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Cracking noise in firewall during hard shifts


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Hello all, havin a small issue but havent found much insight on it yet. The car is a 08 spec b modded with just a turbo back exhuast and a pro tune by cryotuning. The downpipe is a rev9 downpipe I got off a friend and there seems to be no fitment issues whatsoever, quite a good gap between the firewall.

 

Now I do drive the car pretty aggressively, I often take it on high speed canyon runs and do occasionally launch it for fun. I know its harsh on pretty much everything doing that but I'm actually a subaru mechanic and am not afraid to do some work if it goes and also take absolute meticulous care of the car in order to drive it hard.

 

As of lately I've noticed a few times that on a launch or during a flat foot shift the car is making this really weird cracking noise in the firewall it sounds like. Cant really feel it, doesnt effect driveability at all, car still continues to perform very nicely, but its definitely making this weird but pretty loud pop/crack noise only during a shift, or when power is engaged via the clutch pretty aggressively.

 

My first thoughts could be engine mounts worn causing the engine to torque a bunch, that or the rear tranny mount being torn. Maybe the pitch stop mount that's mounted on top of the tranny and to the firewall is absolutely toast. I'm not too sure as I havent had a chance to look at it but I was curious if anybody else has had this issue? I thought I remember reading something about the firewall welds being garbage? Not sure if it affected these cars? I've also seen master cylinder braces for sale everywhere, does that mean these have an issue flexing around a bunch?

 

If I find the mounts are shot I'll likely be upgrading the engine and tranny mounts to poly mounts with likely a larger pitch stop mount as well, if that is the case any recommendations on the best poly mounts out there? I am aware it will make the car a little more harsh, as you feel more of the transmission movements transferring through the chassis but am fully prepared. I have a spare subie almost always and currently an H6 outback is very soon being purchased, that being said, the spec b is slowly becoming more or a 50/50 split between being able to drive on the road while still holding it's own on the track. Anyways any insight on the issue is very much appreciated!

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Yeah I thought I heard something about welds having issues. I'll have to take a look at all the mounts. Hopefully changing to poly engine and transmission mounts wont make it worse. I think I might start with the mounts and if I can locate the the broken welds, weld that thing back up. Thank you for the insight
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I found that my pitch stop, engine mounts, and trans mount were all equally beat to shit at the same time. Replacing all three if you haven't over the life of the car with 100K+ on it would be a good idea regardless of whether or not is solves your problem. I highly recommend Group N parts for all three. I have a Perrin pitch stop and it's a little too stiff and and adds a little too much NVH for my liking.

 

Also, I have found this car to be much harder to learn to shift smoothly in than any other manual car I've ever driven. You gotta get back on the throttle a little faster between shifts to prevent some of the drivetrain slop that comes with an imperfect upshift. Flat-foot shifting is an absolute no on these things, even if you have the much more durable 6-speed.

 

You say you're a Subaru tech. Can you have another tech look in the engine bay of your car while you have the car on a four-post and lift it 6 inches off the ground, then do whatever recreates the problem? Having a stethoscope might help too if you have one handy.

 

As for symptoms in this car with failed mounts, for me it was pretty much impossible to shift smoothly with worn everything. Starting from a stop required feathering the throttle and clutch just right. One of my engine mounts actually started peeling like an orange, which is when I had Surgeline replace them. Another user mentioned spot welds. I wouldn't know symptoms of failure here. My car has been an occasionally spirited drive kinda daily car. If you're a tech though, I'm sure you'll be of more use than us shadetree guys on here :p

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When I bought this turbo Baja it regularly made a clunk from firewall area when engaging the clutch. PO had installed an aftermarket pitch stop, and it just wasn't tightened. Snugged up its bolts to cure the problem.

So yeah, check out engine and trans mounts as well.

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Thank you much on the insight everybody, I have been away for awhile and while I was away I installed some bc racing coilovers on the car. While I had it up I took the opportunity to run an inspection on the car. All checked out good other than a very slight oil leak at the oil cooler, per usual. Engine mounts and tranny mount checked out looking pretty much brand new with no cracks or excess softness. Since I was under the car I have yet to check the pitch stop mount but at least I can eliminate a larger portion of the potential issues.

 

The next time I get my hands on the car I will have to pull the intercooler and really dig into the pitch stop and see what's going on. I've never had any issues shifting minus a 4th gear synchro that's been picky since I first got the car. Ran a service on the gearbox and it definitely helped. While i know the flat foots dont help it by any means, it so far hasnt given me any issues but really helps cutting time on shifts. I will happily deal with whatever consequences come my way from using it lol

 

As a plus/side note, I'm extremely satisfied with my coilovers. The bc racing br series seems to have found a nice balance of not shattering your spine on the road but still seriously holding it's own on a track or setting similar to one. The car no longer squats or nose dives on hard braking or acceleration and the body roll has been drastically improved over the B6 series bilsteins. Now I have no idea if any of these are at all connected but the car is a much more planted unit, less power is being lost through moving around the body and is more quickly going to the wheels instead. That being said, i havent been able to replicate this issue after slapping these puppies on which doesnt quite make sense. Not entirely sure but slowly starting to be sold on the fact that it might actually be a firewall weld.

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Actually no, they were brand new setups. I replaced them with new stock ones as I generally enjoy stock suspension but I was disappointed with how little it changed. With the 30 way dampening I've been able to tune the car to ride and respond over bumps very similarly to the B6s but it shines much brighter in the corners. No complaints here, seem to be pretty quality pieces for what I have in store for them
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Are you planning to track the car a lot? Hate to be that guy but the valving will get quite hot in those on track and they won’t last very long. Otherwise, they’re fine for a daily car that sees occasional spirited driving.
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Dont track it a ton no sir. It's mostly a daily driver between this and my 05 outback ll bean I plan on lifting. The car definitely sees a ton of spirited driving on the canyons near by but will realistically speaking only see a track occasionally
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This may be completely off track, but thought I’d mention it (funny enough a co-worker told me about it today). 08-10 WRXs have what sounds to be a similar issue-spot welds coming lose on the firewall around the clutch pedal. There’s several companies that make kits to correct it but I’ve not heard/seen much in the LGT community...(though take that with a grain of salt cause I’m a noob who drives an auto. #fail. #wannabea6speedsoobie). :rolleyes: Just a thought. I
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