....or is this known as a 999 trans ? What years and model cars did this come in ?

The trans gear ratios and trans designations are independent of each other.

The use of the low gearset came about to allow use of a numerically lower rear axle ratio for fuel economy - used in either a 904/998/999.

The 904/998/999 designation came from relative torque capacity - the number of clutch discs and band widths used.

My recollection is the low gearset became available in 1980.

Just about any Mopar that had 2.45:1 and 2.20:1 ring and pinion had the A999.
My J body Mirada did.
The 1995 GTE Phone repair Dodge B van with the 3.9 we scrapped did also.

The 80s fury's ,diplomat's and fifth avenues were good sources, some of the wheel drive trucks in those years had them too

First A999 was '74, first low gear set was '80, by '82 all of the 904 family had the low gear set.

a999 also had a 5 clutch front drum

How do you read the stamping on the transmission cases to determine the year of manufacture?

As I understand it, all 8 cylinder. lock up trans (late 70s, 80s F bodies, big cars) have the 2.74. Correct?

The last 4 digits of the numbers stamped on the pan rail are the build date based on a 10,000 day calendar. Post the number to decode.

None of the 904 family had the low gear set in the seventies.

I have two 8 cylinder. lock up trans that don't have low gear sets or 5 disc drums.. There are a lot of variations so you don't really know what you have until you tear it down.

What specific vehicles are those ?

That's true of any aged trans, never know what's been done at overhaul but the part number stamped in the pan rail tells how it left the factory. What inside parts are correct can be determined by perusing the factory parts catalog.

They were early 80s cars if I remember correctly. I looked up the numbers. I scrapped one of the cases because it was cracked and the other is in my race car. I tried to get the numbers off it but the shifter bracket is in the way.
John is correct one of the tranny's was gone through but the one I ended using looked untouched but who knows.

When I bought all my parts from CRT he told me about all the variations he has seen.

I've worn Google out....and I must be wording my search wrong. Can't find what my transmission came out of! It's a lockup for sure. The number on the drivers side of the pan rail is P4295887 7966 5768. I'm hoping it has the low 1st gear. I'm putting it in a 65 Barracuda. Any help appreciated.

Looks like 84-85 904 in a big car (Mirada, Cordoba, 5th Ave). 318.

Best way to tell is pull it apart and look.

I think that the lockup usually goes hand in hand with the low gear, they did it because they were using some steep gears like 2.2:1. I'm pretty sure my fifth avenue has the low 1st and the convertor locks up around 54 mph

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Thank you guys. Now I know what year parts to buy if I get brave enough to tackle it myself. My local transmission shop has been good to me by helping me with late model stuff, and has yet to charge me a dime to answer questions. He quoted me a very fair price for a bench job, so I will probably just throw it his way. Thanks again!

JD ... define reasonable?

$600 with shift kit and converter.