Recently I fixed my windshield wipers, which wouldn't work on high speed. I'd suggest anyone who's had problems with their wipers read this post. My van is a 1990 E150 ClubWagon XLT with 302 engine.
After eliminating the wiper switch and the nearby pulse control box as problems, I managed to reach under the dash and get my hand on the cylindrical housing of the wiper motor.
By wriggling and twisting the motor housing I could get high speed, but only intermittently.
I reckoned the problem might be the brushes that carry current to the armature/commutator i.e. the contacts on the shaft of the motor. The brushes are worn away with time. And as it turned out, the high-speed brush was worn away (the brushes are springloaded so they feed out as they wear).
The brushes are contained in the plastic housing on the base of the motor. The housing is held on by a metal clip (basically a formed piece of wire) that goes around the motor. It swings at the top of the motor and locates over the brush housing on a little slotted metal cap/dome to hold the brush housing in place.
Here's what to do, from memory. Apologies if I've omitted anything, it was a few weeks ago:
* Move the fusebox out of the way (involves removal of one screw on my van).
* Move the (annoying) warning buzzer box out of the way by rotating it 90 degrees and pulling it away from its bracket. Disconnect it or move it aside.
* Disconnect the wiring harness from the brush housing at the base of the motor. You may have to prise a retaining clip clear. If the clip breaks, the connector will probably go back in and stay there anyway as it's a tight fit.
* Mark the position of the metal cap/dome with a permanent marker in relation to the plastic brush housing, and the brush housing in relation to the motor housing too.
* Now swing the clip off the little metal cap/dome. This is v. hard. I inserted a screwdriver between the clip and the base of the motor as a lever.
* The little metal cap and possibly the plastic brush housing will fall off. Black graphite dust crud (the result of wear to the brushes) will fall out too.
* I replaced the brush housing with one containing good brushes from a donor van. New brushes can probably be sourced from Ford or an auto electrician if you want to do it that way.
* Reinstalling is tricky because you need to keep the brushes clear of the motor shaft, otherwise the brush housing won't go back on. There are three notches that allow for insertion of some sort of tool to hold the springloaded brushes back, but that's probably intended for doing it on a bench. Here's how I handled it:
- Get three pieces of matchstick (I had to use half a matchstick, split lengthways) and a socket that is a slightly loose fit into the recess where the metal dome/cap goes. Insert the matchsticks into the slots so they push the brushes back. At the same time insert the socket so it holds the matchsticks in place. You may need to try several different sockets. You'll get the best result if you position each match so it comes about halfway up the face of the brush.
* Now, you need to put the base back on. The socket and matchsticks will be pushed out by the motor shaft as you slide the brush housing into place.
* Put the dome/cap back on. Getting the clip back over the little hump on the cap and into its groove is REALLY difficult. I filed the hump down just enough to let the clip slip over possible, while leaving enough of a hump that the clip is still securely located in the groove. This is trial and error. The tension in the brush springs should hold the brush housing in place while you experiment with that little cap.
* The rest of the job is essentially a downhill run, reconnecting wires and reinstalling fusebox etc. before heading out into the toreential rain!
So that's it. Sorry if my descriptions and methods are un-mechanical.
For the record, the relevant Chilton's manual was completely wrong on almost all aspects of my wiper set-up. The motor assembly is completely different from the diagram.
Hope this helps someone!