M21 transmition 660 case vs 661

[P.J.]

My gm book says that all 1970 chevelles that had m21 tranies installed were 661 cases, 584 tail housing,648 side covers. Could early built 70 chevelles Kansas built cars have m21 660 cases?
Peter

[Mr70]

Yes Peter.
I've personally seen 660's used on early assembled cars,& not just Kansas Leeds built,but all plants,& cars..And Crash just posted this a few weeks ago.

"660 main cases were used as late as Dec. 1969... 661 main cases were used as early as Sept. 1969. I have examples of each... The beginning of the 1970 model year the engineering drawings were change on the Muncie main case so that a fill plug and drain plug were tapped into ALL muncie main cases, so you can tell early 1970 model 660 cases, because they have drain plugs, M-20's, 21's, 22's... Hope this helps...crash"

[P.J.]

Thanks Rick
My car could have been fitted with either case
660 with a drain plug or a 661 case.I guess that the only
way to tell for sure is to find a Nov 11 assembled car from
the Kansas City plant.
Peter

[P.J.]

I received this email re the M21 660 case and the 661 case.
HEY PETER, I PERSONALLY HAVEN'T SEEN A 660 M20 OR M21 THAT HAD A DRAIN PLUG. M22'S ARE THE ONLY 660 CASE I HAVE SEEN WITH THE PLUG. THAT'S NOT TO SAY THEY DON'T EXIST!! THE M21 I HAVE DON'T HAVE THE PREFIX B THAT DENOTES ITS A M21 EITHER BUT IT IS. I THINK THEIR ARE A LOT OF LITTLE THINGS THAT SOME TRANNYS HAVE THAT ARE FACTORY BUT NOT REALLY MENTIONED AS A GIVEN RULE. ALL 661 CASES HAVE A DRAIN PLUG NO MATTER IF ITS A M20 21 OR 22 OR NOT. ----- Original Message -----

[crash]

He just hasn't seen enough cases, I have over 20 examples of 1970 model year 660 cases and they all have drain plugs with A or B ratio codes.
The A,B,C, ratio code didn't start until end of Oct. 1968 so early 1969 model year Muncie's didn't get stamped with a ratio code...Hope this helps...Crash

[P.J.]

Thanks Crash
experience experience,experience. 34 years later this information is important more so now than when we were blowing them up. Then it did not matter much,pic taken
at cayuga drag strip 1966 with the 55 blue beast.