Rear glass leak fix, an infamous problem for Ford trucks.

One of my regular customers, (let’s call him Tim), called about a problem with his vehicle fleet’s recent addition. It is a newly purchased, pre-owned 2008 Ford F-250 Super-duty crew cab truck. He said that he hasn’t owned the truck long when he realized that he had a rear glass leak. A few days ago, he was driving in a rainstorm when his passengers noticed his back glass was wet with streaming water. Tim’s truck has a powered, 3 panel, encapsulated rear glass with solar privacy glass.  The center glass slides open when the button is pushed in the drivers’ area.  The other back glass option for this truck would be a 1 piece of glass that does not open or slide.

I told Tim that the powered rear back glass assemblies have drain ports/drain holes built in the bottom of them. They are designed to take water from rain that runs into the bottom of the window channel. This allows water to drain out the bottom. Over time, these drain ports can collect dirt, pollen, and other small debris causing clogged drain holes.  As a result, water pools up inside the channel until it leaks down the bottom of the glass. Down into the carpeted rear area of the cab. After I questioned Tim where the water seemed to be coming from, the drain ports didn’t seem like the problem.

Rear glass leak: An Odd problem of Ford truck

I speculated that the alternative cause of the water leak is a failed seal of the rear glass. This seal, which is made up of a strand of butyl tape, surrounds the face of the glass assembly. It mates to the metal pinch weld of the glass opening. 

Additionally, the glass assembly also has threaded studs that protrude through the metal pinch weld.  10mm nuts thread onto the protruding threaded studs that are now sticking through the pinch weld holes, about 15 in total. Once the 10mm nuts are secured on the inside of the cab it creates a waterproof barrier by pulling the glass assembly inward towards the cab. As the 10mm nuts are tightened, the butyl tape sandwiched in the middle between the glass assembly and metal pinch weld acts as a waterproof barrier. It keeps water out of the interior of the vehicle.

Butyl tape is very sticky, tacky, and messy. It does not break down like rubber or foam gasket seals. So, I was hesitant to pursue this as a possible cause for a water leak.

I told Tim that I would be over later that afternoon. I am all set to diagnose and repair the water leak on his truck. When I pulled into Tim’s driveway, his truck’s rear window was facing towards me. I am already scanning the back cab of the truck for potential problems. The first thing I noticed in the immediate vicinity of the rear glass was an aftermarket third brake light above the rear glass of the truck. This was of interest to me because this was my potential water leak problem staring me down!

The culprit

Ford trucks manufactured between 1997 to 2014 are notorious for leaking water around the third brake light lens just above the rearview window. The problem is usually not with the plastic brake light assembly. Rather, it is the foam gasket seal. The third brake lights leak around the hole in the cab, where the brake light mates to the back of the truck cab. It has a foam gasket seal that sits between the brake light fixture and the back of the truck cab. The foam gasket seal can deteriorate or pull away. This results in water leaking into the cab through the hole from the third brake light. 20180905_124235

In Tim’s case, the foam gasket seal was present but it was old, smashed down, and no longer doing its job of keeping water out. When it rains, the water runs down the back of the roof of the truck. Then down to the third brake light and into the cab. The water would travel further the rear back glass on the inside of the glass, down to the floor and carpet. Tim told me that this problem has been going on for a while because the bottom of his rear floorboard was rusty beneath the carpet. Below is the picture of the old foam gasket seal.  20180905_124243

The Much Awaited Fix

Confident that I had found the source of the rear glass leak, I showed Tim the third brake light assembly and the old foam gasket seal attached to it.  I told him I would make a new foam gasket seal and re-install the third brake light.  I replaced the seal and water. Then, tested the third brake light with a water hose.  Tim watched the inside of the back glass from the rear seat as I sprayed down the third brake light assembly and back glass for 2 to 3 minutes.  Alas! The rear glass leak was no longer present.  I am glad because I would not have to remove the glass and replace the messy, black butyl tape! Tim was also happy because his repair bill was considerably less than removing and re-installing the entire back glass assembly.

A proper fix for rear glass leak brake light assembly

A quick google search for Ford third brake light leaking will reveal a variety of different fixes that other people have come up with. The most common fix that people seem to do is to permanently seal the third brake light assembly to the back of the cab with an adhesive such as glue or urethane. DO NOT DO THIS!  The next time your third brake light needs a bulb replacement you will have a mess to deal with. The adhesive will either pull the paint off the back of the truck cab when you pull the brake light assembly, crack the brake light assembly, or have to be removed by cutting. The latter will most likely result in scratched paint.

I used a piece of 7/32 foam gasket seal that attaches with a piece of built-in adhesive tape. This is the same type of material attached to the edges of windshields to keep dirt and water out of the pinch weld. You can purchase this type of gasket seal online and some automotive stores. If you cannot find the same material that I used, you can purchase a 3M double-sided foam adhesive tape at your local parts store.

Demonstration of a rear glass leak fix. Repairing the seal.

Tools/items needed: 3M double-sided tape, razor blade/cutting tool, rubbing alcohol & hand towel, a water source for water leak testing.

  1.  Remove the old foam gasket from the third brake light assembly
  2. Wipe down the brake light assembly with rubbing alcohol where the old gasket was removed.
  3. Evenly apply the double-sided 3M tape around the entire edge of the third brake light.
  4. Carefully trim any excess double-sided foam tape with a razor knife.
  5. Re-install the third brake light assembly and tighten 2 Phillips screws.

How to do a simple water leak test

This is a very simple way to check for leaks yourself.  You will need a spray bottle filled with soapy water and compressed air.  This technique will work for checking water leaks around any solid-mounted glass on your vehicle.  The compressed air can be in the form of a compressed can of air if an air compressor and nozzle are not available.

  1.  Spray the soapy water around the entire outside area of the glass to be checked.
  2.  From the inside of the vehicle, one person blows the compressed air slowly around the entire outer edge of the glass while the second person watches the glass from the outside of the vehicle watching for soap bubbles to appear.  Where the soap bubbles appear on the outside is where the leak is located.  The compressed air passes around the glass forming the soapy bubble.

To schedule a windshield replacement or for more useful information check us out at RVA Glass Repair. You can also call or text us at 804-519-4218 or fill out a brief contact form and we’ll get back to you soon.

As always RVA Glass offers FREE Mobile Service! That’s right, as always we come to you at no extra charge for every windshield repair and windshield replacement in the greater Richmond VA area including Short Pump VA, Glen Allen VA, North Chesterfield VA, Midlothian VA, Chester VA, Bon Air, VA, Forest Hill VA, Colonial Heights VA, and Chesterfield VA.

You may like to read about the costs of newer windshields, and how we handle service during a crisis. or when there is strong rain. 

RVA Glass services include but are not limited to:
  1. Free windshield replacement or repair quote.
  2. Windshield repair for minor damages. You can read about the different types here.  
  3. The windshield replacement for major damage types and breaks.
  4. All auto glass repair. Anywhere on your vehicle, you have damage, we can help fix it.
  5. Windshield rock chip repair usually resulting from small debris striking the windshield while driving.
  6. Window motor regulator replacement. If your windows stop working, normally it is the motor that is the issue. Contact us for a free quote.
  7. Rearview mirror repair or replacement. We can fix all internal glass structures on the interior of the vehicle as well.
  8. The back glass could leak or get broken. When inclement weather or age strikes, RVA Glass can be the solution you need for an affordable price.
  9. Often, when parked or driving, your side view mirrors could suffer impact. Or, due to age, they may become structurally compromised. Usually, this can be an expensive fix at most shops. Call us to see how we can repair your side-view mirrors. We are fully mobile so we can come to you!
  10. Leaking windshield or back glass usually is a problem with the seal or gaskets. Normally this can be a relatively simple fix so contact us now for a free estimate.
  11. Although we can work on almost any vehicle, we are very adept at working on Jeep Wranglers, Subaru Outbacks, Toyota Rav 4s, and Toyota Camrys.


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