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Discussion Starter #1
I’m looking to get an aluminum water pump for my 66 Mustang with a 289. Some of them come with the backing plate and some do not, what’s the deal? I’m pretty sure the cast iron one on there now has a backing plate why would aluminum come with no backing plate? Is it just a different style pump that doesn’t require it to have a backing plate? BTW, these are standard rotation passenger side outlet water pumps Im looking at.
 

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Early 1965 used an aluminum water pump without a backing plate, later in 65 and on they started using a cast iron water pump with a backing plate. They use different timing covers so you can't interchange them, but there are aluminum water pumps made now with a backing plate that I believe may all be high volume pumps.
 

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Yes, the water pump, timing cover, and camshaft retainer were changed with Change Level 7, as a "running change" during the 1965 model year. The 'before' CL 7 pump was aluminum, the 'after' CL 7 pump was iron. Naturally, aftermarket pumps can be made with whatever material the manufacturer decides.
 

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The plate is there to create the correct spacing for the water pumps vane to push the water. The vanes need to be close to the plate. If the plate was not there the water would be forced rearward towards the timing cover.

You do need to make sure you are using the correct timing cover and water pump for the year of your engine. You cannot always count on the parts you remove being the correct one. You have no idea what somebody has done to it before you got it. The plate is also there to prevent electrolysis from eating a hole right through the timing cover. We had this problem at work on Dodge 360 engines. They would eat a hole right through the timing cover, right behind the water pump vanes. All of them were doing it (poor engineering) .The oil pan would have coolant in it and you would start thinking about all the bad things that could cause coolant to end-up in the oil pan when all it was is a pinhole in the timing cover. You can bet that if the Ford engineers added that plate to the water pump there is a good reason for it.
 

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my 14 Aug 64 coupe has a backing plate. IDK what it came off the line with, but its on there now.
 

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Discussion Starter #7
Here’s what I ordered. It’s aluminum and has the backing plate to replace the cast iron one I have now.
347ED219-EF18-449B-994E-FADF483B5C3D.jpeg
 
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