A.I.R. tubes & exhaust man. bolts

[Joe L.]

Mark----

Your bellhousing casting number of "385103", if correct, is not a Corvette bellhousing and I cannot identify its origin.

Your transmission's main case casting number of 3925660 and extension shaft housing (not "shifter") number of 3857584, identify your transmission as a 1968-70 Muncie 4 speed transmission which could have originally been installed in a number of Chevrolet vehicles of the period.

Your transmission's identity is further narrowed down by the transmission assembly part number found on the tag affixed to the sidecover. Most probably the complete number is 3915090. This would be a Muncie M-21 transmission which could have originally been installed in a 1968 Corvette with L79 engine option. However, the same part number could also have been installed in other 1968 Chevrolet passenger cars. No matter, though, as there was no difference between Muncie transmissions used in Corvettes or other Chevrolet cars and, obviously, this transmission is not original for your car.

Your starter motor, #1998437, was not originally a Corvette starter. I cannot tell you for sure what vehicle "donated" it other than to say it was an early 80's GM product. It could be further identified, but it really wouldn't be worth the effort.

[Gary S.]

A.I.R. tubes & exhaust man. bolts

OK there A.I.R. experts. I am trying to put the ignition shielding back on my 72 with A.I.R. and to do this I have to remove the aft exhaust manifold bolts to slip the the "L" shaped brace on. The long bolts hit the A.I.R. tubes and will not come out. Do I really have to remove the tube tree to get the exhaust manifold bolt out? Is there something I am missing here?

Open to suggestions. Thanks as always, Gary 21316

[Mark J.]

Yes and No

Gary,

Assuming your A.I.R. vent tubes are the same configuration as those on my '66, the driver's side manifold bolts will clear the tubes, but the passenger side bolts will not. On mine, I would have to remove the vent tube on the passenger side to get the manifold bolts out.

A word of caution about removing the vent tubes: If they appear to be original equipment they may be siezed in the manifold from years of heat exposure and corrosion. Soak the connections with a good penetrant before attempting to loosen them. I mangled one vent tube pretty badly by not taking my own advice. Be prepared to replace the vent tube if needed. Chevrolet can order replacements for about $25 or $30. Catelogs want more.

Mark

[Mark J.]

Addendum

The vent tube fittings will distort easily if seized in the manifold. I recommend using a brake line wrench to get the best grab on the fitting.

Mark

[Gary S.]

Re: Yes and No

Maybe I am looking at the wrong catalog, but where can you get the four armed vent tubes for $25-30? I have looked in Paragon and they are about $100 for two. I don't have my catalog with me so I can't be more exact.

BTW, thanks for the information confirming my suspicions. Since my AIR system is only recently installed, I have no trouble getting the 1/2" nuts out using the flare nut wrenchs.

Gary

[Mark J.]

Call Your Local Chevy Dealer

Ask the parts department to quote you a price. I believe they will have to order it though.

Mark

[Joe L.]

Re: Call Your Local Chevy Dealer

Gary and Mark-----

The tubes are GM #333831, left side, and GM #331832, right side. They currently GM list for $41.50 and $30.25, respectively. These tubes replace the GM #3890415, left side, and GM #3877480, right side, which were originally used on your '66. In my experience, the replacement tube assemblies that I've seen (and have in my collection) are very similar to the originals, including the crimped end fittings. Some folks say that later replacements have swaged ends, but I've never seen them on a GM tube.

[Jim T.]

Re: Call Your Local Chevy Dealer

Joe are the AIR tube part numbers for the 72 the same for a 68 327 L79?

[Gary S.]

Re: Call Your Local Chevy Dealer

Joe, Great work. I called the local Chvy dealer and he found the parts as you described with the exception of the right injection tube number. The parts fellow says that the part is GM #333832, which is in keeping with the left side which is correctly posted as GM #333831. Your post stated that the right side is GM #331832, the third digit "1" being incorrect. I would never argue with you, just reporting what the local Chevy parts guy stated. The price was right on for both.

Thanks, Gary

[Joe L.]

Re: Call Your Local Chevy Dealer

Jim-----

Yes, the part numbers that I provided are applicable to all 66-74 Corvette small blocks with AIR. These numbers are PRODUCTION and SERVICE part numbers for 1974 and SERVICE part numbers for 66-73. However, as I mentioned, in my experience they are very similar to the 66-73 PRODUCTION parts.

[Joe L.]

Re: Call Your Local Chevy Dealer

Gary-----

Yes, that was a typo on my part that got missed when I proof-read the message. I make many typos but, usually, I try to be real careful about part number typos; somebody after a washer might end up ordering an engine assembly. One wrong digit in a part number can make a BIG DIFFERENCE.

[Michael W.]

Joe: you said....

somebody after a washer might end up ordering an engine assembly.

Not a problem if the price is the same; gimme a dozen!

[Mark J.]

Two Caveates

First, when I purchased the A.I.R. vent tubes from Chevy last year, they came tapered, not crimped. I shelved them when I found correct NOS crimped tubes for sale by a local Corvette used parts vendor. Second, the '66 driver's side vent tube is a one-year-only version in which the check valve points up, not forward, as it does on the '67 and later models. The Chevy dealer showed me a footnote on the computer that said that I may have to cut the '66 hose in order to use the tube. I can only speculate that the reason the vent tube was changed in '67 was to get the check valve away from the manifold and/or take the bend out of the hose connected to the check valve. Luckily, I found an original '66 vent tube and did not have to cut the hose.

Mark

[Joe L.]

Re: Two Caveates

Mark------

Yes, like I mentioned, the currently available tubes are SERVICE-only for 66-73 Corvettes. They are not identical to the original PRODUCTION parts for those years. However, in my experience they are very similar to the PRODUCTION parts and, as you mentioned, there is the curvature difference for 66 models.

I was not aware that the configuration of the currently available SERVICE parts had changed. I have several sets of these that I have purchased new over the years and all are crimped. Apparently, GM must have changed suppliers. Perhaps, they changed to the suppliers of the big block and/or 78+ tubes which are tapered and not crimped.