Our 1960 Monza Coupe

[jmiahman]

The issue I have is the Differential seems to be original (made in June BR code etc..) but maybe I'm reading it wrong. So if a different Differential was needed seems like it would have been swapped out, but maybe like you (and others) say it's a drop in replacement. After I get the engine going I should probably look into the diff a bit more and make sure all is well there.

The car was parked by my grandfather for 40 years and I don't think it would have just been because of a blown head gasket (I got it to start with it), especially since these things are known to loose a cylinder and keep running. My grandfather was also no stranger to car issues and most likely received the car for some work he did with his welding business. So I am suspicious of this Trans change and if maybe it continued to have problems because of it and that's really why it was parked. Then again maybe it was just a head gasket and he just didn't have the time to work on it, but it's rather complete, and other than some rust which probably happened while it sat for 40+ years I am wondering why it sat. He and my grandmother have long passed, my Dad doesn't even remember the car and my Aunt says he was having eye problems and could never work on it, so maybe that's it, but he helped me with other small projects (a ATC Honda 110) as a kid and didn't seem to skip a beat. I'm just anticipating the next big issue to be Trans or Diff.

Another question probably no one else can answer is this model was made in June I would think at that point GM would know they were putting off the 4Speed until later, why still stamp a crankcase with YD? The only thing I can come up with for the 95 HP option as don't think they wanted to offer a 95HP option without a 4 Speed so maybe there wasn't an ID for a 95HP three speed so they just used YD as it was at least 95HP. Would they bundle RPOs like that or did they most likely have a letter scheme just for the 95HP and for some reason still stamped it YD indicating it should have been a 4 Speed?

[RexJohnson]

Have you checked the casting date on the diff? It is located on the vertical surface between the diff cover and the top of the bell housing. The casting date will be laid out like what is on the trans. The original diff could have been used but you would need to change the pinion shaft to mate to the newer trans. Did you check to see if it has 2 short stub axles or 1 long and 1 short? What I find interesting is the engine code says 95hp with 4sp. All of the other codes that I can think of the codes are just manual or auto and they don't care which manual trans. So that code that spells out which manual trans must be a '60 thing.

[cnicol]

More fun:
BR is the differential code for a '60 95hp 3sp! How's that going to fit a later 3-sp with it's completely different output shaft? Is it possible your diff is a BP?

Let's say you're GM and you have built some YD motors but the 4-sp option is delayed until the next model year. What are you going to do with those built engines, especially considering they're exactly the same as the 3-sp version. (Answer you're going to put them in 3-sp vehicles)

The late Bob Helt, author of "The Classic Corvair" and a stickler for accuracy would have loved to see and hear about your YD engine. Here's what's in his book:

While I think we've landed on the probable history of your car, how the '60 3-sp diff is accepting the '63 3-sp is a mystery. Perhaps someone swapped the differential pinion shaft to the later type? Perhaps it's really a BP differential and the only trans that would fit between the differential and the suspension crossmember is a 61-5 3-sp?

[jmiahman]

More fun:
BR is the differential code for a '60 95hp 3sp! How's that going to fit a later 3-sp with it's completely different output shaft?
DSCF7102 MU.jpg

Let's say you're GM and you have built some YD motors but the 4-sp option is delayed until the next model year. What are you going to do with those built engines, especially considering they're exactly the same as the 3-sp version. (Answer you're going to put them in 3-sp vehicles)

The late Bob Helt, author of "The Classic Corvair" and a stickler for accuracy would have loved to see and hear about your YD engine. Here's what's in his book:
DSCF7103 MU.jpg
DSCF7104 MU.jpg

While I think we've landed on the probably history of your car, how the '60 3-sp diff is accepting the '63 3-sp is a mystery. Perhaps someone swapped the differential pinion shaft to the later type? Perhaps it's really a BP differential and the only trans that would fit between the differential and the suspension crossmember is a 61-5 3-sp?

This is good stuff I'll have to look at the Differential to tell and find the measurements for the pinion shaft to compare. My only question if the car was built in June and the Crankcase stamped in June seems like they wouldn't have stamped it knowing a 3 speed was all they could do, then again I'm not sure how that all would have worked, somehow I don't think they just had prestamped blocks for June sitting around, but maybe they did. These are times I wish my other grandfather was around he worked for Ford and probably could of clued me in on the production process even though it was a Chevy. Speaking of Bob I feel like we are missing a lot of good people that knew good history and something like this would of been a lot more fun investigating with these guys still around.

[cnicol]

The engines were built ahead of time in Tonowanda, NY and shipped complete to the various final assembly plants.
They were built to a specific final configuration and stamped as such at Tonowanda. From Tonowanda (That's the "T" in you engine ID code), they were shipped in crates to the various assembly factories. Typically engine assembly precedes final assembly by one to three weeks.

Since the option was planned, the planners order all the parts from vendors, manuals and other literature are written and printed. It's all good until there's a hangup in a critical part and all that already made and printed stuff is looking for a home. There's a guy in the plant, euphemistically called a "quality engineer" whose job it is to figure out how to make a complete car when there a critical part missing. Easy when it's the lack of a set of whitewall tires; a bit more complicated when it's a transmission that echoes into other components.

One of the guys in my L.A. club was a quality engineer for a Chevrolet factory in L.A. and that's where I got my info about the process.

[jmiahman]

That's a pretty awesome description so I have a oh shoot car lol. Sometime between the order and the delivery things (4-Speed transmission) went amiss and they made it work with that they had. I wonder how many YDs there are? At what point did Tonowanda get the memo stop with the YDs or did they just keep building 95HP 3 Speeds until 61 when they replaced the YD for an actual 4 Speed.

[jmiahman]

If you check your axles I'm betting that you will have 2 different lengths.

They both measure about 23 inches and seem to be the same length. Here's the differential information from the first post:

Differential:
Date code: B660 (6th day of June?)
3780263
BR6 6 (Type BR 6th day of June)

Looks to me to be the original, and as much as I hoped it was a BP and not a BR it is a BR.

[cnicol]

Regarding "axle length", Rex was referring to the little stub-axles that go into the differential. '60s had two identical "short" stub axles, while open-differentials in 61-64 cars had stub axles of different lengths. Totally inaccurate numbers, but just to give you an idea, "short" stub axles measure about 3" while "long" stub axles are more like 5" long.

A "short/short" combination would be '60 (or later with positraction).
A "short/long" combination would be '61-4 open differential

If it's "Short/Long", it's not built like a regular '60 differential and with the "june 1960" date code you found, which is late in the model year, it was probably built for '61 production. Assembly of '61 cars starts in August so the June date code is "possible" for '61 MY.

[jmiahman]

Regarding "axle length", Rex was referring to the little stub-axles that go into the differential. '60s had two identical "short" stub axles, while open-differentials in 61-64 cars had stub axles of different lengths. Totally inaccurate numbers, but just to give you an idea, "short" stub axles measure about 3" while "long" stub axles are more like 5" long.

A "short/short" combination would be '60 (or later with positraction).
A "short/long" combination would be '61-4 open differential

If it's "Short/Long", it's not built like a regular '60 differential and with the "june 1960" date code you found, which is late in the model year, it was probably built for '61 production. Assembly of '61 cars starts in August so the June date code is "possible" for '61 MY.

Thank you so much for the clarification, yes both are 2 5/8 inches.. nice guess with the 3. I have no doubt diff is a 60, but anyone with more knowledge feel free to correct me. Now to see what they may have had to change to get those two parts together.

[cnicol]

So... since your car has a '60 BR differential and a 63 transmission, someone has definitely altered one or the other because they definitely won't work together.

A 60 3-sp differential is set up to accept a 3-sp transmission with a short output shaft like this: (see stub shaft at right)

While a 61-5 3-sp (or 4-sp) has a long output shaft like this:

As you might imagine, there's no way you can bolt the two together without modification.

- Either someone changed the '63 transmission mainshaft to the short '60 style
OR
- Someone changed the pinion shaft in the differential to accept the longer output shaft found on '61-5 3-sp and 4-sp transmissions.

[jmiahman]

As you might imagine, there's no way you can bolt the two together without modification.

- Either someone changed the '63 transmission mainshaft to the short '60 style
OR
- Someone changed the pinion shaft in the differential to accept the longer output shaft found on '61-5 3-sp and 4-sp transmissions.

Thank you for being a treasure trove of information, I'll let you know which one it is soon. I was trying to get the crankcase cleaned up and the main bearings in before looking into the trans diff issue, but curiosity just may kill this cat, or at least my goals.

[RexJohnson]

The early posi's still used the long/short stub axles as the open diffs did. The posi side (short if I remember correctly) did use a special very flat shield washer.

[jmiahman]

The early posi's still used the long/short stub axles as the open diffs did. The posi side (short if I remember correctly) did use a special very flat shield washer.

So I don't have an early Posi.. but curiosity did get the better of me last night and I just wanted to take a peak into the transmission and see what type of condition it was in, were all the teeth good, any chipped etc.. plus my daily driver is a Ford Expedition with a stupid "filled for life" 6R80 that no transmission shop will touch but only swap out for a new 6R80. I'm not a fan of things that aren't serviceable and to compare the two transmissions is a fun thought, the Corvair trans is so tiny lol, obviously the Expedition has a lot more power etc.. but to just be able to take the top off this one and look inside to see all the gears etc.. brings me great joy lol. So I did:

and I knew right away it wasn't going to give me any answers to my differential questions but at least everything looked decent. Didn't see any chipped teeth etc.. and marvelled at all the cool mechanics that went into it. To learn a bit more I checked out my 1960 Assembly manual which had a picture of it but no breakdown of parts, so I went to the 1960-1969 Owners Workshop Manual which was useless. It did have two transmissions a 3 Speed and a 4 Speed diagrammed but neither was my transmission. This is where I am glad Joe (from Cathy's Corvair fame) told me to get a 1960 Shop Manual when I saw him at the meet-up at the beginning of the month, cause there it was in section 6. I also found a diagram for it on GM Parts Wiki for anyone in the future who may need it, but get yourself a Shop Manual for your year, they are worth it:

[jmiahman]

- Either someone changed the '63 transmission mainshaft to the short '60 style

I wonder how hard it was to do?

Maybe the mainshaft was interchangeable?
https://ssl.corvair.com//user-cgi/catal ... w_page=129

[joelsplace]

Something I didn't see mentioned is that sometimes the guy stamping things made a mistake and sometimes the person writing the charts made a mistake.
I have several blocks with codes that don't match anything and I also have some heads with casting numbers that don't match anything. I bought the heads from someone on the dead forum after there was a lengthy discussion on how to ID them. No answer.

[caroseiii]

When the aluminum case transmissions failed, or were not serviceable, they were replaced with a cast-iron case. This transmission is in excellent condition internally so perhaps it was a factory replacement transmission that was installed after 1961. Possibly the vehicle was late production and the new cases were introduced for the transmission kind of like the 1961 block castings with FC/SW dipstick bosses, 145 cid pistons and cylinders, and 1961 cylinder heads with head temperature castings were used in late production on 1960 engines.

If you read about the failure mode of the aluminum case transmission causing differential seizure warranty claims, one can understand why the aluminum case was replaced with the cast-iron one.

All of 1960 internals are interchangeable with later cases. Likewise, you can build a 1960 case to 1964-65 FC specifications to look stock but with improved torque multiplication and stronger input shaft.