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  #1  
Old 18th August 2015, 05:18 AM
AndrewT AndrewT is offline
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Default Driveline noise on decelleration

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.
http://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.
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  #2  
Old 18th August 2015, 09:22 AM
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duncanm duncanm is offline
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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.
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Old 18th August 2015, 10:36 AM
AndrewT AndrewT is offline
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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.
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Old 18th August 2015, 01:58 PM
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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 !
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Old 18th August 2015, 11:33 PM
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Quote:
Originally Posted by jf1sf5 View Post
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?
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Old 19th August 2015, 08:50 AM
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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...
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Old 26th August 2015, 10:03 AM
BenLukkie BenLukkie is offline
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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..
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Old 26th August 2015, 08:56 PM
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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.. :D
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Old 31st August 2015, 10:08 AM
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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
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Old 14th September 2015, 10:42 AM
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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
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