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Question from Roger (1974):
What do you call the part of the car below the windshield wipers that has either a wire or plastic screen across it? What purpose, other than hold the wiper, does this chamber provide? Does it let fresh air into the car, does it have a drain in it at the far end by the fenders? When I spray water in this chamber directed at the passenger side only, I get a rather large water leak on my floor board. What causes this problem? You can not see in this area or get your hand in very far. Also, the drain for this chamber at the back of the engine block is open.
I call it the vent plenum. It does let fresh air into the car. It is supposed to have a couple drains, but they do get plugged. However, that isn't your problem. It is remotely possible that the seals where your windshield wiper parts pass through are bad. If so, you are lucky. These are relatively easy to fix, although while you are laying under there trying to do it, you will exercise your vocabulary.
I would bet money that your have a rust hole in there somewhere. Try laying on the floor and have someone spary water in there to see where it comes from. You may end up removing a bunch of stuff to be able to pack something up from the under side to fill the hole. It may be at a panel joint, which is a lot like chasing a roof leak. I am pretty sure that you will not be able to reqch it from the top side.
Oh boy, what a coincidence! Roger, I think I have a leak in this same area. I can tell you right now, from my experience at least, tracking down a water leak is extremely hard to do.
On some cars you can get your hand up in there to clear the plenum out. Sometimes there is a vent down by the kickpanel, or behind it. If you remove that you can get your hand in there-- or-- what I did was snake a vacuum cleaner hose in there to get out the gunk. (Thinking that years of accumulated debris might be causing the leak somehow.) There are usually drainholes at the very bottom of this area. If you probe around with a screwdriver you can find them and clear them out. Whether this will help you with your leak or not, I don't know. But it's a good idea to do it anyway so you have good flow thru this area and don't have anything in there to trap moisture and cause rust.
I think in my case my leak was actually several leaks. I finally found one of the major ones in the firewall. There was a connector holding a piece of sound deadening insulation in place; directly below that connector was a gap where 2 panels had been welded together. There was some body sealer or whatever you want to call it in this crack, but it was old and there was a hole in it. You could see daylight through it. When I pulled back the carpet I could see a trace of a little wet trail from this hole to the puddle in my floorboard. So I sealed that up.
For 2 rains it was dry as a bone. "Success!" thought I. No, not hardly. The next time it rained, big puddle in floorboard. So then I moved to the next suspect, the weatherstripping, or seal, around the windshield. I just completed resealing that this weekend and it rained like a sunuvagun last night. But no leaks this morning! So . . . maybe success.
I even taped a hose with a spray nozzle on a ladder and tried to simulate rain over this area while I crawled around on my back, looking up under the dash, and I never could find the leak. It can be quite frustrating!
The only thing I can say is, the hole you are looking for may be VERY small. Don't be deceived by the large amount of water in your car into thinking that you have a big leak-- you may not. Confucious say, "Small hole can cause big leak." (I think it was Confucious, it may have been Socrates.) Also, it helped me to try to trace the leak back to its source by pulling up the carpet right after it got wet and looking for the trail. Try that.
The wiper mechanisms on '74 - '78 Imperials and New Yorkers DO NOT pass through the firewall like other Mopar models. This cannot therefore be a point for leaks like it is for some other Mopars.
That grille is where the fresh cabin air comes into the car. That cavity also contains ALL of the wiper linkage etc. There are two drains in
this cavity. There is one drain on each side of the car. The firewall material tends to rust out around where the blower motor and duct assembly
pass through the firewall. To inspect for this rust, you'd have to first remove (at least take all the fasteners out of) the right inner fender well,
remove the fender brace that runs from the top of the fender to the firewall, remove the power antenna, remove the blower motor, then you can remove the big duct assembly from the firewall. You may have to disconnect a few heater hoses etc. to gain access to the air box.
There is no system like this on the left side (driver's side in North America) so this type of leak is rare over there.
It is a poor design, just like the design of the inside of the rear quarters on the '74 - '78 Chryslers.
I don't think this is neccessarily related to other rust on the car. I think it has mostly to do with how much trash has been allowed to get down into that cavity and how wet it has been for how long. People chuckle at me when I labourously pick dried leaves out of that grate below the wipers but leaves turn to dirt and dirt gets wet and water rusts, simple as that.
The only thing I can see that a person can do is to take those little plastic (most often) grates out of there and blast the cavity with water. A garden hose would be good but a pressure washer is best of course. Like Roger pointed out though, keep a watch on the inside of the car for leaks.
Taking that air box off is not that bad. I've parted out a few of these cars and it would just be a bunch of twisting nuts and bots to do the job.
I've thought about doing it on my '78 Newport because on that car, the condensate from the AC evapourator makes its way into the car and soaks the front seat passenger's floor carpet with REALLY HOT WATER!...that can't be good. It doesn't help the AC cool the car off any either when there is a kettle boiling water on the floor on the other side.
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