After the installation of the Milltek exhaust I was very surprised with the increase of vibration, while also surprised with how tame the exhaust sound is with the more aggressive catback without a resonator that I purchased over the one with resonator. As I put more mileage on the Mini, I begin to suspect there is minor rubber something. I thought most likely the catback muffler system must be touching something somewhere.
Jacking up the Mini and put it onto jackstands, this time I tap and wiggle the exhaust harder trying to find areas where the exhaust either come into contact with the Mini body or heat shield. It did not take long and I found that the passenger side muffler is actually pressing against the aluminum heat shield above it. Examining the design of the Milltek exhaust a bit, it became crystal clear that Milltek mufflers are hung too high despite they are much smaller than the stock counterpart. On the other muffler that is not rubbing against the heat shield the tightest spot has only about 3/8" clearance.
I thought I may need to fabricate a spacer for the inner muffler hanger in order to lower it enough to increase the clearance. I wanted to make it out of phenolic for its high temperature resistance property, as I know I have a scarp piece somewhere. Searching the house and I could not locate it. I found a piece of Delrin instead. It should work since being the spacer for the hangers, it is not exposed to direct radiant heat of the muffler (on the track).
I was preparing to make a 1/4" spacer out of this piece of Delrin for the muffler hanger
As there are two hangers on each muffler I first try to determine which is the hanger that pull the muffler the hardest up against the underbelly of the Mini. This can only be determined by loosening the nuts of the two hanger brackets.
the area marked in red is where the passenger side muffler comes into contact with the aluminum heat shield
Interestingly of the two hangers (inner and outer), it is the outer hanger that exerts most force to pull the muffler up against the underbelly. Once the outer hanger nuts are remove I can pull the muffler lower enough to gain sufficient clearance. Since the hanger has a steel bar I can bend the bar to lower the engaging point of the silicone rubber hanger, instead of going through the trouble of making a spacer for the bracket. Good!
the outside hanger on the passenger side muffler
the inner hanger is fine despite it is closest to the area of interference
I clamped the outer hanger into the vice - had to think carefully which direction to bend in order to lower the hanger
checked twice (actually three times) and bended once; I estimated the ballpark amount of bend needed; I used this crescent wrench to bend the hanger arm
I just eyeballed how much to bend, and my first try was perfect! After tightening all the fasteners I shook the catback exhaust hard and even pound on it against the underbelly and I could not get the exhaust to touch anything. Time to go for a test drive to be sure.
WTF, it seems the problem is now worst. Something does not make sense. I pulled onto the driveway and shake the tail pipes hard and I could not get the exhaust to contact the body of the car. Yet even on a relatively smooth road surface I am getting very troublesome knocks.
Up onto the jack stands the Mini for the 3th time this weekend, and I was determine to get to the bottom of this before the rain comes at 4 PM today. Crawled under the Mini and repeated the examination that I have done before. This time I am absolutely sure the knock was not due to the exhaust. It just happened that the Milltek exhaust rubbing problem is masking this new knocking sound that is likely due to something in the rear suspension. I have two problems and one was fixed.
I would not get into all the things that I was able to quickly eliminated as suspects, with the help of a rubber mallet. Next I used a piece of 2x4 as lever, I compressed the left and right side of the rear suspensions by tugging up at the trailing arms. I can hear the noise only on the driver side. Good. I begun to home in to the problem. Now I needed a helper to tug on the 2x4 while I listen and feel the suspension. My neighbor was gracious to come and help. The rain was forecasted to arrive by 4 pm, so failure is not an option.
the piece of 2x4 used to compress the suspension
It did not take long for me to locate the source of the knocking sound. Of course tugging on the trailing arm the sound does not sound like the knocks I hear while driving, but I knew what to look for. I ended up using my hand to feel where the slight click came from. It is the upper joint of the drop link for the rear sway bar. The nut has worked slight loose. Turning it with a wrench confirm it has loosen by about a turn. We cheered for our teamwork in so rapidly locating the problem. I was so confident that was the cause that I immediately put the wheels back on, lower the Mini off the jack stands and went for a test drive. No more knocking and no more rattles from the muffler. This is a problem I would not want to leave it unattended to right away. I am very please that the rubbing issue of the Milltek muffler is resolved. In retrospect much of the increase in vibration was due to the passenger side muffler pressing tightly against the heat shield.
I think the size of the rear sway bar has a lot to do with the nut came loose. The 22mm bar that I installed over the factory 16mm bar put much more stress on the drop links. If it come loose again I would add a dab of red Loctite.
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