Originally Posted by whunter

A broken transmission mount adds stress/torque to the engine mounts, causing premature failure.

Failure mode:
* Turns to marshmallow goo.
* Rips apart.

Testing:
* Put a board on the transmission oil pan, and lift with a floor jack.
* You are checking for gummie stretch or separation.
Note: A new mount feels like fresh tire side wall rubber.


Other possible causes for broken mounts:

(rare issue, increasing with age) Weak or broken Ip rack return spring, (sloppy/eratic idle).

Ip rack return spring r&r
Ip rack return spring r&r

(Common issue) Weak, broken or superseded rack damper bolt:

so, what does that rack damper bolt (617) actually do?
http://www.peachparts.com/shopforum/diesel-discussion/183139-so-what-does-rack-damper-bolt-617-actually-do.html#post1458468

Part# rack dampener pin for 1985 300SD
http://www.peachparts.com/shopforum/diesel-discussion/120005-part-rack-damper-pin-1985-300sd.html#post858324

Adjusting the Rack Damper Bolt
http://articles.mbz.org/engine/diesel/rackbolt/

Replacing Rack dampener pin
http://www.peachparts.com/shopforum/diesel-discussion/176580-replacing-rack-dampener-pin.html#post1391845



Topic related threads:

Bad engine mounts
http://www.peachparts.com/shopforum/diesel-discussion/121286-bad-engine-mounts-post868339.html

Heat shield OM617 engine mount
http://www.peachparts.com/shopforum/diesel-discussion/121452-heat-shield-om617-engine-mount-post873875.html

Engine / motor mount DIY
http://www.peachparts.com/shopforum/diesel-discussion/146482-engine-motor-mount-diy.html#post1104023

300D engine mount blues
http://www.peachparts.com/shopforum/diesel-discussion/109264-300d-engine-mount-blues.html#post758340



Have a great day.