Had issues at the track today and didn't even make it 1 lap. The minute I accelerated from the pits to enter the track, my car started making a shuttering sound from the rear when accelerating. The noise/vibration strongly appears when accelerating on throttle; when coasting it's almost non-existent. The sound and feel it makes is just like driving over rumble strips. I can control the volume by applying more throttle. The shaking is like the rear wheels are bouncing left to right, kinda like a shimmy.

I'm thinking either bad axle or diff/LSD. When making turns full lock from a stop, the diff does not make any unusual noise. No ticking/clicking noise from the axle cups either. The sounds is definately from the rear, and looks to come from the center (not biased to either side). My rear axle nuts have been properly torqued, staked and marked, so nothing unusual there. All wheels were rebalanced. Suspension is healthy and was recently revalved 3 months ago. No vibe when braking, rotors are straight. Wheel bearings are good, no freeplay.

Thoughts?

 

Change diff fluid and see if you have a river of metal flakes drain out

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Just drained oil. Came out as good as new (which was replaced 4k miles ago). Magnet is also clean.

Anyway to troubleshoot which axle is suspect? Any can someone explain how an axle can make this noise/shudder happen?

 

had the exact same problem you are describing, fixed it this weekend as well!

my problem was (could be yours) the left rear inner CV joint receiver had a large wear mark in it. and after raising the car from its previous ride height it caused the CV joint to run in and out of that wear mark creating a vibration.

it is really easy to remove the axles

1. remove the tire
2. unstake and remove the axle nut
3. unbolt the upper control arm and lower (leave the lower nut in place) you may need to use a mallet to brake loose the ball joint, dont hit the joint! hit the side of the spindle.
4. unbolt the 6 bolts from the diff reveiver
5. remove the 10mm bolt from the speed sensor for ease of access.
6.remove the lower control arm nut and lift out the assembly carefully, watch for the brake line!
7. pull out axle
8.using needle nose pliers, remove the clamp around the inner CV boot. Save the clamp they are reusable!
9. carefully remove the axle, holding the three bearings from falling off and lay it on a clean surface.
10. inspect the receiver for excessive wear =D
11. on reassembly make sure to re lube everything with CV grease

now, if you do find excessive wear you can swap the left and right inner receivers, if the vibration goes away then thats your problem.

 

Thanks, after researching a bit sounds like the classic example of CV cup wear.

 

Drive Shaft Shop has a great upgrade:

New S2000 500HP Level 2.9 Axles. We here at The Driveshaft Shop are always looking to improve our axles and shafts. Over the years the inner CV on the S2000 has been an problem with the stock axles. The factory tripod bearing just isn't up to the task and will wear into the inner CV housing. The tripod has only 3 points in where it makes contact and will dig right into the housing causing the part to wear, creating noise, vibration and eventually failure. We have decided to change our popular Level 2.9 500HP Axles over to a Porsche 930-style or 108mm Inner CV so there is a full 6 contact points, instead of 3. This will be a strength advantage over past designs, and since it is a ball and cage design, it will be better at running at an angle. Especially when the S2000 is lowered it puts the inner CV into a significant angle putting more stress on the inner CV. This new design will be not only be tougher but also smoother at transferring power as well. Axles will include a set of adapter plates and hardware to mount them. It's designed to fit the standard 28 spline factory hubs and these axles come with removable ABS rings. Price is for both left and right axles.
PART# RA2000X2 / RA2001X2


http://www.driveshaftshop.com/import...evel-2-9-axles

 

My bet is inner CV joints. Swapping then left to right gives fresh contact surfaces and is a good medium term fix.

 

Swapped the CV cups last week & fixed the issue. I'm a happy camper now