OFM Low Loader info please

I’d just go for two air/hydraulic master cylinders.
If you think about it, multiple master cylinder air chambers is the same as each wheel having a chamber as in “S” cam brakes.

One other thing to consider is that there is no park brake which can make hitching up and parking on hills a bit tricky. As built there was a manual wind on to pull the master on (for temporary application). The valve to the booster provides break away protection but that is only good for as long as there is air in the trailer air cylinder. I drain the air when parking up so as not to encourage leaks and stresses. Being hydraulic you can't use maxi's.
I would support the idea of twin booster/ master cylinders but go further and have them at the back so there is less hydraulic line/friction to worry about.
They are only a small booster anyway and you could play around with 24's or 30's. My master has the tin can reservoir but the PBR book shows that a year later it was superseded by the version with the (much smaller) integrated reservoir. Would be interesting to see if you could still get them.

dragged it home today, looking forward to getting stuck into the resto. thanks for all the input regarding the brakes, great to have so much knowledge still around. here's a pic of the trailer as it sits, still has the military green on the underside and inside of the frame. I'm thinking going white with maroon hubs to match the kenworth. re-build the brakes, tidy up the ramps, new boards, wiring and we should be off for a roadworthy and club plates, see you all on crawling the hume!

 

OFM low loader in service in during the Vietnam war
source: Australian war memorial

 

here are some pics of the brake assembly; looking from the hub side (hub, brake drum and bearings all slide off as an assembly) The snail cams control amont of shoe travel
the components showing that the bottom pins are eccentric for adjustment.

Looking out at the back showing how the back plate is fixed to a flange welded to the axle beam. While the the spring retainer is clamped tight to the axle the springs top and bottom remains free to wriggle thus providing articulation.

thats brilliant mammoth, thanks for the info and pictures. good to see that they are pretty simple. planning on getting the slaves and master stainless sleeved and rebuilt, haven't started taking the hubs off to assess the shoes or drums yet.
one issue I ran into was the king pin, I dont know if it's original or has been replaced but the protrusion thought the skid plate to the lower should of the kingpin is only 65mm not the standard 70mm. took a fair yank from a case 930 to get it back off the truck. going to have replace it with a modern spec kingpin unfortunately!

gr8 pix Mammoth
brings back ol memmories
the anchor pins are a adjustable cam
the snail u call it is the adjuster one on each side of the shoes..... they often freeze up thru lack of use think a 7/8 ring spanner to adjust
Can vaguely remmber PBR came out with a conversion to convert from Air Hyd to Air mechanical 'S" cam brakes
U only needed to unbolt the backing plate and bolt on the conversion and all the hardware to go with it
I have looked thru my collection of PBR books/manuals but cannot find any evidense
LOL
cya

The anchor pins are more likely to freeze up and is impossible to know what is happening adjustment wise unless you mark them on the outside end to tell what is the high and low points. Lots of trial and error.
No sign of a conversion kit in my PBR books either. The conversion would consist of a stub axle welded to the flange/back plate. Could be done but would have to be pretty sure of that weld holding. Spring packs getting in the way would determine where the S cam shafts would go

The conversion kit has been shared on here (the forum here) before so maybe some searching and with any luch it was after photo bucket went caput


Paul

Wouldn't be too hard to convert with full size wheels as S cam back plates are available, at least to fit full diameter (5") axles, however with these little wheels there isn't enough room, compounded by the small size axle beam.