[1project2many]

Folks know the Muncie SM420 heavy duty 4 spd used in these trucks is one tough unit but the trans can make a whine that's downright obnoxious. The noise seems to come right out of the shifter and over the years I've seen a lot of homegrown "fixes" including resting your hand on the shifter, a bungee cord under the dash to put pressure on the shifter, and even rags / rubber bands / leather gloves wrapped around the shifter to dampen the sound. Other fixes I've seen suggested on forum boards are add STP, use thicker oil, put sawdust in the trans, and even rebuild the trans completely. None of this will address the problem in an acceptable way and many a good trans has been removed because the noise was just too much for the owner.

The original shifter is a solid piece of steel from shift knob all the way down to the bottom where it contacts the slides of the shift forks. In later years when the SM465 was produced the shifter was changed to a multiple piece unit with the shifter rod attached to the lower portion of the shifter using a sleeve and pin arrangement. This significantly reduces gear noise transmitted through the shifter and the same approach can be used for the SM420 without a large amount of work. I did this in my truck over 15 years ago and I've never seen anyone suggest the same modification so it's time to post it.

The top picture is the shifter from the SM420. Bottom is the SM465. It's not too hard to see the work needed to make the modification. The 465 shifter pictured has been welded where the sleeve and shifter handle meet but I believe mine was just pinned. In my case I wanted a slightly shorter shifter throw so I used a complete shifter handle from a 1990 465 which is shorter but has a single bend back toward the seat like the original shifter. As my memory has it, the total distance from the pivot ball to the end of the shifter is longer on the 420 transmission so I cut the original shifter and used the end with the 465 sleeve. This required grinding it flat to fit into the sleeve. These days I don't like the slight bend over to the shifter so much and I'd probably cut the original shifter and weld the sleeve on, then use the cut off piece in the sleeve to make up the difference. One thing to note is that the bottom of the 465 shifter just doesn't fit into the 420 shift gate without being ground and I just decided it would be easier to use the end of the 420 shifter in the sleeve.

Sorry I don't have more pics but at least this might help someone hoping to keep the original trans from going crazy due to gear noise.