OFM Low Loader info please

Bigcam

There is a reasonable chance it has a bolt on backing plate holding the Brake shoes. If this is the case then it may be possible to fit full air to the axles. The problem with hydraulic Brakes is they are unreliable and very expensive to maintain. No doubt you will be dismantling the Axles at some time in the future and at that time with some more information we could see if full air is possible.

Rex

Hi Rex, thanks for the info.
I've actually sold the trailer to a mate of mine. I offered to buy it back and he didn't seem to keen so I went and bought a flat top and then converted it into a dropdeck with a beavertail. About a week after I started this little project he rang me and said I could have it back, but by then I was into the other trailer. Would have been a lot easier to do something with the little float than what I did with the other trailer.

Well they say what goes 'round comes 'round, and I am now the owner of this low loader built by Ordanance Factory Maribyrnong in 1964.
Have got the single line hydraulic brakes freed off and working but adjustment wise they either drag or run out of master cylinder travel. The back plates are fixed by bolts on a 150mm pcd with drums 5' x 12"dia. The axle beams are solid bar 80 x 90mm high.
Upshot is I am looking for S cam axles hub to hub. Maybe someone has converted a step deck from 15" wheels to 20" low profiles and has the old axles lying around.

Hi Guys, I've just purchased one of these OFM floats, serial number 7. its reasonably tidy but the brakes haven't worked in my lifetime by the looks of it. anyone end up finding any info on converting them over to S-cam, are parts for the Hydraulic system obtainable? haven't dug into them yet, waiting for things to dry up so i can drag the old girl home. here's hoping i can get a bit of aussie history back on the road. Derek.shoecraft, id love to see some pictures of you trailers axles if you still had some to share!

Ordanance Factory built 2 designs of low loader - this is the 20 ton of which there were about 36 built and a smaller run of something like 50 ton. Don't have the details to hand and there is bugger all information available on what OFM actually did. The actual brakes on mine were very good, so good that the shoes would often stick in the drums but chamfering the ends seems to have fixed that. The hydraulic lines were full of holes and had to be replaced. The biggest issue for me, living in the mountains as I do, is that there is one master cylinder driving 4 double slaves which means that if the drums expand there is a high risk of running out of travel in the master. I looked at idea of grafting on S cam ends to the bar axles but it just can't be done. The suspension system is actually a neat design as the bar axle is not clamped, just trapped, thus allowing for articulation without straining the springs and brackets.
I have since bought a complete K Hitch suspension and axle set up. The 15" tyres have a low speed rating and have a propensity to go pop so there is a set of 236/70,17.5 waiting in the wings with M (120km/hr) speed rating

thanks for the info mammoth, mine would be one of the 20t models. from what I saw when I inspected the trailer ill be running all new lines for mine, and will definitely have to rebuild the master cylinder. I'm on the flatland carting a few vintage tractors to rallies, so the brake performance isn't as much of an issue for me, just need to be able to pass a roady! plus I'm running an 8v71 with Jakes, so as you'd imagine, I use them as much as possible . I'm a Mechanical engineer by trade, so I kind of like the design challenge of fitting s cams, but if I can get the air over hydraulic working relatively cheaply then that will be the go. mines had landing gear fitted pretty well aswell which is a bonus! looking forward to getting it all prettied up and behind the kenworth.
Jake.

From someone who is not an engineer but read of an issue about the master cylinder would a dual cicuit master cylinder be able to be fitted and spread the load around the system?

cobbadog I'm thinking the same thing to solve the issue of running out of master cylinder stroke, but you'd have to run double air chamber actuators so you don't halve your system pressure, then would you run into issues with uneven brake bias between the two axles? I'm not an expert on braking systems by any means, but food for thought!

Mate, I'm full of silly ideas. However there is a possible way around the bias problem using one of those adjustable valves from under a 1 tonner. Heavier load more brake pressure.

Simple fix, replace the master cylinder with one of a bigger bore. I had the same problem in a hot rod I was building many years ago. Brakes were good just before the peddle hit the floor and no amount of adjustment or whatever improved it. I replaced the 3/4" bore master cylinder with one of 1.25" and they were perfect, if a little bit too good. I could have got away with a 1" bore, but I had the bigger one.