gstrudler

I'm trying to diagnose a strange transmission noise that I can't seem to figure out; it is probably best described as a squeak. Car is a 1997 Prelude SH with a M2U4 transmission which was rebuilt about 9,000 miles ago. It was fine for about 2,000 miles and then this squeaking noise appeared.

The noise only happens once the transmission is warmed up, never cold. The noise appears in any gear and also out of gear; clutch engaged or disengaged. When the car is moving it becomes a consistent, rhythmic squeaking sound; at idle it is either a constant whine or non-existent. I've replaced the TB and the ISB with no change. I've finally decided it must be somewhere in the countershaft as the other day I was stopped at idle with the car in neutral and it was whining as it sometimes does; I let my foot off the brake and let the car roll forward slightly and all of a sudden it stopped. I've since experimented when at a stop and by letting the car roll forward (or back) I can either get it to whine or not whine depending clearly on the position of the vehicle and therefore the diff and the countershaft.

I have also observed that when I accelerate the noise goes away, but then when either under engine-braking or coasting/idling the noise returns; this is very consistent once the car is warmed up. Transmission oil used is Torco RTF.

Thoughts? At this point it's got to be either a countershaft bearing or one of the diff bearings I'm assuming. I know the sound going away under load has to be a key, but I'm not sure which bearing to go looking for. I've had the transmission apart twice replacing the TB and then the ISB since the rebuild (no small feat if you know about the Prelude SH) and don't really want to do it more than one last time to get this fixed. When I had it apart replacing the ISB all the other bearings seemed to be fine, but clearly one is not. The only other possibility I guess is if it's in the ATTS unit, but that seems unlikely.

extralargenog

iTrader: (1)

It snot a diff bearing if its doing int standing still.. Out of curiosity why torco RTF for a Stockish car. Unnecessary.

Hows the T/O bearing

extralargenog

iTrader: (1)

Wondering if one of the shafts is making contact with the oil directors that funnel oil intro the shafts

gstrudler

Went with RTF b/c it's a good quality lube that is also supposed to offer better cold-temp operation and protection; I do know it's probably overkill. Especially with transmission oils that only get changed infrequently on a street car, however, I don't mind spending what is honestly not a lot of money (extra $30?) to get the better fluids, even if it's unnecessary.

The more I think about it, the more I think it can't be a bearing for the countershaft either since the countershaft isn't moving when the car isn't moving, unless it's caused by vibration, but that seems really remote. However, given that vehicle position clearly correlates (rolling forward and back changes the noise), I have to believe the CS is involved somehow.

The fact that the noise goes away under acceleration but returns on decel is also intriguing and pushes me back towards bearings and certain thrust loads that change as the shafts move slightly under power.

slowcivic2k

There is only one bearing that controls axial load on the countershaft, the snap ring bearing.

What did the "rebuild" include exactly. "Rebuild" is a vague term that must be defined.

gstrudler

The master rebuild kit from Synchrotech, so basically shaft bearings (5 of them), synchro hubs, and synchro sleeves, plus I replaced the 5th gear fork. Also did a little massaging on the 5th gear and reverse gear to sharpen up the teeth as they were worn down. Exedy stage 1 clutch and ACT flywheel installed at the same time as well. I did all of the work. The 2 bearings installed into the clutch housing were done with a press and I made sure all the bearings were oriented the correction direction. What I did not do, however, was recheck the heights for the shim on the countershaft or check the preload as I did not have the specialty tools to do either of those.

Mista Bone

Failure to check the shim clearances could have caused accelerated wear from the clearances being too tight.

How were the roller 5-6 roller bearings under the gears?

gstrudler

They all looked good when I tore it down originally, so I didn't replace them. I haven't looked at them since then as I didn't pull the gear stacks apart when I replaced the TB and ISB.

My thought process at this point is to take the car as-is to a local transmission shop so they can hear the noise and I can describe the symptoms to them, then I'll pull the tranny at home and bring it to them to inspect since they should have the tools to check all the clearances and they'll know a bit better if something isn't looking right.

I still can't figure out how it is making noise with the car at a stop and the clutch disengaged. Theoretically nothing in the transmission should be moving at that point. And then by moving the countershaft slightly (rolling the car forward or back), the noise disappears.

I originally thought the noise was tracking engine RPM and not vehicle speed, which is why I did the ISB, but after paying closer attention, it does in fact follow the vehicle speed, so it has to be something on the countershaft side OR some interaction between the two shafts.

Mista Bone

So you tore apart the tranny but didn't clean and inspect the gear stacks?

extralargenog

iTrader: (1)

LOL THIS.




and oh..... Ugh, Yes.. The countershaft DOES move when the cars not moving LOL.. The only time its not is if the clutch is in... neither on is at that point.

gstrudler

That's what I'm saying, though, it will still make noise with the clutch in and the vehicle stopped and theoretically nothing in the transmission moving.

And I'm clearly no transmission expert, but I was under the distinct impression the countershaft is connected directly to the differential and therefore the drive wheels. If the car is stopped, so is the countershaft. That's why you can't have it in gear at idle and the clutch out; the engine is moving but the wheels are not. Just like selecting gear pairs is choosing what gears you are engaging between the mainshaft and countershaft; that's what determines at what rate the countershaft (and therefore wheels) are turning. I could be wrong on all of that, but that's how I logic through it.

And no, I didn't disassemble the gear stacks the second time around. Clearly a mistake since I was trying to diagnose a problem, but at the time I was reasonably sure it was the ISB that was the problem, and I had just torn down everything 7,500 miles previous. Given those things, it didn't seem entirely necessary plus I was on a time crunch since it's my DD. Hindsight is 20/20 and I should have done it since I was that far into it and it would have only taken a couple more hours, so lesson learned. Yes, I did do a quick visual inspection and checked the shaft bearings for play to see if there were any issues, but I did not do a full tear-down.

slowcivic2k

With the clutch not pressed, noises that are produced will be from the main shaft of the transmission. You are correct that the differential and countershaft do not turn, they are mechnically connected.

Any noise produced with the clutch pressed is obviously clutch-related, meaning release bearing, crank bearing, (mitsu's mostly) etc.

Is the noise rhythmic with the engine? or with wheel speed? You describe both, at idle and while moving? Is it both? you may have two separate problems.

gstrudler

Well I took the car into a shop and of course on the test drive it hardly made any noise at all After describing the symptoms to the mechanic it got me thinking again about the cause (which he thought couldn't possibly be the trans).

The good news is I finally got it fixed and the better news is it was free and took 5 minutes. The culprit?... The breather hose from the ATTS unit. When I had rebuilt the motor I had re-attached it to the IM and I think now it's supposed to just hang free and vent to atmosphere like the tranny breather. I still don't understand why it was making a rhythmic (instead of constant) noise, but I don't care as much at this point. I did take a vid of the noise; if I get a chance I might post it for future reference.

Thanks for the help though guys.