Rear End Clunk – Diagnosis

Originally posted on: 01-31-2013

I found the source of my rear end clunk. Yay!

Can any of you eagle eyed readers notice anything missing from this picture?

IMG_20130131_211908

Damage report:

IMG_20130131_212641

Where the shock machined away the top-hat:

IMG_20130131_212901

Metal shavings:

IMG_20130131_212910

Originally posted on: 02-01-2013

this may turn out to be not as painful as I anticipated.
I ordered new shock mount hardware (for all 4) from Mazda today, and after a call to Flyin’ Miata found that they sell service parts for the shock hats. I’ve got a new bearing for the damaged one and new sleeves for both rears coming in as well.

I also talked to Koni Lee (if you’ve dealt with Koni motorsports before, you likely know who that is) today. He took a look at the pictures of the shocks and thinks that the threads are likely salvageable. I’ve got a call in with a fabricator friend to see if he’s got the right die for the threads (they’re 12×1.25, and I’ve only got 12×1.5 and x1.75… figures) to see if I can’t salvage what’s there. Worst case, I’ll have to replace the shock, which’ll come out cheaper than repairing / refurbing them. For the race & higher-end shocks (28 / 30 series) it’s way cheaper to service them, but the OTS stuff is about the price of a rebuild without the down time. So, we’ll see how that pans out.

In the mean time, here’s some close-ups to the damage on the shock hats.

Now that I’ve had some time on them, I absolutely love the design of these things:

IMG_20130201_104742

IMG_20130201_104945

Metal-shavings on the bearing:

IMG_20130201_105408

Originally posted on: 02-02-2013

After further discussion with Lee, and playing with the “good” one out of the car (it, also, had the nut loose, but not to the point of damaging anything, yet), I think we’ve found the Root Cause of this. The way they ship from FM, there’s a lock washer that basically fills the area in the hat just over the spherical-bearing, with a nut on top of that. This essentially doesn’t allow much deflection in the bearing. That deflection put a lot of force on the washer and nut, wearing away at the housing and forcing the nut loose, which we can see here:

IMG_20130131_213744

Solution: instead of using the lock washer directly on top of the spherical, I’ve got a couple of conical retaining washers for spherical bearings coming in to use that will allow the needed deflection, taking a lot of force off of the lock washer and nut, and side forces off the shock shaft.

Now the final piece of this is to see if I can repair the shock myself, or if I need to order a new one. Fingers crossed. Yay for problem diagnosis!

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