VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 48 Transmission Problem

Transmission jumps out of third(high) gear when using engine braking. Got worse over time. For a while could hold in third with gear shift lever. Now, can't hold it and can't get back in to third. Other gears work fine. Checked linkage, all OK, proper third lever movement with engine off.

The jumping out of high problem is most commonly caused by wear in the internal transmission parts.The bearings (14 rollers) may be bad-the go between the front main drive gear and the rear main shaft.The syncro. drum may be worn or the ball bearings have a lot of end play.There can be some minor things like loose trans. to bell housing bolts but I believe that removing and inspecting the transmission internaly will be nesessary :confused:

Gene I didn't know the 48 tranny had the 14 rollers betwen the front and rear mainshafts like the 51 thru whatever, but that seems logical, I had a 51 that did that and it was the rollers, they , what were left welded to the male stub shaft, this apparently caused the sync to get egg shaped or visa versa and the car would not stay in high.

All of the 1937-52s had the 14 rollers.Then in 1953 they changed it to two rows of rollers-one of 14 and one of 24.This was done to correct an ongoing problem that some '49-'52s had of jumping out of high gear at higher speeds.The front and rear shafts from a '53 could be installed in those years along with the neessary rollers to correct the problem.

I recently cured the same problem in my 52, I replaced the front ball bearing, all 14 rollers, second gear thrust washer, the bushing at output shaft at the rear of the transmsission (Northwest transmission had this particular part) installed a combination bushing/seal unit from the filling station. The thrust washer had signs of wear, the rear transmission bushing was worn to the point of looseness, the front bushing in the drive shaft torque tube had actually spun out and was moving around in the tube. The front ball bearing was slightly rough, probably did not require replacing but as long as I was that far into it thought I might as well.I have had no problem whatsoever since replacing the above parts. MY guess is that the worn 2nd gear thrust washer and the loose rear bushing were alowing the shaft to move up and down causing high gear to disengage. The 49/54 manual does a good job of describing th problem.

One small note-the 1948 and down does not have a rear bushing in the transmission..Also anyone removing their transmission on any of the torque tube years should consider replacing the drive shaft bushings.When loose and worn they cause a drumming vibration thru the car at higher speeds.The Oakie kits from the Filling Station and Chevs of the 40s are the best way to go.

Thanks for the replies. When I removed the side cover the problem was quite apparent. The 2nd & 3rd shifter yoke assembly(Group 4.303-Part No. 591738) had worn so extensively on the 3rd gear side that the metal got so thin it just bent to the side, thus there was no metal left to engage 3rd. Now, I need the shifter yoke assembly. I haven't checked the catalogs to see if any are listed.

eBay - Item numbers: 2424383961 and 2424506022

40 -48 CHEV NEW 2ND+3RD SHIFTER YOKE ASSEMBLY!

Jim

Wow Larry-that was fast.One is even in your home state e