Opinions requested: Throwout bearing wear on transmission case

Hi all, taking a breaking my persistent lurking to ask for some advice about throwout bearings and noises. I'm on the younger side, and have only succesfully pulled of one clutch job to completion on my miata, which was a breeze. I've currently got the transmission from my brothers former daily, a 2001 Honda Civic sitting on the floor in the garage. He replaced the car because it had been diagnosed as needing a new transmission due to the noise it was making: When accelerating, especially in lower gear (very bad in 1st), it would sound like a gear hitting a flappy bit of plastic repeatedly, kind of a RrRrRrRrR noise, frequency dependent with RPM, quieted by pushing the clutch in, and would be lightly present in neutral. It definitely got worse when loading the transmission up. When I pulled the transmission off the engine, I noticed that the throwout bearing seemed kind of loose -- I could actually move it over a 1/16" on the snout around the input shaft. Upon removing it, I observed that the snout had some worn areas from the bearing riding on it. The transmission however, displayed no signs of any bad bearings (from my reading, it sounds like the input bearing commonly goes bad): I can spin the trans by hand easily, it spins smoothly, makes good sounds when doing so, the transmission oil (ran for maybe 3k mi as the noise got louder) came out as clear as the day it went in, and the input shaft has no play in it.

This clutch is a push style clutch, so due to the spring in the slave cylinder, and the throwout bearing is consistently pressed against the pressure plate. When combined with the play upon the snout, could this be making the noise? Or is it wishful thinking? This is not a failure mode I can find much information on, especially not in Hondas. Subarus have the same problem, and I found some diagnosis of needing The bearing would then be loaded up and moved to a different position, not allowing it to rattle anymore, explaining why the noise went away with the clutch pressed in. I don't feel that this adequately explains the difference in noise volume when under load (shouldn't it be the same in neutral as in gear?), so I will split the case and open it up to be sure -- I had kind of been looking forward to replacing these bearings as a learning experience, but if there is a consensus that the throwout bearing is the problem that I would be happy to save the time for a different journey.

In summary, the throwout bearing feels fine and smooth. The transmission turns smoothly by hand in all gears, with no play on the input shaft or signs of having been opened. The throwout bearing does have noticeably play on the snout of the transmission, especially in the plane of the clutch fork. Is this play capable of making the noise described? Or does it have to be coming from the transmission? It would make the noise whenever the clutch was out, but it would sound much louder when accelerating, especially in first gear. Could this be explained by the mounts rocking over and transmitting more noise to the cabin? Secondarily, if this isn't the root cause, how concerning is this wear on the trans housing (I've attached an image, may be useful)? I know there are snout sleave kits with over sized bearings available for Subarus, but none seem available for the Honda SLW. Worst case, JB weld and sand smooth, best case get someone with a TIG to build it back up? Interested to hear what the hivemind has to say.

Oh, and why I'm bothering with it: Seemed like a decent way to make some change vs sending it straight to CL, rebuilding a manual trans sounds fun. Could even keep it as a winter beater / rally cross car for another couple years here in the northeast as it has plenty of life left in the snows, except I already own one car my 6'3" frame won't fit in and don't need a second. Oh and to boot I have a line on a real cheap '92 Volvo wagon I'd rather play with...

That wear does not look significant to cause that sort of noise.  I thought my WRX had a bad throw out bearing, sleeved it with a snout fix kit, noise persisted.  Ended up being two chipped teeth in the center diff.

There is a chipped tooth or slightly bad bearing inside the trans, that only makes noise when it has torque on it.  The release bearing is always a bit sloppy on the nose of the trans so it can move easily.

Is that a 5 speed transaxle? if it is, does it make the noise in 4th?

Im thinking it may be the bearing between the input shaft and main shaft.

First gear has the biggest rpm differential between the shafts, leading to most noise.  4th gear would be 1:1, so the shafts are locked together with no speed difference between shafts leading to no noise in 4th.

Neutral has almost no load on the shaft, but the input shaft is spinning and the main shaft is stationary leading to noise, but not excessive since there is no load  

Just spitballing based on the quick read I gave the post, so I could be in left field. 

In reply to No Time :

Yep, a five speed -- I don't think the noise ever went away completely. If the clutch was out, it made the noise, volume proportional to throtle position when moving and frequency proportional to engine RPM. I like your thinking, but there's no bearing between the shafts. There are two shafts, the reverse idler, and the diff.

So tonight I went ahead and split the case of the transmission. The slip ring / circlip gave me a little trouble, had to get another pair of hands to pull the case while I spread the ring. Didn't find any big chunks, grit, or chipped teeth. Went ahead and remove the shafts and shift forks, again verified no chipped teeth, and inspected the bearings. They all turn smoothly and look good, the input shaft bearing seems questionable. It doesn't have any play, but doesn't spin quite as smoothly as the others. It definitely doesn't feel like it's failed in a way proportional to the noise, but that could be inexperience. This video shows a bad bearing, and I don't think mine is worse it, but it's not a whole lot better I think. Since I'm in here anyway, might as well buy a new input bearing, seal, and output seals from Rockauto. I also need to order new front control arms, rear hubs, and brakes all around, and while that all arrives, I've got plenty of subframe to POR-15.

MrRobogoat said:

In reply to No Time :

Yep, a five speed -- I don't think the noise ever went away completely. If the clutch was out, it made the noise, volume proportional to throtle position when moving and frequency proportional to engine RPM. I like your thinking, but there's no bearing between the shafts. There are two shafts, the reverse idler, and the diff.

I was think RWD where the input shaft and main shaft are typically separate with a bearing in between. 

You might be able order the parts as a rebuild kit for less than separate components and replace other bearings in the kit while it’s a part.

It is not unheard of for the transmission casting to have shift which misaligns the snout of the shaft in the bearing.  On cars with a removable bellhousing, you can just bolt up the housing and use measuring tools to check it and then offset dowels to correct it.  It's one of those things that usually doesn't matter in a DD, but they can be significantly off.

On a transaxle or non-removable bellhousing, I take the clutch off, take the bushing/bearing out, and fill the crank pocket with clay or play-doh.  Then I install the trans back into place letting the input shaft squish into the clay.  Careful removal will then show you how far off it is.

It also couldn't hurt to put it in a gear and spin the output and watch the input shaft for runout/wobble.

I think I have a full understanding of what happened now: I took the clutch off last night, and found some weird wear on the flywheel:

See that weird ring just outside of the mounting bolts? Clearly something had been rubbing on the flywheel where it should have been. Looking at the disk, I found the corresponding wear:

Two of the springs were like this, and I could move them in and out of the disc with my fingers. Note the chunk missing out of the tab that retains the damping springss... Now, this can't be the cause of the noise, as the two parts only rotate past each other with the clutch pedal pressed down; however, I figure that if the springs didn't get knocked back into position by the flywheel, that they might cause torquing on the input shaft to the transmission, wearing on the input shaft bearing. I went ahead and slipped the input shaft back into the bearing and case, and spun it around -- sure enough, there is a distinct ridge in the bearing which presented itself only when loaded back up with the shaft. Made a slight click once per revolution, matching the frequency of the noise. I feel pretty good about that this theory adequately explains things and I won't find that I missed any parts during reassembly.

In reply to Curtis :

Interesting, I did not know this was a failure mode. Is this common for cars with a removable bellhousing? The transmission is now rather apart, but when I get it back together I will check this out.

What does the other side of the disc look like? Is the clutch center section offset to one side?

It may be the the disc was in the wrong way causing the strange wear to occur. 

I’ve seen cases in the past where the disc was installed facing the wrong way causing contact between the hub and flywheel/bolts. It created weird noises and also inconsistent clutch behavior. 

MrRobogoat said:

In reply to Curtis :

Interesting, I did not know this was a failure mode. Is this common for cars with a removable bellhousing? The transmission is now rather apart, but when I get it back together I will check this out.

Just like with engine blocks, there can be core shift.  When the machining happens, if the core is off by 1/16", the machining is off by 1/16".  It is less common since the 80s/90s as casting technology became more accurate and CNC machining became more common, but yes it can be an issue.  9 times out of 10, it is caught before assembly and the castings go back to be melted down, but they slip through.

Having said that, you can take 100 SBCs and 100 Muncie transmissions and slap them together and they'll work beautifully, but sometimes you'll notice difficult shifting or an excessive noise.  The first place I look is that pilot bushing/bearing.  If the input shaft is not centered, the friction keeps the input shaft moving making it harder for the synchros to do their job.  With "vintage" RWD stuff, it isn't common to blueprint the bellhousing alignment, but it becomes more common with higher performance applications.

In reply to No Time :

The center section is offset to one side, and offset enough that the clutch cannot be assembled with it in backwards. When I have put clutches together I've been very cautious about installing anything wrong, so I checked that right away. Nope, springs were peaking out instead.