Alan:

Interesting comparison photo's. Your explanation makes sense to me, however I would add that this would indicate that the internals (or assembly there of) have changed as well between the two versions to allow the input side of one version to become the output side of the other version. On the installations that I have seen, the vacuum fitting is always on the side of the valve facing the carburetors.

Sorry also to jump into this so late. This is one of those conversations that sends you to the garage for a while! Her Majesty had her emissions removed as a child and never has had all that garbage, but Princess 27 has been turning out to be a remarkably original car - - - covered in rust. Everything seems to be there. The AB valve is like your one on the right, Marty. It has the angled fitting for the hose to the carb and it has the slot in the bottom of the casting. I took pictures and will post them later.

Carl,

You are correct, and if you look at the diagram in the parts CD, when the valve turns 90 degrees to fit the later style the straight vacuum take off is put on the other side of the valve for that very purpose.

It's easier to see when you've got the two items in your hand.

Alan.

Alan,

Thanks for digging out your old part. I went back to the parts CD for a closer look. Initially I only looked at the earlier version (which is what I needed) which you don't see the take off tube very well at all. When I zoomed in on the later version, I could clearly see that the take off tube is at a 90 degree angle.

In the mean time, I went to Kats website. His car is almost identical to mine, being built only a couple of months earlier. His has the take off tube at a 45 degree angle also, just like the new part I got. And we all know what a stickler for details he is!!!

What really confused me was that my 70 and my early 71 (blt 1/71) both apparently got fitted with the later version of the A-B valve some where along the way. I guess that also solves the mystery of whether it will work or not. The car doesn't care which side the take off is on. It is just a matter of which is more CORRECT for the year of your car, if you even care about that.

Well, I am really happy I got the right part. These things are getting like hens teeth to find.

A big thanks to all of you guys for helping to figure this out.

Marty

Now to put that bad boy where it belongs!

so what does it do again??

no one helped me out

Post #11 by Mark answers your question.

so what does it do again??

no one helped me out

I'm disappointed, dude! I spent ALL that time writing up the answer above!

no one helped me out

No one looked.

Well, it involved reading, Carl.

Hey Mark! Your two valves on the right match mine. Notice the brand new one is correct, but the casting is not the same?

Hey Mark! Your two valves on the right match mine. Notice the brand new one is correct, but the casting is not the same?

Well that's good! At least I seemingly have two used correct ones. The angle of the vacuum line on the new one is wrong, though. It is parallel to the other inlet/outlet ports instead of angled out. As I noted, the casting is totally different - all one, cheap piece. The older ones are much heavier castings, and the inlet/outlet ports seem to be pressed in, and not integral.

Probably an example of the original part being over engineered initially, and later redesigned in deference to the bean counters.

ohh ohh... i'm so sorry!!

I was browsing through it so fast.. and kept noticing the differences between the two.

Very good description Thank you very much mdbrandy...

please excuse my dumb-ness

So it's alot like todays Idle Air Control Valve when the throttle shuts right? Primarily for decleration though ??