55 V8 Differential code - What's yours?

[David B.]

Re: 55 V8 Differential code - What's yours?

Troy, I think you might be misinterpreting the data I sent. As previously stated, GM changed the rear axle designations in 1955 (1st series) & (2nd series). Starting with the 2nd series, ONLY the 1st letter designates the plant. (Important), the 2nd letter indicates the series car, type rear end and the gear ratio to be installed. Once assigned, the second letter will continue in subsequent years as long as the series and type axle is being assembled. "AE" is a Corvette powerglide 3.55 ratio built at G & A followed by the stamped assembly month and day. No need to stamp the year since that is cast into the carrier along with the casting Number.
The standard 3 spd. Corvette required a 3.70 gear ratio and would be stamped "AH". The optional Corvette gear ratio 3.27 was stamped "AD". The 56-57 JM p. 213 & 214 explains fairly well but does have some errors as well.
The data sent was from Chevrolet Motor Division, GM Corp. "Special Information Catalog" dated 10-1-61.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

Thanks for your clarifications.

Not sure what the difference between first and second series may be but we might be looking for first series data. Do you have that? It may not be the same.

The column with the two letter code is labeled "Plant Identification". Nevertheless, I see your point that it is actually Plant Identification and gear ratio. My guess is this change may have had something to do with the introduction of various ratio options available for Corvettes, which to my knowledge really expanded in 56-57. Prior to 1955 you had only 3.55:1. According to this referenced document there were 3 choices in 55.

You are correct about the AH vs AD. I was relying on the footnote that said AD was 55-56 only. So it appears by this record that there were two rear axels for 55 3 speeds with different gear ratios. That's news.

Are you sure AH 55 3 speeds had a 3.70:1 ratio? The ratio is not shown in the document you sent. Perhaps this is in the 56-57 TIMJG you mentioned.

Has anyone ever seen a AH or AD rear axel in a 1955 Corvette? Currently the TIMJG says they were all AE, same as Corvettes with Powerglide. I would bet this is based on the 1955 Corvette Model Year Specification Information that was supplied by Chevrolet to the Automobile Manufacturers Association for Corvette Convertible (Model 2934) on 10-29-54, revised on 6-1-55, which lists only AE as the Type Designation for rear axel. Perhaps the 3 speed variant was not listed since it was yet to come. Or has some prior investigation revealed only AE rears were found in 3 speed cars?

While 53 and 54 rear sections also have a casting date they chose to indicate the model year of assembly in the letter code - L or M. Then they changed in 55 for some reason and relied on the casting date to indicate the year. Interesting progression.

The reason I wanted to know when the information was published is to judge how accurate the data might be for 55. The farther from 55 the more errors can creep in.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

The NCRS Corvette Specifications Guide published in 1989 indicates the 1955 AH is 3.55:1 whereas in 1956 and later it is the 3.70:1 as you stated. Seems odd.

Also there is a footnote on the AD 3.27:1 rear stating it may not have been used in 55. I doubt it was.

[John S.]

Re: 55 V8 Differential code - What's yours?

1578, AH 8 08 as recorded in the C1 registry. All you have to do is ask the owner of 699 and 700 for information on 3 speeds to confirm late rear ends.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

I've did that days ago. He's on a cruise.

You know the understanding that the last 75 of the 700 55s were the 3 speed cars. #578 is out of that range by far. Noland did report that occasionally they produced a very few 3 speed cars earlier for testing. #578 would have to be one of those rare examples. The August date code does jive with the understanding from Noland's production records that #578 was built in early August.

[John S.]

Re: 55 V8 Differential code - What's yours?

I've did that days ago. He's on a cruise.

You know the understanding that the last 75 of the 700 55s were the 3 speed cars. #578 is out of that range by far. Noland did report that occasionally they produced a very few 3 speed cars earlier for testing. #578 would have to be one of those rare examples. The August date code does jive with the understanding from Noland's production records that #578 was built in early August.

Your slipping a little. It was believed there were 75 3-speeds. The last 25 are 3-speeds. 675 is a automatic. Once the washer pedal was moved to not interfere with the clutch pedal is when you could expect to see 3-speeds. That took place a little before #550.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

Yikes! Major mistake. Thank you for correcting me.

Noland reported that the few early 3 speeds scattered about probably included 353, 422 and 551. If so wonder what washer would 353 and 452 have and if AH/AD differentials were available that early?

[John S.]

Re: 55 V8 Differential code - What's yours?

Yikes! Major mistake. Thank you for correcting me.

Noland reported that the few early 3 speeds scattered about probably included 353, 422 and 551. If so wonder what washer would 353 and 452 have and if AH/AD differentials were available that early?

I doubt if you would learn much from any of those cars. Roy Braatz had mentioned owning 353 and also 422 on past posts on corvette forums. #353 has a 56 style rear end meaning it is welded. When owner of 353 passed away, his nephew stated that a incorrect transmission was in the car. I viewed #551 in 2010. Starting with the engine that was dated way too early and at the time I think it had a FG on the engine pad. I have a hard time believing that the overdrive transmission is original to the car.

[Ronald R.]

Re: 55 V8 Differential code - What's yours?

car number 480



QUOTE=Troy Pyles (14528);830507]I have an early (#78) 55 V8 with a MW differential made in May (presumably 1954). Number 29 also has a MW made in May. Book says both should be AE coded.

I have a theory that, just like the frames, side curtains and tan tops, left over 54 MW differentials were used in at least early 55 and maybe well into the model year. If you have a 55 please let me know what differential code you have and your car number.

A previous 53-55 team leader and 55 restorer told me he had never seen an AE rear. But I believe they exist as I've seen photos of two...assuming they have not been changed to meet judging expectations. Nevertheless his experience may be telling us that MW differentials were prevalent in 55.

I have another theory about the differential codes.

We understand the stamped numbers are the month and day of assembly. But its very odd that there is no year in the date code. The other thing that is odd is LW, MW, and AE rears seem to be identical - same gears, same bearings, same seals, same gaskets. So if they are the same why do they have a different letter code? My theory is the letter code tells us the year of manufacture and not necessarily the year of installation in a car.[/QUOTE]

[Ronald R.]

Re: 55 V8 Differential code - What's yours?

mt car was built 2 days before yours/480

[Troy P.]

Re: 55 V8 Differential code - What's yours?

Your car was assembled very close to the last day of July. So July 6th date code fits well.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

Here is the answer we've been waiting for:

1955 #699 and #700 are both 3 speed cars and they both have AE rears. Date codes 11 23 and 8 31. Just as the Chevy documentation says all 55s with Powerglide were AE it is also wrong on the 3 speed rears. That's why I trust verifiable survey results more than the documentation.

So to summarize -

Early 55s came with left over MW rears. All were Powerglide of course. The last two 2 speed cars came with AE rears. Those two cars were recently purchased from the original owners - two sisters. John told us a car listed in the Corvette Registry is reported as having an AD rear. No AD or AH rears turned up in my survey.

The 53-55 TIMJG says all 55 6 cylinder cars will have a MW rear but all 55 V-8 cars with Powerglide will have an AE rear. Not correct.

The 53-55 TIMJG says all 55 V-8 3 speed cars will have an AE rear. That seems to be correct.

If someone wants to continue the survey there are two things worth looking into.
#1 When did they run out of MW rears made in 54 and start using AE?
#2 Are there any verifiable 3 speed cars with something other than an AE?

[John S.]

Re: 55 V8 Differential code - What's yours?

Here is the answer we've been waiting for:

1955 #699 and #700 are both 3 speed cars and they both have AE rears. Date codes 11 23 and 8 31. Just as the Chevy documentation says all 55s with Powerglide were AE it is also wrong on the 3 speed rears. That's why I trust verifiable survey results more than the documentation.

So to summarize -

Early 55s came with left over MW rears. All were Powerglide of course. The last two 2 speed cars came with AE rears. Those two cars were recently purchased from the original owners - two sisters. John told us a car listed in the Corvette Registry is reported as having an AD rear. No AD or AH rears turned up in my survey.

The 53-55 TIMJG says all 55 6 cylinder cars will have a MW rear but all 55 V-8 cars with Powerglide will have an AE rear. Not correct.

The 53-55 TIMJG says all 55 V-8 3 speed cars will have an AE rear. That seems to be correct.

If someone wants to continue the survey there are two things worth looking into.
#1 When did they run out of MW rears made in 54 and start using AE?
#2 Are there any verifiable 3 speed cars with something other than an AE?

AH, not AD, was the rear end reported on #578. Only one of the cars was from the original owner's family. The other car was originally owned by someone else. One of the cars had a 4-speed installed, so it would be important to keep track of the dates on the rear ends in case it is found that a rear end was replaced.

[Troy P.]

Re: 55 V8 Differential code - What's yours?

Have to disagree with you about the ownership according to the documentation.

[John S.]

Re: 55 V8 Differential code - What's yours?

Have to disagree with you about the ownership according to the documentation.

Have Emails and phone calls from Carol(#699) that told me how the 2nd car was acquired. Whether original owner was a very close friend or uncle was not clear to me. Was given information and pictures of these cars from Roy and Carol before both these cars were for sale.