I want to follow up on my last post (Mar 27, 2012) on this thread. I KNOW, it's been a year, but I had a covered place to park the truck and only drove it in Fair Weather, so I was in no hurry to tackle it!!!
As far as a leak at the windshield and heater air intake area I could not find any leaks. I water tested it thoroughly, even elevated the front wheels on ramps and could not find any. I used a lighted inspection mirror and a rotating inspection scope and did not see any rust, deterioration or any assembly defects, in the heater air intake under the hood.
I moved to the clearance lights. I removed each lamp; the gaskets were in good condition, the paint under each lamp looked “new” was clean and without any sign of water streaks. I took some silicon grease between my thumb and first finger and reverted to my old days (50s & 60s before RTV), when I would replace a thermostat, by working a thin film of the grease on both sides of the gasket to fill in any voids and let the grease seal out any water that may come in contact with it. I was very careful when replacing the lamps by using an even “torque down” method to prevent cracking the UV dried plastic lamps. For some extra insurance, I cleaned the upper side of the lens near the cab roof with paint thinner and applied a thin bead of clear RTV around the upper half of the lens, using my finger dipped in water to smooth it which makes it all most invisible.
When the TSB came out about a water leak at the Cab stop light, I purchased the new gasket. I removed the lamp and found the original gasket OK, paint clean and streak free. Using my old days again, I greased the new gasket. As you know the gasket sets back from the edge of the lens. Here is where I moved “out of the Box” a little, I adopted the plumber's method of installing a set of faucets. I used plumber putty, rolled out a string about the size of a small drinking straw. Placed it under the edge of the lens and did a torque down again. Because I need to “squeeze” the putty, I used my hand to push down on the lens around each screw while tighten, to spread out the force away from the screw heads. I did about a half a turn on each screw to get an even torque down and to prevent cracking the lens. It worked well. I did not apply any RTV to the upper side.
This only thing left was the rear sliding window. I removed the rear seat and rolled back the carpet. Removed the passenger door sill trim, because the water only wet the passenger side and rolled back the carpet and removed the Club Cab trim around and below the side window. Let me pause here, I worked for a small AMC dealer in the mid sixties as a service manager. The factory was having a problem with a water leak in one of the models; they held a half day training class at each Zone office. The instructor started out saying, testing for “rain” water leaks using a water hose can be very difficult. The reason being, rain water is “soft,” free of minerals and water treatment chemicals and will penetrate the surface tension around the paint and rubber gasket and will enter into any void between them. Where water hose water will generally be “Hard” water, loaded with minerals and have some surface tension properties itself and often will not penetrate the void, End of Pause.
I was working in my garage at the time and when I was ready to do a water test, it started to rain. I decided to back the truck outside and let the rain do the testing. Using a scale of; Light, Medium, or Heavy rain, it rained Medium for about 30 minutes. When the rain stopped, I pulled it back in the garage. I got in the passenger side of Club Cab AND there it was, water was dripping from the lower outboard corner the rear window gasket (RWG), BUT in was leaking out between the gasket Lip and the cab. There was no water leaking from the stationary glass channel of the gasket or from the track for the sliding glass!
It took a while to figure out, how the water would leak in under the outside lip of the gasket at the top of the cab and come out under the inside bottom lip at the outboard corner. You have to look at where the cab roof is joined to the Club Cab side panel; the joint is wide where it is spot welded together. If you look at the service manual, it shows a plastic trim piece they use to cover the spot welds and it is attached with double sided tape. This joint starts at the door opening and runs rearward over the back edge of the cab down and into the rear window opening, close to the upper outboard corner. The body joint with the plastic trim ends up under the window gasket.
Here lies the problem, the void on each side of the plastic trim acts like a gutter and carries the water to the RWG. If it's not properly sealed at that point, the water enters the body channel of the gasket and takes it to the bottom of this channel, which is below the lip of the channel. Remember, this point is near the top outboard corner of the opening. So the water will take a path of least resistant and follow the channel the short distant to the side of the body opening and down the side to the lower outboard corner. As the water travels down the side it could pass over the body opening lip at this point or when it backs up at the bottom of the channel, and spills over the lip and will leave the channel and drip to the interior bottom corner of the cab.
I sealed, using clear RTV, the voids on both sides of the plastic trim to the edges of the body joint from the RWG to the door opening. At the door opening end of the trim I seal up the end of the plastic trim and the voids. I did the same to the driver's side. I used a wet finger to get a neat clean look.
It was still raining, after waiting about 45 minutes of setup time; I backed outside and let the rain do the testing again. I left it out for about 30 to 40 minutes and brought back in. NO WATER LEAKS COULD BE FOUND!!!!
To help understand how the water could enter the RWG body channel under the outside lip and crossover the metal lip of the body opening and leak out of the inside lip into the interior of the cab. The body opening for the rear window has to be large enough to allow the inter lip of the RWG to be pulled in to the inside of the cab doing the installation of the rear window assembly. Once the installation is complete, the window assembly will settle down in the opening and the base of the body channel of the RWG that runs along the bottom section of the body opening will rest on the lip of that section of the body opening. This lets the ends and top section of the body channel of the RWG to have a clearance/void area between the body opening lip and the base of the channel. The outside lip of the gasket is sealed, to prevent, rain water and water used doing vehicle washing, etc. , from getting into the interior of the cab.
With the outside lip sealed, when the water got under the lip at the roof/side panel joint, it entered into the void area and ran down the end void area to the lower outboard corner and collected there because the body channel of the gasket, along the bottom section of the body opening, was resting on the body opening lip and that closed off that void. The only place the water could go was out under the inter lip and rundown to the rear corner in the cab. From there the water will run in a trough under the jack storage bin and never touch the rear section of the mat, on to the door opening along the sill area and then to the foot pan area of the passenger seat.
That is another reason I was mislead to where the leak was, with the rear mat area dry and the front mat area wet, I thought the leak had to be in the front somewhere!
As an extra precaution, I sealed the sliding window section, which I haven't used for 15 or16 years.
Now I know I'm preaching to the choir, to a lot of you on this, but I can tell by reading some of the Threads and Posts there are many of the readers who I hope will find this helpful.