: Internal Differential Clunk - 4th Gen Diif



KaMaSuTrA
05-07-13, 04:29 PM
I've posted about this issue in another forum and I'm trying to get some more insight here as well.

I'm experiencing a "loud clunk" that is occurring inside my 4th gen differential. It's centered around where the driveshaft connects to the pinion. This clunk is replicated when downshifting without a revmatch in low mph or by attempting to launch the car (2-3k steady). In both instances it can be heard audibly (like a loud bang). It can also be heard when coasting through 3rd-4th gears as the car is moving (way less audible than the other two instances but still there).

The car just got a new clutch setup back in March (Diamond Stg 2 w/ 15 lb flywheel), 95A Revshift Flex Disc, 95A Revshift Rear Cradle & Trailing Arm Bushings, Original KARS Stage III Kit, DSS Anti-Wheelhop Axle Bars.

It also has Creative Steel Motor Mounts & Trans Mount. It had a Creative Steel Diff Bushing that helped with the clunk but it eventually came back. It has since been replaced with a Revshift 95A Diff Bushing over last weekend. Now originally I also thought that the clunk might have been driveshaft related but I figured I'd wait until I replace the diff bushing again and report back.

When going through the car I found out that my Creative Steel Trans Mount isn't looking too good, it's still there but I can feel the polyurethane deteriorating. If you look closely at the picture, you can see it's beginning to shift slightly off the mount. :(

https://fbcdn-sphotos-f-a.akamaihd.net/hphotos-ak-ash3/577584_10151487803154272_1002074070_n.jpg

There was some random grease that was scattered around the diff pinion seal and heat shield. Discovered that was coming from the driveshaft end. Looks like I'm going to need a driveshaft regardless...:halo:

https://sphotos-a.xx.fbcdn.net/hphotos-ash3/941970_10151487802959272_1652069302_n.jpg

Drained the fluid, some metal shavings on the magnet, nothing out of the norm though. Mechanic used a camera to see if we can find any chipped teeth or carnage inside but there was nothing visible outside the norm.

https://fbcdn-sphotos-f-a.akamaihd.net/hphotos-ak-prn1/931166_10151487802969272_1950961784_n.jpg

https://fbcdn-sphotos-b-a.akamaihd.net/hphotos-ak-ash4/182566_10151487803219272_716068064_n.jpg

https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-ash3/943111_10151487802949272_2139944632_n.jpg

https://sphotos-b.xx.fbcdn.net/hphotos-ash3/943592_10151487803054272_279529566_n.jpg

The differential had to come out completely because the old CS bushing still had to be pressed out. Last time I rented the CS tool that allowed us to keep the diff in the car. This time we improvised with a drill bit, air chisel, and an electric hacksaw for the sleeve.

https://fbcdn-sphotos-a-a.akamaihd.net/hphotos-ak-prn1/946401_10151487803134272_1767823664_n.jpg

https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-prn1/944809_10151487803114272_2008252263_n.jpg

https://fbcdn-sphotos-d-a.akamaihd.net/hphotos-ak-ash3/945365_10151487803034272_1566415385_n.jpg

https://sphotos-b.xx.fbcdn.net/hphotos-ash4/393057_10151487803039272_1257205756_n.jpg

We also took out the pinion gear just so we could get a better view at what the camera wasn't able to see. Nothing other than wear for the car's mileage. Do I have severe backlash? Probably, I honestly don't know what to think anymore, maybe I should accept the fact that it's German garbage and move on....

I had some light whine before, now it's more pronounced. Is the car better with the new Revshift diff bushing? Absolutely! Did it completely fix my problem? No, it appears that I have more problems than a new diff bushing would fix. :eek2:

Suggestions are welcome (I already know a V2 would fix everything but it's too far out right now)

Anyone have experience with an internal noise in the differential like this?

darkman
05-07-13, 08:17 PM
The actual back lash is measured at the pinion and specification is a few thousandths of an inch. The "apparent" back lash of the unit, which is observed as the amount of pinion rotation that occurs before movement is felt at the output shaft can be on the order of a quarter of a turn. This extra "back lash" comes from the clutch cage of the limited slip unit, which houses the clutch set. If you eliminate the "cushion" in the rest of the driveline associated with the various OEM bushings and mounts you simply amplify the shock force that hits the limited-slip clutch pack.

KaMaSuTrA
05-07-13, 09:14 PM
The actual back lash is measured at the pinion and specification is a few thousandths of an inch. The "apparent" back lash of the unit, which is observed as the amount of pinion rotation that occurs before movement is felt at the output shaft can be on the order of a quarter of a turn. This extra "back lash" comes from the clutch cage of the limited slip unit, which houses the clutch set. If you eliminate the "cushion" in the rest of the driveline associated with the various OEM bushings and mounts you simply amplify the shock force that hits the limited-slip clutch pack.

I see what you're saying and it does make sense but it also clunked before any of this stock. Maybe I was just too late within getting this done to tell the difference in what exactly was clunking. Eliminate the parade clunk only to develop this internal pinion clunk now.

I want to say the only sloppy thing left is the stock driveshaft and I'm going to check it again to see if it continues to throw those small bits of grease all over the front of the diff and heat shield again.

I currently do not have the KARS kit connected at the diff support, I left it disconnected to compare how the car reacts. I'll connect it again and see what happens after I inspect the front of the diff.

KaMaSuTrA
11-17-13, 10:21 PM
I wanted to post some updates to this thread.

October 21st 2013

My driveshaft started acting up 2-3 weeks ago, the center bearing started to chirp like a cricket off/on and
the rear clunk got even worse to the point where I could feel the windup and backlash transferring to the FRONT of the car. The CV joint has most likely ran out of grease.

Unfortunately not enough funds were allocated for a 9" swap so I have to make due with what I can since this is my daily driver.

I have a DSS aluminum one piece driveshaft on the way and I ended up ordering a new 4th Gen Differential from Luke at Lindsay Cadillac. I'll be reusing the Revshit 95A differential bushing.

So this is it, there are no more excuses. Short of getting a 9" swap, this is about as good as it's going to get for me. All the stock shit is gone from the driveline minus the new differential. We'll see how this goes..

November 11th 2013

So the new DSS 1 Piece Aluminum Driveshaft is installed along with a brand new 4th Gen Differential.

The initial impressions are some-what positive. I need to drive like a grandma for the break-in period so I can't comment on how it feels under real acceleration or a launch.

Is it better than before? Yes, there are less vibrations and acceleration is smoother. The car feels like it will squat hard under WOT. No differential whine even with the KARS III kit, 95A rear cradle bushings and the 95A differential bushing, there's still a howl that comes from the KARS III kit but that's "normal" for that setup.

Is the clunk gone? NO...this was the first thing I tested as soon as the car came off the lift. I accelerated lightly and then clutched in...CLUNK. I reversed lightly and then clutched in...CLUNK. Under normal driving it will clunk, but if you give it some more throttle and clutch out gently, its subdued. This clunk is all engagement and internal to the differential.

I remember reading threads where dealerships commented on the clunk with "That's just the way it is." I'm a believer now. This series of Getrag differentials are not engineered right at all. I bet I could have just changed my driveshaft and would have ended up with the same result on my old 4th gen diff. In other words, there was nothing wrong with my old 4th gen diff other than the typical whine that develops over time.

Thought about removing the KARS III kit and take it around the block just to see how it feels without it, although I doubt that removing the kit will ease the clunk. We'll see...pics and more info to follow.

November 15th 2013

Here's are the pics of the install....

New 4th Gen Differential

https://scontent-a-ord.xx.fbcdn.net/hphotos-ash3/q71/s720x720/558943_10151878196534272_618784885_n.jpg

New 4th Gen Stock Bushing removed

https://scontent-b-ord.xx.fbcdn.net/hphotos-ash3/q71/s720x720/945455_10151878196539272_625794735_n.jpg

New DSS 1 Piece Aluminum Driveshaft (I have a PISNUOFF short throw shifter so I had to flip the nylon cup and shifter plate bushings for clearance)

https://scontent-b-ord.xx.fbcdn.net/hphotos-frc3/q72/s720x720/1462922_10151878196634272_1401295468_n.jpg

Old 4th Gen getting removed

https://scontent-b-ord.xx.fbcdn.net/hphotos-ash4/q77/s720x720/1385914_10151878196654272_1513639305_n.jpg

Old 4th Gen Revshift 95A Bushing removed

https://scontent-a-ord.xx.fbcdn.net/hphotos-prn1/q73/s720x720/544165_10151878196734272_1575245811_n.jpg

New 4th Gen and Old 4th Gen

https://fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-prn2/q71/s720x720/1468544_10151878196859272_286319955_n.jpg

New 4th Gen w/ Revshift 95A Bushing

https://scontent-a-ord.xx.fbcdn.net/hphotos-ash3/q72/s720x720/1472971_10151878196954272_1296973755_n.jpg

New 4th Gen Diff installed

https://scontent-a-ord.xx.fbcdn.net/hphotos-ash3/q73/s720x720/1455182_10151878197069272_1387497609_n.jpg

Without KARS III Kit

https://scontent-b-ord.xx.fbcdn.net/hphotos-ash4/q73/s720x720/1452223_10151878197299272_825604941_n.jpg

With KARS III Kit

https://scontent-b-ord.xx.fbcdn.net/hphotos-frc1/q71/s720x720/1426562_10151878197259272_1266758025_n.jpg

The clunk will never go away...

https://scontent-a-ord.xx.fbcdn.net/hphotos-ash3/q71/s720x720/936012_10151878197169272_1280221572_n.jpg