There have been reports of the Melling stock replacement pumps breaking off part way up the leg that bolts them to the main cap....but that was several years ago and Melling seems to have fixed that problem. It was a big issue though, at the time.
For a while, and i believe still....Melling does not recommend stock pumps in performance applications.

If you look down the distributor hole and don't see a pump drive, you'll know if that is what has happened.

About the only other thing that could effect oil pressure is the pick-up fell off the pump.

The pump bypass may be stuck open...but that should still show a small amount of pressure on the gauge....maybe at idle and with synthetic and warm it could show zero?

 

Only problem I have ever had was with the pickup falling out (not welded) or the bypass spring that stuck, otherwise never had one fail.

 

I have never had a problem with a Melling oil pump. I used them on everything. abou twenty years ao G / M changed the design of the SBC oil pump and weakened it at the neck where it bolts to the rear main cap. I understand that they had problems with this redesign. I have never used one of these pumps nor would i have used one not even in a stock build. I always replaced the oil pump on a build with the old M_ 55 A z-28 pump. If the customer wanted an economy build i would rebuild the original pump weld the pick up and use the pink Melling z-28 spring or the white G/M #3848911. I have only seen one of these cheap pumps. In all my years i have never seen a bad G/M gear type oil pump they would still pump oil even sludged up. I understand the pump to use now is the Melling 10552 pump with the bolt on pick up screen. .If all you can get is the light weight version rebuild the oriinal pump with a Melling rebuild kit. Alex

 

If it was the stock pump shaft, it could have sheared the tangs off for one reason or another. All of my small and big block Chevy builds have always gotten the HD pump shaft with the steel collar.

 

Do a search ,,all is explained . Been discussed in detail .
At least 4 different generations
1st gen all ok
2nd gen had neck reduced on the standard pumps [basically 1st gen redone ]
People remember the 3rd gen Gen Performance units were called ,,,,M--SELECT released same time as 2nd gen

4th gen are shark tooth versions

Problem was the marketing dept did a really really bad job .
The part numbering was confusing .
Some people fitted the cheapest pump in a performance application and found major issues .
Perf pumps were a separate line up / series of units .

Unless your running big sumpl , oil restrictors ,large clearances ,,turbo/supercharger , big oil cooler NO NEED to run PLUS+ 25% volume

10% + volume is enough

3different springs come with the high end units with screw in relief plug
THESE DONOT INTERCHANGE with std. units

Many unit versions come with a bolt on pick up . Recommended to wire tie and loktite bolts

 

Could it be a faulty oil pressure sender ???
Guy

 

No, I have an electric gauge and the sender is in a T with the stock oil light sender. I am extremely thankful right now that I decided to do that. Pulling up to stage, I would likely never have looked down at the gauge, which is mounted on the console. Anyway, the light came on, which alerted me to look down at the gauge.

 

Pump shaft is still accessible but spinning it with a drill has no resistance. Looks like the pan will have to come off as soon as I can get it in on the lift. Bummer.

 

Curious to see what you find. I have used Melling pumps pretty much exclusively for the last 35 years and never had a problem.

 

Well the good news is that light probably saved you an engine. While you have the pan off you might want to look at the bearings just to be safe.

 

Well, I ordered a new Melling 10555st shark tooth pump. Not much point in pulling it apart and not going with a better pump. It's probably going to at least mid-week before I can get into it. It also depends on whether I can get the engine high enough to get the pan off or if I have to pull it out.

Good advice. I do plan to do that even though I don't expect to see any damage. I shut it off within a second or two of the light coming on. Still, better safe than sorry as long as I have access.

 

I always keep the indicator lights. Then I use block mounted mechanical gauges.

On Pontiacs the bypass would stick and the oil pressure will go down. A couple good bursts in first or a downshift burst at 20 mph usually freed it.

 

hi
The spiral /helical =sharktooth already flow more because they are longer than straight cut
10552st
+10% flow
3 pressure spring
bolt on pickup 3/4 inch

 

Bill,
What Eric said Sounds like the bypass was stuck open. Sometimes it wont come all the way out due to a little burr where the pin hole is but otherwise it should slide back and forth in its bore very easily. If somebody welded the pickup without taking the bypass out first that could be what caused it. I take the bypass out of every pump I use and make sure it moves freely.

 

I did weld the pickup without taking the bypass out. My mistake. I have been doing that for more years than I can remember and this is the first time I've ever had an issue but this is certainly a valuable lesson to learn. I had ordered the 10555st pump and got it on Wednesday, but after further reading on these pumps I decided to send it back and get the 10552st. I have a busy weekend but hope to get some time to start putting it back together. I also plan to install the yellow spring and step down to 10W30 oil from the 10W40 that I've been using.

I haven't visited this site much the past few years except to research something, and I always find the answer. You guys are more helpful than you may know. Thank you.

 

Well, I finally managed the time to get it back together. Melling 10552st pump with the yellow pressure spring. Cold idle: 44psi. Cold@2,000rpm: 60psi. Hot idle: 22psi. Hot @ a WOT pull to about 4,000rpm:: 60psi. Mobil 1 10w30 oil. I was a little nervous about this pump after reading about some of the issues with them having too much pressure but right now I'm very happy with the results. Thanks everyone for all your help

 

AutoMeter Pro-Lite Warning Lights 3240
Mine is set to be on below 20 psi.

 

hi
Skylark
Any idea of crank /rod clearances ?? Are u using H series bearings ??

10W-30 , 10w--40 ,, 15w--40 all ok to use

 

I just had a engine fresh out of the machine shop and the guy at first didn't think it was possible, that was on Saturday and took it back today and he showed me another Melling oil pump where the shaft broke on another moter just priming the oil pump . He is 60 and been doing machine work since he was 18 and said this is the 2nd pump in 48 hours that was brand new that broke a shaft

 

I had a pump seize on my Ford 302 at 6g . It sheared the distributor gear roll pin and twisted the shaft. This was a Melling stock pump with maybe 1200 miles on the new built engine. There was No debris in the pump or pan . The bushing in the pump wore on one side due to shaft deflection which caused the impeller to jam. I just upgraded to the performance Melling which has a bushing in the cap as well. Hope this information was helpful