The common failure mode of the wiper motor is a loss of it's ability to keep the vacuum contained. Allowing the failed motor to keep wasting vacuum will severely limit the other wiper's ability to perform at an acceptable level. So a shutoff valve on the wiper motor is a useful addition. However the original M38A1 wiper motors had no shutoff valve on them.
This issue has been hashed out 100's of times in the last 20 years here on the web.
If you want a factory original show M38A1 you'll need the Trico 63527, WO# 681080, ORD# 7375189 wiper motor in both positions.
It will look like the left one in this photo:
If you want function for a motor pool resto or driver and you have one original and one with a shutoff valve put the shutoff valve wiper on the Passenger side. Then if it fails you can turn it off and still be able to use the drivers. Or if your vacuum is getting weak you shutoff the passenger side to improve the performance of the driver's side.
Joined: Mar 21, 2017 Posts: 68 Location: Peoria, AZ
Posted: Mon Nov 26, 2018 10:44 am Post subject:
Thx Wes, I had read the other entry on G503 but it did not adequately explain the need for two switches - I am using a used vac wiper motor from another vehicle that had the built-in cutoff switch - while I understand that wasn't original, I will use it anyway just to have a vacuum wiper for discussion. _________________ Lee Long
1953 M38A1 USMC
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