68 sill plate underlayment ?

[Gene M.]

Re: 68 sill plate underlayment ?

Nov 67 build Convertible, no pads.

[Dale C.]

Re: 68 sill plate underlayment ?

Terry
Here is a better picture of the revision box.
Dale
IMG_6676.jpg

[Sal C.]

Re: 68 sill plate underlayment ?

revision in the 1969 AIM states that pad 3945261 was removed 8/16/68. On a related subject...didn't early 1968s have a narrower sill plate?

[Mark D.]

Re: 68 sill plate underlayment ?

I would have better success attempting brain surgery than I would judging interiors but, I believe 68 sill plates were narrower, at least to a certain point. It would be good for Bill Vyn to jump in here.

This discussion on the underlayment is awesome and really helps to better understand the cars. Even if it isn't judged, if it's something the car had from production, it's my opinion it should be included during restoration.

Correct and authentic should always be the goal...it's the NCRS way. Thanks for starting this thread.

[Joe L.]

Re: 68 sill plate underlayment ?

Terry
Here is a better picture of the revision box.
Dale
[ATTACH=CONFIG]46171[/ATTACH]

Dale-------



Note that the symbols in this revision block begin with "7". That means there were items #1-6 that were on previous page(s) and are not included in this copy of the AIM.

[Joe L.]

Re: 68 sill plate underlayment ?

revision in the 1969 AIM states that pad 3945261 was removed 8/16/68. On a related subject...didn't early 1968s have a narrower sill plate?

Sal------



If they did, the change happened within a part number. The same plate GM #3912660 was used for 1968-77 Corvettes.

[Jeff P.]

Re: 68 sill plate underlayment ?

When the time comes ill clean and reinstall it.

[Terry M.]

Re: 68 sill plate underlayment ?

Dale-------



Note that the symbols in this revision block begin with "7". That means there were items #1-6 that were on previous page(s) and are not included in this copy of the AIM.

I can scan and post that page next week, but there is no pad on that page.

[Dale C.]

Re: 68 sill plate underlayment ?

Sal
Grant Wong had something on the narrow sill plates. I think it was a rather early in the production chage from thin to wider ones. My car is a March car and as I recall it happened before mine.
Dale

[William V.]

Re: 68 sill plate underlayment ?

I'm fairly sure that early 68's had sill plates that were 1/2" wider than those used later in that year and subsequent years. Here're some pics:


This is a big enough change that I'd expect a different part number. As an extruded part, a new die had to be made. But what do I know?

The big question is when did the change take place? I've found this very difficult to get information on as the parts get scuffed and are very commonly replaced. One thing to look for on an early car with the narrow plate is an indentation in the carpet where the wider plate originally extended to. But this is tough when carpets are also commonly replaced.

It's seemed to me that GM tends to rework an area rather than just do a single part at a time. It's possible that the underlayment was dropped when they switched to the narrower plate. But I'm just speculating.

[Joe L.]

Re: 68 sill plate underlayment ?

I'm fairly sure that early 68's had sill plates that were 1/2" wider than those used later in that year and subsequent years. Here're some pics:


This is a big enough change that I'd expect a different part number. As an extruded part, a new die had to be made. But what do I know?

The big question is when did the change take place? I've found this very difficult to get information on as the parts get scuffed and are very commonly replaced. One thing to look for on an early car with the narrow plate is an indentation in the carpet where the wider plate originally extended to. But this is tough when carpets are also commonly replaced.

It's seemed to me that GM tends to rework an area rather than just do a single part at a time. It's possible that the underlayment was dropped when they switched to the narrower plate. But I'm just speculating.

Bill-----


I agree; it would seem like a part number change would have occurred. However, I can find no indication that any earlier part number existed. If there was one, it was never available in SERVICE and it's not shown in any AIM I have seen. Plus, the 3912660 part number looks like a number that would date right back to the beginning of 1968 production.

A possibility: the original supplier of these plates manufactured them incorrectly or, if GM supplied the dies, they were incorrect. Before the error was found, a bunch had been installed on 1968's that were "out the door". This would be the kind of error in the parts that the folks at St. Louis could easily have missed.

[Jeff P.]

Re: 68 sill plate underlayment ?

My March 68 Coupe sills are 4 3/16 wide. Same as the June Convertible.

[Russ S.]

Re: 68 sill plate underlayment ?

Here are a couple pictures of my May 68 coupe. The mastic material (no padding) extended into the sill plate area.
Slifer-1968-2 005.jpgSlifer-1968-2 002.jpg

[Patrick N.]

Re: 68 sill plate underlayment ?

Great pics Russ- do you have a similar pic of the rear compartment area?

[Jeff P.]

Re: 68 sill plate underlayment ?

Russ, did you find any surprises such as build sheets , build numbers? Do you plan on re using it in the new install. Jeff