I have a 63 cadillac and I took it to a mechanic for a motor tune up long story short the fuel pump gave out and hes tried twice to order it and he says it didnt fit the original pump is smaller on the round part then the one they sent him but I dont know why is it bigger ?so when he goes to put it on it hits the motor he wants to go with an electric fuel pump but I dont want electric anyone out there know why we keep getting the wrong pump?
Daniel, my best guess is that your mechanic is ordering a fuel pump for a Cadillac 390 engine, needs to order one for a 1963 390 engine. Normally would not be an issue, but we are talking Cadillacs here.
There are two different 390 engines — a 1962 and 1963 Cadillac
The 63 is a smaller redesigned 390 engine so that may be part of the problem in getting a correct 390 fuel pump for yours
Do stay with a mechanical pump if possible
If you go with electric be sure you install a shut off valve in case of an accident to shut the pump down
You may have to open the new mechanical fuel pump and be sure the valves in the fuel pump are staked ( attached to the fuel pumps base ) as some have not been staked which cause a problem with being very short lived
Hope that helps some
Those numbers are not the engine S/N# (VIN) Here is where to find that:
The VIN will tell you exactly what the motor is but here is a quick dirty method to tell the difference between the old and new 390:
59-62 390 - distributor is in the rear of the engine.
63 390 - distributor is in the front of the engine.
There are 2 versions of fuel pumps used. Both work as advertised. the pump on the botton in the second pic is the original design. There has been problems with the remanufactured original design pumps (new and reman) The valves pop out after a tear to 3 years.
Fortunately it looks like a new internal design has hit the market. The valves are installed from a different direction, so the fuel pushes the valves against the seats, instead of trying to push them out.
First pic shows the new design. Best way to identify the new design is the screws on the bottom of the pump. The new design has Philips screws.
The brand of the new design is HERKO
You can get a rebuild kit for the original pump, it’s a pretty straightforward task. It took me about an hour and a half.
I bought the Carter M3993 pump for my 64 429. The 63 390 takes the same pump. It fit and works perfectly. I got mine from Rockauto. They have it in stock. Amazon has it too but Rockauto is cheaper by more than $10, and they ship faster too.
Something is really off here, because that is the correct pump. Check the photo of my engine with this pump installed...