Transmission Synchro/Output Shaft Noise After a Concerning Sound
 

Hey all.

I'll try my best to explain what occurred to me yesterday, so bear with me and ask any question about the sounds or troubleshooting you need.

Yesterday, I was just testing some different angles of my foot for heel-toe downshifting to see what would be most functional and comfortable. I normally just use the pinky toe side of my right foot on the gas since I have larger feet, but I wanted to try a more traditional pivot and heel the gas.

Anyway, I was slowing down to a stoplight - not hard braking or anything, just seeing what's comfortable - and because I was so focused on the foot position, I think I started slotting from 4th to 1st (probably at 30mph and still slowing). I didn't engage the gear by taking off the clutch, but by the time I heard the synchros screaming at me there was what I can only describe it as a pressure relief/blowoff noise. Similar to taking off a quick attachment from an air hose. Just a quick PSSH.

I unslotted the gear before I made a complete stop, but when I had to reslot first to get going, the gear felt more grindy and as if I were trying to row through a few lines of marbles. That got me instantly concerned, but 2nd felt normal, same with 3rd.

At the next stoplight, no more than 40 yards away, I came to a complete stop and just row through the gears to feel it out. 1st was normal again as well as all other gears.

Once I had parked the car for a while I needed to hit the road for something.
Once I started off, some shaft either internal to the trans, or the slip yoke at the front of the driveshaft was making a much higher pitch noise (I have a single piece aluminum driveshaft). I could only really hear it in 1st and 2nd, but my guess is it's present in 3rd, but I just can't hear it due to road noise.

Weird thing is after 30 seconds or so, that noise disappears during normal driving. It also doesn't happen even single startup. I couldn't hear it at all this morning after it had drizzled all night, and I was listening intently for it.

I know it's a long shot, but has anyone encountered this before or know if I'm in need of a synchro rebuild/replacement trans before something goes catastrophically wrong?

I'd probably change gearbox oil as simplest to do from all the possibilities & check for metal shavings in it. Any real diagnostics would require disassembly of gearbox, much longer and more expensive thing to do.

I didn't see any leaks, and I'm - unfortunately - not new to working on the trans (clutch issues) but that does seem like a good first option.

I'm just having a hard time thinking I'll see glitter due to the initial noise. It wasn't a clunk, bang, pow, or ping.

It was like the first second of when you need to deflate an air mattress and you pop the cap. Very intense but very fast trail off.

I'll just start a list to myself.

Any other suggestions?

Did you ram it into 1st thinking it was 3rd or were you intentionally going to 1st and just applying pressure on the syncro waiting for it to catch up? You didn't possibly aim towards the reverse gate did you? Like maybe you've had the shifter apart before and didn't get the reverse lockout plate aligned perfectly. If you aimed at reverse it would make a bunch of noise but not like a blow off sound.

If your syncros wear out it will not make anything catastrophic go wrong. You just will not be able to downshift anymore without double clutching. I drove an Integra for years with completely worn out syncros and it's actually not that bad if you can double clutch.

I can't imagine what would make a blow off sound in the tranny though. The gear whine is normal on this tranny in all but 5th (1:1). Maybe you just never listened that intently or maybe it is something wrong. Who knows.

Speaking about synchros .. if it will come to change them, imho nice option are verus/synchrotech carbon lined ones. But still, work at shop for gearbox overhaul/synchros change might get on expensive side.

I didn't ram it at all, I don't usually put a ton of pressure on a gear to downshift fully knowing if I did I'd be money downshifting, if that's a thing.

I daily my car and downshift a lot, so I'm fairly aware of the normal noises. This was quite abnormal.

I can guarantee it wasn't reverse. I have to make considerable effort to get it to go in reverse (short shifter with properly placed "gate").

As for gear whine, this is definitely a new type of whine. I'm not new at all to the woes of gear whine (trans insert, subframe bushings, engine mounts, shifter bushing, single piece driveshaft - I hear EVERYTHING) but this one is a new noise. Hopefully lucky for me, but it doesn't sound like an expensive noise...yet.

Which is why I'm seeing if this has happened to anyone.

Thanks for the input, though. Everything helps.

If I'm honest, I would rather buy a used trans that currently works well enough, swap them, tear my own down for a rebuild specifically because I want to go through that hell at least once. Also for self brownie points of doing a trans rebuild.

I'd definitely upgrade the gears themselves to something more stout if it came to that.

I often get this noise when I heal and toe, just after I pump the accelerator.

I wondered if it was some mild type of exhaust pop.

I'm interested in knowing how it goes for you.