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Old 07-16-2021, 07:38 PM
GMCM76 GMCM76 is offline
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Default 1970 grand prix 4 speed help

What is the correct number muncie 4 speed for a 1970 Grand Prix SJ 455 i have either 478218 or 478173??

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Old 07-20-2021, 12:17 AM
joegpho joegpho is offline
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I don't have access to my GM parts books, so all I know is that for 1970 the transmission should be an M-21. More help, perhaps, via this link:

https://www.motortrend.com/how-to/gu...-transmissions

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Old 07-20-2021, 03:10 PM
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unruhjonny unruhjonny is online now
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where did you glean either of those numbers from?

I'd like to help, but am confused by the question.

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1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.


1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
1 Corinthians 2:12-14 / Ephesians 2: 8-9 / Luke 23: 39-43 / 2 Timothy 3:1-5;12
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Old 07-20-2021, 09:39 PM
'ol Pinion head 'ol Pinion head is offline
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Quote:
Originally Posted by unruhjonny View Post
where did you glean either of those numbers from?

I'd like to help, but am confused by the question.
The numbers the OP gave are out of an early to mid 70's dated Pontiac Master Parts book. That might have worked at the dealer 4 plus decades ago. Such an over the counter complete new Muncie 4sod for such a '70 model would have CTC- (a single digit number) stamped in very small digits into two spots on a "661" case.

Looking for a correct '70 GP 455 application Muncie 4spd, it would indeed be the close ratio/ M21 with correct speedo drive gear for 3.31 & 3.55 rear gear. Same two letter coded M21 was avail behind a '70 455 GTO. Originally, a very early '70 model application would have a "660" casting Muncie case. Later in the Fall of '69, Muncie 4speeds were built with the first "661" casting cases. Both casting cases were combined with the same small output tailshaft housing for thus applucation. Not extremely hard to come up with either '70 casting number M21, it's coming up with a correct dated one that will be a challenge if one is very serous about restoration.

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Old 07-20-2021, 11:45 PM
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unruhjonny unruhjonny is online now
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Quote:
Originally Posted by 'ol Pinion head View Post
The numbers the OP gave are out of (a) ... Pontiac Master Parts book. ...
Thanks!

That was my guess, but my knee-jerk reaction was that the logical numbers to use for determining the correct transmission might be the main case casting numbers, or maybe tail housing casting numbers - not a part number that has gone obsolete with time.

Would either of those 478--- numbers be observed on a Muncie ID tag?
(which would have also had the transmission code)

I might not know much about GP's, but that doesn't mean I'm not interested;
I would have thought that finding an four speed in the GP would have meant it was the M20.



I take it both of those part 478--- numbers were used for the M21.

Sorry for disrupting the conversation.
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__________________
1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.


1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
1 Corinthians 2:12-14 / Ephesians 2: 8-9 / Luke 23: 39-43 / 2 Timothy 3:1-5;12

Last edited by unruhjonny; 07-20-2021 at 11:55 PM.
  #6  
Old 07-21-2021, 05:06 PM
'ol Pinion head 'ol Pinion head is offline
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Quote:
Originally Posted by unruhjonny View Post
Thanks!

That was my guess, but my knee-jerk reaction was that the logical numbers to use for determining the correct transmission might be the main case casting numbers, or maybe tail housing casting numbers - not a part number that has gone obsolete with time.

Would either of those 478--- numbers be observed on a Muncie ID tag?
(which would have also had the transmission code)

I might not know much about GP's, but that doesn't mean I'm not interested;
I would have thought that finding an four speed in the GP would have meant it was the M20.

I take it both of those part 478--- numbers were used for the M21.

Sorry for disrupting the conversation.

Short, and to the point!

"part #"...."pick code"..... USAGE

478173.......(DJ)...........'70 233-235-237 & GTO 400 M20
478174.......(DL)...........'70 GTO 400 usage M21 w 3.90 & 4.33 gears (6 tooth speedo drive gear)
478218...... (DP).......... '70 GTO/GP 455 usage M21 w 3.31 & 3.55 gears (believe... 8 tooth drive gear, will have to confirm in '70 DP coded M21)

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  #7  
Old 07-21-2021, 05:39 PM
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unruhjonny unruhjonny is online now
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thanks

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