Hey C4 guys, I am a C3 owner and have a 700R4 tranny a friend gave me that I'm having trouble decoding. It has the original nubmbers stamped in the correct place, but then it also was rebuilt for GM. The original stamped numbers on the passenger side are CHB 127451 and on the case itself is MD8. I believe this is a 4L60 trans. There is a rebuild tag on the drivers side with this info stamped in. 08YZ M4 035 859428 Then a sticker with 8YZ. From what I have been able to find out this is either an 88 or 92 model. I just can't seem to locate any kind of code that tells me what this thing is. I was told by a supposed GM trans expert that this is a high performance Corvette Trans with all the good stuff put in it from the factory. I'm hoping it is at least a good year rebuild. I am planing this swap for winter, so any help would really be appreciated.

 

You have a GM replacement trans. They grind off the factory code stamped in the pass side pan rail, before putting their new sticker on it. There is a date cast into a small circle on the side of the trans near the shifter boss. That will tell you the date cast, and you can figure out the model year from there.
If the bottom of the trans has a boss and drilled, tapped holes for a typical trans mount, it is not a vette trans. If there is a large V cast into the side of the bellhousing, it is a vette case.

If GM was the last one to rebuild it, there is nothing special inside.

 

I'll check that all tomorrow, But I don't think I have a Vette Tranny. Will advise though

 

Well here we go, more numbers. There are two circles above right of the shifter lever. in one is 11 3 86 kind of obvious there. in the other is 8663 and 549 and on the case itself a 4, no V. A sticker from GM R D O T has part number 14102721, serial 602495 and on the drivers side back on a square boss is 13 3086 0259. With all the numbers supplied and this being a rebuilt trans I'm still confused, because if it is an 86, when they rebuilt it they put in a 30 spline input shaft. Wish I could decode that rebuild tag 08YZ.

 

It should be safe to assume that the Y means it is a Y body (vette) transmission. It should look something like This

Note the (c4) vette tailshaft and the V on the bellhousing.

Can't help you with the year, although the 8 suggests 88.

 

85 and up contained a 30 spline input shaft. If you pull the pan and it does not have an aux valve body (and it should not), further disassembly will likely find a 7 vane pump, a small lo-roller and a 26 element sprag.
If the above is accurate, it is not a desirable trans. You would be better off with an 88-92, as it is a beefier trans in stock form.

 

I have a differant tailshaft, Will try to take some pics

 

For something that was free, this thing sure has cost me some brain cells. Will continue to ex[lore as per your suggestion

 

Yeah, they have a way if keeping you from becoming bored

 

Oh well thanks for the input, Will either keep trans for the next project or keep passing it on until someone who is not afraid of it, uses it. Too many codes and numbers to know whats really going on inside that case... and why open up something that may hbe what the next guy needs. See ya all, I'm back to the C3 forums..