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Vibration

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110
154
Exp. Type
Autocross
Exp. Level
20+ Years
Olsburg, KS
During a warm up lap at Hallett earlier this week, I was coming into a corner and during a downshift my auto blip activated and I heard a bit of a "pop" and my engine/drivetrain started to vibrate a bit. It's completely rpm dependent, makes no difference whether the clutch is in or out, and there are no codes. I can barely feel it at idle and anything below 2k is hardly noticeable. By 3k it's pretty obvious, and I haven't revved it any harder than that. It's not getting any worse or better, everything still functions normally and there are no codes. My first thought is that something let go on the clutch and is giving it an imbalance. It would have to be in the part that's connected to the engine, as I can have it in gear with the clutch depressed and it still vibrates. I ended up driving it to a friend's place about 20 miles down the road and it's still the same. Is there anything in the engine that could have let go and caused an imbalance without affecting performance? My first plan is to pull the transmission and look at the clutch, but if I don't find anything it about has to be something internal to the engine. It's my supercharged 2018 Roush. Any ideas?
 
110
154
Exp. Type
Autocross
Exp. Level
20+ Years
Olsburg, KS
Perhaps one of the engine mounts let go?
A possibility, but it's not really acting like other broken mounts I've dealt with. I would expect engine load to change the vibration if it was a mount. It's only been old vehicles that I've dealt with mounts on in the past, though. I'll check and make sure that's not it. Thanks!
 
110
154
Exp. Type
Autocross
Exp. Level
20+ Years
Olsburg, KS
Perhaps one of the engine mounts let go?
On the other hand... Drove it slowly with an eye/ear toward detecting whether it might be a mount, and I think you're probably right. I'll try to get it confirmed tomorrow. The vibration is definitely rpm dependent, but the intensity changes slightly during loading changes. My slow crawl through a parking lot where I was on and off the clutch quite a bit made it seem like a mount is highly suspect. Thanks for your suggestion!
 
110
154
Exp. Type
Autocross
Exp. Level
20+ Years
Olsburg, KS
Well, it didn't turn out quite like I expected. Those lines on the original mount ended up just being molding/casting lines. I got the mounts changed out and nothing changed. I'll touch on the BMR mounts in a bit. As for the noise, see exhibit A below. I crawled back under the car and started feeling around for something jammed in between the engine and frame and ended up finding this rock wedged between the upper and lower transmission mounts. It was enough to sound and feel like metal to metal contact (that's a TOUGH rock!). I have no idea how long it was there or where it came from, but apparently my downshift was enough to let it get jammed between the two halves of the mount. What are the chances of that? Live and learn, I guess. As far as the BMR mounts, they definitely let more NVH through than the factory mounts. I mostly notice it at low rpm. It's worst around 1500rpm under no or very light load. Cruising down the road it seems to be less. I'll leave them in for now. I will say, changing them out is relatively easy, but ended up being very time consuming. They used mount to frame bolts that were probably an inch longer than they needed to be and were lathered in Loctite. I think the weldnuts in the K-member are probably locknuts, too. They were an absolute B!tch to get out. I rounded the head off on one of them, but was able to spot weld a flex socket to it (passenger side rear) and get it out. The original ones came out by just raising the engine up, so removing the upper mount wasn't necessary. Removing the steering shaft u-joint definitely was, though. One other thing with the mount was that when used at stock height the main bolt was too short. The nylock threads barely engaged. There are several standards for how far a bolt should stick through a bolt, and it met none of those criteria. I ended up pulling a 1/4" spacer out of it and now it looks acceptable. I'll try the new mounts for a while and see if the NVH is acceptable. Even like this it's probably still the best vehicle I have as far as NVH.


PXL_20240713_024431679.MP.jpg
 

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