Transmission Case Bosses and Case Paint

Mike1291

Mike1291

Senior Member
How can I tell if the bosses in my case are too worn out?

I was lent a transmission case to compare my current one against one that was refreshed. However, I noticed that the inside of the refreshed case was painted. I don't understand why this is since the case thrust bosses fit against the cluster gear set and I would think the paint would wear out and contaminate the oil in the transmission.
 

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It is very common to paint the inside of gear cases (and motors, and differentials) with Glyptal insulating paint.

Glyptal is what was originally used to paint the windings and internals of various electrical equipment: motors, generators, transformers. It is alcohol based and creates a coating that is die-electric, impervious to oil, besides some mechanical strength against scratching/removal.

Its use on motor cases was part of the "rebuilding" technology post WWII. Glyptal tends to "seal in" any embedded sandblasting sand or sand from the original casting - and the coating won't lift in the oil, peel, and it is resistant to wear.

Glyptal standard has a "red" color.

As to your use and question, generally coating of any kind runs in the 0.002 to 0.005 inch thickness, which is probably not enough to affect the positioning of gear components in a Model A ******. Yours may be Glyptal but it may also be "Rustoleum Primer" or any of the others of commercial rattle can.

Glyptal comes in rattle can, quart, or gallons. The rattle can runs $67 and the quart about the same.

Joe K
 
You could try removing it with acetone just on the thrust surfaces I would actually leave the internal cast surfaces painted With the spur cut gears there's virtually no load touching those surfaces I wouldn't worry about the very light wear marks.
 
I am negative on painting the inside of any casting on the Model "A" because eventually most coatings fail when continuously exposed to petroleum products. I especially am negative on coating the internal of a gas tank. The Model "A" is a fantastic success story lasting almost 100 years without any internal coatings. What is the rational for internal coatings?
 
What is the rational for internal coatings?
Click to expand...
I first heard about this from my brother the drag-racer. He had connections to the Owner of Epping Motor Speedway who to this day "put on a good show." Advice to those who attend: wear clothes you don't mind getting soiled - particularly if your seating is within 300 feet of the start.

The point of coating is...

1. Seal in any extraneous embedded sand/grit from either original casting, or subsequent sandblast.
2. Provide a surface that is easily cleaned with oil based solvent.
3. The internal surface is rendered "slippery" to the oil lubricant and oil returns faster to the sump bringing wear particles away from the point of damage quicker.
4. The slippery surface "thins" the returning oil which aids in cooling the box.

Admittedly adhesion of the coating to the internals of the gearbox can't be predicted.

I wouldn't coat a box or gearcase without first preparing the surface to "white metal" by blasting (and possibly creating the need to coat.)

But the results work so well. A box that has been prepared with Glyptal is a PLEASURE to tear down and clean in the parts washer.

But that is but one reaction to the surprise of finding someone has been in a gearbox before me. And seemingly someone who "cared" about the quality of their work.

Now define "quality."

"Quality exists in the mind of the beholder."

Joe K
 
I have had a bad experience with gas tank coating but I don't know if it was installed properly. It was coming off and plugging the fuel line and carb. Maybe if done correctly it would be OK but I'm leery of it.
 
Fuel is the toughest environment for coatings. Aviation uses coatings in wet wings but the stuff they use is expensive and time consuming to use. God forbid if it needs to be removed.

The stuff marketed for automotive fuel tanks also has to be perfectly cleaned and prepped or it will never completely adhere to the surfaces. If properly done, it will last a long time but model A tanks are near impossible to treat unless the tank is opened up.

Glyptal has been used inside engines for years. If it is properly treated and applied, I wouldn't worry about it coming off. Even if it does, it's doubtful that is would hurt anything in there.

The best way to check for wear on the thrust surfaces is to install the gears & shafts and see how much the gears move in end play. Thrust washers can take up most play. The straight cut gears don't have much thrust loading anyway. It was the later helical cut gears that had a lot of thrust loads. I'd be more concerned about cracks than thrust load wear.
 
i guess the only way to know if the bosses are too badly worn would be by checking end play of the assembled gears in the ******.
which would mean that you would need specifications on that movement. i don't know what those are or where to find that info, but someone must know of a source for that.

the other way to find a measurement would be to check the endplay on gears of a known good transmission. i don't have an assembled one so i can not help you with that.
 
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