68 deVille A.I.R. pump revisited

[Steve W]

So, from time to time over the years, I have complained long and loud about the #%&@* A.I.R. pump in my car. I hate it! The first one froze up, then this replacement was making this awful sound...like a muffled popcorn machine but louder. It seemingly works, but just sounds terrible, making that beautiful 472 sound remakably UN-Cadillac! 

Over the years, and frequently discussed here, I looked at all the various options of deleting it altogether, but the remedy was either beyond my budget or skillset...or both! So I just lived with it...hated it, complained about it...but lived with it.

Then yesterday, I was again listening to this noisy contraption, and was looking very closely at the way it's configured, and doing some more research...and I got my long "listening tool" and put it up against the pump as its running...and all I could hear was the normal rotation of the pulley, that soft whirring sound...same as the alternator makes. Nothing out of the ordinary there. So...I saw this large rubber hose that goes from the pump to the T that feeds the metal tube that feed the heads, and while the car was running, I pulled it off...what a racket coming from that metal tube! So, I examined the hose, no blockage, no holes, clamp OK, so I turned my attention to the T that feeds the tubes that feed the head, and just covered it with my hand...and...silence! That horrible sound was gone! That sound that I had hated, and lived with all these years...gone! 

So, I rummaged around and found a rubber cap that fit the top of the tube, and put the hose back on over it, and went for a drive. No back firing, no loss of acceleration or anything. Around town, freeway. No difference at all, except for that noise was gone.

So...this thing that sits atop the A.I.R. pump, where the big hose is coming from, I believe that's called "the silencer". I'm assuming it is in place to silence that awful racket, and mine is broken? I just dont know. I don't know enough about how this thing actually works, but if the noise is emanating from the tube without the a.i.r. pump hose attached, does that mean that that sound is coming from my heads? With my listening tool, I don't hear it in the engine at all! But if I pop off that cap and that hose....its back. So I'm keeping it capped, unless someone here tells me that it's bad for my engine to do so.  Thoughts?

[TJ Hopland]

I believe the assembly on the outside of the pump is called the diverter valve.  Its job in this case is to either send the air to the heads or divert it to the silencer thing. Its vacuum operated.  I think over the years they messed with when it goes where.  I know one time it diverts away from the heads is deceleration.  Not sure what it does other times,  I think its mostly sending air to the heads.

What often kills em is the check valve fails and lets the exhaust back feed through the system.  It first kills the valve then the bearings in the pump.   The check valve is the large nut adapter thing on the crossover pipe that transitions to the nipple that has the hose on it.  That same check valve was used on many American engines so they were available last time I looked for one.     

[Steve W]

I believe the assembly on the outside of the pump is called the diverter valve.  Its job in this case is to either send the air to the heads or divert it to the silencer thing. Its vacuum operated.  I think over the years they messed with when it goes where.  I know one time it diverts away from the heads is deceleration.  Not sure what it does other times,  I think its mostly sending air to the heads.

What often kills em is the check valve fails and lets the exhaust back feed through the system.  It first kills the valve then the bearings in the pump.   The check valve is the large nut adapter thing on the crossover pipe that transitions to the nipple that has the hose on it.  That same check valve was used on many American engines so they were available last time I looked for one.     

Bingo! Yep, it's the check valve making the racket! Now I just have to try to find one for my 'most-parts-are-one-year-only' beast! Thanks TJ!!

[Roger Zimmermann]

What would happen if you are disconnecting the vacuum hose going to the diverter? Would the noise go away?

[Steve W]

What would happen if you are disconnecting the vacuum hose going to the diverter? Would the noise go away?

If you're talking about the little vacuum hose, it makes no difference. But when I disconnected the big hose to the check valve..,that's when I discovered the source of the noise. It's the check valve, and, of course, I've been looking online for a replacement, and when I do find one, the pop up says "does not fit your 1968 DeVille".

[Gene Beaird]

I think the check valve is a 'standard-for-GM' part, vs. all the one-offs the 68 has.  Still, the valve is getting hard to find.  Our Calais developed a hole where the adapter from the A.I.R. pump goes into the head.  Luckily, a spot of JB Weld fixed that, and has held for several decades.  One of the very few times I've ever used the stuff. 

[TJ Hopland]

I did a little searching and the valve that is available says it only goes back to 77 on Cadillac.  Got me wondering if maybe it was metric threads?  But the same valve goes back to the 60's for say a Buick or Chrysler product so metric seems unlikely to be the change.

Maybe the threads are the same but the hose size changed?  I think the later one is 5/8 maybe earlier Cadillac used 3/4 so it would be something that would be easy to work around?  I don't think I have any of those sorts of parts around to look at.

It would not be the direction because the allowed flow is always from the hose to the threaded part.

I don't think there were really any different pressure settings because everyone more or less was using a similar pump so its not like Cad was using 15 psi vs 10 for others.

There are both male and female thread versions.  Was that a change maybe?

By the 80's they were putting one down near the cat converter, maybe those were able to take a higher temp than ones that were under the hood?

[TJ Hopland]

Look up Napa Part #: CRB 229000 and look at what it fits, Cad to 75 but there are other brands like BMW and Buick back into the 60's.   It also lists the thread as 1/2"-14 and the hose end as 3/4.  Strange that BMW and Fiat were using SAE threads but maybe they were buying the emissions parts from Delco or Mopar and fitting them on the cars they were importing to the USA to meet USA emissions? 

Cadillac 1975 could be when they made a new crossover pipe with a slightly different bend to clear the new larger HEI distributor. 

[Steve W]

Thanks TJ. I just don't know, but maybe I'll keep looking around, and if I can't find anything better, I'll try it and report back!

[Roger Zimmermann]

Some time ago, I had to buy a steering box cover for a 1975 car. I had the part number, but all on-line sellers who had the part did not listed this car. They stopped usually by 1981, the year when the VIN became a 17 position affair.
I bought one giving a wrong year/VIN; the part was OK for my application.
The part number should be, group 3.670 # 5354978, valve, pump check, on manifold. Was used for 1968 & 69 and, surprise, 71-75.

[TJ Hopland]

Roger, what year range was the book you got that number from?  Did it go past 75?  Just wondering if the part changed after 75 or if that was just when that book ended.  It would seem promising if it includes 75 because the one I found also includes 75.   Makes sense that there was no 70 because I don't think any 70's had that system.

[Roger Zimmermann]

My parts list is going through 1975. As I was leaving home, I had no time to check into another book. In two weeks I can do it...