The Stovebolt Site Forums The Shop Area Paint and Body Shop 1955.1 GMC Manual vs Automatic Cab Question

Does somebody know why the firewall area behind the brake pedal is removable for an automatic cab?

http://jbhardin-gallery.com/trucks/differences.html

Just a guess: To be able gain access to the top of the flywheel (to be able to rotate the flywheel)?

access to the trans dipstick and fill location

Bill

There is a large circular cover screwed to the transmission cover - remove that circular cover to check/fill the transmission fluid.

The trans dipstick is through a circle hole in the gigantic transmission cover. The removable part behind the brake pedal is not near the transmission.

https://picasaweb.google.com/utasil...v1sRgCOPc-ODm5sSK5wE#6067132638113174850

The transmission cover change is designed to give access to the transmission bellhousing bolts. The trans mount crossmembers are heavier and designed so that the center sections unbolt. The brake lines are re-routed to run behind the transmission tailhousing. It is designed so that the transmission can be removed from under the truck for service. There is actually a special tool that hooks between the frame rails and supports the rear of the engine as the transmission bellhousing is actually the rear engine supports. Bottom line is that due to the size and weight, provisions were made to aid serviceability.

I think the removable part (one hole brake pedal plate) behind the brake pedal, you are talking about.
Is unique to GMC trucks, that came equipped with factory Automatic or Hydra-Matic transmissions.

This is what I think GMC did when they were assembling a truck with a Hydra-Matic transmission.
They spot welded into the cab a specially stamped out toe board with a arch to access the Hydramatic tranny flywheel and bell housing bolts.
Then, where the brake pedal is, they just cut a big Hole in the toe board.
This made it easier to lower the lower the CAB onto the chassis, over the already installed steering column.(minus steering wheel)
Then they used the removable part (one hole brake pedal plate) and bolted it onto the toe board to covered the hole.

Chevrolet does not have the removable part (one hole brake pedal plate)
picture TB 1
Picture TB 2
I think Chevrolet had a little more finesse, then GMC when they equipped their trucks with the RPO 314

I'm still trying figure out, if the toe board and firewall were one stamped out piece of metal or two pieces welded together.

jorb, I assumed from catalogs that the toe-board was different piece from firewall but I cannot see any sign that they are not one piece. If you compare your toe-board to a manual trans truck, you will see the differences in the stamped strengthening ribs.

I am changing my truck to a manual. Can I just weld in that toe board section from a manual donor cab?

Yes and right about now, keithfielder is about to offer you a transmission cover trade.

Cool beans. One less removable thing should mean less rattle sounds. Rattle sounds drive me bonkers.

Like Greg_H said, Yes you can weld in a manual tranny toe board section.

But here's the catch, the big removable hydra-matic tranny service panel floorboard cover
with the gas pedal attached to it, is wider than the manual tranny service panel floor board cover.

So if you use the manual tranny service panel, you will ether have to extend both sides of the
floorboard tranny opening inward a couple inches or weld in reproduced manual tranny floorboard sheet metal to narrow the opening.
pic 1 right side
pic 2 left side
There are vendors that sell the Left & Right side with floorboard & toe board attached.
Left panel
Right panel

I'm not sure but I think both the 3 & 4 speed tranny service panels are the same width.

Update:
After I got my head out my butt.
All 47-55 1st series Hydra-Matic & Manual Transmission Service Cover/Panel are the same width.
Difference is the lengths.

1929 - 1957 Chevrolet Master Parts & Accessories Catalog says:
Group number 16.547 Cover, Transmission
47-55 1/2 3/4 TON (3 SPD), 15 3/4 wide x 20 1/4 long
47-55 1/2 3/4 TON (4 SPD), 15 3/4 wide x 20 long
54-55 COMM w/H.T. Trans, 15 3/4 wide x 34 7/8 long
1929-1957 Chevrolet MPC LINK

Note:
1929-1954 Master Parts and Accessories Catalog,
Group number 16.547,
Does not have the Hydra-Matic Service Cover/Panel listed.

I was going to leave the gigantic hydra-matic service panel alone. I figure it will make the power brake upgrade and T5 swap easier.

The left floor needs to be replaced. My thought it to buy a manual truck left floorboard with toe board. I will have to trim it to fit the gigantic hydra-matic service panel. The right floor is in surprisingly good shape. I only need to replace a 2-3 inch strip where it meets the kick panel.

keithfielder wants to excange your HM cover with his manual cover.
If your going change from auto to manual you really don't need the HM cover.
You could fabricated a new cover just for the new tranny you are putting in.
No sense cutting up a original HM cover, when a fellow bolter needs one to keep his trucks stock set-up.

Most of all of my hydra-matic specific parts will be for sell. If someone needs something, please encourage them to message me. I want those rare parts to have good homes.

I was not planning on selling the HM cover since it is part of my floor and firewall. I would have to make a new cover to fit that spot. If someone wants the original cover, I would need a replacement.

Greg_H

You are right about the stamped strengthening ribs differences.

After looking at These Guys assembling a brand new cab from brand new sheet metal, inside a specially designed jig.
I've come to the realization that the firewall & toe board was a one stamped out piece.
Nothing like working with no rust sheet metal.
I like that JIG !

Joseph_Y

Sorry for the incorrect information. Read below.

Update:
After I got my head out my butt.
All 47-55 1st series Hydra-Matic & Manual Transmission Service Cover/Panels are the same width.
Difference is the length.

1929 - 1957 Chevrolet Master Parts & Accessories Catalog says:
Group number 16.547 Cover, Transmission
47-55 1/2 3/4 TON (3 SPD), 15 3/4 wide x 20 1/4 long
47-55 1/2 3/4 TON (4 SPD), 15 3/4 wide x 20 long
54-55 COMM w/H.T. Trans, 15 3/4 wide x 34 7/8 long
1929-1957 Chevrolet MPC LINK

Note:
1929-1954 Master Parts and Accessories Catalog,
Group number 16.547,
Does not have the Hydra-Matic Service Cover/Panel listed.

The incorrect POST in this thread has been corrected to reflect this post.

i am interested in the floor cover from
the auto trans.
please let me know?