Driveline noise on decelleration

[AndrewT]

Hi all,

I'm just test driving my L series now that it's "just" to a state that it will move under it's own steam (build thread coming sometime soon).

As part of ironing out teething issues, I'm Dealing with a noise I'd rather not have.

Basically the driveline works perfectly, but when I back off the power, but still keep just a tiny bit of accelerator on (but still decelerating), I get a noise.

It gets worse the higher gear I am in.

It is a pretty horrible "grinding" "metal on metal" "rattling" noise coming from around the gearstick / centre diff area.

It's quite prevalent at the moment as I have no carpet, no sound deadening, and no gearstick surround at all (can see the road). That being said, it's not normal and shouldn't be there.

The driveline setup is:
- SF Forester gearbox (I drove it in the stock SF Forester before removing it, the noise was definitely not there). Has not been split, at least not since I've had it.
- Original SF Forester flywheel (from the same Forester donor vehicle), but I had had it skimmed before installing
- EXEDY "heavy duty" clutch pressure plate (brand new...the part number kit to suit SF Forester)
- EXEDY clutch disk (brand new, came in the above kit)
- Brand new thrust and spigot bearings, also came in the above kit
- I greased the input shaft for the thrust bearing to slide properly on
- I have installed a DCCD to the rear of the SF gearbox (including it's full DCCD housing) from a 5spd sti gearbox of some sort - NO controller installed yet.

I've thought about it, and also discussed briefly with Doug at Stechnic.

A few thoughts so far:

- Something rubbing on the driveline
I'm quite confident this isn't the case.

- "Heavy Duty" clutches, especially EXEDY ones are known to cause this exact issue.
https://i.imgur.com/djyzQMn.jpg
Apparently the springs don't dampen properly, something like that. I sure hope this isn't it because I really do need a "heavy duty" clutch and also I'm not too keen on buying another one as this one is litterally brand new.

- Lightened flywheel issues
These are also known to add to this noise issue. However this isn't applicable to me. Sure mine is skimmed, but the amount of metal removed is negligible to the weight.

- Spigot bearing bad
I don't think this is the case. Normally with a bad spigot bearing you hear a few bad noises at idle with the clutch out. Nothing like that, at idle everything seems totally perfect. Also it's brand new.

- Thrust bearing bad
I don't think this is the case. Normally you'd hear noises at idle when operating the clutch in and out. Nothing like that. Also it's brand new.

- Bad input bearing in gearbox.
I don't think this is the case unless it somehow went bad in between taking it out of the Forester and putting it in this case. There was no noise in the Forester.

- Bad bearing in the DCCD centre
I suppose this is a possibility. The seller didn't mention anything about it being shoddy but to be honest I didn't really spend any time inspecting the bearings before I put it on the gearbox. He would have had it in a very loud WRX so maybe he couldn't hear it.

- No DCCD controller
I do have a controller (DCCD Pro full manual) but haven't installed it yet. I have been told that partially locking the centre diff using the controller will reduce this noise. Okay that's fine, but I should be able to drive around with the dccd off without there being horrible noises. Sure this might help to reduce it but I don't see that as a solution.

- Tyre pressures
I've heard of people increasing or reducing tyre pressures on the back tyres VS front tyres to help with this. I think this relates to the DCCD controller thoughts above. This might increase loading on the centre diff a bit and perhaps reduce the noise, but I don't see that as a solution either.

- Bad tailshaft alignment
I've been told this could cause it. This is a possibility. My car has 2" lift, and I do have the little spacers on the centre bearing to space it down, but looking at it, it would actualy be more alligned if those weren't there. The rear end of my car (the K frame) actually doesn't have any lift blocks, it's at the original mounting location - the car just has 2" spacers on top of the rear shockies. I should try removing the tailshaft centre bearing spacers and see if it makes a difference.

- Bad tailshaft uni joints
Definitely not. This is a brand new tailshaft I've had made up, including both tubes replaced, yolk replaced, every single uni joint replaced (with replaceable holden units). The only thing which is from the original tailshaft is the centre bearing.

- Bad tailshaft centre bearing
I suppose it's a possibility but I don't think it's likely. The tailshaft place said it was in good condition and it seemed to spin around fine.

- Some kind of issue with the rear end (rear diff, driveshafts)
Maybe.


The clutch works really well. Smooth engagement, no shuddering, great pedal feed. I'm really happy with it. It's literally just this noise.


Something else to note. I had the exact same issue in a totally different car (the previous monsterwagon L series). That setup was:
- EJ20G RSturbo 5speed gearbox
- "Heavy duty" clutch (not a name brand, it was from an old-school clutch specialist workshop place)
- Skimmed flywheel (the standard turbo flywheel)
- Custom tailshaft, with good uni joints
I never actually spent the time to resolve it in that car. I did swap the rear diff for one from a wrecked Liberty (grandpa spec, no thrashing) and it made no difference at all. Interestingly I have carried that whole K frame (diff and driveshafts) over into this car.


Anyway, I'll be buggered if I'm going to put up with this noise this time around. Would really like to find the culprit, but I don't really want to play an expensive "process of elimination game"!

Looking forward to any further thoughts or experiences you guys may have


cheers.

 

[duncanm]

Exhaust heat shields clear of the prop shaft? Check carefully for clearance and scratches

I had a terrible grinding noise on deceleration once, and it turned out to be the heat shield just scraping the shaft - only very minor marks on it - the whole thing acted like a big resonating plate and made it sound like something terminal in the rear of the box.

 

[AndrewT]

Nah nothing like that, pretty sure everything is well clear.
Had a good 20 min drive just now, it does it basically above about 60km/h and is actually happening even with the clutch fully depressed while coasting along. Worse the faster I'm going.
Also feels like there is a fair bit of "slack" in the rear end. Wish I had some spare rear shafts to try out.

 

[jf1sf5]

Sounds like a rear diff problem…like too much play between the pinion and the crown because the pinion shaft has probably some longitudinal play.

Good luck !

 

[AndrewT]

Sounds like a rear diff problem…like too much play between the pinion and the crown because the pinion shaft has probably some longitudinal play.

Good luck !

You know what I'm thinking the same thing now. Late last night I jacked up the rear end to get the rear wheels off the ground. Rotating the tailshaft back and forward a little by hand, and grabbing hold of the rear inner CV cups with my other hand, there is definitely some play there. The CV cups on both sides can rotate a good few mm before the "slack" is taken up. The cups could be loose on the diff's stub axels I suppose, but this seems unlikely. I need to take the cups off and see if the stubs themselves have play in relation to the tailshaft - this would definitely prove an issue in the diff. I imagine it should really have ZERO play as standard.
I wonder, does this mean a part of the diff is actually worn out / cactus? Or would it just require adjustment?

 

[jf1sf5]

Its not an easy fix…you have to take the rear diff off, open it, take the pinion shaft out, put new shims on the pinion shaft that give you the back lash (they are compressible and you can't use them twice), reassemble the diff and do the back lash between pinion and crown (0,13-0'18 mm play) and you're done…

Best is to get another diff from a wrecker...

 

[BenLukkie]

Had/have exactly the same.. Exedy clutches rattle pretty bad (4 springs inside the clutchplate chatter on desceleration) Worse when using an uprated gearbox bracket. Mine rattles quite a lot, but after 7 months I don't hear it anymore. It's there, but it doesn't bother me. I was about to pull the box when I read on Nasioc all exedy clutches chatter..

 

[Robbks]

Are the tailshaft uni's in the correct orientation? (90' offset from each other?)
Tailshaft Centre bearing (although usually sounds like a midget with a hammer bashing the floor)
Quote possibly output bearings in the extension housing.
Rear diff as discussed
or that ****ty Exedy clutch..

 

[taza]

I have about 1/4 turn in rotation in the rear wheels in my Forester with the back end jacked up.. Heaps of slope and you certainly feel the jolting when driving.. Been doing it for the past 50k km. I'm used to it so any normal car feels super smooth haha

 

[El_Freddo]

Dead driveshaft - someone's "flipped" a drive shaft from one side to the other. I know this as I did it on Ruby Scoo. Nice and quiet on acceleration, terrible metal on metal grinding noise when decelerating. It was the front shafts that I flipped. A new set sorted the noise out

Cheers

Bennie

 

[AndrewT]

You sound very confident ElFreddo, that's good...although I used to have the exact same noise in Monsterwagon and that had no front shafts at all at the time.
Fyi I installed two brand new rear shafts and no change at all.

Admittedly the front shafts I'm using are old ones - no clicks on turning etc but I guess they could have other issues. Guess I will look at getting a pair of new front shafts - bit annoying throwing money at it tho.

I just had a look at the centre bearing of the tailshaft. Looks like it will actually be at a much better angle if I remove the little liftkit blocks from it entirely. Trouble is that makes the tailshaft foul on the SF forester shifter linkage - I'll have to modify my custom mount for that to sit it further up in the cabin. Worth a try I guess.

 

[AndrewT]

Actually come to think of it, the front shafts came from the same donor SF forester that the gearbox did. The Forester didn't have this issue when I test drove it, I'm sure i'd have noticed. Perhaps they are worn and I happened to install them to this car the other way around (left to right).

 

[El_Freddo]

Nah if you had the noise without front shafts in the issue won't be drive shafts!

Back to square one

Cheers

Bennie

 

[AndrewT]

That was with the RWD setup in the 6" lift monsterwagon tho.

Anyways, I think this is solved now, just had a test drive a minute ago and the noise is all but gone, just a teency bit if you listen very hard.
It was the tailshaft centre bearing position.
I had it spaced down with the ~1" blocks as part of my 2" lift kit.
But looking at the tailshaft, this put it at an odd angle. I think because my rear K frame isn't actually spaced down at all, only my rear struts.
So I removed the centre bearing blocks and bolted it up at stock location. This fouled my EJ gear shifter so I had to re-do my custom mount for that too.
So yeah, instant change, no noise at all which I'd call out of the ordinary!

I do have two brand new front driveshafts being delivered this week now, but oh well, good to have as spares lol.

 

[Ratbag]

^ good to hear that you have finally found the cause, Andrew :biggrin:.

These things can be very hard to track down, and extremely bloody annoying!

 

[AndrewT]

Such a small change to make a big difference. I would have thought the uni joints and centre bearing mount itself would be able to easily soak up a bit of angle but the grinding noise was just terrible!

 

[El_Freddo]

So what was grinding?

The centre bearing makes sense, too much angle on the first part of the tail shaft without the matching angle made at the centre bearing could have things contacting each other, creating that grinding sound.

Any marks to indicate metal on metal contact?

Cheers

Bennie

 

[AndrewT]

I don't think it was centre bearing, based on having the exact same noise in the previous Monsterwagon which was running RWD with a single piece tailshaft - no centre bearing. Also when I had this tailshaft built, the centre bearing is literally the only piece remaining from the old shaft, and they inspected it saying it was perfectly good.
So maybe the uni joints, but perhaps not as they are brand new and very robust holden jobbies in this shaft now.
No visible evidence I can see from under, but I'm not going to be pulling things out for a very close look at this stage.

Maybe something strange like (thinking "out loud" here) perhaps the extra angle on the centre bearing or unis was creating a sort of "drag" on the tailshaft, which was causing a backlash type issue with the centre diff? The noise certainly sounded very much like it was coming from that area of the gearbox.

I'm happy for the time being anyway. I was going ahead finishing the rest of the build anyway so technically this wasn't holding me up, but I'm very happy to be progressing without this bugbear now!

 

[pontoontodd]

Bumping this thread as I'm having a similar problem. I have a 1999 Legacy Outback with 5MT and an EZ30 swap. Recently first gear lost a tooth. Found a dual range 5MT. Seller had mentioned the brass synchro ring for high range was bad, got a replacement for that. Needle bearing inside that gear looked like it had been overheated, replaced that. I think there was some preload on the input shaft. Had to shim out the input shaft a bit more than it was and then everything seemed to assemble and spin freely. Works great, shifts smoothly. After maybe 50 miles it started making a scraping noise. The noise comes and goes, bad for a minute or so, then quiet for a little while. Mainly makes noise when engine braking or light acceleration. Anything over about 1/4 throttle makes no noise, definitely load dependent. There has also been a squealing noise a few times when accelerating hard, usually in second gear. Driven it about 500 miles now, noise isn't getting noticeably better or worse. Didn't see any shiny spots on the propshaft from rubbing. Thoughts?

 

[duncanm]

My first thoughts were 'propshaft rubbing on heat shields' until I read your last sentence.

That being said - check again for any tiny scratch. When my diff bushes collapsed (*), the prop shaft started rubbing on the heat shield right at the back edge and it made all sorts of weird scrapy noises on deceleration. It only rubbed a tiny bit, but the shield amplified it enormously.

It was fairly obvious with some thought -- as at low speeds, the scraping was modulating with speed (not engine revs), and much faster (say 4.11x) wheel speed.

(*) - only realised many months later after I'd bent the shield up a bit out of the way.