I have two Bellhousings with the same number but there are subtle differences. Is one better than the other or does it really matter? The difference is in the fork pivot ball area.
thanks
John

 

As long as the pivot ***** screw in from the transmission side on both BHs, they ought to be fully interchangeable.

 

This is probably no help but Colvin's book does not list differences in 403 bell housings. It only says that it's identical to the 421 bell housing used in 1963 except for the larger transmission bearing hole.

It says that the 403 was used for small blocks from 1964-1972 (and L88 for 67-69).

The drawing in Colvin's book shows the pivot boss matching your bottom picture, and there is no picture of the earlier 421 - I was wondering if there was a period between the 421s in '63 and the 403s in '64 that might account for the different pivot boss of your top housing, but who knows. Is the pivot boss the only difference? It's the only difference I see.

Any chance that your top one is an early or late housing? What are the dates on them? But my guess is that Jim is correct on them being interchangeable.

 

My best guess more area for more strength

 

Thats what it looks like to me also.

 

ER...

I have not found a date stamp on either one so it is a crap shoot. Everything else is identical. Thinking I will use the one with more material for strength.

Thanks every one for the suggestions.

John

 

The date stamps on cost iron bell housings are the same as for blocks, etc., but some aluminum housings have no dates at all.

If you have a date, look near the casting number for a circle with an "equator" line with a number between 1-12 for the month. Under the equator will be 1-5 cots indicating the week of casting.

 

BETWEEN the 421 (63 ONLY) and the 403, there was the 383. As best as I've been able to determine, the 383 was 64 only. Again, as far as I can determine, the 383 and 403 are totally, completely, 100% interchangeable in every way.
As everyone already knows, the 421-403 are the same except fot the smaller hole in the 421.
ALLLLLLLLLLLLLLLLLLL 63-65 Corvettes (INCLUDING the 425hp/396 in 65) used the small, 153 teeth flywheel/10 1/2in clutch and the 403 bell housing. Beginning in 66, all BBs got the big 168 teeth flywheel and 444/621 bell housing.
Of all the 403 bell housings that I've touched (a bunch), I have never noticed the boss for the ball stud. But on the large 3899621 and the later 464697 housings, there is a distinct difference in the boss for the ball stud. Again, as far as I have been able to determine, the 621 and 697 housings are totally, completely identical in every way and totally interchangeable. From what I've determined the 697 later replaced the 621-----------maybe in the later 70s and it was also a service replacement for the 444-621 housings.
On 444-621 housings, the boss for the ball stud is round and the threaded hole can ONLY be in one position. But on the 697 housing, the boss for the ball stud is a figure 8, thus providing a location for the ball stud hole in 2 different positions (I think maybe for car or some kind of truck application). Even though the housing has ONE casting number, it could have 2 part numbers which were determined by which position the hole was for the ball stud. I have only had 2 697 housings in my position, and I let both of them get away, so I no longer have a 697 to make detailed comparisons with a 621 housing.

 

One other difference may exist and that is the provision for a Z bar ball stud. I have seen photos of the 403 with and without the Z bar boss. I don't think a C2 came with the Z bar boss provision but could be wrong about that. Another 10.5 bell is the 462606 (78-87 years) and is also the same as the 403, 383 but the 606 came in two versions. The 3840383 was the original part number and casting ID. I don't have access to my 64 parts book now, but my 67 parts book shows 3840383 as the part number and notes the 3858403 as the casting ID. I would check both bells for parallel alignment and use the one with the best parallel numbers, then correct for concentric run out after parallel not before. If a Tremec is in the future this is really important. If possible do the parallel and run out before engine assembly with only the crank and flywheel. If the engine is assembled but out of the car do it now because in car and by yourself is no joy.

 

Yes a Tremec is in the future. I plan to use the Browell tool I borrowed from one of the members here. Will update in another thread.

I did find what maybe date codes on both housings.

i went ahead and used the housing with the beefed up mount.

 

If the bellhousing fails to pass with the Browell tool how do you know which of the two planes is out of spec to correct the alignment? I thought it only verified concentric runout being in spec once parallel was confirmed.

 

Vitamin

Smarter minds might be able to answer that one. I assumed using a dial indicator or the Browell tool would pass muster for a Tremec down the road. I am sure the pros on here will come along and set me straight.

I found this online

https://www.hotrod.com/articles/hppp...n-bellhousing/

There are so many here that look for ways to assist.