1938 LASALLE

[DAVID E]

Is it important to have the pipe from the back of the air cleaner? And If so where on the engine block will a port be? and what is the tube made of?
I do have the pipe from the carburetor to the left engine head.
Dave

[harvey b]

Not sure if 37 is the same,on my 37 the tube goes to a rubber grommet in the lifter valley below the intake,it just pushes in the back of the breather and points downward,it is about 1/2 diameter tubing,has a couple of bends in it,its about 18" long,there doesnt seem to be anything holding it in place,it just sits there,mine hasnt moved in about 5000 miles .The other pipe you mention must be the carb stove?,it is neccesary for the choke to work properly,my 37 has an electric choke,it still works too?.my car is in storage now,otherwise i could get you a picture of the pipe. Harvey

[Steve Passmore]

David, the pipe on the back of the air cleaner connects to a fitting under the inlet manifold then as I remember to one of the lifter valley covers. Its made of steel. Its an early form of sealed crankcase ventilation which pulled crankcase fumes into the manifold and air cleaner to recycle it. It was pretty useless as by 41 it was full flow ventilation straight out to the road. On both mine the fitting into the manifold was never drilled as though they realized that part of the plan wasn't going to work in practice.

[Tom Beaver]

David,  I think it is probably a good idea to put the rear breather pipe in.  It is a 1/2" thin wall steel tube about 20" long and goes from the fitting on the back of the air filter housing down through a rubber grommet in the hole on the top of the rear lifter access cover.  There are three bends in the tubing, the first is a 90 deg. bend approximately four inches from the air filter connection which allows the tube to clear the exhaust manifold crossover pipe.  The second and third bends form a dog leg starting approximately 12" below the first bend.  These two bends are not quite 90 deg. and are used to align the tube with the rubber grommet in the rear lifter cover.  The tube is fairly easy to fabricate because all of the bends are in the same plane, especially if you have ready access to the engine.

The front breather is 3/8" tubing that goes from a 90 deg. tube fitting on the bottom of the intake manifold directly under the carburetor to a fitting that presses into a rubber grommet placed in the hole on the front lifter access cover.  Like Steve, I have issues with this particular arrangement because it essentially forms an intake manifold leak as it allows air flow to bypass the carburetor.  Also it potentially allows raw gas to enter the crankcase.  While I have installed this tubing on my engine I have also blanked it off to stop the air flow.

I looked but I don't have any good pictures of either breather pipe.

Tom Beaver

[Steve Passmore]

Tom, this front breather pipe on the 37/38 is a bit of a mystery. When I had my engine apart a few years ago I was checking all pipes were clear as you do and I noticed that the fitting under the manifold was not clear into the manifold interior. Thinking it was crud or rust blocking it I ran a tiny drill bit through it. I seemed to be drilling out cast iron. Thinking that it was a flaw in the factory where they had forgotten to drill it I fitted it back on the car.   It ran absolutely terrible! I took it back off and plugged it and it was fine again. Recently bought another 38 and that too is not drilled through.

[DAVID E]

Thanks for the update.
I will fabricate a rear tube with fitting
I have the 3/8 tube installed, should I disconnect this tube?
so what problems did you have just that the car ran poorly? or hard to start when cold?

[Steve Passmore]

Its idle was as though the pipe was off to the vacuum wiper, shuddering all over the place.

[DAVID E]

Tom,
 on the cover for the lifters, there is a tube coming out and it is going to the oil filter canister. Should there be a union for both lines?
 

[Steve Passmore]

That sounds like its just the return flow from the filter. Don't mix that with the crankcase ventilation tubes that we are discussing.

[DAVID E]

Thanks, Steve I will look around some more.  It must be under further than the return line for the filter

[Brad Ipsen CLC #737]

I have not done a 38 V-8 but the late V-16 (38-40) has a similar design.  The fitting at the intake manifold is not an open fitting.  It is solid with a 0.090" orifice in it.  The size of this orifice should be relative to the size of the engine (cubic inches) so I would expect the V-8 one to be smaller.  As long as you adjust the idle jets and throttle setting with this small air bleed active the idle and starting are fine.  I have this all hooked up as stock on a V-16.  Attached are pictures I obtained some place of a 38 system but I cannot verify that the loop scheme is exactly how Cadillac did it but it seems reasonable.  Interesting how Cadillac had a positive crankcase ventilation system decades before it was mandated but their experience with it in 1938 didn't lead them to try again until it was mandated. 

[Tom Beaver]

Tom,
 on the cover for the lifters, there is a tube coming out and it is going to the oil filter canister. Should there be a union for both lines?
 

David, I have not seen a lifter cover with a tube connection like you are describing.  I think the only year that Cadillac equipped the V8 engines with an oil filter was 1937 and this canister type filter only supplied oil to the hydraulic liters through a single line to the fitting in the middle of the block between the two lifter covers.  After 1937 filters seem to be a dealer or after market item and bypassed oil from oil gallery on the block back to the crankcase.  The only oil return from these filters that I have seen is a tube running from the filter to a hollow bolt on the timing chain cover.  But, as Steve says some installations may have run the return flow back through the lifter cover it probably doesn't make any difference.

Brad's pictures show the 3/8" vent line I was referring to along with the rubber grommet which fits the large hole in the top of the front lifter cover.  Steve, I have two 1938 intake manifolds and both of them have holes that go up into carburetor plenum behind where the vent fitting screws into the manifold.  The holes seem to be rather crude but they go all the way through and my guess is they are more than 0.090".  Brad, is the orifice you are speaking of a separate part that screws into the manifold or is it just a drilled passage or is it part of the brass fitting?

Tom Beaver

[Steve Passmore]

[quote author=.  Steve, I have two 1938 intake manifolds and both of them have holes that go up into carburetor plenum behind where the vent fitting screws into the manifold.  The holes seem to be rather crude but they go all the way through and my guess is they are more than 0.090". 

Tom Beaver
[/quote]
Curiouser and  Curiouser Tom.

Brad, that loop system is correct, to stop fuel running back into the engine I guess. You may well be right about the tiny orifice. If it was even smaller than 0.90 I would never have seen it. 150lbs of air pressure would not blow through it and the smallest piece of wire I had could not find a way through. Its purpose is still a mystery as the car has been running fine for the past 4 years without it?

[DAVID E]

Brad's  picture is correct, the steel tube with a loop goes from the front lifter cover to the bottom of the manifold under the carburetor

Then on the rear of the of the lifter cover the steel tube they have going to the top of the oil filter canister, and then a steel tube from the bottom of the canister goes to the back of the engine block.

I have not seen any more ports.

[Steve Passmore]

On mine David the front cover pipe go's to the manifold fitting you mention but it's a 'T' fitting. The pipe then continues up to the back of the air cleaner.

[DAVID E]

Thanks, Steve,
I just need to put a tee in there and make a new tube line for the air cleaner.

[Tom Beaver]

On mine David the front cover pipe go's to the manifold fitting you mention but it's a 'T' fitting. The pipe then continues up to the back of the air cleaner.

Steve,  that is very interesting, you don't have anything connected to the rear lifter cover?  The 37/38 Cadillac shop manual includes a schematic of the block ventilation system which shows two separate tube arrangements.  The front loop tubing connected to the intake manifold and the front lifter cover which was supposed to operate at idle and slow speed.  The second, a larger pipe, connected between the rear lifter cover and the back of the air cleaner, which was supposed to take over at high speed.  That is the way my 38 was hooked up, as well as two other 38 cars that I have been able to look at.  Maybe at some point they decided they didn't need the second tube.

I have the other engine sitting down in barn I will take a picture of it tomorrow.

Tom Beaver

I took a couple of pictures, one of each vent pipe.  On the rear pipe I added a PCV valve just to be on the safe side and shortened the tube accordingly.

Tom Beaver   

[Steve Passmore]

It is odd how they changed things during the same manufacturing years Tom because David said he has no other connection in his back lifter cover just as mine never. I have not removed the manifold from my latest 38 to see what's on there.

[DAVID E]

Brad,
On your picture under the intake manifold is that a T fitting ? if so what is on the back end of that T fitting ?

[DAVID E]

Steve,
 I do have a port on top in the back of the lifter cover. but they have a  tube going to the oil filter canister from that location.