Old 07-21-2021, 03:23 PM
John V. John V. is offline
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Join Date: Sep 2005
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Default '73 & '74 Muncie 4 spd Details

Been trying to scrounge up some info on these late production Muncie 4 speeds on the '70-'73 Firebird forum, thought I'd come here to see if the A body guys can offer any additional info.

Here is the original thread I started.

I was initially trying to figure out if I had the "correct" side cover for my early production '73 TA. I was advised it should be casting 335308.

I have figured out quite a bit, no thanks to the widely published info on the 'net about the 335308 Side Cover. I even contacted Paul Cangialosi from 5speeds.com who wrote a book on rebuilding and modifying the Muncie published in 2014. It contains all kinds of p/n info and pix. But he had no idea about the early production '73 Pontiac side cover design and seemed uninterested in learning what I had uncovered about the 335308 casting.

His book may even be the source for the incorrect info about the 335308 that has been spewed by numerous other Muncie "expert" sources and websites.

All of these references claim that the 335308 is a LONG shifter shaft boss cover. They further claim that "some" of them were cast with a 1-2 switch boss but that it was "never" drilled and tapped.

None of these claims appears to be correct.

Mr. Cangialosi's book confirms the existence of a 3952642 side cover, saying it is rarer than others and that it is a LONG boss cover, with a switch boss only on the 3-4. He doesn't identify the application(s) of this cover.

Released at the same time was the 3952648 side cover, it being the SHORT boss design, also with a switch boss only on the 3-4.

What I have determined is that all 335308 side covers have a switch boss on the 3-4 which was always drilled and tapped. But all of them also have a switch boss on the 1-2 which was always drilled and tapped for the early production '73 Pontiacs but was not drilled and tapped for some applications.

The 335308 also has the same boss dimension as the 3952648 side cover and should properly be identified as a SHORT shifter shaft boss cover.

For applications needing only the 3-4 switch boss, the 335308 side cover was interchangeable with the 3952648.

If you go by all the published references, you would believe the 3952642 was interchangeable with the 335308 but strictly speaking, you would be wrong.

This is critical because in production, a side cover with the SHORT bosses was assembled with specific short Shifter Shafts which would NOT work with a LONG boss cover. The specific Shifter Shafts used with the LONG boss cover are claimed by some references to not work with a SHORT boss cover. But apparently this is also incorrect. GM eventually discontinued servicing the short Shifter Shafts and only the long Shifter Shafts were available.

The short Shifter Shafts carried various p/ns including 3950308 which were used with the '69 side cover 3950306, this was the first that featured lever tabs secured by bolts instead of nuts. It was a SHORT Shifter Shaft boss design but had no switch bosses. Then there were the 3952651 Shifter Shafts which I believe were also short design. At the same time, the 3952649 Shifter Shafts were released, I believe these were long design and originally used with the 3952642 side cover. Eventually GM discontinued the 3950308 and 3952651 Shifter Shafts and specified the 3952649 Shifter Shafts for all Muncie 4 speed applications. It is obvious that a short Shifter Shaft could not work with a long boss cover. Less obvious that a long Shifter Shaft could be used with a short boss cover. But given the supersedures, I conclude that the 3952649 Shifter Shaft must be the long design.

But the main problem with the published references is the failure to recognize that early production '73 Pontiacs made use of the 1-2 switch boss for the p/n 490751 TCS switch that was part of Pontiac's ill-fated early '73 design TCS/EGR emissions system.

Prior to the EPA demanding Pontiac redesign the '73 TCS/EGR system, Pontiac Muncie 4 speeds used the 335308 side cover and BOTH the 1-2 and 3-4 switch bosses were drilled and tapped. Pontiac installed a thin head plug in the 3-4 switch boss, they had no use for it. The aforementioned TCS switch opened when the trans was shifted from 1st to 2nd gear (the infamous Time Delay Relay controlled the system approx. 30 secs on the 400, 50 secs on the 455 after the shift to 2nd).

When Pontiac redesigned the system beginning for cars produced on March 15, 1973, the design moved the TCS switch (new p/n 494366) to the 3-4 shifter boss.

Since it appears no other manufacturer made use of the 1-2 switch boss, Muncie could have reverted to the 3952648 side cover that had been used thru '72.

Instead, it looks like they continued to use the 335308, but they may have stopped drilling and tapping the 1-2 switch boss.

I am trying to collect as much evidence as I can to determine if this is what was done. Alternately, Muncie could have continued to supply Pontiac with 4 speeds with the TCS switch and plug positions swapped.

And it is also possible that Muncie recognized that the late production '73 and '74 Pontiac Muncie 4 speeds could make use of the 3952648 side cover and installed that instead.

It is entirely possible that a mix of these side cover choices was employed by Muncie during '73 and '74 production.

So I'm asking anybody with a '73 or '74 Muncie 4 speed to provide the side cover casting no. and the Muncie serial no. date code (example P3S02A) and partial VIN stamp (example 23N118765) as stamped on the Main Case.

Also add any comments as to how likely the trans is "original" or "rebuilt/pieced together" to give me some sense as to how likely the side cover is original to the Main Case.

Finally, if you can provide a pic showing the date coding on the side cover casting that would be great. Early 335308 castings had two 1/2" dia. circles that provide cast date info, later ones transitioned to a larger circle with a year (73 or 74 in a small center circle) surrounded by 12 pie shaped segments with dots in some or all of the segments.


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