Driveline noise while in gear decelerating
 

I took the Miata for an 800 mile round-trip drive to Ohio this past weekend, and something that I have noticed previously made itself more pronounced with the top down and at higher speeds.

When decelerating from a freeway exit, I sometimes shift into a lower gear and engine brake. I noticed that there is a grinding/thrashing sound coming somewhere from the driveline, normally getting louder with less revs. It is much more pronounced in second and third gear than fourth or fifth. Depressing the accelerator pedal ever so slightly makes the noise go away, and it seems to be worse when all parts of the car are up to full operating temperature. There is no noise when the transmission is disengaged.

The same noise is sometimes audible, though not nearly as loud, under slow, low-RPM WOT acceleration in a high gear (the car is a stock 1.6).

Any ideas? Should I start scouting a new tranny or pumpkin? I searched around and didn't find much. A Porsche 951 I had years ago had a similar sound that was cured when I did a clutch job and replaced the pilot and throwout bearings (and snapped fork arm, prompting the repair); however, that was a transaxle and a bit different.

As an aside, is it normal for the car to feel like someone threw an anchor out of the rear when turning on the A/C compressor? I've had a couple of small bore 4 cylinders before that lost their umph with the A/C on, but I literally had to hold WOT for 30 seconds to accelerate from 55 to 60 MPH on flat road with the A/C on. Not that I'm too worried for the long run since I'll be taking care of the power deficit, but just to know.

Thanks!

I have the EXACT SAME problem right now. I thought it was the exhaust, but even after changing my whole downpipe/exhaust I still have the sound. I now think it's the throwout bearing, but can't be sure until I crack the tranny open for inspection, etc..

In for the answer... hopefully. I've got the same problem, I changed the tranny fluid out with Red Line MTL, in hopes that it might solve my problem (needed to be changed anyways) but no dice. Maybe a rear-end issue?

Rear-diff. It will slowly but steadily get louder with time, then one day...BOOM. Ask me how I know.

+1 on the diff.

Well, guess it's time for a torsen then.. Even with the top down that sound seems like it's coming from the front end though.

just put someone in the trunk and drive around for a bit, they should be able to tell you where its coming from. :laugh:

Alot of people have fixed it by putting in any 1.8L diff. something to do with some rubber dampner that wears out in time i think

Light flywheel? That causes exactly what you describe. Engine braking in mine makes the trans scream like a rally car with straight cut gears.

Also, trans disengaged as in clutch pressed in, in gear? What does it do at a dead stop in neutral? Anything? But also like stated, could be in the rear end, if it's speed related and not rev related. Still find it unclear, even after a 3 paragraph post. That and it's late.

I assume you are still n/a? I also love the anchor or a/c. If I want to pass at all, I have to turn it off to get enough power, and then it's still slow as shit.

https://www.miataturbo.net/showthrea...light=ruger988

Check that thread out, it was a long time ago (3+ years) and I was a bit dumber then, but my problem turned out to be the diff, read through and see if you can read through my incoherent rambling enough to tell if it's a very similar sound.

Thanks for all of the input, guys! Today it was crappy out, so I had the top up and was able to better hear where the sound was coming from - it is definitely coming from the rear end. Come to think of it, the previous owner told me I should check the rear end as the only mechanical warning that came with the car. Well, after I recover from paying the US Treasury dept. and comptroller of Maryland $1300 or so in taxes, it looks like I'll be saving up for a torsen swap. Hopefully the diff will hold up until then.

If that is indeed what it is and it ends up being anything like my situation, it will progressively get louder until you're rolling down the road one day and BOOM, just don't put too much load on it and stay off hills if at all possible and you should be able to stretch it out a couple weeks or so like I did. Luckily mine blew as I was backing into my driveway, just so happens that that was the day my new diff arrived from Olderguy (I think it was olderguy, maybe turbotim, i dunno.)

front diff

Only on my subie.

Want to buy my 3.9 torsen? Full pumpkin with stalks, no axles. I'm nearby.

If you still have it in a couple of months after I recover from the checks I needed to write Uncle Sam and Martin O'Malley today, I'd take it from you, provided I can find axles and a drive shaft. Where in Baltimore are you? I work in Canton, right on the square.

I have some odd noise as well. Decell in 4th is the worst. Almost sounds like I left some tools in the truck and it's vibrating on the metal back there. It get's pretty loud. I checked and there is nothing loose back there so it must be the driveline.

I do have a Kaaz diff which is loud to begin with, but also solid diff mounts, so that may be the reason right there. I just don't remember it making that much noise for the first 1000 or so miles after the install. :???:

i have a 1.8 diff with OS giken in it. doesnt make noises at all.
Puddymodracing stage 2 assembly.

Right by the stadium.

I feel like some of these points are invalid, heres my examples I have the same noise on decel had the same noise after changing the open diff to a torsen, then still had the noise after changing to a 1.8 flywheel and clutch, still the same noise then procceded to change tranny fluid guess what... same noise... I would like to know what mine is as well but I'm leaning more to the whole tranny dying part

Have you aligned the PPF/gearbox to the correct distance from the chassis?

Loosen off the 3 big bolts that hold the gearbox to the PPF, Jack up the gearbox so it sits 65mm (I think the factory manual specifies between 55 and 65mm), between floorpan and bottom of frame where the gearbox bolts to it, then re-tighten the bolts. You will find the gearknob will sit slightly higher than before.

Cured my gearbox lash noise on the overrun...

Stock 1.6? Check the shielding on the Cat. It rattles if its loose and you decel. Sounds stupid but a lot of ppl found out that that was the problem.

How long have you had the problem for? Do you still beat on your car?

Can we be more specific on where to measure from to? Where on the floor pan and where on the trans?

all I know is, since replacing my trans and clutch last weekend, I have zero draintrain noise like this anymore. It's win.

the floor's pretty flat and it's not an exact measurement, there is a range given ;) you're not measuring from the chassis rails, just use a bit that's near to the gearbox.

I don't really know how to be more specific on the gearbox part?!?

Where the PPF bolts to the gearbox.

The floor of the car right?

Is it possible that the diff could also be out of alignment? And is there a spec for doing that as well?

No.


Turns out we broke the 2nd diff in a mile and that was the noise. Now it has a 1.8 diff, well see how long this one lasts.

Hmm...I just put this damn thing in and its already making noise :vash:

You sure...? :dunno: Never heard of this before, and can't see where that would cause any noise. I can't imagine you could get any more than maybe 3/4''-1'' of total play out of the PPF in that area around the bolts, and I don't see how that would affect anything. Maybe the angle of the output to the drive shaft, but that little bit shouldn't cause any kind of noise.

Sorry for beating an old post.

Definitely confirmed. I raised up the tranny a little bit, and my driveline noise just got about 10 times quieter. Tits!

I wonder why? I can't picture in my head what changes to make this happen. Maybe this would alleviate my horrible transmission noises, though I'm quite sure it's simply worn out. I know my PPF was forced into place with a crow bar, then bolted up as it sat with the trans and engine weight pushing it down. Maybe I should crack them loose and jack it up a bit and tighten them back up.

The only thing I can think of is the output shaft/pinion bearings taking too much lateral load or the pinion being pushed in some odd way, or some crazy nonsense like that that you would never think of.

Yeah, it would have to be something there, since the other end is snug against the block. Maybe this weekend I can get around to it.

Went on a long drive and really got everything warmed up. Wanted to make sure I wasn't imagining a quieter drivetrain. Still way less drivetrain noise.

I think it's prop alignment, the straighter is exits the gearbox the better.

It is in the Mazda service manual afaik. Though I know of some aftermarket MX5 specialists in the UK who swear such a thing doesn't exist and even that there isn't any play in the gearbox/PPF alignment.

Fair enough if they aren't aware of the procedure, but to blindly refuse it's even possible is rather obtuse.

Oh it's on page K-130 in the manual Braineack kindly hosted on here


https://www.miataturbo.net/showthread.php?t=48633

Well damn. I thought I had it fixed. I jacked up the car and secured it, then I loosened up the 3 PPF bolts and put a jack under the tailshaft housing and jacked it up about an inch from where it previously was. Bolted it all back down and I'll be damned if the noise wasn't 90% gone (though replaced with a slightly unsettling sound. Almost sounded like the engine sound changed under load, a deeper roar). It would idle silently and even when the a/c would kick on, it was silent. When the a/c kicks on, it used to go into violent rattle noise mode like the trans was about to start dropping parts under the car. Drove it a bit, still no sound, GREAT! Let it sit for a few hours, get back in it and drive and the damn noise comes back completely. I doubt the bolts slipped since I put a bunch of ass on them. Maybe my trans is just that worn out. I can go from on throttle to off throttle in gear and hear and feel the slack in all gears, worst being 4th. I'm just driving it till it blows, then find either a lower mileage 5 speed or a 6 speed if I'm lucky enough.

So this jack up the PPF thing does work, but only temporarily in my car, not sure why yet. Might check it out again next weekend. Just got hot and I'm not leaving the house again for the rest of the day.

Hmm, I've realized my gear rattle comes back too, but not in a few hours, more like a few days. Mine is also really bad in 4th, not as bad in other gears. :vash:

Make sure the wiring along the PPF is ziptied. The wiring was causing loud rattles on my 1.6. There is even a TSB about it: http://www.miata.net/garage/tsb/sb011_98.html

Not the same kind of rattles, in my case anyway.


Hmm, this sucks. I also noticed I had a lot of output shaft play. Oh well, new trans.

Here is what sucks. I had this exact problem before, and I swapped transmissions because of a different issue. Everything was identical, even the excessive loudness in 4th gear. Noise was still there. Upgraded to a Torsen...noise was COMPLETELY gone. Really hope my diff isn't ready to blow already.

Update:
:laugh:
Changed out my trans oil with Amsoil MTG. Gear noise is GREATLY reduced(damn near gone). I guess that shit was just old.