Automatic Transmission Pan finish

[Frederick W.]

I've got my pan off to work on the kickdown solenoid. (68 with TH400)

The pan has a mottled look due to many areas of rust pitting.

How should I spruce it up.

Rust remover?
Steel wool?
Glass bead blast?

Is it painted, sealed or natural finish?

thanks
Fred

[Joe L.]

Re: Automatic Transmission Pan finish

I've got my pan off to work on the kickdown solenoid. (68 with TH400)

The pan has a mottled look due to many areas of rust pitting.

How should I spruce it up.

Rust remover?
Steel wool?
Glass bead blast?

Is it painted, sealed or natural finish?

thanks
Fred

Fred------

I believe these transmission pans were originally natural, unfinished steel. This finish will be difficult to restore precisely as-original. I would use the least aggressive method first. So, a chemical rust remover would be my first choice.

[Edward J.]

Re: Automatic Transmission Pan finish

Fred, as Joe says there are natural, But I did clean my thm400 pan( Steel Wool) and painted it with a dupli color engine- natural aluminum look paint. Its not NCRS buts looks great.

[Frederick W.]

Re: Automatic Transmission Pan finish

Thanks guys, I gathered it was a natural steel finish, and went with naval jelly and steel wool first. Inadequate.
So I just chucked in my blast cabinet and glass bead blasted it. Looked pretty good. I left it like this and reinstalled (after wire wheeling all the bolts on my bench grinder.
I'd say it looks pretty natural, you'd have to be pretty nit picky to find fault with it. Only problem is, I'm not sure how long it will stay this way without an applied coating.

Fred

[Joe L.]

Re: Automatic Transmission Pan finish

Thanks guys, I gathered it was a natural steel finish, and went with naval jelly and steel wool first. Inadequate.
So I just chucked in my blast cabinet and glass bead blasted it. Looked pretty good. I left it like this and reinstalled (after wire wheeling all the bolts on my bench grinder.
I'd say it looks pretty natural, you'd have to be pretty nit picky to find fault with it. Only problem is, I'm not sure how long it will stay this way without an applied coating.

Fred

Fred------

I would give it a very light "mist" coat with a satin or low gloss finish, clear urethane. This will do two things: first, it will seal and protect the surface from corrosion. Second, it will actually make a bead blasted steel finish look more like its natural, original appearance.

[Frederick W.]

Re: Automatic Transmission Pan finish

Fred------

I would give it a very light "mist" coat with a satin or low gloss finish, clear urethane. This will do two things: first, it will seal and protect the surface from corrosion. Second, it will actually make a bead blasted steel finish look more like its natural, original appearance.

Good tip Joe
I'll try it.

[Frederick W.]

Re: Automatic Transmission Pan finish

Fred, as Joe says there are natural, But I did clean my thm400 pan( Steel Wool) and painted it with a dupli color engine- natural aluminum look paint. Its not NCRS buts looks great.

Haven't seen this paint. I'll check it out.

[Jim T.]

Re: Automatic Transmission Pan finish

Frederick, I have maintained my 1970 turbo 400 with fluid and filter changes for over 40 years. About 20 years ago I bought a new turbo 400 transmission pan from GM #8655021. One of the best improvements I have installed on my 1970. Although I always used a torque wrench to tighen the original tranmission pan bolts and used the gasket that came with the GM filter, transmission fluid would show up sooner or later on the transmission pan. With the GM #8655021 installation and still using a torque wrench to tighten the transmission bolts, no more leaking/seeping transmission fluid. I attribute this to the fact that the #8655021 turbo 400 transmission pan is a much thicker steel.
This thicker pan will lose points if judged, however I like driving my 1970.

[Joe L.]

Re: Automatic Transmission Pan finish

Frederick, I have maintained my 1970 turbo 400 with fluid and filter changes for over 40 years. About 20 years ago I bought a new turbo 400 transmission pan from GM #8655021. One of the best improvements I have installed on my 1970. Although I always used a torque wrench to tighen the original tranmission pan bolts and used the gasket that came with the GM filter, transmission fluid would show up sooner or later on the transmission pan. With the GM #8655021 installation and still using a torque wrench to tighten the transmission bolts, no more leaking/seeping transmission fluid. I attribute this to the fact that the #8655021 turbo 400 transmission pan is a much thicker steel.
This thicker pan will lose points if judged, however I like driving my 1970.

Jim------


Very common. Many GM stamped steel parts were too thin, distorted in service and caused leaks when a fluid was involved.

The GM #8655021 transmission pan was discontinued from SERVICE in February, 1993 and replaced by GM #8679995. I presume the latter still uses the heavier gauge construction but probably has other revised features (some of which might even improve sealing over the 8655021). It remains available from GM for a GM List of about 100 bucks.

[Terry M.]

Re: Automatic Transmission Pan finish

Fred------

I believe these transmission pans were originally natural, unfinished steel. This finish will be difficult to restore precisely as-original. I would use the least aggressive method first. So, a chemical rust remover would be my first choice.

I have been thinking about this, and I am not so sure about the pan finish. If we mean natural in the sense of unpainted I would agree -- BUT I would bet there was some process used to coat the steel prior to drawing it into the pan shape that may have provided lubrication for the drawing process. Or perhaps the raw steel was coated in some way as purchased before the drawing operation in order to enhance the drawing operation.

While not from a TH 400 I stumbled across these 4L60E pans in the garage. I am not sure which car these are from, but they are from one of the former police cars -- which means they had about 5 years and 90K miles of service in North Carolina before they came to me. These have been sitting in the midwest garage for another five years after I replaced them.

I am not sure it is worth a scientific analysis, but I am convinced these are not raw steel and I don't believe the original TH 400 pans were either.

[Joe L.]

Re: Automatic Transmission Pan finish

I have been thinking about this, and I am not so sure about the pan finish. If we mean natural in the sense of unpainted I would agree -- BUT I would bet there was some process used to coat the steel prior to drawing it into the pan shape that may have provided lubrication for the drawing process. Or perhaps the raw steel was coated in some way as purchased before the drawing operation in order to enhance the drawing operation.

While not from a TH 400 I stumbled across these 4L60E pans in the garage. I am not sure which car these are from, but they are from one of the former police cars -- which means they had about 5 years and 90K miles of service in North Carolina before they came to me. These have been sitting in the midwest garage for another five years after I replaced them.

I am not sure it is worth a scientific analysis, but I am convinced these are not raw steel and I don't believe the original TH 400 pans were either.

Terry------


By natural, unfinished steel I meant steel that was not painted, electroplated, powder coated, galvanized, etc. I'm quite sure that some sort of lubrication was used to facilitate the drawing operation and whatever was used remained on the part in the new condition. That's why I suggested the use of a "mist" coat of satin or low gloss clear urethane on a bead blasted part to simulate the original appearance.

[Terry M.]

Re: Automatic Transmission Pan finish

Terry------


By natural, unfinished steel I meant steel that was not painted, electroplated, powder coated, galvanized, etc. I'm quite sure that some sort of lubrication was used to facilitate the drawing operation and whatever was used remained on the part in the new condition. That's why I suggested the use of a "mist" coat of satin or low gloss clear urethane on a bead blasted part to simulate the original appearance.

The drawing operation for a transmission pan is one thing -- what is required for drawing an oil pan is quite another. In the early 1960s I worked in research dealing with metal forming operations. We treated raw steel with a process made by Parker Chemical Company called Parkerizing. It was a phosphating operation which gave tooth for a soap style lubricant that was used in sheet drawing operations (the process we are talkig about) as well as rolling and wire drawing operations.

I am not saying that is what was used on transmission oil pans, but it was used in the forming of C3 hood latches and some type of lubricant that changed the surface of the raw steel was used on transmission pans. Perhaps scientific analysis is in order after all. Now all I have to do is find the pan from my TH 400.

[John H.]

Re: Automatic Transmission Pan finish

Several different lubricants were/are used on the surface of the steel blank before it's placed in the first-stage draw die; back in the 60's-70's-80's, they were applied manually, with a MOP. With the advent of high-speed tri-axis transfer presses, the draw compound is sprayed automatically on the blank as it shuttles from the de-stacker into the first stage of the press.

The draw compound also provided some degree of rust protection while the panels were in racks during shipping prior to use at the assembly plant; that's why a hot high-pressure degreasing system was required prior to the iron phosphate stage in the Paint Shop.

[Jim T.]

Re: Automatic Transmission Pan finish

Jim------


Very common. Many GM stamped steel parts were too thin, distorted in service and caused leaks when a fluid was involved.

The GM #8655021 transmission pan was discontinued from SERVICE in February, 1993 and replaced by GM #8679995. I presume the latter still uses the heavier gauge construction but probably has other revised features (some of which might even improve sealing over the 8655021). It remains available from GM for a GM List of about 100 bucks.

Joe thanks for the replacement pan number. I paid $27.00 for the #8655021 pan about 20 years ago.

[Richard M.]

Re: Automatic Transmission Pan finish

Before using any type of paint, I would coat it with Pre Lube 6 avaliable from Quanta works really good on natural finish drive shafts.

Richard Mynatt