1963 differential

[Alan Weeks]

I have recently purchased a 1963 coup that does not have its original engine, and I am not sure if this is the original differential. It presently has a 4:11 differential. Is there a way of finding out which differential this car should/originally have? 3:08 or 3:36? What would be the benifit of changing differential? The car sounds like its overworking at highway speeds. (tach is presently inoperative) Would changing the differential solve this problem?
Also how can I find out the HP of the original engine?
(presently it has a 350 cid)
The VIN # is 30837S101369
The differential # is 3818753-N
Thanks for any help
Alan

[Joe L.]

Re: 1963 differential

Alan-----

The differential housing casting number is correct for your 1963, but that's all we can tell from the information which you've provided. The "internals" of the housing (i.e. ring and pinion gearset) may have been changed at some time or they may not have been.

What is the differential code stamped on the bottom of the housing just forward of the cover mounting surface? This will be a 2 alpha-character code. If the differential housing is original to the car or from another 63 or 64 it will begin with "C".

Also, what is the red-line of the tachometer installed in the car. It doesn't sound like this is rthe kind of car that someone would have gone through the trouble to change for "originality" or, obviously, functional purposes, so it may give us a reliable "hint" as to what engine was originally installed.

Regardless of what engine was originally installed, I don't recommend the use of a 4.11:1 rear axle ratio if you intend to do any significant driving of the car on the highway. You can change the ratio by obtaining a lower (numerically) gearset and having a competent technician install it in your existing case. It won't be cheap, but it's the only way to go. I really wouldn't recommend anything but a 3.36 if you plan to do any significant highway driving. In my opinion, that's the "perfect" ratio for most all-around usage.

[Alan Weeks]

Re: 1963 differential

Joe,
The differential code is CB 10862
The tach has an orange section from 50-53 and red from 53-55
Thanks for the response and I will have the gearing changed to 3:36,
my odometer/speedometer is way off which I am assuming is due to the 4:11 diff.
Thanks again
Alan

[John H.]

Re: 1963 differential

That carrier originally was built with a 3.36 Posi in it; appears to have been a service replacement, as production '63 carriers were coded only with four digits - two for the month and two for the day, no year digits.

[Joe L.]

Re: 1963 differential

Alan------

The tach would indicate that the car was originally equipped with a either a 250 hp or 300 hp 327 engine. That "fits" with a 3.36:1 axle ratio, too.

Like I say, for all-around use, there's nothing better than a 3.36:1. For that matter, a 300 hp 327 is pretty hard to beat, too, for all-around performance and a pleasant driving experience.

[Wayne M.]

Re: 1963 differential

John -- RESTORER Winter '86 article by Armand Filer; photo of his CZ 5 13 63, 3.08 non-posi; also Summer '87 article by Deane Parker; photo of CB 11 29 62 (3.36 posi).

[Wayne M.]

Re: 1963 differential

Sounds like just your ring and pinion gear set were changed. For the 4:11's,they probably used a different posi case (with a thicker ring gear mounting flange). If your trans still has the original blue plastic (20-tooth) plastic driven gear, your speedo will probably read about 22 % higher than actual.

[Alan Weeks]

Re: 1963 differential

Thanks all for the info,
Thats about right Wayne on a measured mile the odometer reads aprox 1.25 miles
Alan

[John H.]

Re: 1963 differential

Right on, Wayne - I was looking at the wrong reference