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Old 04-13-2010, 12:23 AM   #1
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Default 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!
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Old 04-13-2010, 12:55 AM   #2
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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..
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Old 04-13-2010, 05:15 AM   #3
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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?
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Old 04-13-2010, 05:48 AM   #4
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Rear-diff. It will slowly but steadily get louder with time, then one day...BOOM. Ask me how I know.
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Old 04-13-2010, 12:01 PM   #5
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+1 on the diff.
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Old 04-13-2010, 12:11 PM   #6
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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.
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Old 04-14-2010, 01:00 AM   #7
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just put someone in the trunk and drive around for a bit, they should be able to tell you where its coming from.
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Old 04-14-2010, 01:31 AM   #8
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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
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Old 04-14-2010, 02:38 AM   #9
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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 ****.
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Old 04-14-2010, 02:47 AM   #10
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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.
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Old 04-15-2010, 12:42 AM   #11
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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.
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Old 04-15-2010, 12:45 AM   #12
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Quote:
Originally Posted by hotspoons View Post
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.)
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Old 04-15-2010, 10:16 AM   #13
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Quote:
Originally Posted by KPLAFIN View Post
Rear-diff. It will slowly but steadily get louder with time, then one day...BOOM. Ask me how I know.
front diff
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Old 04-15-2010, 10:18 AM   #14
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Quote:
Originally Posted by hustler View Post
front diff
Only on my subie.
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Old 04-15-2010, 03:19 PM   #15
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Want to buy my 3.9 torsen? Full pumpkin with stalks, no axles. I'm nearby.
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Old 04-15-2010, 08:03 PM   #16
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Quote:
Originally Posted by faeflora View Post
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.
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Old 04-15-2010, 09:28 PM   #17
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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. :???:
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Old 04-15-2010, 09:36 PM   #18
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i have a 1.8 diff with OS giken in it. doesnt make noises at all.
Puddymodracing stage 2 assembly.
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Old 04-16-2010, 12:48 AM   #19
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Quote:
Originally Posted by hotspoons View Post
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.
Right by the stadium.
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Old 04-16-2010, 01:26 AM   #20
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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
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