My Diamond T, which is a mid size model 509 (14,700 GVW) came with an under dash vacuum reservoir. It is aproximately 1 gal capacity. It seems to give you about 10 seconds of vacuum reserve, with the wipers running.
There is no doubt that electric wipers are best, based on the fact that all modern cars use them. I, however, like the "charm" of the vacuum wipers. None of my trucks are daily drivers but all have been driven in the rain and I am old enough to remember riding in a car with vacuum wipers, when that is all we had.
In addition to the vacuum reserve canister, there is the Trico Electro Vac. One of these came with my COE and it works great. When switched on it comes on only when it detects loss of manifold vacuum. It is capable of pulling 14 inches of Hg vacuum, which is enough to run the wipers just fine all by itself. Yes, I get the irony of using an electric motor to boost vacuum so that your vacuum motor works.
My '42 came with electric wipers (previous owner had already converted to 12 volts). The truck has dual wipers that are independent, without linkage. Thus, the wipers never were synchronized or parked correctly (they were wired through the same switch). Just for the fun of it, I removed the electric wipers, found wiper cores on Ebay, and had them rebuilt by the Wiperman. I found the original vacuum line in the A pillar. They work great and look fantastic when parked. So, I may be one of the few that went the other direction and re-installed vacuum motors. As mentioned above, they have a speed valve, so I like them better than the electric ones.
Kent
