Trying to Diagnose Transmission Clunking Noise

[Smash]

I've looked all over the place for info on this, but no luck finding a clear answer so far.

My transmission seems to have developed a bit of a clunk when setting off and when getting back on throttle after coasting. If I'm in D and I let the car creep first, there is no clunk when I apply throttle. However, if I take my foot off the brake at a standstill and go right to the throttle, even light application results in a big clunk which you can hear and feel through the floor.

The same thing happens when I get back on the throttle after braking and coasting. I've had to start very gently tapping the throttle to allow everything to re-engage before getting back on the throttle properly to prevent the clunk from happening.

The clunk sounds a lot like a metallic 'thunk' and it sort of feels like the clutch is taking too long to engage and is then suddenly kicking in which causes the whole car to jerk or as if there's a lot of slack suddenly being taken up by the driveline.

Once in motion, the car and gearbox are absolutely perfect. No slow shifts or weird behaviour at all. Nice and smooth.

The car is on 36k miles and has been well looked after (though its relatively new to me). The gearbox and haldex were last serviced in 2019 (about 3000 miles ago). The clunking issue was not there when I got the car and seems to be getting a bit worse over time. I have launched the car twice since I got it and I think that may be where it started. The car has a forge intercooler and milltek exhaust so its a little up on stock HP.

It's worth mentioning as well that I had an inner CV joint fail a while back and I replaced the whole FL driveshaft which fixed the issue (car was juddering really bad on throttle). The FR driveshaft has not been replaced yet, doesn't seem to have any issues, but I have one ready to go in. I figure I may as well do both, to keep everything 'even' and on the same maintenance schedule. The new ones are much beefier looking too.

So, my initial thoughts are that either an engine or trans mount has failed/is failing. I know its a common issue and I know this car has been sat in dry storage for a long time which may have caused the mounts to get brittle. I've also read that low or bad oil in the gearbox can generate similar symptoms, but it was serviced not long ago, there's no visible oil leaks and the gearbox is otherwise perfect once the car is in motion.

Is there anything else that I should look? What's the best way to check the gearbox/engine mounts?

Thanks all.

 

[dave_beastttt]

I've looked all over the place for info on this, but no luck finding a clear answer so far.

My transmission seems to have developed a bit of a clunk when setting off and when getting back on throttle after coasting. If I'm in D and I let the car creep first, there is no clunk when I apply throttle. However, if I take my foot off the brake at a standstill and go right to the throttle, even light application results in a big clunk which you can hear and feel through the floor.

The same thing happens when I get back on the throttle after braking and coasting. I've had to start very gently tapping the throttle to allow everything to re-engage before getting back on the throttle properly to prevent the clunk from happening.

The clunk sounds a lot like a metallic 'thunk' and it sort of feels like the clutch is taking too long to engage and is then suddenly kicking in which causes the whole car to jerk or as if there's a lot of slack suddenly being taken up by the driveline.

Once in motion, the car and gearbox are absolutely perfect. No slow shifts or weird behaviour at all. Nice and smooth.

The car is on 36k miles and has been well looked after (though its relatively new to me). The gearbox and haldex were last serviced in 2019 (about 3000 miles ago). The clunking issue was not there when I got the car and seems to be getting a bit worse over time. I have launched the car twice since I got it and I think that may be where it started. The car has a forge intercooler and milltek exhaust so its a little up on stock HP.

It's worth mentioning as well that I had an inner CV joint fail a while back and I replaced the whole FL driveshaft which fixed the issue (car was juddering really bad on throttle). The FR driveshaft has not been replaced yet, doesn't seem to have any issues, but I have one ready to go in. I figure I may as well do both, to keep everything 'even' and on the same maintenance schedule. The new ones are much beefier looking too.

So, my initial thoughts are that either an engine or trans mount has failed/is failing. I know its a common issue and I know this car has been sat in dry storage for a long time which may have caused the mounts to get brittle. I've also read that low or bad oil in the gearbox can generate similar symptoms, but it was serviced not long ago, there's no visible oil leaks and the gearbox is otherwise perfect once the car is in motion.

Is there anything else that I should look? What's the best way to check the gearbox/engine mounts?

Thanks all.

Try this, with ignition off, depress the accelerator fully, then switch the ignition on but don't start the car. Keep the accelerator depressed for at least 30 seconds, then release, start the car normally and go for a short drive. This should reset the clutches.

 

[Smash]

Try this, with ignition off, depress the accelerator fully, then switch the ignition on but don't start the car. Keep the accelerator depressed for at least 30 seconds, then release, start the car normally and go for a short drive. This should reset the clutches.

Thanks for the tip. I gave this a try today and it actually improved things quite a bit. Pulling away is still jerky, but not as violent as before. Shifting in general is snappier and when I brake > coast > throttle it's significantly smoother.

The issue is still there, but it's a lot more forgiving now. I have to be a lot faster with my feet to get it to clunk. It feels as though the clutches are engaging a lot quicker than before and so it's taking up the slack before I get back on the throttle most of the time.

This (I think) reinforces my theory that it's the dogbone mount that needs sorting. Before I was convinced it was totally fubar'd, but now I think it might just need an insert to stiffen it up just a little.

 

[Smash]

So update on this;

After a few more regular drives, the issue started to come back again until it ended up pretty much back to square one. I assume this is down to the gearbox gradually trying to adjust to the drivetrain slop and thus it gets progressively worse over time.

As per my original post, I finally got around to installing my other front axle (driver side), front brakes and I got a good look at the dogbone mount. Straight away, it seemed very apparent that the dogbone mount is the issue. The rubber is cracking and there are visible marks where the central rubber mount has made contact with the rubber circumference. It's also very easy to wiggle the mount around with a tiny bit of leverage (like a screwdriver's worth). I didn't have the parts to fix it so I went ahead an ordered a PowerFlex yellow insert and will report back when it arrives. I figure that I may as well try the 5 minute fix and see how that fairs before I commit to a subframe-out job to replace the OEM mounts.

The new front driveshaft (which now matches the new one on other side) made quite a significant different on its own. The old driveshaft felt relatively fine - especially compared to the other one I replaced which had definitely failed - but it had a bit of rotational slack to it. I believe this rotational slack along with the worn dogbone mount were the source of the massive clunk. Basically the driveshaft suddenly taking up the slack and sending a shockwave into the dogbone mount which bottoms it out. Since replacing the driveshaft, I don't think I can get it to clunk at all now. There's still a slight feeling of slop which I am very confident will be eliminated by the PowerFlex insert, but no more fancy footwork required to get a smooth drive out of it. I have a feeling I will have this thing feeling absolutely brand new again soon.

Not sure when the PowerFlex insert will arrive, but hopefully this week so I can throw it in on the weekend. Either way, I'll post my findings when I can.

 

[dave_beastttt]

Yep, that bush is Jacobs mate (cream crackered)

 

[Smash]

So an update;

I finally got around to fitting the Powerflex (yellow) insert on the weekend. It was a battle getting it in because clearly the OEM mount had shifted around so much that it no longer settles in the center so the fitment is extremely tight on one end vs the other. Anyway I got it in and seated eventually. Unfortunately, it hasn't made much of a difference. It feels slightly less likely to clunk when going from brakes > coast > drive when in motion, but that's about it. I also did another gearbox reset (as per @dave_beastttt's post) and there was no change.

I certainly feel a new sense of rigidity and there's noticeably more vibration through the cabin when in reverse which suggests the mount is indeed solid now, so now I'm at a bit of a loss.

Is it possible that the OEM rubber bushes are still the issue and the insert just isn't enough to solve the problem?

Is there something else like the dogbone itself that could be worn out/in need of replacement? Top engine mounts maybe? The clunk is still very obviously coming from the front end and from some sort of drivetrain slop.

Could it be that the brand new drive axles I installed are shot already and they're actually the culprit?

Or is there something in the front diff that could be amiss?

I really don't think the gearbox is the issue because as mentioned, it shifts beautifully everywhere else. It's only when the drive kicks in after being in neutral when it happens.

Help is greatly appreciated!

 

[flybynite]

First thing I would do is change the oils, just because there is a record does not mean it was done. Take it somewhere you trust or DIY. Front and rear diffs, Haldex and DSG. Don't rely on a dealer they have been known to skip difficult stuff that is hard to check. Ask me how I know.

Try and see (preferably measure) what comes out, tells you a lot.

Front transfer/bevel box is weak on RS3s of all ages and only now been given a 20K service interval on the 8Y. The oil gets old or evaporates and the bearings wear. The eccentric movement and low oil trashes the bevel gear. The front drive axles then have a lot of play on the bevel box end and won't last.

The fact the inner CV joint failed sounds warning bells to me. Worth checking

 

[Smash]

First thing I would do is change the oils, just because there is a record does not mean it was done. Take it somewhere you trust or DIY. Front and rear diffs, Haldex and DSG. Don't rely on a dealer they have been known to skip difficult stuff that is hard to check. Ask me how I know.

Try and see (preferably measure) what comes out, tells you a lot.

Front transfer/bevel box is weak on RS3s of all ages and only now been given a 20K service interval on the 8Y. The oil gets old or evaporates and the bearings wear. The eccentric movement and low oil trashes the bevel gear. The front drive axles then have a lot of play on the bevel box end and won't last.

The fact the inner CV joint failed sounds warning bells to me. Worth checking

Thanks for info, really appreciate it. There's definitely no places anywhere near me that I would trust as far as I could throw, so I'll definitely be going the DIY route when it comes to oil changes.

Very interesting point about the transfer/bevel box. I did think it was a bit weird that both front drive axles were in bad shape (one pretty much exploded) on such low miles. It has been known to do some weird noises when maneuvering at slow speeds too, which I assume could also be a symptom?

I'll do a deep dive into that and report back.

 

[Smash]

@flybynite I did a whole bunch of reading about the bevel box and I'm not so sure that is the issue. It seems like the common symptoms with those are a whining or constant clunking noise whereas I have one solid thud when pulling away from a stop or when specifically braking and then getting back on throttle whilst moving. In all other scenarios, the driveline feels perfect. The shifts are smooth and fast, no rattles or vibrations anywhere (except 75-80mph because my wheel's need re-balancing). Seems to get worse when the car gets warmer too.

I think given the condition of the rubber in the lower gearbox mount, there's a good chance the upper mounts are gone too. Even if it's not the source of the issue, they need doing anyway, so I'm going to get a whole replacement kit. At least I can definitively rule out engine mounts then.

 

[flybynite]

I did a whole bunch of reading about the bevel box and I'm not so sure that is the issue. It seems like the common symptoms with those are a whining or constant clunking noise whereas I have one solid thud when pulling away from a stop or when specifically braking and then getting back on throttle whilst moving. In all other scenarios, the driveline feels perfect. The shifts are smooth and fast, no rattles or vibrations anywhere (except 75-80mph because my wheel's need re-balancing). Seems to get worse when the car gets warmer too.

Just be aware many talking about bevel box failure are talking about failure of the actual bevel gear itself. As far as I can see it is often the bearing that goes first. If the bearing goes and the bevel gear is still intact the gear will be loose and have too much backlash. That will thud on changes but be quiet on the move Driving it like this eventually destroys the gear with all the catastrophic noises.

It is easy to check on a ramp to see if the inner joint has any play on the gearbox side.

it still could be the engine mounts, replacing them is not a bad thing to do anyway, these engines do move around when you lean on them.

I would still do the oils though, have a look what came out of my FL!

Which oil for transfer/bevel box?

As title really. The 8Y and RSQ3 have a service interval on the oil in the transfer box. The 8V doesn't, it is supposed to be lifetime, but the oil can evap and ... well, we should probably change the oil reguarly based on what I have scoured off the forums. Anyone know which oil it'll take...

www.audi-sport.net

 

[Smash]

Just be aware many talking about bevel box failure are talking about failure of the actual bevel gear itself. As far as I can see it is often the bearing that goes first. If the bearing goes and the bevel gear is still intact the gear will be loose and have too much backlash. That will thud on changes but be quiet on the move Driving it like this eventually destroys the gear with all the catastrophic noises.

It is easy to check on a ramp to see if the inner joint has any play on the gearbox side.

it still could be the engine mounts, replacing them is not a bad thing to do anyway, these engines do move around when you lean on them.

I would still do the oils though, have a look what came out of my FL!

Which oil for transfer/bevel box?

As title really. The 8Y and RSQ3 have a service interval on the oil in the transfer box. The 8V doesn't, it is supposed to be lifetime, but the oil can evap and ... well, we should probably change the oil reguarly based on what I have scoured off the forums. Anyone know which oil it'll take...

www.audi-sport.net

Really appreciate the quick responses, cheers man.

Understood on the bearing vs the gear itself. I still think I'd experience more consistent symptoms if that was the issue. I don't get any complaints from the gears or the front end since doing both front axles and I only get a single clunk when the torque from the engine gets translated into wheel movement and I may have once or twice heard it faintly clunk right as I come to a stop after braking hard. I would've thought that the bevel box would cause a clunk slightly after the front wheels begin moving as it's their movement which gets translated into the prop shaft to the rear. The clunk would be from the bevel gear's bearing as it takes up the slack, correct? My clunk is distinctly happening as the engine's torque goes into the front wheels. It's foot down and then a clunk as the wheels begin moving. To me, everything points towards engine mounts.

I had a look at the top gearbox mount today and noticed that in neutral with the car off, the two halfs of the mount aren't squared up with each other. That seems to confirm that the top mounts are FUBAR'd as well. I've ordered powerflex inserts for both top mounts and that will be my next move. They look to be a bit of a pain to get to (particularly the one under the coolant reservoir) so it'll probably be a weekend job. Maybe I can get it in without removing the mount entirely, but that seems like very wishful thinking.

 

[dave_beastttt]

Have you done a basic adaption setting on the gearbox using Vagcom?

DQ500 DSG 7-speed transmission - Ross-Tech Wiki

wiki.ross-tech.com

 

[Smash]

Have you done a basic adaption setting on the gearbox using Vagcom?

I have not as I would need to find somewhere I trust and that have access to the software, but I it's something I wanted to look into once I have sorted the engine mounts. The clutch engagement does feel a little sharper than it should be when setting off and that's probably causing more of a shock to go through the mounts which (I hope) are the cause of the clunk.

I'm guessing with dodgy mounts or CVs, the extra slack tricks the gearbox into thinking the wheels (and therefore the car) are moving before they actually are. This would cause the clutch to engage 'sooner' than it should and results in a less than smooth acceleration. Like letting the clutch out too fast on a manual. As far as I understand it, it would be a smart idea to do the adaption because of how much slack has been/will be removed by the inserts and new axles. Does that sound right?

 

[Smash]

So this week I installed the Powerflex upper mount insert (on the transmission side) and the issue has finally been fixed!

Not only the clunk when setting off, but clunks I didn't even realise were happening over particularly rough patches of road are entirely gone. It's a difficult sensation to describe, but the whole car just feels super sharp and tight now. Very relieved that the issue wasn't something more expensive and that I can finally enjoy driving it to the fullest again. Thank you guys for the help and advice along the way. Hopefully this thread will be helpful to others in the future.

Now, on a slightly less good note, I did not install an insert on the opposite side upper mount. Long story short, Powerflex messed up the information on their site which lead to me ordering the wrong part. I inquired, they changed the information on the site, and then told me I was in the wrong. Unfortunately for them, I had taken screenshots of the page literally that morning which proved they had retroactively changed the info. Needless to say I am getting a full refund and have since ordered the correct part.

I'll be adding the inserts to the other side when they arrive. The car feels great, but if 2 out of the 3 mounts were knackered, it only makes sense to do the other one as well.

 

[flybynite]

Very relieved that the issue wasn't something more expensive and that I can finally enjoy driving it to the fullest again.

Glad you found the problem and it wasn't the dreaded gearbox issue.

I would still change the oils though.