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Hi guys, long time since my last post.
I need some help with a whine from the rear end of my 90. It's an import with the 4.3 VSLD.

The whine is consistent with speed and doesn't come or go with acceleration/deceleration, it's there consistently, pitch changes a bit, but I'm not sure if thats just the difference in engine noise interfering with my hearing.
I can't hear it with the top down, very noticable with the top up.
I initially thought wheel bearing, but it's not a rumble like I've had with my BF falcon, and doesn't change when turning left and right
Diff fluid is clean, and I can't find anything loose or noticable play or notchy when i rotate the hubs.

How can I differentiate between diff bearings, diff gears, CVs, wheel bearings, universal joint? without just throwing parts at it.

Simply solution is to just drive with the top down all the time (which I do mostly) and wait until it announces it's true identity - this is an option as it's not a daily driver, so i can be without it whilst I fix it.
Ideas?

In my experience, diffs often whine more/less with changes in load.

Really hard to diagnose something like this electronically/over the internet, and noises can travel surprisingly far from their source.

If it is the diff, keep an eye out for a NA8 diff + torsen. You will also need the axles and tail shaft.

That is a puzzle. I have been mulling it over since I read the post earlier.

There is NOTHING on the car behind the crank pulley that does not vary in speed/rpm wnen the car is dríven. Unless it is 12v operated - the fuel pump? Normally that would go on and off, or is the NA a return feed?

If the noise does not vary with road speed, engine revs, gear, engine load, suspension load ... then wait and see is the only option I think.

Roadside service paid up?

Have you put different tyres on the vehicle or are you driving it on different type of sealed road surfaces to which you previously drove on? I ask as those two things seemed to affect rear end noise on my old NA6.

Sorry, wasn't clear.
What i meant was, it's there when both accelerating and decelerating, the pitch does change a bit though
The noise is speed dependent, it increases with speed, decreases with less speed, but it's always there.
Gear selection doesn't matter either, it's the same in neutral, or any gear.
So it's definately something after the gearbox.
I'm sure I could turn the enginge off and roll in neutral and it would be there - might try that this weekend
I've tried tyres - no change.

I am still leaning towards tyres/wheels. Anything stuck in your tread?

That narrows it down. U-joints, diff bearing, wheel bearing. And with the lsd you can't jack up a wheel and isolate one wheel bearing. I would have tipped wheel bearing(s), but if it doesn't change when cornering ... probably not. If you haven't tried hard cornering, that would be worth a shot, but it is sounding like it is inboard of the wheels, so ... diff?

A mechanic could put it on a hoist and maybe diagnose with a stethoscope. If it is inside the diff, you may have a decision to make about how much money to spend on it. The VLSD is a good solution for relatively low power levels (providing the diff oil is changed regularly), but the CWP is the weak link. A long-nose (7in) diff is a definite reliability upgrade (bullet-proof to insane power levels), but though an open diff is pretty cheap, you will need the axles and prop shaft as well (as The American said above).

I'd get it on a hoist and see if a diagnosis can be made, and sooner rather than later. That will give you the maximum opportunity to do your homework on rebuilding the existing diff (if that is the problem), or doing the upgrade - if the latter, time for shopping around for the upgrade parts.

Yes, a hoist will answer it. Wiggle and lever everything. Listen to the diff, etc.

Ross wrote:whine from the rear end of my 90. It's an import with the 4.3 VLSD.

My knowledge of the JDM VLSD is limited, but it's said that by now (age &/or kms) these diffs have ceased operating as a VLSDs, so could it be the case that is manifested by a whine?

93_Clubman wrote:

Ross wrote:whine from the rear end of my 90. It's an import with the 4.3 VLSD.

My knowledge of the JDM VLSD is limited, but it's said that by now (age &/or kms) these diffs have ceased operating as a VLSDs, so could it be the case that is manifested by a whine?

No expert on these either, but my understanding is that the LSD function is dependent on the condition of the diff oil, and when it deteriorates the LSD action becomes less effective. The oil binds rotating plates in the diff to create the LSD effect, AFAIK there is no mechanical contact to create a noise.

So yes, the LSD action may be shot - probably is if the oil is original. If the noise is in the diff, it is more likely to be bearings, possibly worn R&P.

Tks GM - I see from Miata Garage that Lance S reckons the plates can break, the silicone fluid can leak into the diff oil & the tolerance between the plates can wear: https://www.miata.net/garage/vlsd.html And gtxhawaii reckons the VLSD module was sealed at the factory & not serviceable including replacing the silicon oil, so no spares or replacements from Mazda.

I thought Rocky would chime in with the mention of 'whine'.

93_Clubman wrote:Tks GM - I see from Miata Garage that Lance S reckons the plates can break, the silicone fluid can leak into the diff oil & the tolerance between the plates can wear: https://www.miata.net/garage/vlsd.html And gtxhawaii reckons the VLSD module was sealed at the factory & not serviceable including replacing the silicon oil, so no spares or replacements from Mazda.

Interesting, thanks for that! I read a thread on, I thought, MT.net that described a vsl 'rebuild' that was basically a fluid replacement. But my search just now did not turn that up, but did turn up a lot of statements that they are not serviceable, as you say they are a sealed unit inside the diff. But also a lot of comments that the biggest problem is breaking the R&P - not surprising give the what that site is about.

Based on those reports from the big board the noise could be the vlsd itself, as well as the other sources within the diff, and as a result, if it is a noisy diff a 1.8 (7inch) is probably the best long term option. While R&P and bearing repairs would be possible, and/or swap in a non-noisy replacement vsld (or just an open centre), I don't think that would be my choice.

Finally got bad enough that I had to fix it.
Good thing was that it got bad enough that I could identify it to the LHR wheel bearing.
Only had an issue with the hub nut, 1m breaker bar didn't move it. Borrowed the Rattle gun from work and 10 seconds of that and it was off.
It all came apart easily after that and went back together even easier.
Now I can hear other rattles, drones and unidentified noises