Ok guys a have a another problem to solve when i apply the foot brake the over stroke sensor on the rear brake chamber pops down and a alarm comes on the dash,what is this indictating and how do i go about fixing it,i have bleed the brakes but havent bleed the chambers yet.
I am assuming that is on an older wheel loader and that is an air over hydraulic master cylinder. You will generally have an external fluid reservoir many times directly above the cylinder. When the piston goes all the way to the end, it hits that little rod which has a dimple that pushed against a switch. That lights the alarm on the dash. Basically you have an air cylinder pushing the master cylinder piston down. What happens is that the system is leaking oil somewhere or the master cylinder piston is leaking by. Both issues are common on those older machines. Generally the piston and barrel get rusted up pretty bad and the leakage occurs. I don't usually rebuild those anymore either. I generally go back to the OEM for parts but you can find them at a lot of knowledgeable auto part dealers. One caution though is that your system could use hydraulic oil or brake fluid. These fluids are not compatible so make sure you get the right component for the fluid your system calls for. On the brake fluid units I generally just throw away the used unit. Brake fluid getting into the aircan just corrodes the heck out of everything. Good Luck!
Once again cheers for the advice john,the system uses air over hydralic oil,the brakes are inside the diffs,is there any way to narrow it down if it is the master cylinder piston or internaling leaking? if i was to check the oil level holes on planetarys and had excess oil coming out would that indicate internal leaking on that side?.
Does the hydraulic side of the brake system have slack adjusters ..? If so an master cylinder overstroke can easily by caused by a malfunctioning slack adjuster. Worth a check. As you have one master cylinder per axle then try blocking the brake hydraulic lines to one of the brakes on the affected axle and see if the alarm goes away, if it doesn't swap the blanking plug over to the other brake and try again. If have a brake seal failed in a wheel then that should find it PDQ. Echo the comments about brake fluid vs. hydraulic oil. From memory your machine is a WA380 Komatsu and I think they use hydraulic oil in the brake circuit, but check your manual to make sure.
Is Nige correct in the assumption that this is your Komatsu that you have been working on the transmission valve. If so then your system uses hydraulic fluid because brake fluid just doesn't work with gear oil at all. Your stating that the brakes are next to the differentials pretty well nails down what you have. Check for line leaks between the master can and the wheels. Most of the time something has gotten stuck on a tube and rubbed through. If all that is good, I would pull the master out and inspect it. You can do as Nige says and cap the line and the step on the brake and see what happens. Generally though if the cylinder is bad it is easy to tell visually. Checking the oil in the axle might tell you a little but keep in mind that there is a slack adjuster mounted on the axle so there is only a small amount of oil leaking. It might take a lot of refilling the brake reservoirs before it shows on the axle plug. If the leak is on a piston you will have to pull the axle to repair it right. I've heard people brag about how they left one side in the machine but they also call back about a month or two later to troubleshoot it again. Good Luck!
Yep john its a WA380-1 its the later model which use hydralic oil instead of the brake fluid,when i last bleed the rear brakes i bleed them from the wheel ends,this time i bleed the brake chamber as well and so far so good no over stroke stroke. I also checked fliud level in planetarys and no excess oil.there was no leaks in the lines betteewn the chamber and slack adjuster and the slack adjuster to the wheel ends.
Might be an idea to pull the slack adjuster apart and check for signs of piston seizure. If you find anything it's probably better to replace it.
you could join the two wires on the switch, problem solvered Nige has nailed it i think, if there's no leaks and the system is bleed correctly the slave cylinder is stroking too far, either the brakes are worn out or the slack adjuster is faulty/seized, I spent abitta time playing with D350D's, 966/980DEF's and 825C's used to hate these brake systems! FYI if you need the master cylinders rebuilt Repco Industrial in Welshpool used to rebuild them for us
I had a customer do that on a 785B once. The "repair" was only dicovered when the truck ran out of brakes one day while going down a hill loaded and ended up rolling over. I had to do the mechnical inspection for the accident report ........
Thanks guys for ya suggestion, since i have bleed the brake chamber i havent had a problem.
One thing I did not see mentioned was the possibility of the master cylinder seals getting bad and bypassing the piston and letting it overstroke. I'd try holding the brake on with just light pressure for a couple minutes steady to see if it eventually does come on. I say light pressure becasue there are times when a seal is worn it will leak with low pressure but when max pressure is applied it will form a tighter seal against the piston and cylinder. I'd say this one needs careful monitoring for a few weeks to be sure problem does not return. Also keep in mind the small volume of oil that needs to leak oout of the master to activate this switch might not show up in the final drives right away.