74 Original Oil Pump Questions

[Victor S.]

Hi All -

Specifics on my car:
74 454 BB convertible
manual tranny (M-21)



Just trying to figure out what pump should be in there and if 475906 is the correct pump or I'm wasting my time on the wrong pump. I really would like to go back to the factory stock oil pump if I can.


Any thoughts would be greatly appreciated.
Thanks and Happy Holidays to all the Corvette lovers!!!

[Joe L.]

Re: 74 Original Oil Pump Questions

Hi All -

Specifics on my car:
74 454 BB convertible
manual tranny (M-21)

I've searched in my 74 assembly manual and cannot find an oil pump part number - so my first question is:
What is the original part number?

Second Question - would the original factory oil pump have been standard or a high volume pump for my car?

I tried to fit a NOS pump (#475906) but could not get it to fit into the stock oil pan. I’m positive my pan is correct and original but if pump (475906) is correct then possibly the pickup screen is the wrong size as every one of these pumps I’ve seen have slightly different pickup screens – I’m assuming that pump was used on various other big block Chevy’s including vettes. The aftermarket HV pump which was on the car when I got it allows the pan to cover properly - but the 475906 is hanging up – just can’t get the pan on. I have removed the starter and lowered the idler arm for clearance but its hanging somewhere I can't see.

Just trying to figure out what pump should be in there and if 475906 is the correct pump or I'm wasting my time on the wrong pump. I really would like to go back to the factory stock oil pump if I can.


Any thoughts would be greatly appreciated.
Thanks and Happy Holidays to all the Corvette lovers!!!

Victor------


The original oil pump for your application was GM #3904827. This part was discontinued in the mid-1970's and replaced by the GM #475906. The GM #3904827 was not supplied with a pick-up screen. The 475906 may have been supplied with a screen but I do not know what its configuration was.

The configuration of the actual 475906 pump assembly, less the pick-up, should be virtually identical to the original pump. Assuming that the 475906 pump as you have it with attached pick-up actually does not fit (which I kind of doubt), the 475906 pump with a GM #3955282 or GM #6269895 pick-up screen should absolutely fit assuming that you have an original Corvette oil pan.

All big block oil pumps are essentially high volume. However, the pressure relief springs differ.

[Victor S.]

Re: 74 Original Oil Pump Questions

Thank you Joe - really appreciate all your help -

Vic

[Duke W.]

Re: 74 Original Oil Pump Questions

Victor------



All big block oil pumps are essentially high volume. However, the pressure relief springs differ.

There's been a lot of discussion about this over the years, and I think the L-88/ZL1 oil pumps had longer gears, so they were higher volume than plain vanilla pumps used on other big blocks including SHP.

I don't have access to the AMA specs right now, but I recall '67 lists 50-75 psi, hot at 2000 RPM for all three big block engine options, which seems like a rather broad range. The OP should look at the '74 AMA specs to see what the hot oil pressure spec is, but it may be a problem finding a spring that will deliver the proper range.

BTW, the reason why there is nothing about the oil pump and relief spring in the AIM is because those parts were installed at Tonawanda. This applies to a lot of other parts that were delivered to the plant as "assemblies". For example the front knuckles and rear trailing arms were delivered to St. Louis complete with all the brake hardware. Thus, you will not see wheel bearing, caliper, and brake pad part numbers in the AIM, and the assemblies as delivered to the plant were not available through service parts - just the individual knuckles, bearings, trailing arms, and brake parts.

Duke

[Joe L.]

Re: 74 Original Oil Pump Questions

There's been a lot of discussion about this over the years, and I think the L-88/ZL1 oil pumps had longer gears, so they were higher volume than plain vanilla pumps used on other big blocks including SHP.

I don't have access to the AMA specs right now, but I recall '67 lists 50-75 psi, hot at 2000 RPM for all three big block engine options, which seems like a rather broad range. The OP should look at the '74 AMA specs to see what the hot oil pressure spec is, but it may be a problem finding a spring that will deliver the proper range.

BTW, the reason why there is nothing about the oil pump and relief spring in the AIM is because those parts were installed at Tonawanda. This applies to a lot of other parts that were delivered to the plant as "assemblies". For example the front knuckles and rear trailing arms were delivered to St. Louis complete with all the brake hardware. Thus, you will not see wheel bearing, caliper, and brake pad part numbers in the AIM, and the assemblies as delivered to the plant were not available through service parts - just the individual knuckles, bearings, trailing arms, and brake parts.

Duke

Duke------


Only the ZL-1 and LS-7 oil pump ever used the longer gears for higher volume. These gears were 1.3" long. All other big block pumps used 1.1" gears. Of course, there was a difference in installed relief spring depending on the specific engine. L-36, L-68, LS-5, and LS-4 used the lower pressure spring. L-78, L-72, L-71, L-88, LS-6, ZL-1, and LS-7 used the higher pressure spring.

By the way, the ZL-1/LS-7 pump assembly is still available from GM in SERVICE. It can be used for any big block but, for hydraulic lifter engines I think I might substitute the lower pressure spring. This pump is supplied with a tack-welded oil screen/pick-up and will fit perfectly in a Corvette oil pan. It's GM #3969870.

[Justin S.]

Re: 74 Original Oil Pump Questions

Joe,
Irrelative to this thread, since the LS7 wasn't a production option, if you upgraded an LS6 Chevelle back in the day, would the dealer supply the different oil pump as well as the heads?

Justin

[Joe L.]

Re: 74 Original Oil Pump Questions

Joe,
Irrelative to this thread, since the LS7 wasn't a production option, if you upgraded an LS6 Chevelle back in the day, would the dealer supply the different oil pump as well as the heads?

Justin

Justin------

It depends what you asked the dealer for. If you asked for a SERVICE oil pump for an LS-6, you would NOT have been supplied the GM #3969870 oil pump. You would have been supplied the GM #3904826 (or, if much later, the GM #475908). If you asked for the GM #3969870, that's what you would have gotten. If you asked for an LS-7 oil pump, it would depend upon how much the counterman knew about the LS-7 since most LS-7 parts were not cataloged in regular P&A Catalogs.

The same thing holds true for cylinder heads.