^^^ Exactly - The synchros are what allows you to put your car in a gear. Once the gears are locked the synchros job is done. Now it is the job of the gears to stay locked together. Like Kappa said, it is most likely the bearing or possibly worn dog teeth on the gear itself. Either way its not an easy job and will be pretty expensive to fix.

 

Hello. My problem relates to the topic of this thread so I'll post it here.

I might well have the oldest Honda on this site. I may not have it much longer, though. I've been driving it since 1986…

Today I was driving my 1981 Civic SW 1500cc manual transmission to work. While I'm on the freeway going about 60mph my transmission pops out of 5th gear resulting in a high-pitch whine. I thought the transmission had finally gone out after 280,000 miles. After I coasted over to the side, just sneaking in front of a semi, and onto an exit ramp I was subsequently able to shift into every gear but 5th. I drove the rest of the 20 miles to work in no higher than 4th gear.

So my question is this: What is the source of my problem? Clearly, if fixing it will have anything to do with opening up the transmission I might as well just euthanize the car and buy a new one because the car isn't worth more than $500 anyway. But the car has such sentimental and functional value (it's my mountain climbing thrasher car) I will be sad to part with it. I suppose an auto friendship can't last forever.

1. Gear shift linkage rod/fork problem? Could this be replaced without opening the transmission?
2. Bearing problem (maybe same issue as donrob's)?
3. Synchro problem?
4. Dog teeth all gone? I'm thinking maybe the car is so old I had sheared off or worn away all but one of the teeth by now and that finally the last tooth failed this morning. But I don't know for sure.
5. If I do nothing will the problem have a cascading effect to progressively lower gears? Hey hey, maybe in 4 years I'll only have 1st gear left as I limp toward 300,000 miles!