Oil Pump C2 L71?

[Robert K.]

Can anyone identify the following:

Oil Pump number...(top half - bolts to the piece below which houses the impeller

with 5 larger size machine screws which have a "straight slot"):

3906829 with a "GM 20" Logo

Oil Pump Number...(bottom half - body where impeller is):

3904828 with a "GMT"

I've looked pretty closely and these appear to be the numbers - I'm very sure of the 3904828 #......

[Joe L.]

Re: Oil Pump C2 L71?

Bob------

There's no way to positively ID the pump assembly PART NUMBER from the casting numbers which you provided. However, the pump ASSEMBLY is very likely one of the following:

1) GM #3904826-----67-69 with special high performance big block, including L-71. Also SERVICE for 65-66 with SHP;

2) GM #3904827-----67-70 except SHP and HD.

It could also be other pumps, but the above are the most likely.

You could tell the above 2 pumps apart by doing the following: remove the oil pressure relief spring from the pump. Inspect the spring as follows:

24 coils, 2-7/16" free length, 5/16" OD, with light green stripe= GM #3904826

27/64" OD, 2-1/2" free length= GM #3904827