I'm getting a loud and distinct clacking sound from the center vent area of my dash. It is intermittant, but lasts several seconds when it starts. Has anyone experienced this? How hard is it to get in there and see what's wrong. Any tips or links are much appreciated. Thanks.

Steve
'89 S4 Auto

 

comb flap vacuum actuator

 

Thanks Heinrich, now what do I do about it. Is this a symptom of a bad actuator diagphram, or is something just loose. I'm tempted to just plug the vacuum to the comb flap rather than tear into the dash. My dash is perfect and I'd like to keep it that way. Thanks.

Steve

 

Check out Greg Nichol's tips for replacing it. Luckily '89 was the last year before passengerside airbags so you just have to remove the center console, glovebox to perform the surgury requireed to replace it. You can get the rubber actuators from one of the Rennlist Sponsors.

 

If I were you I'd plug it and forget it.

 

H hit is 100% right.....since it really doesn't do much I also vote to cap the line and forget it....thats what I did.....just so you know the "failure" mode of the comb flap is in the down position....which diverts airflow from the center vent to the side vents......which I like better anyway....about the only downside is it does add a touch of wind noise on higher fan settings

 

A clacking comb flap can be caused by a faulty check valve in the vacuum line coming off the brake booster. It's a little blue and black thing about an inch in diameter and it costs peanuts to replace. 928 Intl stock them. Worth a try before you climb into the dash. In my RHD car there is a hole in the duct through which the position of the comb flap can be felt with a finger. It doesn't bite too much.

Colin. 89GT

 

This is also possible.....when checking HVAC vac problems its always wise to start at the brake booster and work your way in from there....I've checked 4 or 5 different 928's blue/black check valve & not one has been 100%....its cheap and easy to fix....then you might as well change the 4 way "T" (on S4+ MY)...since its old and probably loose (also cheap and easy)....then go into the hvac solenoid strip behind the stereo and check each actuator from there...pirtle and tony have great write ups about it!

 

I had the same exact problem on my car. It was only when started and would just eventually disappear. Pull the vents out and while it's still clanking, push on all the permenant vents to see if one is cracked at the bottom. Most likely one of them is and is causing a vibration. You can simply add an epoxy to the spot and voila, your clank is gone!

Give 'er a try!

Todd