I'm restoring a 69 B body, with full undercoat. I know the undercoating was applied after the gas tank, fuel lines brake lines, E-brake cables, body plugs, fender splash shields, rear shocks were installed.
I assume the undercoat was sprayed after the engine, trans, exhaust and rear end were lifted up as an assembly.
I've seen undercoat on the removable trans crossmember. Also the rear spring hangers have undercoat. How did they avoid getting undercoating on the exhaust pipes and mufflers? Were the seats installed first? I recall seeing taped off spots at the seat mounting holes on some cars.
Basically, what parts were not installed before undercoat was applied?

According to RestoRick's Assembly Sequence, "undercoat wheelwells" is number 49. No undercoating of the whole car is mentioned.

Items 50 - 63 all involve the interior or upper body. Items 64 and up include upper control arms and rear axle/springs. If these items didn't get undercoated, then it looks like undercoating the whole car probably belongs at number 49 also.

http://www.restorick.com/tech/topic.asp?TOPIC_ID=58

My car only got the wheelwells undercoated, along with the bottom of the trunk pan, but I did notice there was undercoating under the front spring hanger. And there was undercoating overspray on the gas tank and on rear seat belt bolts, which are in agreement with the list.

That list is how Resto Rick assembles them. Not how the factory did it. Although that is basically the same procedure.

I don't think the engine/trans/rear end/exhaust were on the car before the undercoating was sprayed. The interior was in though. Dave Walden's Valiant shows undercoating on the seat track nuts/studs.

My Challenger's exhaust heat shield is fully covered in undercoating. No way that would happen if the muffler was in place. Obviously things could have varied by body style but I think the full undercoating was sprayed right before "body drop". The font suspension/engine/trans/driveshaft/rear end/ exhaust were all on a cart and installed at the same time.

Let’s be aware of undercoated cars and non undercoated cars from the factory. The non undercoated cars still had the 4 wheel wells and underneath the front fenders done.

Then we have undercoating done at the dealership. This is where you see it at different places on different cars and can cloud the discussion of what was factory sprayed or not.

There is no factory undercoating on the seat studs and nuts. There is a tape outline on the floor covering the seat holes. The seats were one of the last things to go in the car. After the car was running and driving.
No factory undercoating on any of the front suspension, engine/trans/exhaust/trans crossmember, leaf springs/hangers/shackles or rear axle and brake cables. Not on the car yet.

Fuel tank, fuel lines, brake lines, and the bolt on dual exhaust bracket were on the car when undercoated. Also all body panels and bumpers were on the car. Along with wheel well and rocker mouldings.

I should clarify that my observations come from 67-70 B-bodies from St Louis and Lynch Road plants.

Here is the post on the Valiant that talks about the undercoating on the seat studs/nuts. Obviously, A-body details can be different then other body styles.

https://board.moparts.org/ubbthreads/ubbthreads.php/topics/782698/4.html

Wouldn't undercoating vary from factory to factory PLUS worker to worker spraying his own little pattern? Or how much he/she felt like doing or cared? That's alot of variables. Yes I'm sure each line had it's own place in line where undercoating was applied, but how well, how much, or was a car even completely missed? We all know how good quality control was back then.....

I'm thinking there must have been some variance.
I've owned a lot of Mopars, and back in the day when they were in junkyards, crawled over & took parts off dozens more.
Sometimes the seat nuts were undercoated, some not, sometimes a little splatter on gas tanks, some not.
Almost always covering body plugs (which makes sense!) except at quarter drop-offs.
Never on drivetrain or exhaust.
Front wheelhouses always had masked-off sections, rears not, and very often a little spatter over the paint at the wheel opening lips.

One thing to consider. When the body "drop" happened, the engine and transmission, on the K-frame, driveshaft and read diff and springs was below as an assembly. If the body had been fully under coated prior to this, there would be the chance that the undercoat could be sprayed at the transmission crossmember and rear spring hanger mount locations. This would be a big problem for installing the whole drivetrain, if undercoat was on these mounting points. The trans crossmember is a pretty snug fit, and undercoat at that spot would be a major issue. And there is no way they could have undercoat at the spring hangers surface and risk sandwiching undercoat in between.
Unless they used some sort of "mask" to protect these area from the undercoat.
As I mentioned, this car, and others I have restored, have undercoat on the rear spring hangers, and the black painted Trans crossmember is undercoated as well, which makes me believe the rear axle and springs assembly and engine, Trans and K frame was installed prior to full undercoat. Yet there is undercoating on the floor above the mufflers and driveshaft.

Up front I didn't read all of the posts but I always thought all of the cars got the wheel well "sound deadening" for gravel, stones, even to dampen noise from wet or snowy roads and it was NOT undercoating? It seems the same "sound deadening" was used inside the trunk, inside the doors and even inside on the floor pan. I also thought that "rust prevention" undercoating was done by the dealer or someone like Ziebart, etc., Was there a option code for factory rust prevention or was it extra sound deadening?

J55 was full undercoating and hood insulation pad.



If you do a Google search for Dave's Valiant you will see a complete undercarriage picture. The undercoating was kept well away from the trans x-member mounting points.
http://www.ecsautomotive.com/other/As_Bad_As_New.pdf

All cars got the wheelwells done, all rear qtrs have the heavy sound deadening, some race car packages may not. Undercoat is a separate code, j55 I think, can't remember the delete code if there is one. The factory floorpan undercoating is distinct, and easy to tell from dealer or ziebart applied, kinda like restamped blocks, fender tags, original black brackets, you just know it when you see it after looking at enough cars. I caution guys to at least undercoat the insides of the front fenders, and do it heavy, rock dings from inside out will show in your mirror straight paint if you don't.

Just looked up option code J55 and it states "undercoating w/hd pad" so this makes me believe it is being mistaken for rust prevention undercoating when it really sounds (yeah a pun) like it is noise reduction when it includes an under hood sound deadening pad. No way would they include an under hood pad with rust prevention. Also if it were rust prevention undercoating then they surely didn't do a good job by spraying the most likely places where rust starts in the salt/snow/rust belt IMO. J55 should have been named "extra sound deadening undercoat with under hood sound deadening pad" Another thing for example that this "undercoating" would be done differently at each assembly plant is if you take a look at the in trunk quarter panel SOUND DEADENING and how some plants like the LA Assembly Plant put way more on the inside quarters of a B-body than a Lynch Road Assembly B-body. Using one example from one or two restorers that are from the same assembly plant will not tell the story of how to do your car. Best example of differences are the in trunk sound deadening and the jack instructions on a '69 LA plant B-body versus a '69 Lynch Road B-body.

I believe full undercoating happened before the drive train was installed. They had to spray the tunnel and I've never seen any over spray on the tranny or drive shaft of a lot of cars.

I was the new car pre delivery guy at my uncles Dodge dealership. Never saw a full “undercoat” from factory. We sent the car out to the local guy for that. Sound deadener-rock protection came on every car. Later on some telephone company trucks came in with the grease coating covering everything underneath, a mess if you had to fix something. When dad went to work at Fisher Body in Flint Mi the man he stayed with for awhile did the undercoating for the factory, a big operation, always after cars where done. This was in 53
I have a 70 Duster this local guy did, 1” thick in places. Everything was covered. Of course it saved the underside-wheelwells from rust