Gear noise got ya down?
 

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.

Re: Gear noise got ya down?
 

I kinda like the whine. Some of the old roadranger 13speeds were really loud though.

Re: Gear noise got ya down?
 

Thx 1project, I'm on the hunt for a shift lever for my 71 K10 bench seat w/ sm465 and I was wondering the same thing. Great info to have before I started going down that road.

Much appreciated
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Re: Gear noise got ya down?
 

some of those old trans vibrate the shifter a lot!

an additional thought:
S10 T5 shift levers have an internal rubber vibration bushing, You could weld the right size bolt (or a cut off end of the T5 shift mechanism) onto a cut down SM4xx shifter then thread the S10 lever on.

Re: Gear noise got ya down?
 

:chevy::chevy::chevy:

This is a Thread revived and the OP is still on Board. :metal:

Re: Gear noise got ya down?
 

I wasn't going to say anything, :lol:

Re: Gear noise got ya down?
 

raising the dead just before Halloween

Re: Gear noise got ya down?
 

Ahem - since we are here -

I can comment that during the square body era there were two versions of this shifter.

The earlier version had two o-rings positioned inside that sleeve to provide some isolation. The o-rings would get pounded out over time, so there was a second design that had a square rubber isolator molded inside (the shifter and sleeve were changed to accommodate the square shape).

In either case the design was intended to calm down the shifter "buzz", moreso than affect any kind of gear noise airborne transmission.

K

Re: Gear noise got ya down?
 

One of the things that limited me in my career as a development engineer was growing up with Tripower GTOs and Muncie rock crusher transmissions. I didn't have the same threshold of what was acceptable as others in my organization.

I remember one time my boss took me out on the test track and said "hear that gear whine? You gotta fix it!"

"Fix it?" I said. "I LIKE it!!"

K

Re: Gear noise got ya down?
 

Oh come on Say something:lol:

I wonder if 1project2many still has that truck?

Re: Gear noise got ya down?
 

I still have the truck. It still has the original transmission with the modified shifter. I had it out on the highway doing 80+ last weekend. My son has asked if he can have it when I'm done with it so I am hopeful I can keep it in good condition for several more years.

Some day I hope to get back to the NVG4500 swap I started in the mid '90s. I modified a stock bell housing and transmission case to bolt together and I made a sleeve to center the 4500 input shaft bearing retainer in the bell housing. I have a combination of Dodge and GM internals and externals because Dodge used a speedometer cable on some models and GM used an electronic speed sensor. The shifter is located closer to the seat so I will need to get a new shift cover. At this point I think the four speed repro floor mat will be the hardest thing to find.

One other transmission related tip I would add for the original 4 speed is that some of these transmissions have no input shaft seal and the transmission can leak oil out the input shaft. It shouldn't happen, but mine has oiled the clutch disc a number of times. Novak Adapters is able to machine an original input shaft to work with their input bearing retainer so a seal can be installed. Total price is currently about $200 but you have to supply the input shaft.

Re: Gear noise got ya down?
 

Keith Seymore, this is too funny. I have spent way too many hours learning to hear sounds that didn't bother me so I can better address customer concerns. It's very frustrating.

Have you been for a ride in an electric vehicle yet? There really needs to be some type of optional "engine idling" sound for those of us who grew up listening to the exhaust.

Re: Gear noise got ya down?
 

I still have the truck. It still has the original transmission with the modified shifter. I had it out on the highway doing 80+ last weekend. My son has asked if he can have it when I'm done with it so I am hopeful I can keep it in good condition for several more years.

Some day I hope to get back to the NVG4500 swap I started in the mid '90s. I modified a stock bell housing and transmission case to bolt together and I made a sleeve to center the 4500 input shaft bearing retainer in the bell housing. I have a combination of Dodge and GM internals and externals because Dodge used a speedometer cable on some models and GM used an electronic speed sensor. The shifter is located closer to the seat so I will need to get a new shift cover. At this point I think the four speed repro floor mat will be the hardest thing to find.

One other transmission related tip I would add for the original 4 speed is that some of these transmissions have no input shaft seal and the transmission can leak oil out the input shaft. It shouldn't happen, but mine has oiled the clutch disc a number of times. Novak Adapters is able to machine an original input shaft to work with their input bearing retainer so a seal can be installed. Total price is currently about $200 but you have to supply the input shaft.

Re: Gear noise got ya down?
 

Cool that You still have the truck and that your son is Interested in it.:metal:

That is good info about the front seal.
I will have to look at my 420 and see if it has a seal or not.

My brother has a 4500 in his shop floor.
I am hoping he will let go of it one day and put it in my truck.

Re: Gear noise got ya down?
 

i saw mknittle's post and figured he'd risen himself :lol:
then i clicked on his build link and saw chevette and a couple others that haven't been here for years.

Re: Gear noise got ya down?
 

Thanks for posting this mod! With regards to the floor mat, Seth Doulton, is reproducing a 4 speed rubber floor mat now. https://qualityclassicparts.com/prod...uck-oem-design