Bottom Drain Plug On Muncie Transmission...

[Paul B.]

...thought this was an M-22 thing??? All the M-21's I've had did not have a bottom drain plug, so did M-22s???

...the BlackBook says no M-22s in 1972, so what did the '72 ZR-1s have for a 4spd transmission???

...did some or could you get an M-20 in an LT-1??? All three years???

...a friend has a '72 LT-1 with a Muncie which has a bottom drain plug which is also VIN # derivative stamped to his car's VIN #.

...odd thing is I've been in many M-21(still own one)cars where the transmissions were smooth and quiet. This particular '72 LT-1 car has a very distinctive whine to it, unlike anything I've ever heard come from a Muncie transmission.

...the '70-'72 JG says transistor ignition last used in '71 but the BlackBook says '72 ZR-1s had it???

...enough confusion for now.

[Joe L.]

Re: Bottom Drain Plug On Muncie Transmission...

...thought this was an M-22 thing??? All the M-21's I've had did not have a bottom drain plug, so did M-22s???

...the BlackBook says no M-22s in 1972, so what did the '72 ZR-1s have for a 4spd transmission???

...did some or could you get an M-20 in an LT-1??? All three years???

...a friend has a '72 LT-1 with a Muncie which has a bottom drain plug which is also VIN # derivative stamped to his car's VIN #.

...odd thing is I've been in many M-21(still own one)cars where the transmissions were smooth and quiet. This particular '72 LT-1 car has a very distinctive whine to it, unlike anything I've ever heard come from a Muncie transmission.

...the '70-'72 JG says transistor ignition last used in '71 but the BlackBook says '72 ZR-1s had it???

...enough confusion for now.

Paul------


1) 1966-69 Muncie transmission had the drain plug only if M-22. However, 1970-74 Muncie transmissions which used the GM #3925661 main case usually always had the drain plug, regardless of variant;

2) 1972 ZR-1 used the M-22 transmission. It was part of the ZR-1 package but not available separately;

3) The LT-1 was available with M-20 for all three years of LT-1 availability;

4) I have no idea why the gear whine on the 72 LT-1. However, maybe someone swapped in an M-22 at some point or swapped in an M-22 gearset to an original case. Of course, it could also be that there's some mechanical problem with the transmission;

5) No 1972 Corvette was equipped with TI ignition, ZR-1 or otherwise.

[Terry M.]

Re: Bottom Drain Plug On Muncie Transmission...

...thought this was an M-22 thing??? All the M-21's I've had did not have a bottom drain plug, so did M-22s???
That is a C2 thing.

...the BlackBook says no M-22s in 1972, so what did the '72 ZR-1s have for a 4spd transmission???
Don't be confused Paul. The problem is GMs method of record keeping. In 1972 the M22 was part of the ZR1 package -- so no M22 listed separately. Every ZR1 had an M22 from St. Louis.

...did some or could you get an M-20 in an LT-1??? All three years???
I'll kick this one to someone else. I think I know the answer, but I am not 100% sure so someone else can have a chance.

...a friend has a '72 LT-1 with a Muncie which has a bottom drain plug which is also VIN # derivative stamped to his car's VIN #.
I have a very good friend with a 1970 LT1 (original owner too )with a bottom plug on the transmission -- and every other 1970-1972 Corvette manual transmission has a bottom drain plug. The bottom drain plug started in 1968 or 1969 -- I forget which. You have to quit hanging around those C2 guys. They are you.

...odd thing is I've been in many M-21(still own one)cars where the transmissions were smooth and quiet. This particular '72 LT-1 car has a very distinctive whine to it, unlike anything I've ever heard come from a Muncie transmission.
Tell him to get it repaired -- or someone changed the internals.

...the '70-'72 JG says transistor ignition last used in '71 but the BlackBook says '72 ZR-1s had it???
Black book is wrong on this point. Didn't you look at Al Wagners distributor? In Novi tell him you want to look under the skirt of his distributor. He will let you, and you won't even have to kiss him.

...enough confusion for now.

I hope you are no longer confused.

[Paul B.]

Re: Bottom Drain Plug On Muncie Transmission...

I hope you are no longer confused.

...yep, Thanks to Joe L. again, my head is much clearer.

[Tom P.]

Re: Bottom Drain Plug On Muncie Transmission...

Not only do I agree 100% with Joe Lucia, BUUUUUUT, there are other reasons that a Muncie case may (or may not) have a drain plug (or lower plug as you call it). One of the main reasons is that Muncie rebuilders such as myself, installs a magnetic drain plug during every rebuild. Also, the magnetic donut is immediately removed and disposed of. In 40+yrs of rebuilding muncies, I've had ONE customer decline having a magnetic drain plug installed.

Why remove the magnetic donut in the bottom of the case?
First, here is a picture of the donut plus a magnetic plug----------and one which has come loose (the glob). That glob is a magnetic glob that was once glued to the bottom of the case, circulated around inside the tranny and destroyed a perfectly good tranny (second picture).




Also, a tranny without a drain plug CANNOT easily have the oil drained/changed.
With the donut INSIDE the case, any particles that it attracts remains INSIDE the case with no way to remove them.
With a magnetic drain plug, not only can the oil be drained/replaced, but any particles that are attracted to the magnet can also be removed from the tranny.
Is a drain plug correct for a 63-70 Muncie. NO! but neither is it so wonderful to not be able to change the oil or have a gearset destroyed by a circulating magnet!

[Mike M.]

Re: Bottom Drain Plug On Muncie Transmission...

learned something new here today. thanks tom. haven't ever seen a disloged magnetic disc. , but from now on, i'll remove them . always have used the magnetic plugs tho. thanks,mike

[Wayne M.]

Re: Bottom Drain Plug On Muncie Transmission...

I see in the Sept-Oct 1969 Chevrolet Service News (introducing 1970 Chev features), it says: "The Muncie 4-sp aluminum case incorporates a magnet on the fill and drain plugs. The previously used chip collector has been deleted".

My question is: when was the first use the magnetic "doughnut" glued to the bottom of the case ? I looked at two '66 "010" cases I have and see no evidence.

Pic below shows the pre-1970 magnetic plugs (used only on M22's, I believe) and those on all the 1970-up cases (on the right).

[Tom P.]

Re: Bottom Drain Plug On Muncie Transmission...

Wayne,
MOST Muncies that I have ever touched (and that is a BUNCH), beginning with the 63 versions, had the magnetic donut glued in the bottom of the case.
I would speculate that cases which do not have the donut, have been previously opened up by someone, OR, they were originally an M22 which got a magnetic drain plug, thus, no donut.
So, to answer your question, the FIRST Muncies got the donut magnet.
There is NO QUESTION that the magnet in the bottom of the case is a good idea to suck ferrous particles out of the oil. But with no drain plug and no access to the donut unless getting into the tranny, there is no way to remove the metal particles from the donut.
I'm sure the different configuration in magnetic drain plugs is simply due to what was supplied by the vendors. Magnetic drain plugs were also used in other manual trannys (and still are).