Ed,
You're right when you recommend Rain-X. This DOES work, as proven early last year when we went on a club run to Mudgee in the pouring rain, and my wipers failed about 20 minutes after we left. The Rain-X kept the screen clear when the car was travelling above around 30 miles an hour. The water just slides off. They also make a product for the inside of the window that prevents fogging of the inside, handy when the passengers start heavy breathing!!
The wipers had always been sluggish on my car and when I restored it I found that the wiper shafts that comes through the cowl were VERY stiff. Cleaned and oiled this and the whole mechanism and now I get good wiper speed, even up hills.
Like RET says, with the car running remove the hose the comes from the vacuum pump at the wiper motor end and feel for vacuum. While partially covering the hose outlet (or preferably using a vacuum guage) rev the engine and check that the vacuum is maintained. If it is, the problem is in the wiper motor or mechanism, if there's very little or no vacuum the problem is in the pump. The pump is designed to supplement the engine vacuum when the engine is under load or at wider throttle openings, so if you've got good vacuum at idle and none at full throttle, then the pump is buggered. Most likely a cracked or broken diaphragm.
I've had a look on the Rare Spares website and they don't list a vacuum pump kit anymore
About a year ago it was there, about $60.00 or so.
Good Luck.
Cheers,
Craig.
