So I've had this noise/ vibration for awhile that kept getting worse. At first sounded like I had mudder tires like on a 4x4 that progressed to constant loud roar/ vibration. I narrowed it down to be in the rear end so I took it out and opened it up. Ring and pinion look fine. Haven't confirmed backlash yet. Side bearings and the one pinion bearing I can see seem fine. When turning the input all is quiet so I'm thinking the other one is Ok too. What I did find is if I put the axle stubs back in enough to engage the splines and rock them there seems to be a bit of play in the spider gears as seen in this video. Is this normal or potentially the cause of my noise?

 

Can't really make much out from your video, but I do hear the clicking. No, that is not normal. Your spider gears, cross shaft and/or side gears are likely worn. How many miles on that diff? When does the vibration usually occur? During acceleration, deceleration or coast?

I'm on my 3rd diff on my S5 non-turbo, and it seems to me that these diffs have a lifespan of only about 150-200k miles under normal use.

I don't have any firsthand knowledge about the VLSD. I've never worked on a VLSD, but do know how they work in principle. I do know that the VLSD unit is not serviceable. So, maybe that's part of your problem too. You need to pull everything apart, check the parts to see if they meet spec and replace worn/defective parts.

 

The clicking is mostly what I was trying to show as it's hard to see the movement on the video. I can't remember miles exactly but it's somewhere around 310,000. Vibration becomes noticeable above 30mph and gets increasingly worse from there. Always present acceleration, deceleration, or coasting with the clutch in.

FSM doesn't really have anything on the VLSD. Basically a check with a torque wrench on the axle nut with the gearbox in reverse. If it fails the test they say replace it.

 

The FSM says that the VLSD is not serviceable. FSM says to replace it if it's defective. The non-turbo VLSD is NLA from Mazda.

I am the original owner of a 1990 GXL. I replaced the original open diff with 158805 miles in Mar 1999. Problem was I would hear a loud banging sound when driving above about 75 mph. I still have that diff sitting in storage and unopened since I removed it. I replaced it with a used '86 LSD with 60252 miles in Mar 1999. After another 122160 miles, I replaced that diff in Jan 2003 with a new LSD that I bought from Mazda Surplus Parts. So in total, I put 219057 miles on that diff. That diff came with a 3.909 R&P set that I replaced with a 4.300 R&P set. I've now got over 147k miles on that diff.

For the last several months, I've been getting some vibration that I've isolated to my the diff. It seems to vibrate at higher speeds, but only when in coasting mode. I think it's the pinion bearings, but won't know for sure until I open it up.

Based on my past experiences, this leads me to believe that that the average diff lifetime is about 150-200k miles under normal use. It's becoming increasing difficult to buy parts for these diffs. I recently bought a set of SKF bearings (6 bearings in total) from Summit Racing. BTW, saved about $150 buying them from Summit rather than Mazdatrix. The pinion and side seal are NLA from Mazda. So, I had to buy them from Mazdatrix. The spider gear shaft for my current LSD is NLA from Mazda. Like I said, it's becoming harder and harder to buy parts for these old cars.

In your case, I would recommend either buying a used clutch-type LSD form an '86 to '88 RX7 or buying an after market LSD diff such as a Kaaz.

Good luck and happy holidays!

 

Yeah, I think that's my plan except I may go with the Torsen from the Miata if I can't find a clutch type from an '86-'88. I hear good things about them. Happy Holidays to you too.