78 pace car transmission

[Hugh A.]

The various documentation with my 78 pace car alternate between references to M38 automatic transmission and references to MX1 automatic transmission. Any easy way to determine conclusively which is installed?

[Joe L.]

Re: 78 pace car transmission

The various documentation with my 78 pace car alternate between references to M38 automatic transmission and references to MX1 automatic transmission. Any easy way to determine conclusively which is installed?

Hugh-----


They are, essentially, the same thing. M38 indicates a THM-350 transmission. MX1 is a "merchandising option" for a 3 speed automatic transmsission (in this case, a THM-350).

[Gary B.]

Re: 78 pace car transmission

Does your Vette still have the option sticker still on it?

[Tom R.]

Re: 78 pace car transmission

The various documentation with my 78 pace car alternate between references to M38 automatic transmission and references to MX1 automatic transmission. Any easy way to determine conclusively which is installed?

Hugh, an article has submitted to the Restorer that is scheduled for publication I believe in the Winter Edition re 78 transmission and it touches on this topic.

Essentially, GM tagged a number of RPOs codes (regular production option) as merchandising options. It gave zone/factory the option to change the parts out for installation but permited dealers to order the option. MX1 (M38) is the merchandising option for automatic transmissions while MM4 was used for M20 applications.

What this means is that if you matched up a window sticker with same VIN and its build sheet mate...you'll see two different RPOs printed out. MERCHANDISING OPTIONS will always show up on production documents (retail documents) while build RPOs will always show up on build sheets...and these will reconcile with the AIM for that particular model year. MX1 is not a part number...it's an ordering number while the M38 is the actual part number.

I believe in 76 or 77, the M38 was introduced for the lower powered L48 engine while the heavy duty M40 was continued to be used for L82 application...essentially the was a GM cost savings measure. In the case of four-speeds a dealer would order an MM4 but the factory would install a Muncie cast iron 4-speed when L48 was called out while L82 applications got the Borg Warner all-aluminum M20 4-speed.

A study of build sheets confirms what's described above for both MX1s and MM4s and is documented in the article on 1978 four-speeds.

Hope this helps

[Hugh A.]

Re: 78 pace car transmission

Does your Vette still have the option sticker still on it?

Hi Gary, no I don't have the option sticker.

[Hugh A.]

Re: 78 pace car transmission

Hugh-----


They are, essentially, the same thing. M38 indicates a THM-350 transmission. MX1 is a "merchandising option" for a 3 speed automatic transmsission (in this case, a THM-350).

Joe, thank you.

[Hugh A.]

Re: 78 pace car transmission

Tom, thank you for the info - I look forward to reading the article.

[Roy B.]

Re: 78 pace car transmission



I think the MX1 was a 350 trans ordered ( heavy duty )when ordering the trailer package that I did which my 78 had MANY changes to the Corvette , Radiator ., shocks,Alternator,battery,sway bars,trans and so on.

[Hugh A.]

Re: 78 pace car transmission

Roy, thank you.

[Tom R.]

Re: 78 pace car transmission

I think the MX1 was a 350 trans ordered ( heavy duty )when ordering the trailer package that I did which my 78 had MANY changes to the Corvette , Radiator ., shocks,Alternator,battery,sway bars,trans and so on.

Roy...same tranny was used for either application...M38. Read above note re the MX1=MERCHANDISING OPTION.

[Roy B.]

Re: 78 pace car transmission

Roy...same tranny was used for either application...M38. Read above note re the MX1=MERCHANDISING OPTION.

I dont know anything about the MX1 that's why I said (I think it may be)