Differential Woes

Ever since I first test drove the car, I knew the differential was going to be a serious achilles' heel. 5000km ago, on the test drive, it howled at 80kph like any Merc diff that had seen a lot of highway miles. Since I've been driving it, the howling hasn't gotten much worse, only it now happens on 85kph too. New to the situation, however, is a ticking (sometimes a crackle) coming from somewhere near the backseat. I started thinking oh-my-god, the diff is going to let go real soon.

I'd been waiting for fall in order to clean up the wheel lug thread grooves in the front. I figured since there is probably going to be a diff overhaul, and the car will be sitting for a while again, I'm going to do it now, and switch to Pentas/winters while I'm at it. This was last week.

Today I had an appointment at the shop. We opened the diff to start diagnosing the ticking. Well, first off, the diff wasn't dry. I'm not sure how much oil there was exactly but one thing was for sure, it looked pretty awful and it wasn't certain if it was the right kind. The diffs on 560's are pretty cranky about having just the right lubricant. After all, they are viscous LSD's, and Merc ones at that. I read a recommendation for Mobil HD 80W-90 hypoid oil but asked a buddy what he'd bought. He recommended LiquiMoly LS SAE 85W-90 oil which is for Limited Slip Diffs obviously. So that's what I got!

Old Diff Oil

New Diff Oil; LiquiMoly LS SAE 85W-90

I didn't take a very long test drive (road temp was 38C and I was running frictions) but the result is this. The diff feels like it howls a little less, but the ticking is still there.

While I was at the shop, an old taxi driver threw an interesting idea: what if it's a wheel bearing. Well, it certainly could be, and I started leaning in that direction initially, until I remembered something; the car only makes that ticking noise when cruising at 85 kph. If you let off the cas, it stops, and if you accelerate, it stops, even at the precise speed where the noise happens on steady gas. So I'm still thinking it's a bearing in the diff. Oh, and there was no evidence of metal in the old oil, or in the drain plug magnet. It's therefore pretty unlikely that anything else besides a bearing is damaged inside the diff.



Other than the diff problem, 560SEC ownership has been pretty mundane recently. I went to Lappeenranta Cruising a couple weeks back, for which I washed the thing and took the ten minutes to maintain the engine bay's cleanliness. Here's a pic I took while I was cleaning the lug threads.