Oil pressure in my 1976 L48 is low so I am taking the oil pan off to have a look. I plan on replacing the oil pump. I have never done this job before so I am a little green.

My question is this...do I need to buy just the pump or do I have to buy the shaft as well?

Many tell me to put a higher volume pump in. Based on cost it seems like a good idea.

 

didn't come with one from the factory that way. I don't use them.

low pressure can be caused by other things as well like worn bearings (now too much clearance between bearing a crankshaft). don't be suprised that if you change the pump, it doesn't change the pressure much.

 

which pump you use and why will start arguments that will last till next lifetime, Its pretty much a personal choice, my personal favorite is melling in what ever version you feel comfortable with. Replacing the pump shaft with a pinned steel sleeve one is best. The plastic sleeve thats in there will probably break in your fingers. You do know you will need to drop your exhaust, and steering drag link. If you had a little more experience, I would suggest rolling new bearings in, rod's and mains, its an old school way to do a poor mans rebuild along with a few other things. I just completed doing mine , with a melling hi-volume , a steel sleeved shaft, and a Z28 spring, very happy with it. If you decide to go hi-volum, get a hi-volume pickup also. If you have those light rod knocks on startup you are to late for it to last any length of time and will be wasting your money. hope this helps

 

oh , yea, starter and flexplate cover have to come of too

 

If your oil pressure is low, then then likely the bearing clearances have opened up. You could try an HV pump as a crutch...but it's not a lasting solution to the problem.

I personally wouldn't try to swap bearings - I've never seen long-term success with that approach.

The reality is that you're looking at an overhaul. Better (and cheaper) to do it when the engine's together and running than when it goes boom.

 

on an engine with no issues, rod knocks, low compression etc. and bout 80 thousand miles, I do them on a regular basis, good valve seals at the same time, smoke or not, no issues. if you're doing all the work to get to the oil pump and the issue is low oil pressure, no reason not to , you can ,wih good maint. get another 80 thousand, if you're experienced enough to complete it with success. you not hearing much about it doesnt mean its not good tech, it just means you've not heard much 'bout it. hope this helps

 

Thanks for the input.

Yes, I had read to remove the steering linkage and the exhaust pipe. Already started that.

The engine doesn't make any knocking noise. I hadn't used it much when I noticed that it was low. I changed the oil and filter (read bad things about Fram so I put in another filter). Once the oil and filter were changed the pressure dropped even more on start up. I didn't drive it after that.

I thought it might be a good idea to take the pan off and have a look. Perhaps the screen is blocked. If it is I will change the pump while in there, put it back together and see if that improves things. If it doesn't then I will let the car sit for the season and rebuild the engine in the winter.

 

if you only do the pump, upgrade your oil to 20-50 and put a wix filter, make sure to get a hi-volume pickup also, dont want to starve the pump, get a Z28 bypass spring and install it, if you want, should give you 50-70 lbs at all times cold or hot least it does on mine. BTW the Z28 spring is sold by everybody, but GM has a part number for it.
#1255884, been usin it for years

 

I put in a oil pump rebuild kit when I redid the rear main seal. It had new impellers, plastic sleeve and two springs. One was specifically for the Corvette. I cleaned everything I could. It all looked fine. It took some time to get all the crud out of the pickup and screen.

My pressure went up 10-15lbs after the rebuild.

Good Luck

 

Do you know what oil was in it, and what oil did you put in? A major change in viscocity could have also changed the pressure...

 

It would also be a good idea to verify the pressure with a manual gauge before you get too carried away.

 

10W30 was in it.

Pressure verified with a mechanical gauge...it matched what the electronic gauge was reading.

Back to the garage tonight to continue taking things apart.

 

'75 is right. Check your oil pressure with a different gauge to make sure that you really have a low pressure problem...and not just a gauge giving you 'bad' data. If it does check low, then the problem is either engine/bearing wear or oil pump damage (internal leakage).

If you find a 'real' engine problem, drop the oil pan and pull a couple of rod bearing caps to inspect the amount of bearing wear. You will have to find some reference material that will help you judge whether you have a bearing problem, or not. Then, you can also remove your oil pump and disassemble it, so you inspect the surfaces inside the pump for scoring/wear. A 'good' pump will show some light scratches, etc. around the bores of the pump, but should not have any heavy grooving or much wear at the end faces. That heavier wear is what causes loss of pressure in any pump.

If you see no significant wear on bearings or pump, you could also have a problem with the pump sucking air because of some crack/hole/breech of the suction tube above the oil level in the pan. Or, if the O-ring seal on the end of the pickup tube has gotten hard and loose {so that it could suck some air into the pump}, that could also be your problem. Yes, it could be as simple at an old/bad O-ring on that pickup tube.

Lastly, if you aren't doing any heavy racing or going WOT a lot in your car, you would do best to just keep a 'stock' oil pump in it. They were designed to lube the engine well, but not waste energy by pumping unnecessary oil into the system under low rpm or low load condition. Putting a HI-FLO pump into a stock engine with significant miles on it can cause more problems that it might help. Millions of GM cars have been on the road for up to 50 years with those pumps, and they rarely go bad, unless there is some other internal failure that throws trash into the oil circuits. Basically, there's no need to throw money at a problem if there is NO problem.

 

.that a lot of ifs, to the op , stick to your original plan, whichever pump you use make sure to install a good copper gasket in between it and the mounting surface, make sure you torque it to specs. its only one bolt, gently insert the pump shaft into the bottom of the engine and if it doesnt seat ,bring it down and rotate the shaft till it will, if you dont have the experience , dont get caught up in the pull this , check that, if you didnt have rod knocks before you wont have them now. I literally just did this on my 76 3 days ago....btw, if you let it drip for a few hours after you drop the pan, you wont have it dripping in your face....as much.

 

There is no o-ring on a GEN I SBC oil pump; the pickup tube is a press fit into the cast oil pump body with no seals anywhere, and braized into the pickup end.

 

sometimes....they braze them
if its not brazed , it just means its never been out since new, in my older age , I've started goin with the bolt on pick ups, I pulled pan on a few brazed ones that were sitting loose in the pan.

 

The point is for the OP to see if there are any 'leak paths' for air to enter the pickup screen/tube. If there are, the oil will aerate and the pressure will be low.

P.S. If you don't check out the "IFs", then you're just throwing money at a problem until you 'luck' into fixing it....

 

I agree , 'if' he had the experience to do it. he will learn , in time, when he does his rebuild next winter, but to just get better oil pressure in an engine without any other issue, he's doing fine. imho

 

Thanks to everyone for their input.

Once I get the pan off I will have a look around. I am going to stick with a stock pump because stock has kept it going this long so it should be fine.

On a side note, I was under the car taking things apart. Exhaust bolts are off and only a couple of bolts remain to get the oil pan off (only trying to loosen them while I read how to remove the steering linkage) While laying under the car and making progress some stray German Shepherd came into my garage to get out of the rain. Currently waiting for the Humane Society to come get it so we can find the owner. It is a nice dog. Then I will go back under the car.

 

The pump is now out of the engine. It makes more noise when I spin it by hand than the new one does.

Now to put it all back together.