loomup comments, "...slips out of third gear...."
Slipping out of third is very common. Fortunately, this usually can be repaired without removing your trans. If lucky, you only need to adjust a shift lever on your trans. No so lucky, rebuild or replace a few parts mounted inside on your side shifter plate.
Here is a diagram. I have underlined in red suspect parts. Study this diagram so what I write will make sense to you. Best to open this graphic link in a new browser window so you can switch back and forth between my graphic and here.
3 Speed Trans I will work at keeping this simple.
In my diagram, look at the two shift levers on the outside of a trans, underlined red "LEVER". Those are clamp on levers with serrated teeth. Those will slip around when loose.
Shift your truck into neutral, look under your truck to note the positions of those levers. Shift your truck into 3rd gear. Look under truck to note which lever moved and which way. This is third gear.
Get under your truck, remove the shift rod, usually a cotter pin and washers, remove this WITHOUT MOVING the trans shift lever. Once the rod is off, grasp the trans shift lever and discover if the lever will mover farther in the SAME direction when shifting into third. Move the lever as far into third position as possible. If your shift rod will not slip back into the hole WITHOUT MOVING the lever, you need to adjust this shift lever.
Release the clamping bolt, maybe spread the clamp a little with a screwdriver, pull the lever off the trans. Slip the lever back on just a little bit, just enough to make sure the trans is all the way into third gear. Gently remove the lever again. This time, slip the shift rod back in the lever hole, lift the shift lever and rod up, take out any slack in your shift mechanism by pushing or pulling, then carefully slip your shift lever back onto your trans WITHOUT MOVING the large shift rod protruding from your trans. Now clamp it back up. Install your washers and cotter pin on your shift rod.
All you really have done is to make sure your column shift lever is fully engaging third gear rather than partially.
Road test your truck.
If this problem is still present, you will need to rebuild or replace a few parts on the inside of your shift plate mounted on the side of your trans.
Look at my diagram, find SPRING and FORK, both underlined with red.
Those two springs and associated steel balls, red underlined "SPRING", are "detent" springs which hold a shift fork in position, keeps the fork locked in place. Those springs can be soft or broken. You can buy new springs on the web.
Look at the two forks, red underlined "FORK". Those forks do wear, do become too thin where sliding gears make contact. This is a very small area on "tab" like ends. Wear is easy to spot, looks like you used a grinding wheel on a small area; rough and a high ridge.
Two solutions for a worn shift fork. One is simply to buy a new or good used fork. The other is to take your fork to a machine shop to be specialty arc welded where worn, than machined and polished.
Shift your trans into neutral, set your parking brake or chock your tires. Take your side-plate off, springs and forks will come out with the side plate, and be ready for a lot of trans oil to come out, very messy. Note the relative positions of everything, you need to reassemble just like when this came out. Taking a photograph is a good idea.
Shine a flashlight into your trans, look around for worn gears, broken teeth, wear where the shift forks fit. Stick your fingers in there and test for excessive looseness but do NOT move those gears out of position; just gentle testing.
Now you can inspect the forks. Upon taking the plate mechanism apart, you can look at your detent springs mostly for curiosity. Replace those springs whether broken or not. You cannot easily test for spring load, simply replace those.
Worn fork or forks, you decide if to replace or to have a machine shop repair those.
Shop around, you might find a good deal on springs and forks, just buy all of those if a good price.
Reassemble your side plate then mount back on your trans with a new gasket. You will need to have your forks back in the same position so those will slip over and engage gears. Might have to wiggle your forks around to get the right alignment.
Top off your trans with gear oil. Road test. If still a problem, you need to completely rebuild your trans with giving attention to spacers, shims and wear on sliding gears; too loose inside. This is rarely a problem. Almost always either detent springs or worn shift forks.
Again, carefully adjust your shift levers before anything else, this is a common place for a problem. If not, then remove your side plate and go from there.
Billyray
