Can't get downpipe flush with cat
 

I've spent too many hours now trying to get my new downpipe flange flush with the cat so I can get rid of an exhaust leak. The gap at the top is bigger than the bottom even if I loosen the catback from the cat and jack up the back of the cat. I'm basically out of ideas on how to get this downpipe straight except to maybe loosen it at the turbos and trying to twist it down.

The problem occurred after a shop removed my transmission to replace a synchro. I just put this engine in 200 miles ago and before the transmission was pulled out again everything lined up and I had no problems. I don't know how the shop could have messed this up just in removing the transmission but they did.

The cat studs were stripped and replaced with a set of nuts and bolts, and I don't currently have a bracket to support the rear end of the downpipe. Any ideas?

What brand downpipes, mid pipe, and cat back to you have?

Some of the cheapie Ebay downpipe/midpipes don't fit for crap.

If the downpipe has a lot of slop on the studs it could just need to be loosened, lined up, then tightened back up.

Dale

Take it to any decent muffler shop. They should be able to make it work.

I wouldn't loosen the DP/Manifold in an attempt to pull it down. You won't gain anything and the gasket is fragile. And that one is pricey. Besides, if it fit previously it should fit now. How did other things line up...PPF etc?

Might be worth uninstalling and re-installing the power plant frame according to the shop manual first. It's possible they didn't tighten the bolts in the correct order and the drivetrain is a little cockeyed.

If that doesn't do it you'll have to do the downpipe, it's possible they removed the downpipe when they did the clutch job. You don't have to remove it for a clutch job but it's not obvious that you don't so they may have done it.

Removing the downpipe isn't that big of a deal. If the downpipe is the problem due to removal the bolts won't be seized up so they should come loose in a reasonable fashion. Might be possible just to loosen the 4 nuts, see how much slop that gets you in the end of the downpipe, attach the cat, then tighten the downpipe nuts back up.

The gasket isn't really fragile, it's layered stainless steel and is VERY hardy. As long as you loosen the bolts enough that you aren't grinding the downpipe into the gasket you'll be fine.

Dale

Sounds great, thanks everyone. I will start by loosening the power plant frame and readjusting and only loosen the downpipe if I have to. My only concern is that the engine needs to tilt more down towards the back to close the gap at the top of the flanges, and the PPF already looks tight. It's not crooked side to side.

The studs and nuts on the downpipe are new as of 200 miles ago so hopefully it won't be a problem.

The shop that pulled the transmission specializes in FDs, so I'm guessing they knew not to remove the downpipe. This is the same shop that sold me an "inspected good" transmission with a bad 5th gear synchro in the first place though, so who knows. This is why I try to do all my own car work...

Remember, the whole drivetrain is located by 4 mounts - the 2 engine mounts and the 2 differential mounts. The power plant frame connects the two. If it's twisted or installed improperly it could alter the angle of the drivetrain.

There's a recent thread I did about bent PPF's (I don't think this is your case) and the thread shows the order to tighten the bolts up from the shop manual. You attach it to the diff first then rotate it up onto the transmission and tighten those up. I think some of the trans holes are slotted to enable installation so in theory if you attached it to the trans first the PPF may be out of alignment with the bolt holes.

It's also possible you have shot motor mounts or something. When doing the transmission the engine is supported only on the 2 mounts, if they were broken it could have shifted on those mounts.

Dale

I definitely think the PPF is the problem. I check the measurement on page J-57 in the manual and it was about 3.5" (spec is just under 3"). I loosened all the nuts and followed the procedure in the manual and got the gap just over 3", still a little out of spec. The flanges are closer to lining up but I still have the same leak. How exactly do I keep adjusting the PPF so that gap is in spec? The manual doesn't say.

This may be bass-ackward, but what about bolting up the DP-cat while the PPF is loosened and then seeing if you can still bolt the PPF back up within reasonable tolerances? Even if it doesn't come out exactly right, it might give you more clues about what the issue is.

Alright, I unbolted the front of the PPF again and retightened the nuts while pulling down on the back of the transmission. It's now in spec, under 3". I think having the front end of the car jacked up was working against me. The flanges were ALMOST perfectly flush after that, so I tightened the bolts pretty tight and started it up. I finally didn't feel any exhaust escaping the top of the joint and the car sounds much better.

I'll keep an eye on it to make sure it stays fixed, and if not I'll probably just loosen the downpipe at the turbos and adjust that way.

Thank you for pointing me in the direction of a PPF problem! That was pretty much it