Tranny FALLING out of gear when running!

Good Day
My '56 Chevy 3 speed manual tranny (on the column) has fallen out of gear (that is the engine was running but I was not getting power to the differential!) 2 times in the past week both when driving over 20 min. on freeways, I was able to easily get it back into 3d but this is worrying) The tranny is old and loud and I have another 235 engine/ 3 speed tranny to drop in when I get my daily driver ('64 Impala) running.
The tranny is not syncro-mesh(you know the engine rpms have to be very low before you can shift into first, sometimesrecently there has been a little bit of grinding when getting into first when idling.
The clutch has worked fine for 25 years. ( the '56 wagon for the last 15 years probably has averaged 1500 miles/year.) I hope it's not the shifting mechanism on the steering column. What your ideas?
Thanks much
Rick

I am not much experienced with manual transmissions, so someone can come and add to this, or even correct me, but with my limited experience -

If the transmission will not stay in gear, this can be due to wear or low oil level. Since you said it's old and noisy, it may be a combination of both. Check the oil level and add as necessary.

The column gearshifter is -usually- not to blame.

Correct, either the linkage is worn and your are not completely in 3rd and engine torque pops it out, or the shift forks in the trans are worn also not completely engaging 3rd ,or it is just plain wear in the synchros and drive gears.

From my experience, I agree with worn synchros and it could possibly be shifter related if it has too much slop in it. If it had a floor shifter, I'd run a bungee cord from the shift handle to under the seat and that would "fix" it for a long time. Only 1st gear is non-synchro in those boxes. If it grinds going into 1st, make sure the clutch has enough free play in it. It should engage about an inch off the floor.

With the noisy gear box and questionable linkage, swap out the box and look for a newer synchro unit if possible. If you wish to retain the column shift, face the fact that you probably need to pull the column and rebuild it. Chevy used to carry the parts but I'm sure Danchuk or someone else has them. I've done a few on cars and trucks before and you need a good manual in front of you. An alternative is to pick up a Hurst Indy Shifter and convert it to a floor shifter.

Bob

I used to have a '64 Impala that when going down a hill or letting off of the accelerator pedal it would jump out of 4th gear. It was because of a worn synchronizer. It would only do this while in 4th gear, you could downshift and engine brake fine in third or second gear.

I used to have a '64 Impala that when going down a hill or letting off of the accelerator pedal it would jump out of 4th gear. It was because of a worn synchronizer. It would only do this while in 4th gear, you could downshift and engine brake fine in third or second gear.

Once you take the load off the worn synchro it would do that. The truck I had was a wrecker with the big 4-speed SM420 Muncie box. With the bungee cord on the shifter, in 3rd gear all I had to do was let up on the gas and it would shift by itself into 4th.

Bob

Once you take the load off the worn synchro it would do that. The truck I had was a wrecker with the big 4-speed SM420 Muncie box. With the bungee cord on the shifter, in 3rd gear all I had to do was let up on the gas and it would shift by itself into 4th.

Bob

LOL, I drove a wrecker with the same transmission in it (a '73 C30). That thing had so many miles on it that while it wouldn't shift into neutral on its own (unless the oil was low), you only needed the clutch to start and stop the movement. Upshifting and downshifting was facilitated through a quick 'bump' of the gas pedal.

LOL, I drove a wrecker with the same transmission in it (a '73 C30). That thing had so many miles on it that while it wouldn't shift into neutral on its own (unless the oil was low), you only needed the clutch to start and stop the movement. Upshifting and downshifting was facilitated through a quick 'bump' of the gas pedal.

Yup, I know the drill. I drove a '66 GMC that was once V6 powered but had a tired 327 in it. Straight 50 weight Wolf's Head oil was the ticket to keep the smoke down. It had the SM420 signature 2nd gear whine to it. Of all things on the truck, the clutch or transmission was never touched.

Bob

Third gear is probably worn down. My uncle has a camaro and it slips out of second gear. He said the gear has to be replaced.


EDIT: Post was made by a 12 year old. No transmission or engine experience! Just repeating stories he hears.

Third gear is probably worn down. My uncle has a camaro and it slips out of second gear. He said the gear has to be replaced.


EDIT: Post was made by a 12 year old. No transmission or engine experience! Just repeating stories he hears.


"Gear" is just a general term for those not familiar with the guts of a standard transmission. The more than likely parts that contribute to a popping out of gear condition and worn synchros and blocker rings.

These parts should and do wear out ahead of the gears as part of the design process. Synchros and blocker rings are made of softer materials than the gears and are expected to be replaced at least once in the life of a transmission that is subjected to normal usage.

Bob