Guest Posted March 12, 2008 Share Posted March 12, 2008 Does anyone know about air brakes (ten ton DAF bus). My parking brake is not releasing fully and the air is hissing out of a rear actuator piston when the parking brake lever is set to off. I am guessing that the diaphragm is leaking or some such. My quesuion is how easy to disassemble the unit? It is easy enough to get off but I am concerned about the sprung loaded bit! If I undo the circlip that holds the two halves together will it fly apart and shower the county with parts? If so what is the procedure to unload the spring? For anyone vaguely interested this is an air powered piston that has a spring within it that actuates the brake in the absence of air pressure (a safety feature designed to apply the brakes if the air pressure is lost). The brake is released when air pressure forces the piton back against the spring). Quote Link to comment Share on other sites More sharing options...
donegalwing Posted March 12, 2008 Share Posted March 12, 2008 Francis You need to be extremely carefull with that piston, Im not well up on that particular type of bus, but the normal type would have two diaphrams one outer, which can be changed, and an inner one, which cannot be changed... As far as I am aware if the air is hissing out when the handbrake is applied this is the outer diaphram which should be changeable but if it is when you put your foot on the brake its the inner, which means you need a new piston Depending on the size of the piston, there may be a large spring inside which may take the head off you if you try to open it DONT try and open this as it may be very dangerous, throw it in a skip and buy a new one or get one from a breakers yard which may be ok, but if it has been lying up for a while the diaphram may have hardened up and not last very long Dean Quote Link to comment Share on other sites More sharing options...
Guest Posted March 12, 2008 Share Posted March 12, 2008 FrancisYou need to be extremely carefull with that piston,........ Depending on the size of the piston, there may be a large spring inside which may take the head off you if you try to open it DONT try and open this as it may be very dangerous, ...... Dean hmm thats about what I feared! There must be some decompression tool to open these babies then? like a hydraulic press or somesuch? seems a bit expensive to throw it out for the sake of a bit of rubber; I bet they are a couple of hundred. You must be right about the two diaphragms though, it must be a double acting cylinder, one for the parking brake spring releaser and t'other for the service brake action? Boing.... ouch. edit. turns out there is a "caging" bolt in the centre of the unit to compress the spring, how well thought through is that. turns out the bolt on my unit is broken so looks like a new unit required, bah Quote Link to comment Share on other sites More sharing options...
Guest Posted March 12, 2008 Share Posted March 12, 2008 All, I once made the mistake of opening a loaded front fork top on a 320 bhp drag motorcycle that I raced, (not mended) and the stainless tube held back by the spring sliced a chunk out of the lower part of my thumb never to be seen again. the mechanics laughed at my silly mistake and the lack of a chunk of thumb "leave it to someone who knows what they are doing" I think I remember being chanted to me..... If in doubt, send it off to someone who is not! and save your thumbs and knows what they are doing. SW Quote Link to comment Share on other sites More sharing options...
martinbg Posted March 12, 2008 Share Posted March 12, 2008 Hi Francis If the old one is completely knackered, and it's not too dangerous to take apart (if it is, please don't do it) I wouldn't mind seeing some piccies of the guts of it. Being a sad engineer type I just love being curious about this sort of stuff. On the subject of motorbike forks..... a long time ago when I was 17 (a very long time ago) I was changing the fork oil on my bike. Removed the drain screws at the bottom of the fork on both legs. Oil dribbles out. Too slow for me. So I leant on the handle bars to "help" the oil out. It's amazing how far the oil goes horizontally when you do that. Martin Quote Link to comment Share on other sites More sharing options...
Guest Posted March 12, 2008 Share Posted March 12, 2008 Sure Martin. I usually take pics on this sort of job in case I ever have to do it again in a few years, I wont remeber a thing! Deans warning is well heeded; I will remove the unit and take it to the local DAF shop to dissassemble. Quote Link to comment Share on other sites More sharing options...
Guest Posted March 12, 2008 Share Posted March 12, 2008 Where was Dean!!! So where was Dean to advise me before the 'slicing' hey! SW Quote Link to comment Share on other sites More sharing options...
donegalwing Posted March 13, 2008 Share Posted March 13, 2008 Simon At least they cant say you are all thumbs anymore Dean Quote Link to comment Share on other sites More sharing options...
Guest Posted March 13, 2008 Share Posted March 13, 2008 I will let you off that one as it's early. SW Quote Link to comment Share on other sites More sharing options...
Guest Posted March 13, 2008 Share Posted March 13, 2008 Turns oput they are 160 quid service exchange so i wont be dissassembling mine! Took me all day to slacken the two securing bolts. Now they are spinning and I have to get the actuator separated at the clamp ring. I am still hoping a truck brake expert will pop up and tell me how this should be done. Mike, there is a great manual at http://www.community.gov.yk.ca/pdf/airb ... nglish.pdf and page 24 shows the internals of the actuator. Quote Link to comment Share on other sites More sharing options...
phatboy Posted March 14, 2008 Share Posted March 14, 2008 Hi Francis, If the actuator is leaking with the park brake in the off position, this is not repairable. This is the spring brake portion. Please see picture. Do not under any circumstance release the clamp ring from the spring brake portion (gold and silver in my picture). The air pressure holds the spring in the off or retracted position. In front of this is the service brake or foot brake, this is joined to the spring brake portion usually by a clamp ring. In the back of the spring brake portion there will be a bolt or nut or sometimes a bit like a key this key can be seen on the pic, this enables the spring to be compressed or as we would say “wound off”. Once the brake has been wound off, you can separate the spring portion from the service part or front (the black part). There is a rubber diaphragm along with a light weight return spring inside the service chamber, but this is no more than hand pressure. This should then allow access to the two securing bolts, that you now say are spinning! This spring brake will probably be a type 20/24 or 24/30 these figures denote the surface area of the service brake then the spring brake in square inches, next the air ports M16, or M22 metric or 3/8 imperial. Being a Daf it will probably be metric. dependent on type should be between £60-£160 + vat Please before you try to split this brake actuator be absolutely sure it is as mentioned above give me a call 07836 571055 & I will email you some pics. Once again Never try to split the spring brake portion this is extremely dangerous. I cant upload pic, please follow this link http://www.erentek.co.uk/p1-725.jpg Paul PhatBoy Quote Link to comment Share on other sites More sharing options...
Guest Posted March 14, 2008 Share Posted March 14, 2008 Thanks Paul. I have got a new unit ordered but the wind off bolt on my unit is tripped or loose so cannot wind off the spring. I guess this means that the spring brake is pressing on the service brake so if I release the service brake clamp it wil pop off with quite a force until the spring grounds against its stop? about 1/2 an inch of movement? I need some way of getting the parking brake off. I could use what air pressure there is in the chamber as the leak is small enough to let the parking brake half way off but I dont really want to be down there with the engine running and air pressure inside the unit. So we have a puzzle. How the release the parking brake so the unit can be removed as the mounting bolts are spinning in their holes. Bah, Why arnt the bolts captive in the unit? I will ring you later for advice. Many thanks Edit : NB the spring brake protion on my unit is attached to the service brake portion by a ring of bolts on a flange and not by a clamp ring. There is only one clamp ring and this attaches the unit to the casting that is bolted to the bracket on the axle. Will take photos and attach later. The wind off bolt slides in and out across its threads. It has a hex sockket in the end and a brass coloured nut pinned to the bolt by a 3mm roll pin. Quote Link to comment Share on other sites More sharing options...
Guest Posted March 14, 2008 Share Posted March 14, 2008 This is what you need SW Quote Link to comment Share on other sites More sharing options...
Guest Posted March 14, 2008 Share Posted March 14, 2008 Paul, is the ring of bolts (on the flange) the spring brake section (not to be opened) and the ring clamp the service brake section? I need to undo that ring to reveal the heads of the bolts that secure the unit to the bracket. The winding in bolt is sliding in and out of its hole (seemingly across its threads) so I cannot "cage" the spring. This means that the parking brake is on and the unit is applying spring pressure to the brake. How do I get the b******* off? Quote Link to comment Share on other sites More sharing options...
Guest Posted March 14, 2008 Share Posted March 14, 2008 The bolt that you can slide in and out is the Brake Actuator Bolt which you have to wind fully out (but not remove) to relese / override the brakes. They are very long bolts. Same as ARMY trucks and more than likely many others. SW Quote Link to comment Share on other sites More sharing options...
Guest Posted March 14, 2008 Share Posted March 14, 2008 Could you use a decent Chemical Metal for the leak (as a tempory fix)? SW Quote Link to comment Share on other sites More sharing options...
Guest Posted March 14, 2008 Share Posted March 14, 2008 Could you use a decent Chemical Metal for the leak (as a tempory fix)?SW Its the rubber diaphragm thats leaking I think so chemical rubber compund, yes but..... I am beginning to suspect that is exactly what "Charley" did when I bought the vehicle! I noticed an air leak and pointed it out. He said "no probs, will get my fitter to sort it out". When I took delivery he said that it was a "sticking valve" and it had been fixed. It lasted the journey down from Staines to the Island. Why do people lie like that? It could have been a big mess on the motorway. Anyway, I'm glad its happened here in the yard and not halfway to Semonzo!!!!!!!!! Soon as Ive fixed the brake its MOT time and then Whey Hey...... Quote Link to comment Share on other sites More sharing options...
Guest Posted March 21, 2008 Share Posted March 21, 2008 Many thanks to all who contributed to this thread on and off line. Particularly Dean for alerting me to the potential hazard and Paul for his detailed explanation of the system and possible solutions. It would have been very tempting to take the unit apart in situ and release a very angry spring. Knowledge is power and the power of the forum has shown itself. A valuable resource. Even for non PPG issues. I now have a shiny new brake piston on my bus and the old one will be serviced by DAF and resold to another lucky bus owner. And it only cost me 160. Quote Link to comment Share on other sites More sharing options...
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