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I purchased my 2012 P31 with a few modifications back in April of 2021. Everything seemed tip top and the PPI came back great. (stating this for background). However, during a pre-track event inspection back in February 2022 it was pointed out to me that part of the exhaust was making contact with the end of the driveshaft (near the guibo), in front of the differential. It was suggested that I keep an eye on that to see if its still happening. To that end I applied some high temp paint onto the exhaust in the affected area so that I could check later for any fresh scratches/dents/etc. Well, after a weekend at VIR I noticed fresh scratches.
This is something that I think only occurs when the car is under the stress of immense forces, such as those encountered on a race track or attacking mountain roads. I've never heard any sort of clunking/banging noise related to this, but I'm sure it's so brief and probably occurs when the engine is wailing, so if there's any associated noise it's not possible to hear it. The non-stock exhaust pieces are VRP long tube headers and mid-sections. The rear section, including pipe crossover and mufflers, are OEM. It's where the exhaust splits and curves around the differential where the contact is occuring (see attached photos). I took the car to a reputable exhaust shop and they don't believe the exhaust is the issue (though I'm not sold on analysis). It's quite secure and you have to really yank on it to get any movement. There is a little over an inch of clearance between the driveshaft component and the exhaust pipe. While at the exhaust shop we stood under the car while a technician sat in the car and revved the engine while in Drive, with his foot on the brake. No moment to suggest a problem.
I then took it to a performance shop I trust and after inspecting the car for almost an hour they were stumped. Didn't see anything amiss and suggested that I mount a GoPro under the car and try to recreate the conditions. I don't plan to track the car again soon, though might go in November. In the meantime, I took some video footage while the car was on a dynometer this past weekend (seemed like a good high stress situation). I'm not sure how conclusive the footage is. Might try hard launches/burnouts next.
As far as I know all mounts are OEM and original. Engine & transmission. Ditto all suspension & subframe bushings and exhaust hangers. The car has 86,000 miles and makes roughly 550 hp. Rear tires are 275 width Hankook RS4s. Attached to this post are photos, and 2 video links. I'd appreciate any input/advice the AMG community here has to help
It may be a confluence of events that your static 'high stress' replication attemps aren't actually replicating. Perhaps there is a bit of play in the driveshaft joint since car has 86k mileage and you were stressing it on track when you think it happened. The part you likely aren't replicating is the lateral g forces on track that could cause the exhaust to swing toward the driveshaft. So in a throttle off corner situation with high lateral g and high throttle input you may be getting contact.
They make exhaust hanger bushings that are stiffer than factory rubber that you might try, as the original rubber ones being a decade old and 86k mileage might be worn and can allow excessive movement. At one point in your dyno.video the stock exhaust hanger rubber seems to allow a lot of movement considering its just driveline forces and the car isnt actually moving. I would check driveshaft joints for wear and play (there are rubber flex discs at the joints that wear out but i am not sure how much movement they allow when worn out), and buy stiffer exhaust hangers bushings like powerflex poly isolator bushings. Both are cheap easy fixes to try first.
example: I had slight contact between my exhaust tip and the rw carbon diffuser at Daytona. It was never a problem at Sebring, PBIR or other flat tracks but on the high banking at Daytona the exhaust tip crushed the edge of the diffuser slightly so the exhaust was moving more even though car has less than 10k mileage
Last edited by Dr.Speedfellow; 10-18-2022 at 02:49 PM.
Your exhaust expands with heat, it gets longer, and your long tubes exacerbate that because they are thin tubes compared to the factory cast unit. Your factory exhaust manifold doesn't grow to that extent. When it's at its hottest it will lengthen enough to touch there when combined with the normal play in your hangers
2012 C63;1971 280SE 3.5(Sold);2023 EQS 450 SUV 4 Matic (Wife's)
I have the MBH headers and mid section with x-pipe and I believe that the VRP headers may be based on them. When I installed the x-pipe I did my best to get it as far on the mid-pipes as I could but still would have liked to get the x-pipe on a little further. In the end the installation pushed the OEM rear section of the exhaust back about half an inch. That along with the exhaust expansion with heat, as mentioned by blurred, probably pushes the exhaust another half an inch to the rear. Probably the only way to fix your issue is to figure out how to get the connections in the mid-sections of the VRP header system to move half an inch closer to the engine. Best of luck getting this issue sorted.
Thanks for the input. I'm definitely aware that on track conditions are exceedingly hard to recreate on public roads and in some cases (most, honestly) impossible. I hadn't considered the thermal expansion theory, though in this situation if the exhaust is getting longer it'll move further from the driveshaft where the clearance issue resides (edit: that was wrong). I'll start with the "low hanging fruit" and replace the exhaust hangers. Is anyone aware of AMG specific aftermarket upgrades for those? At a minimum, new OEM ones may be helpful since they won't be 10 years old.
Last edited by WolfpackC63; 10-19-2022 at 01:00 PM.
Here's a map of VIR showing where it rubs the worst. I could feel it through the car. Seemed to only occur during high lateral G left turns. (Thank God VIR is a clockwise track! hah)
I think that the exhaust moving is 100% what's going on here. Maybe modifying the hangers to pull the exhaust further away would fix this issue. Any advice/comments are welcome.
Last edited by WolfpackC63; 11-01-2022 at 04:31 PM.
My mechanic says the Guibo is fine, but I agree in that as far as just throwing parts at it the guibo is the next best (inexpensive) step.
It's not torn, but it's got some dry rot.
The giubo is the only thing affecting driveshaft runout at the end of the shaft, so if your exhaust is where it's supposed to be, it's probably the giubo.
This is assuming your subframe/diff isn't moving around on the bushings under load. Maybe point the camera at that, too.
^I actually set a new personal best. Which I didn't expect to do because my tires lost significant grip since my last visit (which I knew would happen, I street these tires). I even ran off T1 once because I couldn't stop quickly enough
Originally Posted by C43 Fun Haver
i should a tech and my foreman this video, they both went straight to the rear diff bushings and most rear hangers
Thanks for sharing; crowdsourcing can be a powerful tool! However, the rear diff isn't moving at all in the video so what made them suspect this is the issue? As to the rear hanger bushings, I'm skeptical of that being helpful. I replaced the ones shown in the video (red) and it made zero difference. I definitely appreciate the suggestions, just asking for the reasoning behind them.
^I actually set a new personal best. Which I didn't expect to do because my tires lost significant grip since my last visit (which I knew would happen, I street these tires). I even ran off T1 once because I couldn't stop quickly enough
Thanks for sharing; crowdsourcing can be a powerful tool! However, the rear diff isn't moving at all in the video so what made them suspect this is the issue? As to the rear hanger bushings, I'm skeptical of that being helpful. I replaced the ones shown in the video (red) and it made zero difference. I definitely appreciate the suggestions, just asking for the reasoning behind them.
My money is on the Giubo.
I happen to be replacing mine this weekend while installing my LSD.
Here is the original with 83k miles. I'm bending it with my weak arm and f'd-up shoulder.
I could not bend the new one anywhere near this much with my entire upper body.
Last edited by AMGSIXTHREE; 11-11-2022 at 10:42 PM.
Alright, thanks! I'll make plans to do that. And IIRC, it's fairly easy to replace the guibo?
Yep, not bad. There are eight bolts/nuts for the giubo itself. You'll need to disconnect the center support bearing bracket from the chassis to separate the driveshaft from the diff, so there's some time spent getting to that. But none of it is difficult.
@AMGSIXTHREE did you loosen and/or disconnect any exhaust pieces? I should have seen this coming, but my exhaust is so close to the end of driveshaft that I'm not getting enough clearance to slip out the old guibo.
Last edited by WolfpackC63; 11-20-2022 at 02:11 PM.
@AMGSIXTHREE did you loosen and/or disconnect any exhaust pieces? I should have seen this coming, but my exhaust is so close to the end of driveshaft that I'm not getting enough clearance to slip out the old guibo.
I replaced mine while replacing the diff, so I had the driver's side muffler off at the time.
Do you have your center support bearing disconnected? If not, then you're gonna need to. The driveshaft has a collar that slides onto the little snout on the diff's pinion flange (see pic). The shaft will have to slide about an inch forward (toward the front of the car) to separate it from the diff. And the giubo can't come out without separating them.
Once the shaft is separated from the diff you should be able to move well out of the way and have plenty of space to get the giubo out. But again, you're gonna need the center support bearing disconnected to do that.
Last edited by AMGSIXTHREE; 11-20-2022 at 07:23 PM.
^Thanks for the detailed response, and yes I have the center support bearing disconnected. But I still can't get even an inch of room between the driveshaft and the piece sticking out of the differential. There's not enough play front to rear for me to push the driveshaft (towards front of the vehicle) to have room. And I can't move the driveshaft diagonally either (toward front of the car but also downward to either side) because the exhaust is there.
Tomorrow morning I'm going to try lowering and/or disconnecting part of the exhaust. Hopefully that gives me enough room. I really do not want to have to also disconnect the front flex disc to get more freedom of movement.
10-18-2022, 10:07 AM
Exhaust Clearance Issue
