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Curing the SM465 Sloppy Shifter By Bill "BillaVista" Ansell |
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IntroductionGood old-fashioned all-gear cast-iron heavy-duty 4-speed manual truck transmissions are great transmissions for hardcore trail rigs – the SM465 is one of the best and most popular. I've driven many different transmissions, both automatic and manual, and I love my SM465; except for one thing – the notoriously sloppy shifter. With a low-geared, manual tranny rock rig, finding and confirming you're in neutral can be critical. In addition, though you're not likely to be able to slam through the gears and win a drag race with one of these old 4-speeds, being able to make a reasonably positive, rapid shift into reverse can be a real roll-over saver. Unfortunately, with my SM465 and with many other old-school manual truck transmissions, better than 25 years of hard service has left the shifting weak and sloppy. |
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I decided to tear into my shifter to see if there was anything that could be done. Here's what I found:
Figure 1 – 4-speed shift tower housing showing "ball-and-socket" joint The shifter has a "snout" on it that engages the shift rail in the transmission. Just above this there is a ball-shaped support that is factory tack-welded onto the shift lever. This ball sits in a corresponding cup or socket in the transmission cover plate (shift tower housing), held in place by two roll pins. A compression spring exerts pressure on the ball to keep it seated in the cup. The resulting "ball-and-socket joint" (Figure 1) is what controls the range of motion and positioning of the shift lever. It looks and works in a similar fashion to a human hip or shoulder joint. |
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The problem is, after many years of use and abuse, the tack welds holding the ball onto the shifter are prone to cracking (Figure 2). Figure 2 – cracked tack welds |
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In addition, the two slots in the ball that are engaged by the roll pins become worn (Figure 3), as do the roll pins themselves. Figure 3 – worn pin seat groove |
The cracked welds leave the stick sloppy in the ball, and the worn pins and pin seats leave the ball sloppy in the shift tower housing. It all adds up to a slack, sloppy shifter. Result: the quick waggle you do to confirm neutral ends up telling you nothing as the whole shifter flops and slops around in a most disconcerting fashion. The solutions was simple – sort of. First I ran a bead of weld all the way around the joint between the underside of the ball and the shifter, completely overlapping the old tack welds. Next I gobbed some weld onto the pin seat grooves of the ball and then cleaned them up with a die grinder and small hand file. |
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The tricky parts was cleaning up the steel and getting a good weld because the ball and shifter had spent a lifetime in an oil-soaked environment leaving the steel heavily impregnated with oil. That's my excuse anyway - Figure 4 begs the question: "Which is worse - my photography or my welding?!" Figure 4 – ball welded to shifter |
To complete the job I reinstalled the shifter with two new 5/16" x ¾" roll pins. WARNING: oil-soaked steel subjected to the heat of welding is potentially explosive – take proper safety precautions and undertake this at your own risk. Ideally you should bake or steam the part prior to welding in order to drive off the hydrogen. Even after this minor surgery I found that banging the shifter around like a man possessed, which is my preferred driving style, caused the roll pins to walk out, re-introducing some unwanted slop. My first solution, even though I knew it wouldn't work, was to try to tack-weld the roll pins to the shift tower housing. Of course it didn't work – the shift tower housing is cast-iron and a quick MIG tack weld was bound to crack. The one thing I don't know, is why I always do things I know won't work? Laziness and stupidity are the top two contenders! |
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In the end I used a couple of hose clamps to hold the roll pins in place (Figure 5) – even though a single larger one would have been neater (score one for laziness I guess!) Figure 5 – hose clamps holding roll pins in place |
An appropriately sized muffler clamp might also work. The clamps definitely improved things, but those little pins still shift around more than I like, so one day I just may remove the shift tower housing, tap the roll pin holes, and then use some threaded pins instead of roll pins. If you have a manual transmission with which you have a love-hate relationship because of a sloppy shifter, open it up and start sticking metal together like a 3rd grader with a hot glue gun. You'll be thrilled at the improved shifting and can then happily get back to smashing your rig into rocks! |
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