Busted Diff Mount?

[gabkwong]

Do you think I have busted diff mount? When coming out a tight turn and shifting from second to third, I occasionally have gears smashing. I already have the MS motor mount. I doubt is the engine mounts are broken and the motor is shifting around is the problem. How often does the MS motor mount breaks on a normal aspirated NB?! Is there a sure way to diagnose if the diff mount is toasted? Do I really have to take the diff off entirely to find out?

[Nails]

The diff housing has a yoke, or two arms that go out to the side to support it. The right arm has a notch in it about midway on the top side. This is factory done and is the weak spot that will break the arm in a collision to save the diff inside. Carazzie's was broken a year ago in a rear ender and Jim Otterbein at Town North Mazda said he sees that happen alot. That's the extent of my experience with diffs, good luck finding the source.

[ckearns]

The whole diff mounting assembly is visible from the yoke through the ppf up to the transmission with the car up on jack stands.

When you're feeling the grind, it is on your shifter hand, on the wheel hand, or in the seat of your pants?

Stock motor mounts are a 100k+ mile part on a non FI car - if they were recently replaced, it's probably worth while to nut and bolt check both sides to make sure everything's still tight. Worn motor mounts don't make for grinding gears though, they make for missed shifts (2->5 instead of 2->3 when the motor is torqued up, generally). A wonky diff would make noise all the time, not just on occasional 2-3 shifts.

I'm thinking it's somewhere in the linkage or synchro system in the trans where this is coming from, but need more info on the circumstance where you're getting the grind and where you're not - can you repo it in a straight line, is does it only happen when your shift point is over x,000 rpm and speed is over y mph, are you shifting quickly, etc.

Chris

[Jiggerachi]

I've had almost the same thing, except it happens on either hot days when driving aggressively or on cold mornings. I sometimes get a *chink* from 2 - 3, and more often on 4 - 3, sometimes more of a grind on downshifts. Happens in straight line as well as turns. I went through the hydraulics thinking the clutch wasnt letting go all the way, but everything's working fine. My motormounts are shot as well as the u-joints, I was hoping the new driveshaft and the MS motormounts I have waiting to go in would help, but I fear more and more it's a synchro.

I'm interested to see what you find as this has been a gremlin of mine for some time.

*edit. On mine I can definitely feel the grind through the shifter.

[nealb]

I recently found a big crack in the diff carrier right where Nails said to look. If that is the cause, you can see it from under the car. I think miataracer has one he would sell if that is the prob.

[SirHustlerEsq]

It sounds like a trans issue to me. Now you can tell me about how you're running a GL-5 gear oil. Then, 90% of the forum will say that Lord BRG Aryamehr The Imperial, Esq. is wrong and that GL-5 can be used in a GL-4 specified "yellow metal" trans. A few years ago I'd go through the motions and provide a study on yellow metal synchronizers and how the EP modifiers in the GL-5 hold a bond stronger than the material strength of the synchronizer causing the grind. Then, if by some chance you are a member of the 10% who choose to wing it, heed my advice fueled by the Illuminati of the lubricant world, you will try AMSoil MTG and be rewarded with a synchronizer that will eventually fix itself as my old 5-speed did.

[gabkwong]

I feel it in stick and also hear the grinding noise! It only happen coming out of a tight turn when the car is at the last 25% of the turn, like a street corner, and at WOT from 2nd to 3rd. Come to think about it, I think "mr brg" is on to something! This thing started since I switch to this 'French" product a few months ago! I guess I will give the AMsoil MTG a try. Is any local source for this? I never have this problem with M1 and Red Line. Of course, I can not for sure can blame the 'French" product until I drain and refill again.

[Radio-Active]

Their warehouse in in Arlington. Become a prefered customer and you get a 25% discount.

linkie:

[Radio-Active]

Almost all of the Amsoil dealers are independant. You can locate one of the dealers on the amsoil website I gave you if you don't want to drive over to Arlington or pay for shipping.

[circuitmstr]

I have solid motor mounts on my na and i was getting movement from the rear end that would make it less confident to go in gear. I replaced the diff carrier bushings with the energy suspension bushings and this all went away. Well worth it! I do have increased diff noise, but i have the kaaz clutch type diff so its noisy anyways...
i dont know if this helps but my car shifts so much easier and smoother. The rear drivetrain has more confidence and is more predictable...

[circuitmstr]

BTW: Im trying to get hold of you to buy your seats...