I recently replaced the pilot bushing, flywheel, clutch and throw out bearing and a rebuilt 3 speed transmission on my 1952 1/2 ton 3100 truck. The transmission came from a closed repair place that had about 40 presumed to be rebuilt transmissions on shelves for years. It had no side cover and had only minor surface dirt and dust. The gears were lightly lubed and shifted easy through the gears. Main and rear shafts and bearings were tight like after a rebuilt. Did the maiden trip two weeks ago with temps in the 70s and it shifted smoothly into all gears with no noise or effort. Only once after 30 miles driving did the high gear jump out into neutral at around 55 mph and 2300 rpm. Drove it again yesterday with temps in the 50s. This time I could hardly get close to 50 mph when the 3rd gear jumped out several times. Unlike a worn out transmission I had I the past, I could not hold the shifter down in place - it really wanted to go out into neutral and no force applied to the shift lever kept it in gear. It never jumps out of gear in first or second and also never when decelerating in any gear. It stays in gear when under load or with light load if kept around 2000 rpm. But on a level road as the speed goes up, you can hear the typical gear-whine on these truck transmissions, with needle bearings in the counter gear, getting louder and brighter, as the intake vacuum increases and the load gets lighter in high gear. That is new to me after driving two previous transmission for 24 years and well over 100K miles up to 75 mph on long freeway trips. Anybody has experience with that scenario? My first transmission was really worn out, but never increased in gear whine noise under light load and it very rarely jumped out of 3rd gear on downhill freeway sections, but you could hold the shift lever down and keep it in gear. This one really wants to jump out of gear with strong determination. I can feel it driving the shift lever firmly out of gear, if I try to hold it down in gear. However I can also get it right back into gear effortless, until the cycle starts again. Was it the low temps? Shall I use Lucas gear oil for a while until it breaks in? Rainy season starts tonight, which means I normally use my truck as the daily driver. Any help is greatly appreciated.
on the main drive gear (aka. the input shaft gear), there are splines at the end inside the transmission. If these splines have wear on the sides of them, it will be more likely to jump out of gear. Also, if the splines inside the synchro drum that mate with these splines are worn, same thing... misalignment of the transmission to crankshaft, worn shifter detents, and a few other things will contribute to the problem.
x2 You must make sure that the linkage puts into 3rd all the way. Then the detent needs to be working. Then it could be worn fork, but likely the small teeth are worn at an angle from jumping gear. It should not have gear whine in 2nd or 3rd. Sounds like a worn out trans & gears by your description. Needle bearings are silent if good. If you can pull the side cover and get a close-up clear pic of the forward upper gears (while in 2nd gear), we could tell if the small teeth on the input shaft are junk.
You said it had NO side cover, and that's where the shift forks connect to the sliders. In attaching a side cover and the shift forks, I wonder if maybe the 2-3 fork is "flipped" 180 degrees? The R-1 fork is really obvious, the 2-3 fork not so much. Just a thought. I am Butch/56sedandelivery.
Sounds like I have to go inside the transmission. I wonder if I can replace the main input shaft after just pulling the front bearing. Have to look up the manual.
Do you mean this shift fork? Just took this photo of a new one I have, but it is perfectly symmetrical with no reference of orientation.
That gear shift lever inside the trans cover. I has a narrow slot that fits over the syncro that shifts second and third gear. It could be worn and not shifting all the way into third gear? If your getting full engagement then like Squirrel stated the syncro and front inpuit shaft gear are worn out.. Now you can remove the front shaft. mill the face of the gear side about 20 thousands. remove bearing and place a .020 shin between the bearing and gear. that will place the gear farther in the syncro. Old junkman fix that don't cost much to do.
Yes, but maybe I should have mentioned the "wear" factor. I'm sure that would be obvious. I had an OT Nova that had some warranty problems with the Saginaw 4 speed, and the dealership just kept replacing the fork (don't remember which one, it was 1972), and the slider would just wear the new one back down too. I finally just swapped in a Borg Warner T-10 I had. Now I see Old wolf has already mentioned it too. I am Butch/56sedandelivery.
Here's how to fix these high gear jumper torque tube 318s … The snap ring groove in the rear of the case is worn. The entire top train is moving back & forth. You need to shim between the 2nd gear thrust washer & the rear bearing with the right amount of thickness to eliminate MOST of the play. I've used shims from VW parts, truck king pin thrust washers or whatever I can find to do the job. Another way to do it - a shim between the clutch gear & front bearing.
I am coming back to this thread I posted in November with one last question. Is it possible, if you have failing rear end pinion bearings, that the transmission would jump out of gear around 2000 rpm in high gear? I am asking because these bearings disintegrated in January (see photos) and I wonder if that transmission is actually good or really needs repair. Thanks for any help.
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