Fresh air intake plenum leaks

[64ragtop]

The fresh air intake ducts on my ragtop (on all '64 Darts, according to the manual) are fed by a "ram air feature" from what I believe is correctly called a "plenum" at the base of the windshield. The ducts attach to the floor of the plenum at locations that are rolled upward which, it seems, are designed to prevent water in the plenum from entering the ducts. There are drains at the sides of the plenum, which can be seen and felt with some difficulty under the hood torsion bar ends. Pouring water into the plenum through the grill at the base of the windshield results in water draining properly into the inside of the fender and on out the bottom.

My problem is that water is leaking from the plenum, not into the fresh air ducts, but down both sides of the firewall. It seems the floor of the plenum is leaking at the area that is rolled up. I have found no serious rust issues on the car, so I don't think there are rust holes at the lip of the duct holes in the plenum floor. I've removed the driver side duct, and stuck my hand up through the passenger side duct and can just barely feel around the lip, but don't feel any holes. I've cleaned the accumulated leaves from the area with a long extension on a blow gun powered by my air compressor, inserted through the grill at the base of the windshield, up the fresh air ducts, and into the plenum by way of the oval holes in the firewall, and the area seems to be free of debris, but there is just no way short of making new holes to get an eyeball look at the areas.

I'm at a loss to figure out how to apply some kind of sealant aroung the rolled up lips in the plenum floor. Any ideas?

I stripped out three layers of old carpet to find the mildew in the jute padding under what I suppose was the original carpet. I've primed the bare floorboards, installed new foil and foam type insulation and bought new carpet and I'd like to fix these leaks. HELP!!!

 

[64dartwagon]

Welcome to the leaky cowl club. There is alot of discussion about these problems and fixes. It's best to do a search under "cowl". Typically it's the wiper seals, or lack of them.

 

[64ragtop]

Thanks for the prompt reply, 64dartwagon (wish I could find one of those). What's got me confused is the place where I see the water tracks. It's right at the junction of the firewall and the side panel, behind the fresh air ducts. Hard to imagine the problem is the wiper seals, but I do know that water can run from the actual leak to a point some distance away. This would just depend on the contour of the bottom of the plenum, I suppose. I have a set of the wiper shaft seals that schumaker sells (I got 'em from Dante's, but they look identical to some from engineswaps.com I saw a while back). Since I have the seats out anyway (as well as the radio and glove box) I suppose I may as well dig just a bit deeper and install those seals now. Thanks for the search suggestion, too. I read the posts that came up and learned a bit. Since the P.O. kept the car garaged, and I've only had it sitting out for a couple of years, I'm pretty sure I don't have any major structural rot. Removing the pugs in the firewall and blowing compressed air throughout with a long wand on the blowgun seems to have dislodged the builtup debris. At least I can't feel any when I stick my hands up into the plenum through the fresh air ducts.

 

[64dartwagon]

You can always lay under the dash with someone running a water hose into the cowl, and just make sure you wear a snorkel and goggles. This spot has a tendency to get pinholes real bad. My car had been outside since day one and across the US multiple times. The lip inside the cowl to keep the water out of the fresh air vents was all but gone on the passenger side. I have found the best way to clean the cowl is to open the fresh air vents, roll down all the windows, hop on the freeway, floor it and keep my mouth shut as the krap flies. Must look interesting from behind.