View Full Version : B5 A4 1.8T: Cat/Downpipe removal and installation

10-31-2006, 11:48 AM
b5 a4 1.8 tq cat / downpipe removal and installation

i had a hell of a time figuring out how to get at the cat>dp connection while putting my exhaust in. i didn't see a great install guide anywhere so i thought i'd throw a few notes together in the hopes that someone else will benefit from my 45 minutes under my car contemplating my downpipe's existential reality.

first, it LOOKS a lot worse than it actually is because the 3 bolts are so miserably hidden in the depths of the 'tunnel' that the dp lives in. hit the cat>dp bolts with pbalster or similar the night before. you can squirt them from the engine bay. what i found that worked was:

1. loosen front pass wheel bolts w/ car on ground [how many times have i forgotten to do that.. "HONEY, can you come stand on my brake pedal?!?!?"]

2. jack the front up. get it way up, you'll want the room. jackstands baby. don't wantcha gettin squished.

3. get the airbox out of the way. 10mm bolt on the fender, undo the connections + hose clamps and flip it up so it rests on the battery cover. you don't have to take it all the way out.

4. loosen the cat>turbo bolts [3x14mm] to give the cat some wiggle room. these are a pita to get a socket on - the stud is too long to get a normal socket on all the way [you can only get the socket about 1/2 on the bolt] and a deep socket won't work bc the ratchet will interfere w/ the cat. there isn't enough wiggle room to turn a box end wrench on it. i found that a gearwrench was perfect [bought a set of flexhead gearwrenches for this job - love em].

5. remove the cv boot heat sheild. on my 98 it was 2 pieces. the main sheild and a little 'sub-sheild' that uses 2 of the 3 bolts. it's 3x #10? hex heads. you can get at them easilly with a LONG extension on a ratchet via the pass wheel well, looking over the axle.

5.5 right about now i'm trying to kick my own n-ts for not doing this when i had the suspension and both axles out. grrrrrrr.....

6. i loosened the 3x13mm cat>dp bolts with a couple of extensions on a ratchet and a swivel on the end from under the car. the nuts are welded to the cat [fyi]. be careful not to strip the bolt heads because the swivels are a PITA to out torque on.

7. pull the cat up and out, past the turbo if you're r+ring it. i was putting on an exhaust so this wasn't relevant.

8. install is pretty much the reverse. install new cat/dp, and then the heatsheild[s]. with the heat sheild out of the way, you can start the cat>dp bolts with your fingers then finish them off with socket/swivel, gearwrench, maybe even a stubby wrench.

you may need to loosen the dp>exhaust connections to get things to fit. always install everything loose then tighten when it's all together. how many times have i tightened all the bolts on x part only to have to loosen them all to get connecting part to fit? grrrrr... that's why i'm not quitting my day job.