DL501 catastrophic gear failure

[one_sk]

Hello everyone,

I am a long time reader of these forums from Russia (sorry for possibly quirky English, as it's not my native language). I'm an owner of a 2010 NA B8 with roughly 60k miles on the clock. The car is APR st.2+, motor+gearbox, and was mostly running fine to these days. Last year I used it extensively in autocross and track days, but in 2016 I had little spare for these activities so the car was used mostly as a grocery getter and for long distance cruising (450+ miles one way, 90-110 mph on cruise).

This was the case last weekend, when I was heading Moscow on a highway, feeling not very well because of flu, on cruise control, with my only desire being only to get home before the traffic jams start. 60 miles from the city, I've heard clunks from the tunnel, immediately turned on emergency lights and pulled over. I power cycled the car, read it out with VAS 5054a, getting some error codes typically responsible for mechatronic failure. I tried moving slowly, and heard the distinctive noise from the tunnel. I decided to not push my luck any further, and called a flatbed from Moscow to come and get me to the transmission shop.



It was really hard to believe that this had something to do with the gearbox, because the general consensus is that DL501 transmission is reliable in mechanical department, it's major quirks being the mechatronic failures. However, listening to the running car proved that the noise was coming from the tail end of the gearbox, where transfer case is residing. We removed the gearbox from the car and disassembled it for inspection, seeing quite an interesting thing:










The seventh gear got destroyed completely. If that was the second or third, I would have attributed it to autocrossing/trackdays and stage 2 power levels, but that is the gear used on highway on low load. Transmission shop guys say that this is the first case in their practice of DL501 failing so miserably. The situation is also strange because the hypoid gear oil level was perfect, there were no leaks on underside, and all the other mechanical components (Torsen transfer, front final drive, other gears, clutch basket) look perfectly okay. I have nothing to think of it other that I'm unlucky enough to have come by manufacturing defect which demonstrated itself on 60k mileage only.

What I try to achieve with this thread is to gain insight on how widespread is mechanical failure of DL501, and how true is the wide belief that mechatronic failure is the only thing to be afraid of. Please share your experience, and maybe insight on what may have lead to what we see on the pictures.

[SteveYem]

Unfortunately I do not have any experience with the S-tronic transmission so I cannot offer any advice there, but I would suggest contacting Audi Corporate and sharing these photographs with them. Even at Stage 2 power levels, I do not see why the 7th gear would have failed like that. It sure seems like it is a fluke manufacturing defect, otherwise I think we would see a lot more Stage 2 users reporting this failure.

[hodrosS42001]

Hello everyone,

I am a long time reader of these forums from Russia (sorry for possibly quirky English, as it's not my native language). I'm an owner of a 2010 NA B8 with roughly 60k miles on the clock. The car is APR st.2+, motor+gearbox, and was mostly running fine to these days. Last year I used it extensively in autocross and track days, but in 2016 I had little spare for these activities so the car was used mostly as a grocery getter and for long distance cruising (450+ miles one way, 90-110 mph on cruise).

This was the case last weekend, when I was heading Moscow on a highway, feeling not very well because of flu, on cruise control, with my only desire only to get home before the traffic jams start. 60 miles from the city, I've heard clunks from the tunnel, immediately turned on emergency lights and pulled over. I power cycled the car, read it out with VAS 5054a, getting some error codes typically responsible for mechatronic failure. I tried moving slowly, and heard the distinctive noise from the tunnel. I decided to not push my luck any further, and called a flatbed from Moscow to come and get me to the transmission shop.



It was really hard to believe that this had something to do with the gearbox, because the general consensus is that DL501 transmission is reliable in mechanical department, it's major quirks being the mechatronic failures. However, listening to the running car proved that the noise was coming from the tail end of the gearbox, where transfer case is residing. We removed the gearbox from the car and disassembled it for inspection, seeing quite an interesting thing:










The seventh gear got destroyed completely. If that was the second or third, I would have attributed it to autocrossing/trackdays and stage 2 power levels, but that is the gear used on highway on low load. Transmission shop guys say that this is the first case in their practice of DL501 failing so miserably. The situation is also strange because the hypoid gear oil level was perfect, there were no leaks on underside, and all the other mechanical components (Torsen transfer, front final drive, other gears, clutch basket) look perfectly okay. I have nothing to think of it other that I'm unlucky enough to have come by manufacturing defect which demonstrated itself on 60k mileage only.

What I try to achieve with this thread is to gain insight on how widespread is mechanical failure of DL501, and how true is the wide belief that mechatronic failure is the only think to be afraid of. Please share your experience, and maybe insight on what may have lead to what we see on the pictures.

Very interesting. I would bring this up to Audi, even being modified. They might want to know about this. I have not heard of any DL501/511 having stripped teeth in any gear.

[bmoreS4]

Very interesting. I would bring this up to Audi, even being modified. They might want to know about this. I have not heard of any DL501/511 having stripped teeth in any gear.

Thanks for reposting all of that, well done.

Anyway, OP call Audi corporate and show them pics, say nothing about your stage 2. See what they say.


Sent from my iPhone using Tapatalk

[13jfp]

Prolonged cruise in overdrive at 100 mph? That poor little gear provably overheated and failed. I doubt Audi ever durability tested the dl501 like that. The torque on that gear at 100mph going up a hill with a stage 2 tune...ouch.

[RyanJon]

Prolonged cruise in overdrive at 100 mph? That poor little gear provably overheated and failed. I doubt Audi ever durability tested the dl501 like that. The torque on that gear at 100mph going up a hill with a stage 2 tune...ouch.

So Audi, a German firm, home of the unrestricted autobahn never tested their gearbox at 100mph plus?? Hahaha! Pull the other one pal, it's a 1 off failure in a car that is designed to sit at well over 100mph all day long

[13jfp]

Real world driving for hours at a time at over 100 mph on cruise? I bet only a handful of s4 owners with stage 2 plus have done that. It will be interesting to hear how Audi responds.

[whiped]

Real world driving for hours at a time at over 100 mph on cruise? I bet only a handful of s4 owners with stage 2 plus have done that. It will be interesting to hear how Audi responds.

You think cruising at 100 mph puts more stress on it than a 120-190mph pull after driving for 4 hours?

I agree, hopefully a one off thing. As others have stated I would contact Audi Corporate and see what they say.

[13jfp]

In overdrive at 100 mph for hours the heat generated on the teeth of the failed gear would be significant without a lot of mass to dissipate it. Add in road and driveline harmonics, any vibration, or backlash from wear. Autocrossing probably had the thrust bearing on that shaft a little worn already. I totally belive it might fail under those conditions.

[13jfp]

Actual time of failure is often unrelated to the root cause of a failure. People assume that the overdrive gear is immune to failure. But if u understand the mechanical forces on it and its limitations due to its size this failure makes sense.

[13jfp]

You also have to consider the loading effects on the backside of the od gear due to engine braking in overdrive at over 100 mph if that was routinely done. It could damage a hot overdrive gear very quickly. When I used to drag race my old blown mustang i always made sure to never engine brake at high speed (got into overdrive at 120 mph). I would put it in neutral and use the brakes.

[mrmomo313]

Sorry to hear OP. I've only had the mech unit fail on my 2010 at 57k miles.

If the transmission gives any hint of issues I will sell the car immediately. It's the only part of my car I worry about.

[one_sk]

Sorry to hear OP. I've only had the mech unit fail on my 2010 at 57k miles.

If the transmission gives any hint of issues I will sell the car immediately. It's the only part of my car I worry about.

Thank you for your understanding, but this is actually not a big upset for me. These transmission shop guys are extremely inventive in ways to solve big problems with little cash, and have already found me a replacement set of gear shafts from a 10k mileage MNL box. These box was bought by a local breaker shop from an Audi dealer, which once had a habit of replacing entire gearboxes for mechatronic failure. Amazing how things can stack up in your favour after being at such odds with you a few days ago. I doubt this would hold me back for more than a single grand. What really puzzles me is the root cause of _why_ this happened in first place.

In overdrive at 100 mph for hours the heat generated on the teeth of the failed gear would be significant without a lot of mass to dissipate it. Add in road and driveline harmonics, any vibration, or backlash from wear. Autocrossing probably had the thrust bearing on that shaft a little worn already. I totally belive it might fail under those conditions.

All you say has its merit, but as I've mentioned, the bearings are all fine. The road is pristine too, it's E30 highway. Also, I'm not very good with imperial-metric conversions in my head, and 100 mph is quite an overestimate, the typical cruise speed being 140 km/h (~87mph). Nothing extraordinary, at this speed I get tailgated by Ladas all the time :)

As for cooling, all this gears are submerged in a very considerable amount of hypoid oil, which, as I've mentioned, was at perfectly good level. Quoting the shop worker, "I wouldn't have asked a question if there was little oil, but now after I've drained it and measured the level I'm really puzzled".

[bhvrdr]

Real world driving for hours at a time at over 100 mph on cruise? I bet only a handful of s4 owners with stage 2 plus have done that. It will be interesting to hear how Audi responds.

??? I know in s fl I routinely put my cc on at 94mph and I don't seem to be alone lol. Looks like the op was only doing less than 90 but yeah in germany where these cars are from 100 mph would not be a rare cruising speed depending on the area.


Sorry for your luck op. Definitely a freak occurance. I do agree it may be worthwhile to submit photos and a letter from your mechanic to audi and ask for some goodwill. Its been done for the regular engine failures the 2.0tfsi was having. Btw your English is impeccable.

Mike

[jran76]

but yeah in germany where these cars are from 100 mph would not be a rare cruising speed depending on the area.

No doubt. I've cruised for almost 3 hours straight on the autobahn at 125-130 mph (220 kph).

[Vogz]

You also have to consider the loading effects on the backside of the od gear due to engine braking in overdrive at over 100 mph if that was routinely done. It could damage a hot overdrive gear very quickly. When I used to drag race my old blown mustang i always made sure to never engine brake at high speed (got into overdrive at 120 mph). I would put it in neutral and use the brakes.

lol, do you know how ridiculous that sounds? If a gear is getting overheated in street driving then theres not enough gear oil to cool it. OP stated that gear oil level in trans was perfect. This is clearly an isolated failure due to a flaw in the gear. I doubt whomever builds these transmissions is using a magnaflux to inspect every gear. It could have looked perfect to the naked eye but had a microcrack in one of the teeth. The load that 7th would see in steady state cruise isn't something that is going to break gear teeth off. The only way I've ever seen that happen to gears was transmission shock from hard launches or hard shifts with aggressive clutches and drag tires.


Not engine braking after a drag racing pass to "save" the transmission is retarded. The trans will see zero shock (the thing that breaks gears the most) and only a fraction of the load that it saw during the 1/4 mile pass. Not only that but engine braking helps prevent brakes from fading and also keeps the oil pressure up in the engine so you aren't under-lubricating really hot internals.

[13jfp]

Wish we had the roads to drive like that in the US

[13jfp]

Op, glad to hear that getting it repaired isnt going to cost much.

[Brother Owl]

...but yeah in germany where these cars are from 100 mph would not be a rare cruising speed depending on the area.

No doubt. I've cruised for almost 3 hours straight on the autobahn at 125-130 mph (220 kph).

I've cruised I-70 @ 100-130(w/a few stabs at the govmnt limiter) for almost the entire state of Utah. Granted I'm a 6MT

Btw your English is impeccable.

Better than a lot of native english speakers on this forum... GL with repair OP, $1k repair is far better than I was thinking lol

[timzcat]

I'd be curious if all other gears and metal parts are damage free or not. All it takes is a small piece of hardened steel to land in a helical gears to tear it apart. One broken tooth leads to many broken teeth, especially on a smaller gear set.