want it to be still to help with the stupid clutch linkage that is anchored to the frame and the bellhousing. (Want to go hydraulic, but no $$$$) [img]images/graemlins/mad.gif[/img]
uglyjeepoffroad is offline  
Sponsored Links
Advertisement
 
post #4 of (permalink) Old 01-24-2004, 11:34 AM
Keyboard Implanted
 
Smokngun's Avatar
 
Join Date: Sep 1999
Location: Palmyra, WI
Posts: 2,209
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Solid Tranny mount? Good, Bad, or indifferent

I know the shock loads are different in drag cars than with off roaders, but every race car I've seen that the owner solid mounted the trans, cracked the case. Even with solid motor mounts or motor plates, you should use a 'soft' trans mount. Rubber or urethane.
Smokngun is offline  
post #5 of (permalink) Old 01-24-2004, 01:30 PM
I Might Just Know What I'm Talking About
 
Randyzzz's Avatar
 
Join Date: Jul 2001
Location: Sisters, Oregon
Posts: 1,988
Thanks: 0
Thanked 1 Time in 1 Post
 
Re: Solid Tranny mount? Good, Bad, or indifferent

Instead of just bolting that tube for the mount to the skid plate, weld some tubes at each end for poly spring bushings to fit into, weld some tabs on the skid- you won't get much stronger! Just don't get the trans mount stiffer than the motor mounts...or something will give from the torque twist....
Randyzzz is offline  
post #6 of (permalink) Old 01-24-2004, 05:39 PM
Moderator
 
Jim_Lou's Avatar
 
Join Date: Dec 2001
Location: Belleville, Illinois
Posts: 11,487
Thanks: 15
Thanked 22 Times in 17 Posts
         
Re: Solid Tranny mount? Good, Bad, or indifferent

</font><blockquote><font class="small">In reply to:</font><hr />
What would start breaking with my proposed setup?


[/ QUOTE ]

In short, the weakest point.

The horizontal bar where it bolts to the transmission might be the first to go. If you use a thicker bar, then it might break where it bolts to the skid plate. Or if the bar is really stiff, the skidplate might break out around the bolt holes.

To solid-mount a power plant, the whole setup has to be so stiff that nothing will flex. If it does flex, the area that flexes will fatigue and break. The one way to do it might be to use a spring for the tranny mount bar, but then it's not really a solid mount.

Fatigue damage is nasty business. The cracks are usually hairline with no displacement, so theyre hard to see. And it takes only a tiny amount of bending to cause fatigue damage. Probably a fourth of the off-the-street welding jobs in my shop are fatigue repairs. One of the most common failures is lawnmowers with stamped steel housings, where the motor mount bolts have a spider web of little cracks radiating out from them. Often the cracking is so bad that the motor will almost fall out.
Jim_Lou is offline  
post #7 of (permalink) Old 01-24-2004, 05:44 PM
Keyboard Implanted
 
Aaron871's Avatar
 
Join Date: Feb 2003
Location: Homeless in the Hammers... / Mexico
Posts: 3,160
Thanks: 0
Thanked 1 Time in 1 Post
 
Re: Solid Tranny mount? Good, Bad, or indifferent

Uglyjeep, I tried hard mounting the T-18 like your pic shows. It lasted about an hour on the trail. It needs to be able to flex a little. I went poly and have been ok for a few trips.
Aaron871 is offline  
post #8 of (permalink) Old 01-24-2004, 05:46 PM
Moderator
 
Jim_Lou's Avatar
 
Join Date: Dec 2001
Location: Belleville, Illinois
Posts: 11,487
Thanks: 15
Thanked 22 Times in 17 Posts
         
Re: Solid Tranny mount? Good, Bad, or indifferent

</font><blockquote><font class="small">In reply to:</font><hr />
if it was held in place tighter, it would flex less and not move in the mounts as much.

[/ QUOTE ]

The 'as much' is the root of the problem. If it moves any, something will fatigue crack.


</font><blockquote><font class="small">In reply to:</font><hr />
I want it to be still to help with the stupid clutch linkage that is anchored to the frame and the bellhousing.

[/ QUOTE ]

Lots of CJs have that clutch bellcrank linkage, and it works fine. It might be better to get the linkage working properly. What's the matter with it?
Jim_Lou is offline  
post #9 of (permalink) Old 01-26-2004, 01:02 PM
jumpinNrollin
Guest
 
Posts: n/a
Re: Solid Tranny mount? Good, Bad, or indifferent

Don't solid mount it. Find out what is wrong and why the Tranny mount is taking all the movement. Most likely you have a bad or wornout motor mount and the whole drive train is twisting under load. Maybe...Maybe not... That is what I would check.
post #10 of (permalink) Old 01-26-2004, 01:13 PM Thread Starter
Pooh-Bah
 
uglyjeepoffroad's Avatar
 
Join Date: Oct 2000
Location: Hickory, NC
Posts: 2,339
Thanks: 0
Thanked 0 Times in 0 Posts
 
Re: Solid Tranny mount? Good, Bad, or indifferent

Okay. You guys have shown me the light.
I may make the mount with the spring bushings on either end and replace the motor mounts with poly. That should help.
Thanks. I will get some pics when I get it done.
uglyjeepoffroad is offline  
Sponsored Links
Advertisement
 
Reply

Quick Reply
Message:
Options

Register Now



In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in










Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode



Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome