66 3.08 Rear Ratio

[Rob M.]

Does anyone know approximate production numbers of 1966 SB's with a ratio of 3.08:1? Just curious if it was fairly rare. Noland's book says that the option was dropped for 1966, but his supplemental data doesn't indicate it. What's the story?

Thanks,
Rob

[Jack H.]

Re: 66 3.08 Rear Ratio

You might be confusing G81 (posi rear) with G91 (3.08:1 highway crusing axle). It's only the G91 option Noland says was dropped prior to production startup...

For how many 3.08 rear end cars were built, look at the ECL code tables on pages 342 and 343 then add the numbers....

BA 1692
DA 0
JA 693
---------
Total= 2385

and see if this doesn't answer the question from the data Noland documents. Says only base engine SB and base engine BB cars were built with the cruising geared rear end....

[Mark J.]

Re: 66 3.08 Rear Ratio

Which also matches the Power Team combinations listed in the Spec Guide (pgs. 42 and 58).

One other factor to consider is that 2380 Corvettes came equipped with an Air Injection Reactor (AIR) system (RPO K19) (See Spec Guide pg. 42). I don't remember the source, but I recall that to reduce emissions and increase fuel economy, the K19 was matched with the wide ratio transmission and 3.08:1 gear ratio. If my memory serves me correctly, this would account for all but five of the 3.08 gears installed in '66.

Mark R. Johnson

[Rob M.]

Re: 66 3.08 Rear Ratio

Mark and John,

First, thank you both for the information.

How hard is it to determine if a car originally came with K19 from the factory (if you don't have a build sheet)? I would like to figure this out, considering my car doesn't have K19 and has what I believe to be the original 3.08 posi unit in it.

Again, thank you for the help.

[William C.]

Re: 66 3.08 Rear Ratio

A start would be to verify all the castng numbers, dates, and stamped codes on the rear end housing.

[Craig S.]

Re: 66 3.08 Rear Ratio

Rob - besides what Bill mentions, you can start looking at the other items that differed, in case any is still present. My 67 K19 uses a 3814 instead of a 3810 Holley carb, I can't recall if 66 used the same or different but if it is original it will have a large vacuum connection on the passenger side rear of the baseplate. Of course the air cleaner base has large plumbing connections similar to the breather can connection in the back on the drivers side to the crankcase valley. The exhaust manifold castings are different numbers and would have the fitting connections on the exhaust port bosses. The engine suffix would be different if original, 67 327/350 used a KH if the car also had AC and PS. BTW, my 67 K17 327/350 has a 3.55 gear ratio, paired with the M20 Muncie. If I recall from memory correctly, the code was AN on the rear end, and the build date is two weeks before the car build date.......Craig

[Rob M.]

Re:3.08 Rear Ratio

Bill and Craig,

Here is what I do know:

I can't read/find all the numbers on the posi unit, but what I can find is AL 4-19-66. The engine stamp pad is F0427HE 6121064 (5-5-66). The carb is a 3367. The exhaust manifold #s are hard to read, but there are no fitting connections. The air cleaner base does not have the extra connection in the front. The trany is an M20 stamped with the correct vin#.

I think it would be fun to find that the car is one of only 5 so equipped for that year. Just having fun learning about my car.

Rob

[William C.]

Re:3.08 Rear Ratio

The stampes codes are a big key as they will key to the original ratio fitted into the case.

[Craig S.]

Re:3.08 Rear Ratio

Rob - now you have given us what we need. The rear end code you mention....with the AL code, does translate to a 3.08 POSI rear end for a 327 in 1966. It would have ubolt attachment of the halfshafts to the yokes. The 427 version with 3.08 was an AT code, with posi, and would have the stub axle caps instead of ubolts. There was also an AT code unit for 327's that was 3.08 and not posi.

If your original gearset is still installed, who knows, anything will fit. But at least your case would be correct for this vintage of 3.08 posi, and the date sounds right for your vette.

[Rob M.]

Re:3.08 Rear Ratio

Thanks Craig,

Here are a couple of other numbers I found on the unit this morning. 3871375 was upside down by the tire tub and I think it's, B 4 6 (the numbers are corroded and gunked up) on the driver's side output area.

Question, did they use a number or a letter to represent the month in the casting date?

Thanks in advance

[Craig S.]

Re:3.08 Rear Ratio

Rob - the upside down 3871375 is the casting number for the rear cover/spring mount. This is correct, but there were others for various years. For 66, the differential carrier should be 3876476N (after Feb 65) and in 67, this changed to 3899143. The date is Alpha for the month, then day, then year. So your cast date stands for February 4, 1966 on the carrier. The numbers I reference above are on the passenger side of the carrier behind the pinion yoke. The dates you reference B46 should have been on the drivers side. Also, on the 3871375 cover, this was used for many years, and was dated starting in 1968, on the rear facing flange near the filler plug. 1967 back to the prior cover (I think it was in 1965 sometime) were undated.

You need to get the book "Corvette by the Numbers" by Alan Colvin, sold here on the website, there is a few dollars off for NCRS discount. Time to invest in some books so you can research these items......Craig