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Tom the rears are easy - straight shot and you can use air as long as don't make a mess.
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Does it have the "Do It Yourself" manual transmission, or the superior "Fully Equipped by Porsche" Automatic Transmission? George Layton March 2014
928 Owners are ".....a secret sect of quietly assured Porsche pragmatists who in near anonymity appreciate the prodigious, easy going prowess of the 928."
Resolved the blockage on my right side front drain.
The tube that protrudes below the fender was trapped between the washer fluid container and the engine bay wall. Flat as a pancake and no way weed wacker line or anything else would have broken through. Now repositioned and working as it should be.
I just fixed a front tube that I noticed wasn't draining. The weed eater cord wouldn't go thru from the top.
I poured some water in the sunroof well so I could check my progress and see if it would start to drain.
After removing the wheel well liner, I noticed the tube was not protruding much from the hole, so I gently pulled it down a bit.
At that point the water started flowing. I poured more water and it flowed out quickly. It appears fixed. I didn't see any debris come out.
The only thing I can figure is maybe the tube can form some kind of air lock if it gets pushed up and bends into an "S" shape. What would have caused it to get pushed up like that is a mystery to me. Maybe it is something that can happen over the seasons over time.
I just fixed a front tube that I noticed wasn't draining. The weed eater cord wouldn't go thru from the top.
I poured some water in the sunroof well so I could check my progress and see if it would start to drain.
After removing the wheel well liner, I noticed the tube was not protruding much from the hole, so I gently pulled it down a bit.
At that point the water started flowing. I poured more water and it flowed out quickly. It appears fixed. I didn't see any debris come out.
The only thing I can figure is maybe the tube can form some kind of air lock if it gets pushed up and bends into an "S" shape. What would have caused it to get pushed up like that is a mystery to me. Maybe it is something that can happen over the seasons over time.
That is exactly the same issue I had with mine ... see my post #14. Once I pulled down on it from inside the wheel well it pulled out the kink inside, which from marks on the hose showed that it had been there since manufacture. When new, with no silt in it, there was obviously just enough opening for it to work, and it silted up over time and stopped draining.
I'm sure there are lots more out there that have those kinks, and the hose trapped and squashed behind other components, that left the factory like that.
It's worth checking the hose exit point in the wheel well, if you have any difficulty getting a line through ... like I did. It might be squashed or kinked.
I've cleared my 944 drains with compressed air before. Don't do it from the bottom. I'm still finding mud in weird places in the interior months later
Don't use compressed air from the top on a 928 or you can blow the tube off the spigot, which is impossible to fix with the headliner in position. BTDT
You can safely use air from the bottom to help clear a blockage, but you have to turn the pressure on your regulator way down, to gently clear it ... and anticipate all the crap that will come out the top, and tape plastic over the opening, and have a towel there to soak it up. BTDT
If you just use normal pressure from below you will definitely have crap from one end of the car to the other ... as you've found out.
Reporting another front drain fix. Mine were also retracted. Pulling them down a bit and flushed them with a lot of soapy water. This should be a standard item to check whenever the wheel well liners are off.
Un plugged/ un flattened mine today on the passenger side it was smashed by the bottle. must have drained some over the years, because it just started overflowing last week