K-Spaz

I know, it's a 427, not a Z... can't seem to get any answers in the tech section. I've got the diff and trans out of my 427 due to a noise in the rear on deceleration. Sent samples to blackstone and they are happy with the trans but the rear they found aluminum in As the rear warms up, the sound and vibration gets worse and the shifter starts to vibrate and it's a pretty hefty whine. No question, something is drastically wrong. I wanted to be proactive and find the problem before it became a disaster.

I ordered a service manual and got that late yesterday, but never got a chance to even open it up. I can make tools at work so that's not an issue. But I'd like to discuss with someone familiar with the process, just what I should be looking for. I tried to video the noise in the car but could not get anything what actually showed the issue. I didn't want to drive it till the rear was warmed up again, the noise was there but the camera just doesn't pick it up.

The car wheelhopped 2 hops one day and this on brand new MPSS. I expected it to continue to continue with a percentage of slip like the previous tires did, so I didn't lift to save it right away. Well, it drove into pretty hefty tire spin and hopped hard twice. Seemed to be no big deal, but over the next few weeks it developed a noise that's troubling.

Car is 100% stock. 26k miles.

I could use help on sourcing parts for the thing, at a minimum I need a gasket kit to reassemble. I've got the rear cover off and see nothing. Well, I see I need a spanner wrench made for that nut. But this is the sort of stuff I'd like to know before proceeding is what to mess with and what not to.

Anyone willing to help out? I tried in C6 tech and got 200+ views and no responses. Was told to try here but I see 427 isn't a tag option. It's like there is no section for the 427 Vert.

Nowanker

Since you already have the trans out, the hard work is done!
I don't know for sure, but I'd expect the 427 convertible to use the same driveline as the Z06.
I replaced the friction discs in my LSD a while back, and it's easy enough to dismantle the unit for inspection.
https://www.corvetteforum.com/forums...pictorial.html
Let us know what you find!

K-Spaz

Thanks very much. I'm gonna mow my grass and then go in to work and pull it apart. I looked as closely at your gears as I can and I can't see the mark I have on mine at the very outer edge. I have a very tiny shiny spot on the ring teeth I'd say .070 wide by .175 long. The rest of the gear surfaces look fine, as well as I can see. But that bothered me some. Thing is, that doesn't explain aluminum in the oil. I have a friend who suggested a spun race but I can't see that making noise only on the coast side. If I simply pop into neutral and coast to a stop there's no noise.

It's a weird one for sure.

I'll get pics later once I pull that right side cover off.

Nowanker

Check for excess backlash between the ring and pinion before disassembly, and for any play in the pinion shaft. I could see a failed pinion bearing leading to the race spinning in the case... and excess play leading to the noises you describe.
I hate diff work! IMO, one of those specialty areas to be sublet.

K-Spaz

Well this is definitely not normal.


Might take a minute for the video to finish processing

K-Spaz

Here's the marks I said on those gears. At the very outside edge at the point.

Millenium Z06

If your report found aluminium in the rear diff case, you've got something very wrong as there are no wearable aluminum parts in the diff. Sounds like something may be moving around and grinding on the housing

K-Spaz

As best I can tell it looks like the pinion nut backed off. That's about all I can find. No damage of any sort. I'll post some pics later.

K-Spaz

Looking at this area where the threads are supposed to be staked, seems like they've given plenty of room to do so but doesn't seem like anyone did that to the pinion nut.

The spacer for the bearing races is a-ok. Not a mark on it.

Had to use a wrench to get the pinion nut off in spite of it having been loose at least a full turn or so. I didn't measure it and now I sorta wish I had, but the video shows it was a lot. When putting it back on I can turn it by hand and spin it down till it's tight. I don't think I should be able to do that. I should expect that top ring on that nut to have been peened/staked into that recess to stop it from backing off. Why does that have no evidence of ever being staked?

Nut is back on. Did not use the wrench to put it on, only to remove.

Fully expected to see damage to this bearing carrier. It's pristine.

Other side of the carrier.

Yet another view of it.

All in all I'd say it took about 15ft lbs to remove that nut. Maybe not even that. I'm guessing on that but it wasn't much. The slop had to be nearly a full turn and the bearing race had spread apart so as to make contact with the nut and make it appear to still be tight.

Pounder

you need very specific tools to set pre-load on the pinion bearings and side adj. for the ring gear !!!

K-Spaz

They've already been set at the factory.

PS. I can make tools.

K-Spaz

I did read in the service manual some and it's not a big deal. I think more is made of that than it's worth. The tools they show pics of in the book look simple to make. Standard machine shop stuff.

Pounder

just junk it and get a 3.90 diff. !!!!!!!!!!!!

K-Spaz

If I went to anything it would be a 3.31 or 3.23.

No interest in hole-shots.

K-Spaz

Just doing a little reading and that nut is supposed to need 370 ft lb. Looks like I'll be doing some more work on my wrench to get that on there.

Nowanker

Thanks for posting the pix!
Looks like they use a spacer shim instead of a crush sleeve, that's good news for the reassembly.
370 ft/lb? that's tight...
Cool spanner wrench you built there!

K-Spaz

In the service manual for the C5 they have about 6 special tools for the diff. For the C6 they have about 25. Most are measuring gauges for setting up the gears and selecting shims. My guess is this diff is a lot simpler than ones other guys are accustomed to on previous cars. Even the pinion nut is a different animal from the standard cars.

Guy who works for me also does some work on the side on cars and he talked about a crush sleeve, thankfully that's not a thing here. This is just a hard steel spacer and it doesn't compress.

The service manual says that once assembled properly, the pinion module should have 12-14 in lbs or torque to turn it. IOW, the bearings are in a compression, 0 backlash. Mine feels close enough to suit me. Feels very nice. Also helps that I never found a single particle of anything inside the diff.

I was a bit worried about the spanner wrench because I made it before I knew what torque it had to withstand. Had I known, I would have built that thing overkill deluxe!

For anyone who'd want to build one, I used 3.149" on center spacing x 6 for 6mm dowels. Drilled and reamed the holes after welding up the tabs (quick and dirty to save time), held up just fine. That center is just a piece of 2-1/2" steel pipe. (edit)

I didn't use a torquewrench on it. Mine only goes to 250 anyway. I used a big gajuna pipe wrench and braced my feet against the bench with the part in the vise on a tool I made from 3/4x2" 6061 alum bar. Just rounded off the edges some so it would fit inside the cloverleaf in the pinion carrier. Put that in the vise, stuck the pinion on it with the spanner wrench already installed, and reefed on it hard as I could. I'm betting it's 370. Maybe 371.

K-Spaz

Another nice thing, the Diff, part number 24264061 is NOT listed in the service manual... As is nothing else 427 Vert related. I have yet to see a reference to the car, and I've looked. Just bought the manuals... They do sorta work, but it would be nice to see them refer to the car once in a while...

Don'tcha just love it. I even specifically asked if it covered the 427 and was replied, all models including the special editions. Yea, right..

K-Spaz

This is just a bar of 6061 I rounded the edges on so it fit inside the pinion. No need for a spline tool for this, though I admit it would have been nicer.


And this is the way that nut should have looked 7 years ago.

Millenium Z06

Nice

As for the 427, just refer to Z06, same power/drive train