Fixing a common cab 12 design problem

[Keith Webb]

Because of the timber frame used to hold the roof onto the cab 12 (and I suspect cab 11) we see a number of different solutions to the problem.

What happens is as the wood shrinks and softens with age the cab separates at the windscreen pillars. I've seen this even in wartime images, so it was definitely a design problem.

Fixes range from long braces to this relatively elegant (but ultimately failed) solution.



What examples of running repairs have you seen?

[Keith Webb]

This one was designed not to come apart!

[Keith Webb]

Fit a cab 13 roof of course! Problem solved.

[aj.lec]

couple of other modifications

[Keith Webb]

Originally Posted by aj.lec

couple of other modifications

The mudguard braces are a popular solution aren't they?

[hrpearce]

Keith another one you know about, I've seen these brackets around farms but carn't remember what they are for.

[Alex van de Wetering]

Nice thread subject Keith! It's the same with the cab 11 indeed....rotting wood doesn't help.
A few weeks ago I removed the winter cover from my unrestored C8 cab 11. I stood on the bumper to remove the timber frame I built over the truck to hold the "tent" when the complete windscreen dropped inside the cab with a loud bang......Which made me wonder how the cab 11/12 windscreen frame is supposed to be attached to the rest of the cab in the first place?And is there a difference between the cab 11 and 12, because the 12 has the "opening" windscreen. Are the brackets (used to the sure the frame to the cab with bolts) welded to the round windscreen tube-frame? or do the brackets have a round section and does the round frame just slide over it? I welded mine temporary, but it seemed I was not the first individual that had a go at "fixing' the frame.

Alex

[Keith Webb]

Originally Posted by hrpearce

Keith another one you know about, I've seen these brackets around farms but carn't remember what they are for.

Yes, that looks familiar, Robert.

The annoying thing is they made a hole in the roof which I'll have to repair!

[Ganmain Tony]

On my beast Keefy, it almost started happening straight away. I attribute it to the fact the cab is bolted rigid to the Chassis. A massive improvement was acheived in changing this in the Cab 13 design.

Any movement over bumps and the poor old thing sounds like a square rigged ship of the line in Nelsons Column...

It may also have been exacerbated by the excursion I had into a table drain when I came around a blind corner on a dirt road at 70 km/h and discovered I was at a T intersection.

The ensuing bump when the front wheels touched ground again caused suprisingly minimal damage, but they did cause those two timbers to come loose at that left hand windscreen corner.

Ive seen some impressive mods including the entire frame replaced with metal and welded to resemble the hull of a T34.

But in the end, they all seem to come apart

[Hanno Spoelstra]

Or fit a new windscreen and cab top. . .

AWM ID Number: 116992 / Summary: SINGAPORE, STRAITS SETTLEMENTS. 1945-09-05. TROOPS OF THE MADRAS REGIMENT, 5TH INDIAN DIVISION SUPERVISING JAPANESE PRISONERS OF WAR AS THEY REMOVE AN UNSERVICEABLE TRUCK FROM HILL STREET.

[Keith Webb]

Here's another example from NSW:

[Keith Webb]

This is one of Max's cabs:

[Keith Webb]

This one from near Bendigo was more discrete:

[Keith Webb]

How about a lump of wood?

[Keith Webb]

The inevitable collapse, seen around 1972.

[Keith Webb]

This time in Warburton.

[Bob Carriere]

In response to Alex...... cab 11 and cab 12 windshield/screen are very similar in design.... both weak. The cab 11 has the same external tube frame as the cab 12 ...except the twelve has the inner window frame mobile on top hinges for opening...... whether the glass frame is in place or not it adds nothing to the structural integrity ( or lack thereof) of the design.

One improvement on the cab 12 is the addition of 1/2 inch steelplate on the outside corners underneath the cab floor which greatly reduces the tendency of the cab back wall to flex forward and backwards..... also keeps the doors better lined up for the simple latch mechanism to work.

There are three weak areas in the cab 11/12 design....both addressed by the cab 13......

One ....the rear most corner fo the window/door opening is entirely dependent ont he small hard wood timber overlapped at 90 degrees......as soon as the wood dries up..... and whatever glue/screws works loose you have lost the 90 degree integrity.

Solution....on the cab 13 that was addressed with an L shaped flat steel welded in place in the cab corner and NO wood used. A similar solution should be feasible on the cab 11 hidden behind the wooden framework.... I say feasible because I am not there yet on my truck but have ascertained that there is sufficient room/space to sandwich a steel plate behind the wood.

Two...on the cab11/12 at the leading edged of the roof / windscreen the windshield frame is attached to the roof by means of a funny shaped wooden board....roof to the wood and the wood to the tube windshield frame. The frame shakes...flexes on the rear wall...wood dries.....bingo

Solution.... on the cab 13 it is solidly bolted.... top of windshield bolted to roof. There must be a way of replacing in part or as a whole the wooden board with a steel tubing properly shaped to fit the space.

One note of caution.....some wood is required to allow screwing small wood screws ( but that could be a small piece of 3/4 inch square wood) that holds that funny moulding the folds around the edge of the cab from the driver's side to the pass. side....... not sure what purpose it serves except that it is needed to hide all the crew holes.

Three....... or as we say in Ottawa tree..... the corners of the tubing for the windshield frame is not the strongest design....although beefed up with a steel insert inside the tube.... the 4 small metal screws in each corner easily distort and work loose over a period of time......most frames I have the corners are loose.

Solution... in most of the trucks I have seen the screws are rusted or busted or the holes enlarged enough to allow movement. I propose to enlarge the screw holes in the tubing and solidly Mig weld the inside insert to the tube then weld the tube corner to create a more rigid framework.

The roof will never serve as a roll bar but with proper bracing should last for a few parades and Sunday drives.

Bob C.

[motto]

Post #6 appears to be a universal exhaust pipe hanger bracket.
David