Muncie assemby date code

[Tom R.]

Going thru some photos for an article, realized I had captured the assembly date code for this Muncie...but looks like a double stamp. Help appreciated. Believe I figured it out but other views appreciated.

Muncie M20 Code rev2.jpg

[John H.]

Re: Muncie assemby date code

What kind of Muncie is that? I've never seen one that had a machined pad anywhere for a date stamp.

[Joe L.]

Re: Muncie assemby date code

What kind of Muncie is that? I've never seen one that had a machined pad anywhere for a date stamp.

John-----


This is the 1978-E79 "Muncie" used with L-48 equipped cars during that period. It was actually a very close derivative of the old Saginaw 4 speed used in the 60's and early 70's. I believe that manufacture of these transmissions was done at the Muncie, IN plant where the original 1963-74 Muncie transmissions were manufactured and thus the moniker "Muncie" was used.

These transmissions have a cast iron main case just like the earlier Saginaw 4 speed.

For some strange reason, GM put these transmissions into production during the late 70's. After 1974, the installation of 4 speeds was low enough that GM just went back to the Borg Warner T-10 for most 4 speed applications. However, for 1978-E79 Corvettes used this "Muncie" transmission for all L-48 with 4 speeds. L-82 used the B-W T-10, as did most other 75-81 Corvettes with 4 speed.

1978-79 were very high production years for Corvettes. It may be that Borg Warner couldn't manufacture enough transmissions so GM had to designate them only for L-82 applications and "bring back" the older cast iron 4 speed to "fill the breach".

During the 78-E79 period, all M-21's were BW-T-10; all M-20 were the revived "Muncie".

[Tom R.]

Re: Muncie assemby date code

What kind of Muncie is that? I've never seen one that had a machined pad anywhere for a date stamp.

Thought it might throw you old Muncie guys! Even threw Colvin in his Book "Corvette by the numbers"

As JL explains this was taken from a low-mileage 78 L48 4 speed built in late June. I've concluded the code is R 8 H 01 and is a double strike. So the tranny was assembled June 1, 1978 and consistent with the build date accompanied with the VIN.

John, maybe you can answer this question or shed some light on the use of RPOs and ordering and JL got into this as well. With L48 or L82 specified and base manual tranny checked off on the dealer order form, MM4 was called out on the dealer order and printed on both the retail sticker (window) and the dealer invoice. However, the M20 RPO was used on the manifest but each application (L48 or L82 base) called out the correct broadcast code...ZU for L82 and S6 for L48 for the factory worker to "pick" the right part for installation. But what has me curious is the use of MM4 as a generic RPO that deferred the ordering to the engine type for base manual transmission. Any insights here?

[Chuck S.]

Re: Muncie assemby date code

Thought it might throw you old Muncie guys! Even threw Colvin in his Book "Corvette by the numbers"

As JL explains this was taken from a low-mileage 78 L48 4 speed built in late June. I've concluded the code is R 8 H 01 and is a double strike. So the tranny was assembled June 1, 1978 and consistent with the build date accompanied with the VIN.

John, maybe you can answer this question or shed some light on the use of RPOs and ordering and JL got into this as well. With L48 or L82 specified and base manual tranny checked off on the dealer order form, MM4 was called out on the dealer order and printed on both the retail sticker (window) and the dealer invoice. However, the M20 RPO was used on the manifest but each application (L48 or L82 base) called out the correct broadcast code...ZU for L82 and S6 for L48 for the factory worker to "pick" the right part for installation. But what has me curious is the use of MM4 as a generic RPO that deferred the ordering to the engine type for base manual transmission. Any insights here?

That practice is still alive and well today.

Whenever different manual transmissions are used in similar but different applications on the C6 Corvette, you only ORDER a generic RPO marketing code for manual transmission (MN6), and the other options ordered will define which transmission code is used according to GM specifications.

For example, if you order manual transmission on the C6, you order MN6. The build sheet for the base car will indicate (Edit: MM6) in the transmission box. But...if you also order Z51 Performance Package, the RPO code in the build sheet transmission box is MZ6.

In the case of the Tremec transmissions, they are distinctly different transmissions, with the differences being in the gear ratios, and provision for fluid cooling in the MZ6. Ironically, because of the wider ratios of the MZ6, the torque rating of the Z51 transmission is slightly lower than for the base Tremec. At least this was true for the early C6s when the T56 was being used...the redesigned Tremec Z51 tranny has no doubt been redesigned for higher torque rating due to the higher torque output of the LS3. The old T56 MZ6 was rated right at the rated torque output of the LS2, 400 ft-ibs.

[Tom R.]

Re: Muncie assemby date code

That practice is still alive and well today.

Whenever different manual transmissions are used in similar but different applications on the C6 Corvette, you only ORDER a generic RPO marketing code for manual transmission (MN6), and the other options ordered will define which transmission code is used according to GM specifications.

For example, if you order manual transmission on the C6, you order MN6. The build sheet for the base car will indicate MN6 in the transmission box. But...if you also order Z51 Performance Package, the RPO code in the build sheet transmission box is MZ6.

Chuck

Interesting...I check my 2000 MN6 Z51 convertible and sure enough. The RPO on the manifest lists MM6 Man tranny while the TRANS box shows M8

[Chuck S.]

Re: Muncie assemby date code

Chuck

Interesting...I check my 2000 MN6 Z51 convertible and sure enough. The RPO on the manifest lists MM6 Man tranny while the TRANS box shows M8

Actually, I think the base transmission code on C6 build sheets is also MM6. Something told me the MN6 marketing code was not right, but I couldn't remember the actual base build code until your post reminded me.