The sliding window latches on '99-'03 seem to be a common failure item. Replacement latch is around $120 and a latch repair kit, containing a new plastic cover, two pot metal pins and a spring costs between $50 and $60. I came up with a repair that costs significantly less and can be done in less than an hour.
The Problem Edit
The problem with my latch, was that both of the locking pins were broken, enabling the window to open and close with no way to lock it in either position.
Latch Operation Edit
Instead of buying a repair kit in order to replace the pins, I decided that given the simple mechanism, it must be possible to re-engineer this latch in an inexpensive way. The two pins get sandwiched together between the two levers, which hook over the little nubs at the top of the pins. The levers rotate around a pivot pin in order to pull the pins straight up. The left lever attaches to the rear pin, and the right lever to the front pin (directions here from the perspective of sitting inside the van, looking at the latch in its natural position, although I did remove the window for this repair, it likely was not necessary). This arrangement requires that the operator squeeze both "buttons" on the latch in order to unlock and slide the window. I didn't see a reason for the two pins to not just be a single pin. When holding the two pins together in their assembled position, they form a round rod, so I had the idea that I could just get a piece of aluminum rod, cut to the correct length and then figure out a way to attach it to the levers.
The Solution Edit
First, to evaluate the problem, I had to disassemble the latch. This is a little tricky, and I presume the reason that the repair kit comes with a new plastic cover is that most people end up destroying their plastic cover trying to get it off. I found that it's held onto the latch base with three little tabs. One at the top and two at the bottom (See image).
To remove it from the base, I used a pick with a right angle at the end, to hook under the cover and pry it up and back. Then I depressed both lever buttons and used the hook to gently push and prod the bottom of the cover until it worked itself off of the base. It came off relatively damage-free.
After removing the cover, the rest is pretty straightforward. First I took the right side lever off by pulling it straight back from the latch, while rotating it gently side to side to get it to clear the nub on the locking pin, as well as the pivot pin, taking care not to lose the spring that sits between the two levers. With the right lever removed, the first pin can be pulled it. It might have a tendency to fall down, but using the pick it can be pushed back up through the bottom of latch and removed. Once the first pin is removed, the 2nd pin comes out and finally the left lever button. At this point I checked all components and evaluated the situation and found that in my case, the only problem was the locking pins were both broken off, but the rest of the parts were still in order. If the spring is determined to be broken, it's highly likely that a suitable spring can be found at a hardware store or automotive parts store. My spring was fine, so I moved on to trying to replace the pins for less than $50.
I held the two pins together and found that they resemble a single rod, and there doesn't seem to be any real good reason for them not to be replaced with a single rod, other than the assembly process is a little tricky. Hopefully though, this repair will outlive the rest of the van, so if you can get it assembled one time, it'll be the last time.
The diameter of the two halves together was around 8mm. I measured with some digital calipers and noted it down and was about to head to the hardware store to see what I could find, when I found an old 12-gauge shotgun cleaning kit in my garage that I had no use for. If I recall, this kit was relatively inexpensive and found at any sporting goods store. It just so happened that the diameter of the rod was right about perfect for my purposes, so I skipped the trip to the hardware store and got to work.
I eyeballed the measurement that I'd need, by holding the gun cleaning kit rod up to the latch and then clamped the rod into a bench vise and cut off the section I needed with a hacksaw. Afterward, I used a file to smooth out the cut end.
I held the cut piece into the latch and held up the broken locking pins to see about where I need to put the little nubs for the levers to hook onto.
Finding a way to replicate the nubs appeared to be the most difficult part of this repair, but while going through my drawer of miscellaneous junk, I found a generic box of various clips and pins and decided cross drilling the rod and inserting a roll pin would be perfect.
I went through the assortment of roll pins and found a few that looked like they would work (they'd fit the holes in the levers). Then I went through my collection of drill bits until I found a pin and a drill bit that fit each other, which would fit the holes in the levers. It ended up being a 1/8" drill bit. I'm not sure the size of the pin, but it fits snugly and needs to be lightly tapped with a small hammer to insert into the hole.
I put the new aluminum locking pin into the vise and carefully cross drilled a hole through it at the right location to mimic the original locking pins and their nubs. Then I tapped the roll pin through the hole, but stopped when the back end was flush to the back of the hole.
Next I re-inserted the left side lever button back onto the latch, then slid the new locking pin down through its hole. Once I got it into the right position, I tapped lightly on the roll pin to get it seated down into the hole in the lever. This was probably the most difficult part. If you tap the roll pin all the way through before installing in the latch, you can't get it in. It needs to be assembled in place. This is the reason for there being two pins in the original latch mechanism. Once I was satisfied with the left lever being securely attached to the roll pin, I inserted the spring and slid the right side lever down over its pivot pin and the roll pin.
At this point, the latch was completely operational. The added benefit is that the latch can be activated by either lever or both levers, and the locking pin slides up the same either way. This seems more natural to me, although perhaps it puts excess stress on a single lever. Use your best judgment here on how you actually open the window when it's all said and done. At this point, it's important to test out the latch and window to make sure the pin comes up enough to clear the locking rail, but also goes down enough to actually lock the window. Mine worked out just right on the first try. Once that is verified, all that is left is to pop the cover back on.
If the roll pin you used was too long to actually get the cover back on, simply use an angle grinder or cut-off wheel to trim the roll pin down so that it is almost flush with the right side lever hole. Then snap the cover back on, after ensuring the spring is seated properly and everything works well.