Sm-420 gear whine

[Coach529]

Ok....so I have a couple hundred miles on Henry now. Still tracking down rattles and other issues.

One question is gear whine from the stock 4 speed, a Sm-420. Anyway to quite it down?

75% of the time the only noise I hear is the transmission not the motor.

[mknittle]

I used Lucas gear oil additive. that helped.

[OrrieG]

STP will also help. Old school guys also added sawdust right before selling it....

[Rufton]

I would drain/siphon gear oil and inspect for metal shavings just to be on safe side.
If no time, a quick finger swipe is better than nothing.
I would also shoot temp w/ IR gun after long drive to be sure temp is normal.

[NEWFISHER]

Lucas or banana peels
Posted via Mobile Device

[mark '87 930]

Just curios.. and in no means want to hijack the thread, but what about Swepco 201? I used that in my sportscar in the past to quiet it down (the transmission). It's really thick and blue.

[Coach529]

Originally Posted by NEWFISHER

Lucas or banana peels
Posted via Mobile Device

You have my attention.....

[mknittle]

they are just noisy. I would worry more if mine stopped whining.

[Katrina/10]

Mine is noisy in second or third, but quiet in fourth.

[Coach529]

Originally Posted by mknittle

they are just noisy. I would worry more if mine stopped whining.

That is what I am finding out. I have nothing to compare it to.

[sweet70beast]

These are stout transmissions and the gears inside mesh almost straight across which makes them noisy. They usually have one or two teeth in mesh with the driven gear. Modern transmissions gears are cut at a big angle to each other so they mesh at an angle which makes them quiet. Modern trans have several gears in mesh because of the angle they are cut.

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[lmdangerous]

My Sm 420 got real quiet after i went straight Lucas

[1project2many]

Banana peels... another '80s dealer trick. It can help, but if you do it don't ever drain the fluid out of that trans again. The smell is bad enough to clear out a small western town.

Now, here's something to think about. If it's gear noise, and the 420 has a lot of it, you're going to hear it in 1-3 but not in 4th. 4th gear is direct drive, no gears involved. If you're hearing a whine in 4th you've got another issue to look at, most likely bearings. For gear noise, most of the "fixes" you'll hear are an attempt to reduce noise transfer by using the oil to absorb sound energy. I've seen some other neat stuff, too. Inside the cab you can "hear" the noise in the shifter and if you put a little pressure on the shifter it usually quiets down. I've seen bungee cords from dash to shifter, rags tied onto the shifter, giant rubber O rings rolled up and down the shifter, heater hose on the shifter, all with some degree of success but none were really effective. If you're getting noise through the shifter you need to reduce sound transfer through the shifter.

The SM420 shifter is one piece from top to bottom. Similar to this one:


The later SM465 shifter is multiple pieces, like so:

Notice the roll pins and sleeve? There are three parts to that shifter.

I've seen posts that say you can directly swap shifters. Maybe so with the right year trucks but my experience is different. For my truck I used a shifter from a '90 pickup (last year for SM465) because it had only one bend so the shifter angle was close to stock. Plus it had reduced length which made it possible to shift a bit quicker. I'm not so young now and I probably have the patience to use a full length shifter. Anyway, the ball fit into the socket but the lower portion of the shifter was too short and too wide to fit in the stock shift rail. So I removed the roll pin from the sleeve and discarded the bottom piece. I cut the bottom of my stock shifter where it engaged the shift rail, ground and drilled as appropriate, and installed it into the sleeve. What a difference! There's still plenty of gear noise but it's outside the cab.

If you want to dampen the noise from the trans itself you could try undercoating the exterior as well as the "thick oil" fixes mentioned above. If you're not showing off the trans, any type of foam material attached to the trans would serve as a good sound deadener. You could also try those mastik pads used in body panels although I'm not sure they'll put up with the heat. But chances are the shifter changes alone would be enough.

I found some pictures showing differences between the 88-91 465 shifters and the early versions. You might indeed be able to get the early version to fit into the 420 trans and use a torch to get the shifter angle you want. The 88-91 truck shifter is also a much larger diameter and I wonder if the additional metal in the shifter plays a part in keeping it from "ringing" with the gear noise. Here are the photos, though:

[Katrina/10]

Interesting remedy! I wondered what all that extra stuff on a 465 was.

[1project2many]

Correction to above...
"... the bottom of the shifter was too short and wide" should be "too long and wide"

Memory not 100% after 20 yrs has passed.

[mknittle]

I rebuilt the one in my jeep and it whines in 4th only. But maybe that is the only gear I can hear it in. It isn't loud. I sounds like a radio turned down low enough to hear but not make out what song is playing.

[Rufton]

Originally Posted by 1project2many

Banana peels... another '80s dealer trick. It can help, but if you do it don't ever drain the fluid out of that trans again. The smell is bad enough to clear out a small western town.

I'll keep that in mind