Strange NVH issue after clutch change
 

Guys,

I have a strange noise and vibration after a clutch change and I can’t figure out the source so I thought I’d throw it out there to see if someone has experienced this before. Here goes:

A little while ago I had the clutch in my FD changed from an OE clutch to an Exedy stage 1 HD organic sprung clutch. The reason I had the work done in the first place was that the release bearing was noisy and I thought as long as I was in there to fix that I may as well change the clutch…and as long as I was changing the clutch I might as well put a stronger unit in.

During the work, the shop pulled the flywheel to have it resurfaced and discovered that the flywheel that was on my car was an RX8 unit (installed by some previous owner). They had a good used FD flywheel so I bought this and had it installed.

Here is the issue: Ever since the clutch/flywheel work, whenever I accelerate from a stop, or low speed cruise, there is a loud rattle/resonance coming from what seems to be the right side of the car, behind the engine. It sounds just like an exhaust pipe that is contacting a frame rail – like a metallic vibration that is in concert with the exhaust sound as the car accelerates. But, the exhaust is connected properly, all the exhaust mounts are intact and if the exhaust is moved around by hand nothing comes into contact. I thought that the catalyst might have a broken substrate that had some kind of freak resonance when hot, so I installed a low mileage unit replacement – but of course this did not make any difference whatsoever so the cat was fine.

Before the clutch/flywheel work, the car was very smooth when driving and had great NVH even with the RX8 flywheel (that I did not know about). The car has an Apexi Noir catback with OEM main cat and JDM OEM downpipe, and new OEM engine mounts. It was pretty quiet before this problem came up, the only problem was the noisy release bearing. The new clutch itself works great, and the engine is very smooth when free revved in neutral. It just has this loud noise and vibration when accelerating and driving. I have got to think that something is shifting when the engine is outputting some torque, and coming into contact but I can’t find any problem area. This noise was present from the very first acceleration as I drove home from the shop, in retrospect I should have turned around immediately and had them look at it but it was not possible to take the extra time, and at that point I thought it would be an easy fix once I had a look at the car. But this has proved to not be the case.

The work was done by a well known and respected RX7 shop here in SoCal, I am reaching out to them and will bring it in to be checked out hopefully in the next couple of weeks. In the meantime, I thought I’d post this to see if someone had any thoughts. I know it is hard to come up with NVH diagnosis over the internet, though…

Most likely the exhaust or a heat shield is touching. Lot of that stuff can get bent while pulling/reinstalling the trans. Or, they did something silly like install one of the cross braces for the trans tunnel upside down - seen that before, the rear one will touch the cat back if installed upside down.

Dale

Thanks for the ideas, Dale.

I will check the braces, the rear one may be installed correctly since the rear metal heat shield is bolted to it...I imagine that if the rear one was backwards the brace bolt holes would not line up with the heat shield?

Is it possible to install the middle brace above the catalyst backwards? If this is possible and it positions the brace lower relative to the cat then this might be the issue since this seems to be about the location where the noise and vibration is coming from.

I wiggled the exhaust system around by hand and nothing came in contact but I am sure that the engine is torquing on the mounts under load and the exhaust could very well be rising up and contacting something (even if I can't get any noise to replicate by manually moving the exhaust pipe from under the car).

Yeah, you really have to get under there, hammer around, wiggle, beat on things, etc. to find it.

The brace I'm talking about is under the first part of the cat-back if memory serves. Each brace has an arrow showing install direction. It would be fairly obvious, though - the exhaust would be resting against the brace.

Dale

He is talking about the silver one under the midpipe in this picture

https://cimg1.ibsrv.net/gimg/www.rx7...469b149cbf.jpg

Thanks, I will check this weekend but I am afraid it might not be something as simple and easy to fix as a bracket...since my heat shields are attached and it seems like that would not be possible if the brackets were mis-installed (the mounting points would not align).

Heat shields do not mount to that brace.

Okay, so I have this finally figured out. The vibration was caused by the aftermarket shifter housing in my car, which is noticeably taller than the stock shifter housing, coming into contact with the transmission tunnel on the passenger side of the shifter opening. Clearly the alignment of the transmission and PPF was different before the trans R&R, and when it went back together the trans was positioned slightly higher, and contacting the body. With this re-adjusted, no more buzzing resonance!

Thanks for all the help/ideas on this!