Just bought a 936F,very clean strait loader serial# 8AJXXXXX problem is both brake pedals are frozen solid,no movement at all.Looks like the brake linings are in the differentials.All fluids are very clean and no burnt smell.The brake fault light is on.My question is are the brake treadle valves air over hydraulic? And is it common for these to seize,this machine has sat for a year or so.Are they rebuildable or just replace the whole valve.Is there any adjustment to the brake system?Thanks!!
It has air treadle valves that stoke 2 master cylinders behind the cab. Yes it is air over hydraulic. If the light is on that means one or both of the master cylinders has over stroked . It could be the pivot point in the cab on the pedals that are seized. That's pretty common. You can rebuild the treadle valves but you're probably better off to replace them. Each pedals in the cab will work both master cylinders. One master is for front brakes and the other is the rear. #29 and30 in the picture are fluid reservoirs for the master cylinders. The second picture is the treadle valve.
As Mobiltech says pretty simple system. He mentions the "over stroke" this could be cause by a few things. Internal leaking in the master cylinders, leak in an oil line to the axle brakes or leak of the brake piston seals. I guess you need to start by getting the linkage/pivots at the peddles freed up, might work to soak with penetrating fluid but I would prefer to disassemble and clean and polish everything. From the picture those look like basic air brake valves, should be able to get new or rebuilt ones from any place that deals in truck air brake parts. They may be fine but until you get the peddles to work you won't know. Have you checked the fluid level in the two reservoirs? If one or both are low you will need to find out where it went. Either on the ground from a leak or if bypassing the seals at piston into the axles. Also you need to check to be sure what is the correct fluid for the brakes. My first guess would be 10W hyd. oil but do not take that as a fact! And if it is hyd. oil determine if that is what the last person used. Hydraulic oil will damage seals meant for brake fluid(DOT3) not sure if DOT3 will damage seals meant for hydraulic oil. Just don't mix them!
The brake reservoirs on the 936F 8AJ require SAE 10W (ISO AW32) hydraulic oil, not brake fluid ......... wise words from Ken. If someone has put brake fluid in the system you could be in for some major work pulling things apart right down to the brake packs in the axles to put the problem right, although I hope not.
Thanks everyone! I now understand how the system works,and see that it is quite simple.Nothing like the fear of the unknown to get that uneasy feeling.Well the loader is to be delivered this coming week,so I will update as soon as I make progress.
Post back if you need any parts info.
Thanks Nige,just ordered up a service,parts,and operators manual.(E/bay OE cat ones)I have always found them to be worth the cost.Even if it does seem like to much.