Backing up for a minute. I should have asked this first:
How is your overall electric system? Are the alternator and battery in good condition? What does the dash voltmeter read at idle speed? If you revv the engine, does that seem to increase wiper motor speed?
If all those things are okay, go to the wiper diagnostic.
However, it's nice and slow like they all get when they're old. You mentioned rebuilding it at home. What's involved there?
Ahh...there's really not too much, but you'd have to be familiar with small DC motors. Also, you'd have to wing it - there are no rebuild procedures available, that I know of.
Unless you are extremely "thrifty" and have lots of time/patience, you probably don't want to rebuild that motor. Another issue is parts. If inspection/testing doesn't reveal any other obvious
external problems, it's most likely the brushes that are to blame for the slower than normal operation But I don't know if replacement brushes are still available.
Last time I rebuilt a anything with brushes was about a year ago. It was a Bosch alternator. And while a complete voltage regulator assembly was available everywhere, the best price was like $90. I tried for a few days but I couldn't source just the brush set . Ended up buying some similar brushes from an old guy who was still running a auto electric repair shop. I had to file them down to make a custom fit with the rigging. But - he only charged me $5.
I wouldn't jump right to the motor just yet anyway. I would inspect the linkage and run the motor with no load, before tearing into a fairly involved motor repair.
Here are the first tests I would do.
1. Just pull the wiper arms forward until they are locked in the off-glass position. Then, with the arms/blades no longer in contact with the windshield, run the wipers at both speeds. Note whether they now operate at normal speed. If so, inspect/replace the wiper blades. If there is no noticeable increase in speed, do the next test:
2. Run the wipers without the transmission system connected to the motor output shaft. That will confirm/eliminate the transmission system as the problem. The "transmission" system is just a fancy term for the pivots and arms that connect the motor to the wiper arms.
You'll see different ways to disconnect the motor from the linkage.
The standard factory procedure involves removing the air inlet grille panel (AKA the wiper cowling) and the air inlet screen (the plastic strainer under the cowling) and accessing the ball joint through a slot in the steel frame of the cowling.
I just release the 3 mounting bolts. Then I pull the wiper motor body away from the wall - just enough to get a wrench on the motor shaft nut. There is plenty of play and flexibility in the linkage to allow the motor to be pulled out.
You must be registered for see images attach
You must be registered for see images attach
You must be registered for see images attach
With the motor separated from the wiper linkage, arms & blades, you can test run it and see if it runs any faster. You can also play around with the linkage - through the hole - and check it for loose joints or binding.
Make sure the motor is in the parked position when removing and re-installing the crank.
Also, if you use my method for removal, take note of the crank arm position when the motor is parked. It has to go back on in the same direction. The shaft and the hole in the crank arm have flat sides but they can still be 180 degrees off.
