I have seen reference to big block radiator support for 68 - 72. What is the difference or how do you tell if the support is for a big block or a small block?

Same question on identifying a HD or big block differential vs a regular small block differential. I have an option of 2 differentials to rebuild 1 has U-bolts and the other has caps with regular bolts. Is it possible they are both regular small differentials or is the one with bolts a HD unit? Is their any way to tell? The are both in parts cars and sitting on the ground, so a little hard to get under at this time, unless required to do so for ID.

Thanks

Jim

 

Jim, you need to be more specific. 68 corvette core supports are unique. You also have ac and non ac core supports. For a 72 the bb support is one inch wider than the sb.
There were no HD differentials after 1969. But.. all late 72 thru very early 75 used the HD threaded stub axles. There was a difference between bb and sb diffs 65-69 but they all have small window carriers which are inferior to the 70-79, the 76-79 carriers being the best. Bearing caps were improved on housings cast after 1971 but 67-72 castings are better. 65-mid 66 housings are narrow case design and factory shims are not available. Forget about 63-64 cases.
Mike

 

Thanks for that explanation I had no idea they were so different.

 

Hi Jim,
Here's the info on the core supports, their size and usage.

The 68-72 Corvette radiator usage is a little bit confusing, but not too hard to clear up....

All 68-72 small block base cars used the smaller aluminum radiator (3155316) and a separate aluminum surge tank on the fender skirt. This unit mounts on two 1/2" pins on the bottom with round rubber donuts. As mention above Willcox core support would be 25440. A base car is one without any of the following options: Air conditioning, Automatic transmission, or a special motor option like LT1 or L46. If you have any one of these or a combination of them the small block radiator would be the following radiator.

If a 69-72 small block came with automatic, AC, and/or LT1 or L46, then the aluminum radiator was changed to the larger copper/brass radiator. The aluminum surge tank was eliminated because the radiator has a filler neck. The radiator industry referes to this radiator as a 26" core because that is the distance between the headers (mounts). That puts the mounts at about 261/2" center to center. Willcox needs to change the description on this core support (25441) because it was never used on any big block cars.

Big block 69-72 Corvettes used only one radiator, available in automatic and manual options. The core measures 27.5" which puts the mounts about 28" on center to center. This radiator was copper brass, had no filler neck, and used the aluminum surge tank on the fender skirt. Again, Willcox needs to change the description on 25442 because this core support was never used on any small block Corvette.

Confusion happens when people make changes to the factory configuration. The 1973 radiators are identical to the 69-72 BB (27.5) except they have a filler neck and many replacement companies will just sell this one for the earlier models to reduce inventory. Then you have two filler necks or the owner deletes the surge tank as it is no longer needed and that confuses other owners because they thought big block came with surge tanks.

FYI, the two copper supports 25441 (26" SM) and 25442 (27.5" BB) are identical except one item and that is the lower U bracket on the passenger side. It is spot welded on and tough to remove but you can convert one to the other by just moving this bracket in or out. The top left bolt on bracket is the same for both applications while the top right is unique for each unit.

1968 Big block and small blocks with AC or auto used a copper radiator from 1967. It had a core width of 22.5".

This is from Tom DeWitt (THE radiator man!).
I hope it helps you.
Regards,
Alan

 

Wow that is a lot of knowledge and information. After I study the information I'm sure I'll have more questions.

Thank you for all the information.


Jim

 

What year car do you have? More info!

 

If you need any visual help or want to see something I'm over here just on the other side of Dallas.
Mike

 

I have a 72 convertible. I am doing a frame off build with modifications. Things I know I am going to do as of right now. 454, 4 speed, P/S, PB, A/C, and some minor changes.