1963 bellhousing-trans

[Joe C.]

I recently aquired the correct bellhousing for my 1963 corvette its a # 421- But when I went to install the coorect bellhousing iy was too small and the flywheel in there currently is an 11" instead of the correct one. If I change the flywheel to install this bellhousing will my trans fit? I'm worried that the splines on the input shaft won't fit the correct flywheel my trans is a GM 3851325 on right side, the other numbers on the left are # P12077, ON the cover it reads 3831707 and also there is a number that reads 4106963. Is there any one that knows these numbers and will this trans work with a # 421 bellhousing with a smaller flywheel for the 1963 -340 hp ?

[Harry Sadlock]

Re: 1963 bellhousing-trans

Joe,

Joe, from what I can find:

P12077-> P= Muncie, 12 = Dedcember, 07 = 7th day(probably 1964). Can't find the last 7

3831707 -> Side cover from a M21 Close Ratio
3851525 -> Main Case M21 Close Ratio

4106963 -> 1964 with VIN seqquence number 6963.

Can't help with the bell housing except there is a date code on it. It is described in Nolans book on page 88. It's a date marker that just shows month and week produces by using numbers and dots.

I'm sure other will help with the fit.

Harry

[Michael H.]

Re: 1963 bellhousing-trans

Joe,

The original clutch/flywheel for your 63 would have been a 10.5" instead of the 11" that you currently have. In order to use the housing, you will have to replace the entire clutch, disc and flywheel with the correct size components.

That's not going to be the end of the problems though. The 63 (only) clutch housing can only be used with a 63 (only) transmission. The size of the transmission front bearing and it's retainer were reduced for 63 but went back to the original larger size again for 64. The larger 64 and later bearing retainer won't fit into the smaller hole of the 63 clutch housing and from the transmission case number that you listed, it sounds like you have 64 or 65 Muncie. Try to fit the housing onto the transmission and you will see the problem.

In order to complete the installation, you will need a proper 63 transmission and a 63 only coarse spline front drive shaft yoke. If you have an early car that will use a Borg Warner transmission, you will also need a few shifter control rods and levers. Sorry for all the bad news.

Michael

[Tom P.]

Re: 1963 bellhousing-trans

And you are also going to have to change starters. You currently have a starter with a staggered bolt pattern (where it bolts to the bottom of the block). You will need a starter with a straight across bolt pattern. Your current starter uses 2 long bolts, the straight across starter uses one long and one short bolt.
UNLESS it is important to you to have this car 100% correct (or as correct as you can get it), my personal choice would be to retain the bigger bell housing/flywheel/11in clutch.

[Joe L.]

Re: 1963 bellhousing-trans

Joe----

I agree with the other responders. If you want to get it 100% correct, in addition to the bellhousing, you're going to have to change the flywheel, clutch assembly, transmission, output yoke, and starter. You'll also need to change the bellhousing lower cover from what you have. The one you need is GM #354497 and it's still available from GM. It's not exactly like the original as it has 2 little "clips" on the upper radius to secure it to the oil pan lip. This is a BIG improvement over the originals and "the only way to go".

There is an "intermediate" change that you could make if you wanted to achieve "partial original configuration". To do this, you would have to change your flywheel, clutch assembly, starter, and lower cover but you could retain the transmission and output shaft you currently have. To do this, you would need to obtain a GM #3858403 bellhousing. These are very easy to find in good, used condition for about 50 bucks. This bellhosuing is virtually identical to the '421' you have, except for the size of the transmission bearing retainer opening and the casting number on the side.

Doing the above will give you an overall configuration very similar to original, although there will be some minor differences with respect to "numbers". If you want EXACT original configuration, you will have to change ALL the parts described above and by others.

As Tom mentioned, functionally, what you now have with the 11" clutch is a very fine set-up and you won't really gain anything with the '421' bellhousing, 12-3/4" flywheel and 10-1/2" clutch, as original. You might gain a little quicker "revving" due to the lighter flywheel, but you'll lose a little "off-the-line" quickness.

[NANCY CHARLES]

Re: 1963 bellhousing-trans

joe; if you want to use your 11" flywheel & clutch assy. and don"t care about judging use the ( 621 ) bellhousing for a big block .what is the vin. # of your car ? is it a true 327/340 h.p. car ?

[Mike Cobine]

Re: 1963 bellhousing-trans - decide purpose 1st

Joe, while this is a restoration group, and all discussion is geared towards restoration (with a few dozen slips each month), you have to decide what you really want for the car and you.

For restoration, and for judging, you need to replace the '64 Muncie with a 1963 Borg Warner or Muncie, depending on your VIN. You also need to use the -421 bellhousing and the 12-1/2 inch flywheel with 10-1/2 inch pressure plate and clutch disk. This also means the different starter. Odds are the shifter is not correct 100%, but it may be.

But doing so, you need to understand the reason for change in 1964 and the reason so many owners changed their '63s was the smaller input bearing on the '63 transmission was not nearly as strong as the regular size in years before and after. They broke. Being one year only, they are expensive.

The smaller clutch setup will spin faster, letting your car rev faster as you drive down the road, but launch will be different. You will have to slip the clutch a bit more (maybe not really noticable) and under a high load (racing from a stop light) the clutch will slip more and not grip as well when first engaged.

The current setup you have is one that was used possibly because the original broke. It is a good setup to use, especially if you like to get on it or make a pass on the drag strip with a club or try any speed event for which Corvettes were intended.