Firewall thickness

[Stephen_heatherly]

How thick should the plywood firewall on a 1919 be?

Thanks,
Stephen

[Will_Vanderburg]

I believe they are 3/4”

[Humblej]

The Ford factory drawing I have dated 12/8/17 has a thickness shown of .677"-.697"

[Rich P. Bingham]

That would be 5/8"- 11/16" then.
This is interesting to me, having recently made a dash for my '13. It had a reproduction which was 3/4" fir ply. The originals were 13/16".

I don't believe the fit is so critical that 3/4" wouldn't be just fine.

[Allan]

3/4" plywood needs a weeny bit shaved off the edges to fit the rain gutter and the two little tin bits that are on each side below the hinge rod relief. I have just done this on a 1922 car. Easily done with a little Stanley thumb plane. I plane the body side edge, which is not seen when the car is assembled.

Allan from down under.

[John kuehn]

I had a piece of cabinet grade 5/8 plywood that I used for my 1919. Also I had part of an original firewall that had the rain drip edge still on it.
Comparing it to the 5/8 plywood that I used I don’t think the original was as good as what I used.
The original piece had what looked like flat black paint on it so so that was what I used on the new firewall.

Interestingly the original looked like it was 3 pieces of plywood dovetailed together. Did Ford make all his firewalls for the 17-21 T’s the same? Just curious.

[Oldav8tor]

Going from memory here. John Regan strongly recommended to me that I use Baltic Birch for my firewall, stating that it came closest to the original and was more dimensionally stable. It is sold in metric widths and I believe the 18mm was suggested, which is a little narrower than 3/4 inch. I installed a steel drip channel on mine without difficulty and everything seems to match up well.

Baltic birch is not available everywhere. I ended up going to an outfit that sold specialty woods and woodworking tools and bought a 4 x 4 foot piece.