Took a look under the Z06 last weekend and it turned out that the passenger inner CV axle boot had spewed grease everywhere. It was just a pinhole leak but man was that a lot of grease.

Today I:

• pulled the stock/original axle and replaced it with a Durlast brand version. Looks like it was made by GSP which seem to have hit or miss reviews, due in-part to the 3-pleat inner CV axle boot they use (stock & stock-replacement inner CV boots have 5 pleats). At least Autozone provides a lifetime warranty on Duralast axles.
  • I also bought (after a painstaking search) 2 different brands of inner CV boots: EMPI and Mevotech. If the Duralast axle fails in some way, I'll just return it and replace with the re-booted original axle.
• replaced the passenger diff output shaft seal (with AC Delco/GM brand). Yes, I just replaced it with the LSD rebuild. But since I had the axle out anyways I wanted to make sure it wasn't contributing to the apparent diff fluid leak (which might have just been from the vent, but it was a decent amount of fluid). For this I wound up removing the diff side cover so I could replace the seal with my hydraulic press.
• drained and refilled the diff fluid with AC Delco 10-4034 fluid. This has the limited slip additive already included.
• did 10 figure-8s in a parking lot. Afterward the diff noise was quite a bit less, and it's hard to tell if there's any diff noise at all now.

We'll see how this all works out after some miles.

 

It's been almost 500 miles since the diff fluid drain/re-fill, and I'm happy to report that the AC Delco fluid has resulted in ZERO diff noise! DO NOT BUY MOBIL 1 LS DIFF FLUID.
There's still been some diff fluid on the garage floor but I think the amount has been diminishing... so perhaps it's just been burping out excess fluid though the vent (despite filling to the bottom of the fill port with the car level).

 

@MetalMan2 what kind of differential noise where you getting? I notice a sort of mild whine when I'm on the highway at 5th/6th but I have mentally filed it under "mehh, I'll ignore that for now". My 01' Z has 37k miles, when I got it at roughly 34k miles I replaced the diff. fluid with Valvoline 75-90. I can't recall if it seemed to make a difference in the differential whine but I'm open to replacing it again if there is something better to put in there.

 

If you read a few of my prior posts I mentioned the diff noise mine had, which doesn't at all match yours.

FYI inside the transmission the 5/6 gear cluster can get loose on the mainshaft, and from some of my research this can contribute to noise in 5th/6th. My 5/6 gear was almost loose, but I don't think there was any noise in those gears (I fixed the problem anyways, "while I was in there" rebuilding the trans anyways).

 

With the Hinson diff/trans mount around 2000rpm and up the noise and vibration was quite a bit, which detracted from the pleasure of daily-driving my C5Z. A few days ago I swapped it out for my old stock one. There was a pretty substantial reduction in noise and vibration... It's possible that my drivetrain is out of balance, i.e. the clutch/flywheel caused an imbalance and that resulted in extra NVH.

In any case, the Hinson diff/trans mount is for sale. I put a whopping 973 miles on it. First $130 shipped takes it! (they're going for $163 everywhere right now)

Also my diff is still leaking on the passenger side... keep in mind that the side cover O-rings are pretty new, and the output shaft seals are new (replaced passenger side twice), all GM parts. I didn't use anaerobic sealant on the covers because then what's the point of the O-ring?
Wondering if the differential vent is clogged and causing excessive internal pressure, resulting in fluid being pushed out the output shaft seal.
Sounds like the diff vent is a one-way/check valve, and some people have experienced that it clogs and so they turn it into a regular vent. Like this: https://www.corvetteforum.com/forums/c5-tech/2863110-diff-breather-vent-size-and-removal.html#post1577996694
Alternatively it looks like the vent is replaceable, P/N 19132947. Granted it's cheaper/easier to try disassembling the valve first.

 

Went ahead and disassembled the differential vent per my last post. I had a random elbow/hard line arrangement from my old/crashed 2001 A4 (which my Z06 replaced) that fit perfectly on the nipple of the disassembled diff vent. The rubber disc in the old diff vent was concave, which I read about as being problematic for the sake of the differential being able to vent. So I'll be keeping my fingers crossed that the diff will stop puking on my garage floor!

 

I just stumbled into this thread from the link you posted for the custom linkage. I feel that not enough people are aware of what is available for transmission services out there and believe that everyone charges like RPM. You might call a few builders and discuss the issues if they remain ongoing and seek their advice. Jason at TDP became my go to source for the build, and I will say that I got an entire transmission plus the build and the custom sprayers installed for far less than a new gm transmission. And if you ever upgraded to a 6060, the ME2 variant from the C6 ZR1 can be had for 2900 new from Pace, which is amazingly cheap.

 

I had my Z06 down for a few weeks due to an unrelated issue, but I've been able to put 200 miles on it since replacing the differential vent as mentioned previously. And so far so good! Normally by now there would be a noticeable puddle of diff fluid on the floor, and my back bumper would be a bit speckled (probably from diff fluid + dirt). There is neither a puddle nor speckles. Which is awesome!

 

Little update on the differential fluid leak and vent situation:

• When returning home after driving the car, I could smell diff fluid. This is one of the downsides of an open diff vent.
  • I bought a new stock vent:
    GM 19132947
    GM 19132947
    . With the differential still in the car there's insufficient access to remove the old vent body. But it worked out to remove the cap, spring, and diaphragm from the new vent and drop those onto the old vent body that was stuck in the diff.
• There hasn't been any diff fluid odor in my garage, and it seems the diff isn't leaking

Beyond all this, the car has been driving well. No real issues with any of the work I documented in this thread. However, there does seem to be a lot of noise generated by the torque tube (?) that comes through the shifter area. The noise level seems to coincide with changing engine RPM. It doesn't sound "bad", just louder than I would expect.

I came up with and installed my own metal clutch master cylinder kit, which has been a nice replacement for the Luk stock-style MC.

 

Well, the diff has been leaking for a while now with the new vent components. There's a decent puddle going, enough that the fluid traveled along the garage floor maybe 10 inches. Also getting the speckling on the rear bumper. Guess the breather hose has to go back on and at this point the diff surely needs more fluid added.

Ever since replacing the clutch and servicing the torque tube and rebuilding the trans, there has been extra vibration. I would assume it was from replacing the factory clutch with LS7 clutch kit and the "hot balance" being affected. Bill Curlee did a good writeup on "DIY hot balancing" that I'm looking to perform: https://www.corvetteforum.com/forums...post1585929743 https://www.corvetteforum.com/forums...post1587363856
Except that instead of going off a subjective feeling of "balance" I'd like to take a little more scientific approach using a vibration meter. Don't want to spend too much money so maybe something like this:

Lastly, when I get into more aggressive driving (during my commute, since the car is a DD) I'm definitely smelling something after a pull. Not sure if it's engine oil and/or PCV related, though I don't think it's the diff because I can still be moving forward and be able to catch the odor.
One thought is maybe it's related to my Z06 being a 2001, and the piston ring issue that many of these had...

 

Updates:
Hot balance procedure completed, details on that here: https://www.corvetteforum.com/forums...post1604539030

Swapped back in the differential breather vent, and added diff fluid to reach the proper level. It took a decent amount of fluid, and currently there's not really an odor from the vent after a drive, so I'm wondering if low fluid level contributed to previous diff vent odor. It hasn't leaked since the breather vent swap.

Lastly, the current issue I'm contending with: torque tube driveshaft (?) noise.

• With the clutch pedal out and engine idling, there's a noticeable whirr sound seemingly coming from below the shifter. It gets louder + higher pitch with increasing engine speed. Pressing the clutch pedal makes the noise goes away, presumably because the driveshaft slows down and stops spinning when it's decoupled from the engine.
• The noise is a little louder after the car has been driven / warmed up.

As mentioned previously in this thread, I rebuilt the torque tube with new couplers and bearings, and made sure to keep everything aligned. Also replaced the slave cylinder / throwout bearing, clutch/FW, and did a trans rebuild. Everything seems to work fine, FWIW.

Contemplating finding a used torque tube and swapping that in just to try... but in reality I should do some checks first. For example, probe around the torque tube with a stethoscope and try to isolate the noise source. Next up would be diff & trans removal from torque tube to verify the noise remains. Then maybe try rebuilding the torque tube again, and/or replacing it. Looks like replacement torque tubes are going for $400+ without shipping.

 

MetalMan2 - Wow, this thread, and your work, are amazing. Thanks for documenting it all. Good luck with further progress.

 

Fantastic job! I am sitting at Regan International because my flight was cancelled and am waiting 6 hours for another one. I enjoyed your detailed write up. I will use this as a reference when I do some of these repairs in the future.

2000 FRC

 

Getting ready to tackle the following, now that I am driving the car again after completing a power steering rack DIY rebuild:

It kinda seems like the noise has in general gotten slightly louder over the last ~5k miles since torque tube rebuild, but it's hard to tell since it increases throughout a drive cycle anyways. I've got an automotive stethoscope now so at least I can drop the clutch inspection cover and start probing around and see if I can isolate the noise location while the clutch pedal is operated.

 

Didn't end up probing around the torque tube with an automotive stethoscope... chose to avoid the hassle of reinstalling midpipes after dropping the tunnel plate. BUT I did get the torque tube liberated from the car in only about 4 hours!

The driveshaft seems to spin in the torque tube with only mild resistance by hand, and without any grinding or otherwise, but I wanted to spin the driveshaft faster to listen for any unexpected sounds. Tried 2 different ways to achieve this:

• with a drill: wrapped the input shaft with enough layers of blue painters tape that I could tap a socket on over the tape, and hook up a drill to the socket. This worked okay, but I couldn't really hear anything over the sound of the drill, and there was some vibration possibly from a non-concentric interface between the drill and input shaft.
• pulling a string: wrapped a string around the input shaft clutch splines multiple times and pulled it, in a similar fashion used for pull-starting an engine. Considering how slow this spins the driveshaft even compared to an idling engine, I was surprised to hear a slight howling sound, not super loud but louder than I think it should be.

None of the bearings feel off and the couplers I had installed look fine. So at this stage I'm planning to rebuild the torque tube completely again, keeping my fingers crossed.
Have new Febi 05084 (26111227410) couplers on order, as well as all new bearings (SKF 6007-2RS1 & 2x 6008-2RS1), O-rings, slinger, and snap rings. With price shopping I got the total cost of all parts down to $188.

Also ordered a new pilot bearing... can't hurt, right? Just requires removal and subsequent reinstallation of the clutch, and new flywheel bolts I suppose.

This time around, post-rebuild I want to check runout on the TT input shaft's pilot bearing surface. I understand this isn't a great measure because it's affected by the front coupler (since otherwise the input shaft is only supported by 1 bearing), but it's something. By eye I couldn't discern any runout prior to tearing down the TT. Maybe I can also find a way to check runout on the input shaft alone.

There's also the factor of driveshaft balance; during my original TT rebuild I marked the positions of everything, but balance is still an unknown in my mind. Granted, with my string-pull method, that speed isn't nearly enough for imbalance to cause a howling sound.

 

As mentioned above, I completed this work:

• Replaced pilot bearing. Old one seemed fine. Was more of a hassle than expected because the bell housing needs to be loosened to be able to remove the LS7 pressure plate...
• Reinstalled LS7 clutch disk & pressure plate. With 5k miles on them, they and the flywheel still looked pretty much brand new. Used the torque tube/prop shaft input shaft for clutch alignment.
• Rebuilt the torque tube. No surprises there.

I repeated this string-pull method to spin the prop shaft. There is zero detectable noise so hopefully that bodes well.

I didn't check runout on the input shaft alone. Not sure if I'll check runout on the input shaft now that it's installed because of what I mentioned above.

Since I had to lower the front cradle to loosen up the bellhousing anyways and the midpipe is out, I'm going to take this opportunity to replace engine mounts. At this point it's only a little extra work (jack engine up, drop cradle further). For a while I've had some aftermarket stock-style "solid" mounts and will see how those work out.

Also "while I'm in there" with the drivetrain out, I bought a DEI trans tunnel heat shield kit # 050529 and will probably install it tonight.

 

Well, I commuted with the Z06 today after completing everything last night. So far so good! Definitely some more resonance/vibration with the Whiteline polyurethane engine mounts, and although that may improve after they get a chance to "break in", it's looking like I will be swapping them out soon anyways for a set of prototype Vibra-Technics rubber engine mounts (which hopefully will do a great job of restraining engine motion with less NVH than polyurethane).

My main objective of all this work was torque tube rebuild - and so far I can't discern any of the howling/whining sound that previously came from the torque tube. Fingers crossed it stays that way!

I "upgraded" the midpipe/cats to one from a 2003 Z06, which has 2 cats vs 4 cats on my 2001. It came with a rear X-pipe section that doesn't fit super well, and it seems there may be an exhaust leak. Ultimately the stock Ti catback isn't fitting amazingly under the rear bumper. Glad I know a good exhaust shop...

 

Incredible documentation MetalMan2. Happy motoring.

 

Well, 1.5 years since my last update and there's nothing bad to report
My C5Z is approaching 80k miles which means most of this work (minus torque tube) is coming up on 10k miles / 3.5 years.

I ended up taking off the Whiteline polyurethane engine mounts and put in Vibra-Technics mounts about 1.5 years / 4k miles ago and have been very pleased with those.

 

Would be cool to get more updates on this too @MetalMan2