Grinding sound when decelerating
 

Hey guys,

I just got a used 2018 Toyota 86 a couple of days ago and noticed this sound coming from under the car when decelerating at around 3500 - 2500 RPM. Pushing the clutch in seems to get rid of the noise.

Here's a good clip of someone I found with the same problem:
https://drive.google.com/file/d/1iMZ...ew?usp=sharing

So I've seen a couple other topics regarding this on the forum but:
1. They all seem inconclusive
2. None of them have sound clips

If I had to describe it, it sounds like a mix of a grinding noise combined with the noise your engine makes when it starts to lug (without all the vibrations).
Some of the other threads describe a "Jar of marbles" sound, but this doesn't sound like that to me. I've also looked at videos of bad TOB sounds and this doesn't sound like that either.
This is my first manual car so no idea if this sound is normal or not but I don't notice anything wrong with how the car drives. Can shift smoothly into each gear, no problems with the clutch either.

Any help would be appreciated!

EDIT:
Compiling other threads that seems to have the same problem (again no sound clips so can't be totally sure)
https://www.ft86club.com/forums/showthread.php?t=15186
https://www.ft86club.com/forums/showthread.php?t=8344

The consensus from those as well as from some 86/brz facebook groups is that the sound is normal.

Check/change your tranny lube. Motul is considered to be the best by many who think their opinion is important.

if you just feather the clutch slightly(1/8 pedal press, ie; ride the clutch), does the noise go away, or only when pushing the clutch all the way in?

It only goes away when I push the clutch all the way in.

I'm going to change the trans and diff oil to Motul Gear 300 and see how that affects the noise levels.

Pshhh... What do they know?

all the way in would indicate transmission or driveline, as the clutch is disengaging those.

i would inspect the rear diff and the drive shaft first. specifically the rear diff gear lash.

I actually think you're right on the money with this. Been researching on some rear diff sounds and came across this video:

https://www.youtube.com/watch?v=XhxMOj0W_WA

And his car does something similar when he lets off the throttle. He had to get a full rear diff rebuild :cry:

Just waiting for the motul 300 gear oil I ordered before changing the diff fluid. Really hoping that quiets it down. The last change was done 6 months ago (and only 2k kms driven since then) so if I find a lot of gunk on the drain bolt I think that's another sign somethings going wrong.

If the fluid change doesn't work then I'll probably have to find a mechanic to check the rear diff backlash and pattern.

A grossly subjective lash test would be to jack the car up and twist the drive shaft back and forth. There should be only a slight bit of play when you change the direction of twist. The technique is not too scientific but that's where we started in the old days.

Will give that a try as well once I get my jack stands!

Updating this if ever someone with the same problem has the same problem.

Just did a full fluid change:
H-tech 100 plus 0w20
Motul Gear 300 75w90 for the transmission and rear diff

And the noise has not really gone away (Shifting feel however is much better!). My old transmission oil was still in pretty good condition. However my rear diff was pretty dark and had a lot of sludge stuck to the magnetic drain bolt.

I just got used to the noise honestly. You can only hear it on low rpms with the windows closed and no music. Just gunna assume it's nothing unless it gets louder.

Check to see if the car has any aftermarket transmission mounts. My Whiteline one makes the transmission noise very pronounced, especially while coasting.

when I had my car there was a faint sound, only noticeable under WOT.

turns out, a small part of the stock heat shield was rattling. it only vibrated during certain RPM ranges.

went away after I put headers on. went away after I sold the car.

https://www.youtube.com/watch?v=9cAH2hyn4zs

Digging up an older thread since I've also had this noise issue when decelerating at around 2000rpm. Posted a threat but received no reply so I wanted to know if you have an update on the noise.

My noise only occurs when the car is in operating temp. I have done some testing on my own to determine the noise came from the passenger engine bay area; most notably the near the coil packs. I have also taken it to a shop where they had suspected it was due to valve clearance issues. I being OCDed caved in and fix the clearance issue but the noise didn't go away. So now I have given up chasing this sound and just enjoying the car with the windows down and blasting music lol

also forgot to mention, I have gone through the same route before the valve clearance fix and changed the trans fluids with redlines but again, the noise didn't go away.

My car is fully stock too. Maybe it's the back pressure from the exhaust? Maybe an exhaust could fix it who knows...

It’s probably completely off base, but I’ve had random rattles appear under the rear of the car at various times, but always on overrun. Traced to the aftermarket exhaust vibrating. Changing out the muffler bearings (exhaust mount donuts) to STI parts reduced it. Didn’t eliminate it, but significantly improved/changed it.

Anything is possible at this point. Can't really pinpoint where the sound is coming from exactly.

The shop also did a heatshield and exhaust inspection and nothing seems to be loose. But they found that one of my header bolts was stripped and had to drill a new hole to mount it back on. So the noise could be a leak from there.

But if it isn't getting louder or quieter over time then i think its best to just leave it as is. Maybe ill throw on a louder exhaust setup to over the sound :/ Not worth the time and energy over one of many sounds coming from this engine

Sometimes this noise is caused by the unloaded gear teeth "rattling" inside the transmission or diff. I had the OEM clutch with Whiteline inserts at the trans, diff, and subframe, I noticed this noise very faintly only on occasion when decelerating between 3000-2500 rpm. However, after installing an Exedy Stage 1 clutch and OEM flywheel it got obnoxiously loud. Apparently, in my situation, the stiffer axial springs in the new disc hub was all it took to change the frequencies enough to allow this gear rattle to become more prominent throughout the entire drivetrain. A lightweight flywheel is also notorious for causing it because the reduced mass can't dampen these vibrations as easily.

Once I removed the bushing inserts from the trans and diff the noise has almost disappeared. Its still there, but MUCH quieter, virtually a non issue. Still not sure whether it was coming more from the trans or diff, but with all the searching I've done it apparently doesn't affect anything negatively. As much as I hate the idea of that, it's a somewhat common issue that never seems to actually cause problems, it just sounds like it is.

But such gear rattle always annoys as it "feels/seems like something is broken" .. i tried to live with that, but at the end gave up and reverted some bushings to have that noise gone. When i drive the car i'm minding warning indicators on dash and also abnormal noises. Even if some noise is not an issue, it introduced unneeded stressing about.