700R4 Identification Issues- Anybody help?

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Hopefully somebody can help separate the identities and help me out. I am doing a 700R4 trans swap in my '64 C10. I picked up this trans because it was advertised as being out of a 1991 Chevy van and was mated to a later style 1pc rear main SBC (saw for myself). Figured chances were good that seller was telling the truth. Now thinking that the engine and trans may have been earlier (1986) and swapped into the later model van. Regardless, I still have some questions about the trans.

So here's my deal. I have been reading all the posts on how to ID 700R4 transmissions and which ones are desirable and this and that. Unfortunately, there seems to be gaps at least in regards to getting a clear answer on the one I have.

I have been using these posts for reference (amongst others):
http://www.camaros.net/forums/showthread.php?t=157368
http://www.thirdgen.org/techboard/tr...4-year-id.html
http://www.hotrodders.com/articles/T...ification.html

Some say 1986 and on are good, some say 1987 and on are good. All say that the MDB or K case are the most desirable, however disagree on what year the MDB case started. I have seen the Year codes. (However I am still interested in finding a listing of Model codes) and get the Julian date.

All that said. Here is my info:
Stamped number on passenger side rear above pan: 6YKM256H
-Mine also has the "MDB" cast into the case on the passenger side bellhousing (although smaller than others I have seen).
-My valve body appears to be the later version and has a switch for 4/3.
-Tailshaft casting#: 8642547-5
-"14" cast into side of case above TV cable area on both sides of case
-Had the hall effect speedo sender with the metal "reluctor" wheel/gear

So, from what I have read, mine should be a 1986 (possible if van when through drivetrain transplant, I suppose). I have read that the MD8 casting didn't start showing up till 1988? If so, than what is it doing on a 1986 case?


I am not sure how many splines the input shaft has yet (27 or 30) but intend to check this evening. I also noticed that there is another number stamped on a pad on the passenger side of the trans at the bellhousing where it mounts to the engine block ( I have not yet gotten that number). Anybody know what that number relates to? Likewise, I have not looked for a pump serial number. But I will check all this this evening and post my findings.

I am already committed to it and have installed a TCI lock up kit amongst other things. So I will be using it. Just curious to know more about it.

It just seems like kind of an in betweener in regards to information posted on the net and was wondering if anybody had some hard solid facts on it and maybe what the Model code decodes to to see if it actually was a transplant.



I have included some pictures for reference. Thanks for any input in advance.