Correct SB radiator shroud?

[Randy Stockberger]

I have a '70 350/300hp, 4spd, no air, I use it as a daily driver. Bubba removed the fan, fan shroud and fan clutch and put on an electric fan. The radiator is incorrect brass and of unknown origin (it has plumbing fittings soldered on for the lower radiator hose and overflow connections). The radiator has started to leak so this has come to the top of my fixit list. There is enough rust on the radiator surround that it is probably toast.

In looking at the AIM, it appears that the radiator shroud is a simple cylinder that butts against the radiator. The parts catalogs show 2 different setups for the shroud, radiator and surround. One is the cylinder as shown in the AIM and the other is a plastic shroud - rectangular at the radiator end and round at the fan end. Which is correct for my car? My VIN ends with 09701 which would be April or May production.

Thanks in advance
Randy Stockberger - #32888

[Joe L.]

Re: Correct SB radiator shroud?

Randy-----

Your 1970 300/350 with 4 speed trans was originally equipped with an aluminum radiator of GM #3155316. The fan shroud used with ALL 68-72 Corvettes equipped with this radiator was a steel, "circular" fan shroud which abutted the radiator and was insulated from contact via a rubber seal around the front edge. The shroud was attached via 2 "L"-shaped brackets at the bottom and one bracket at the top center which attached to the radiator support. The shroud was GM #3938943.

The shroud, itself, is GM-discontinued and not reproduced. However, used examples can be found and, from time-to-time, I see one on eBay. The radiator was discontinued in about 1985. However, a perfect reproduction is available from DeWitts (www.dewitts.com). They are not what some folks would call inexpensive, but this is THE radiator that you want to use. A copper/brass replacement type radiator, although less expensive, will NOT provide satisfactory cooling in any sort of a high ambient heat condition. I STRONGLY recommend the DeWitts reproduction of the original GM 3155316 radiator. Plus, it comes with a 5 year warranty.

If you need a radiator support, that was originally GM #3966591. However, it's been discontinued for years, too. Once again, reproductions are available as manufactured by Coffman Corvette and are available from Corvette vendors like Dr. Rebuild and others.

[Randy Stockberger]

Re: Correct SB radiator shroud?

Joe:

Thanks for the tips and part numbers. The AIM is correct except it has the shroud as left and right sections with part numbers 3935505 and 3935506 and shows where they are welded. I wonder if they really spot welded these on the assembly line.

Randy Stockberger - #32888

[John H.]

Re: Correct SB radiator shroud?

Randy -

Yes, they were spot-welded together at St. Louis, but not on the assembly line; they were received in oiled raw metal finish, were spot-welded together in an off-line subassembly fixture in the raw metal area, sent through the dip-prime paint system (same one used for wheels, radiator supports, etc. and all other steel parts that had to be black-primed before use), and they were delivered to the assembly line after baking for installation. Anywhere you see an "X" in the A.I.M. and a spot-weld notation, that welding operation was performed at St. Louis.

[John H.]

Re: Correct SB radiator shroud? - Addendum

The same holds true for notations for "arc weld", "gas weld", and "mig weld".

[Joe L.]

Re: Correct SB radiator shroud? - Addendum

John and Randy-----

Yes, and this is another one of those cases in which the PRODUCTION parts were never available in SERVICE and the SERVICE part was never used in PRODUCTION. The "halves" of the fan shroud were never supplied that way in SERVICE; only the completely assembled shroud assembly. GM rarely sold SERVICE parts that required welding prior to SERVICE use.

The thing that I wonder is whether the SERVICE metal fan shroud assemblies were assembled at St. Louis and shipped to GMSPO for SERVICE parts distribution or whether they were otherwhere assembled. If they were otherwhere assembled for SERVICE, I wonder why they weren't shipped to St. Louis already assembled for PRODUCTION?

[John H.]

Re: Correct SB radiator shroud? - Addendum

Joe -

Metal parts such as the fan shroud were normally shipped to assembly plants in pieces for more efficient packaging (more pieces per rack), as the halves "nested" better than the assemblies did; at one point we even studied welding gas tanks together at the assembly plants, as gas tanks are about 95% air and are the prime example of inefficient use of "cube" for shipping; the roller-seam-welding equipment was prohibitively expensive, however, so it never happened (although gas tanks were sourced in California for the California plants at South Gate, Van Nuys, and Fremont to avoid shipping "95% air" all the way from the Midwest to California).

The Regional Parts Depots had spot-welding equipment and dip-prime paint systems - the service fan shroud halves were welded together in (crude) locally-made fixtures, painted, and sent out to local depots and dealers as an assembly. The same was true of front fenders for steel cars, which caused fit issues with replacement fenders; assembly plants had pretty exotic locating/clamping fixtures for spot-welding the fender skin to the heavy-gauge "shotgun" lengthwise reinforcement and the rear and lower reinforcements, which they "tuned" with shims and added locators to "crown" the top of the welded fender to match the "crown" of the edge of the hoods, and this fixture "tuning" changed from time to time if the hoods changed. The regional depots also had the same welding fixtures, but they simply welded the detail parts together in the fixture "to spec" and never made any changes; as a result, sometimes a service fender had a different "crown" than the production fender on the other side, which made getting a hood-to-fender fit a challenge in a dealer's body shop.