This doesn't look right, but what is it? Miata diff content...

Decided to pull the stock replacement cat and exhaust to fit the shiny new FM exhaust and high-flow cat tonight - hey, it's Tuesday, so why not?

When pulling out the exhaust I notice that there was grease, well, not everywhere but nicely flung off the mounting flange of one of the driveshafts:

The flange bolts appear to be reasonably tight - not something the bolts for the rear chassis bracing could have been accused of so someone's been in there - but it awfully looks like this grease/oil/whatever it is is being flung out between the flanges of the driveshaft and the diff.

This is something that started very recently, it wasn't there when I checked over the car for Laguna Seca. The question is, what the heck is it? Diff oil mixed with dirt? Axle grease? It certainly feels greasy to the touch, but I'm a bit stumped where the head gasket mayonaise color is coming from. Oh, and if it does make a difference, the car is supposed to have a Torsen diff.

Oh well, there goes the plan to take it to this weekend's HPDE. At the current rate I need a backup track car .

I've seen grease mixed with water that looked like that.

Tear in the boot somewhere?

I had a quick look at the boot and it looks fine.

Actually, a tear in the boot was my first thought - probably should inspect it more thoroughly tomorrow.

That's a weird flange to have something flinging out of. It's not normally open to anything at either end.

4 bolts and it's off, and you'll have the answer.

I'm no expert, but my guess would be water got in the boot and 'mixed' with the grease and then it was thinner and flung out the flange. Have you been crossing a lot of rivers and streams in your miata lately? It's a 15 min change if you can get a new halfshaft. I wouldn't let it stop me from a hpde. Especiallyif I towed it there.

The grease cap on the end of the CV housing has come loose and centrifugal force has thrown the grease out of the flange. Messy but easily fixable.

That being said, I replaced the whole halfshaft when mine did it.

Dashpot wrote: The grease cap on the end of the CV housing has come loose and centrifugal force has thrown the grease out of the flange. Messy but easily fixable. That being said, I replaced the whole halfshaft when mine did it.

This. Not hard to fix.

That makes sense. Oh well, that allows for a few "while we're in there" jobs but I think I'll have to farm out the halfshaft replacement - I haven't got a torque wrench that goes up high enough to tighten the hub nut so I guess I'll farm it out to my local shop. Oh well, looks like this HPDE season is going about as well as last years. Grmpf.

Curmudgeon wrote:

Dashpot wrote: The grease cap on the end of the CV housing has come loose and centrifugal force has thrown the grease out of the flange. Messy but easily fixable. That being said, I replaced the whole halfshaft when mine did it.

This. Not hard to fix.

Assuming the half-shaft hasn't rust welded itself to the hub, yes no big deal.

Mine on the other hand wouldn't come out after days of soaking, heat, BFH.........I ended up with rebuilt spindles from Planet-Miata and used half-shafts.

Fortunately rust hasn't been a problem on this car so far. Heck, I took the exhaust off last night with a long handle HF wrench and a couple of squirts of penetrating oil. The penetrating oil was really more out of habit than anything else.

I think I could get used to these Western cars.

Yeah the halfshaft can rust to the hub and that's a beeyotch. Even on Western cars I'd slather the thing with anti seize.

As far as loosening/tightening the nut, you don't really need a torque wrench. Use a really strong breaker bar and a pipe to loosen it. Then, reuse the nut and line the 'crimp' back up with the slot and ding it back in place. Never had one come loose etc on me.

If you don't want to do this, remove the top outer bolt from the upper control arm, this will allow the knuckle to lean out enough to get the inner flange far enough out to get to the 'cap'.

Dashpot wrote: The grease cap on the end of the CV housing has come loose and centrifugal force has thrown the grease out of the flange. Messy but easily fixable.

Definitely this. I just had mine apart for a torsen swap. Here's what the CV grease looks like - it's the same stuff coming out of yours.

There's a little metal cap that covers this before it's bolted to the stub. If that's missing or come loose then that will allow the grease to leak out of the flange.

I'm pretty sure the cap should be there as it's only started doing this recently. The suspension upright that carries the hub has some damage from the bent upper suspension arm so I'll change that out at the same time.