I have a 1985 CAT 988B Wheel Loader (S/N 50W07346) that is experiencing steering and braking issues. The steering is stiff while the brake is releasing pressure and the machine stops after covering a very long distance. Initially, I checked out the steering/brake pump and the pump was worn and its body was cut while the seals were leaking so I installed new seals and a brand new aftermarket pump. However, that did not fix the problem at all. Checked the brake planetary system and there is nothing wrong with that either. The operator is experienced and follows the protocols that need to keep this machine running strong. For some reason him and I both cannot figure out what could possibly be wrong and causing the problem. If anyone can help me out here it would be greatly appreciated.
Under the panels behind the cab on the LH side of the machine is a plate with some valves mounted on it. They are the accumulator charging valve, the service brake control and the parking brake control valves. These shouldn't be a problem but the accumulator charge might be. It stores hyd energy like a battery stores electrical energy. To check the accumulator charge, start the machine and run at high idle for a few minutes with park brake applied. Shut off engine, turn the key back on then count the number of full applications you can make until the warning light comes on, you should have six. The brake section of the steering brake pump supplies oil to the steering when the accumulator is charged. Poor accumulator charge will require flow from brake pump more often(hard steering at times) and loss of brake pressure at times, brake pressure holds the park brake off(machine stopping). Later Bob
A good description of how the accumulator works is if you are familiar with a well pump system in a house. When the pump is turned on it pushes water into the tank and compresses the air above the bladder till it gets to the kick out pressure then the pump shuts off. When you turn on a faucet the pressure in the air above the bladder pushes the water out of tank. Then when the pressure drops to the turn on point pump starts up again and fills the water side of the tank. Now if you did not have the air in the tank above the bladder every time you turned on the faucet to get even a teaspoonful of water the pump would cycle on and off and pressure would surge up and down. As Bob says a good test is to run at high idle then with engine off and key on see how many hits of the brakes before warning light comes on, that's assuming the warning light works:beatsme One question I have is does the parking brake work on this loader? If brake pressure drops below a certain amount it should come on and stop the loader. If the parking brake on a 988B is in good condition it should almost put the operator through the windshield when it does come on. Have the brakes been bled on this machine? I know we had some 988B's that would need the brakes bled any time anything to do with the brake system was disconnected, other not so much. Going back to the beginning I would be checking accumulator charge pressure and would prefer to vent the nitrogen side completely to see if there is oil on the nitrogen side, a little is not a problem but if there is five to ten gallons that needs to be addressed. Accumulator is basically a hydraulic cylinder with a piston in side. only difference is no rod coming out the end. Nitrogen above piston and oil below. Sorry if I kind of rambled about but hope this help some. Ken
A bad/ empty accumulator can also give you a real touchy jerky brake,have seen it on a few, on this loader the parking brake is probably not working also, check the oil level in the rears the brakes might be leaking over.
Agree, if the parking brake is working and the brake pressure drops it should stop right now. Running any machine, let alone this large of one, with a non-working parking brake is a serious safety violation! ****** Made me think of another 988B I happened on to at another one of our plants. This one had a problem with the shut down solenoid. The operator mentioned that he had to stall the engine with the hydraulics by putting down pressure on the bucket till it stopped. I asked him what he would do if he had a failed hose in the hydraulic system:beatsme I did repeat my concerns to his boss and my boss. I also showed him the arm on the fuel governor that could be used to kill the engine. Do not recall if we had tried the pull back on the throttle method that will work on some if the linkage is adjusted properly.
When nitrogen pressure is low and you apply the brake , the warning light and audio comes on? The parking brake is prone to get sticky , and does not release fully.. than the brakes overheat and you get burned oil from the final drives (and a lot of screeking) I remember from the b model.
The parking brake is a dry brake and should not get "sticky" a simple hosing off of a machine is a good preventative maintenance practice that can save many problems. Hummmm, The parking brake on a 988B is on the front of the transfer case hard to get the oil in the finals smoking from that dragging! Now you can get the smoke coming off the transfer case for sure. We had a 988 87A years ago where they did not bother to keep the warning system working. Well besides that they did not worry about a few "minor" leaks under floor behind the cab. That was until an operator jumped in and took off without releasing the parking brake. Guess he got a little excited when the flames started up the back of the cab Only thing worse than working on a dirty oil soaked machine is a dirty oil soaked machine that has been on fire:Banghead After replacing about every hose behind the cab we did fix the wiring so the alarm would work in future Some bosses don't think a few oil leaks are that important to be fixed, "Hey a quarry is a dirty business". I always try to mention any leaks with a note that they are fire hazards. Some actually listen, most don't:Banghead One somewhat off topic thing about 988B's and other equipment. In cold weather, like low teens and lower, if a machine is started after sitting overnight give the hydraulic oil a few minutes to warm up before moving any of the controls and then do so slowly at first. I have seen more than one operator crank up a cold machine, put it into gear and pull off the line and turn hard to one side. Then when the pilot valve for the steering can't react fast enough and the relief valve is sluggish the weakest hose in the system pops. Working outside in single diget temps on a machine covered with cold hydraulic oil is not the way any mechanic want to start the day.:Banghead
If the final drives are smoking and the brakes dragging it's likely the Slack Adjusters need resealing. They can cause the brakes to lock up and not release. Later Bob
Bob, I was thinking about slacks when I posted but when I looked in SIS they don't show any for the 988B's Are we both thinking about the 87A 988 machines? I know they used them with the bladder brakes. Been a few years since I worked on a 988B and many more than the 87A Vintage machines!
Ah you are right ofcourse .. been awhile I ve seen one , and even longer I operated one I remeber the leverage of the parking brake behind the cab was sticky. We did lots of load carry and the brakes were always noisy , even after a oil change.. so we got a tip from a old mechanic, throw in some anti screekstuff . You know that stuff you throw in the hydraulic oil when you got sticky seals on rams, and never had any problem with the brakes. Back to the brake issue ... maybe the wetplates are worn? Its a wet clutch in fact but works reverse, so if the stack is not high enough anymore you loose brake power? Or is that not possible?
I worked on a fleet of 988B 50W machines years ago. The thing they were most famous for in our operation (nitrate mine) was cracking wheel spindles. 988B 50W prefix uses multiple disc brakes incorporated into the planetary reduction final drives not expanding bladders like the A models - so no slack adjusters. When you remove a FD on a 988B you just pull a ring of nuts (ref #2 below) on the outside end of the axle housing and the whole shooting match including the brake pack comes out with the FD. The brake pack is directly under the tube marked #7. Parking brake is a spring-applied pressure-released unit mounted on the back side of the transmission transfer case.
One thing popped up.. we had a leak in the oilsupply to the brake in the front axle. We were losing hydraulic oil and no leak, we unscrewed the oilfill and level bolt and there was a gusher.. wow. But I can't remember we had steering issues then..
All machines that had internal wet disc brake systems in those days had the squeal and chatter problem. The manufacturers brought the machines out with tractor hydraulic fluid for the axles. It was a whole lot more expensive than the 30wt. or 50wt engine oil that had been used so everyone just put those oils back in. What they didn't know is that there was a friction modifier that had to be added to enable using the engine oils. Both the local Cat and Komatsu dealers chased brake problems in this area for awhile until the knowledge of the additive got out. Common repairs included warped discs and broken return springs for the brake pistons. The broken return springs amplified the problems because the tangs on the steels and discs would get caught and the discs would not sit square and grooves would get worn into the reaction channels. The discs would then ride together creating heat which would cook out the brake piston seals and then the axles would fill with hydraulic oil. The WA600 Komatsu loaders were more susceptible to this than the 988B. The parking brake on the 988B was a horrible design all the way around. It was a multiple dry disk design installed at the end of one of the drop box shafts and as stated above was a spring applied and hydraulic released mechanism fed from the hydraulic system. It would hold the machine from coasting down a hill but could be driven through real easily in first gear. The actuator in the cab was supposed to lock the transmission lever in neutral. The cave men we usually employed would ham fist the lever and drive through the brake. Driving through the brake for more than a couple of hundred feet usually made things hot enough that the seals on the pistons would cook out and now oil would stream out and often smoked out the cab and sometimes caught fire. The book method of repair required that the cab be removed. We went through that enough that we found ways to get it out without pulling the cab and later on made some tools and actually could repair the thing in the machine. The steering problems on 988B loaders were also always problematic. A ground power pump was installed on the drop box below the parking brake. We at first thought the thing was an emergency device if the steering pump failed. Steering would be enabled as long as the machine was moving. What it was actually for was to supplement steering oil flow when you let off the throttle and tried turning the machine while moving. Imagine driving down a hill and having to make a turn half way down. You are coasting in third or fourth gear and try to turn the wheel and it is nearly locked up. Now you don't want to rev the engine to get the flow back up as that will speed the machine up going into the turn. The ground power pump was supposed to provide that oil and it didn't live up to the theory. We found out about it when the machine was coasting down a hill and the engine died. No pump flow and the ground power pump didn't have enough flow below about five miles per hour to turn the machine anyway. Basically the machine had to keep the engine at high RPM just to steer it. And when the ground power pump went bad it leaked hydraulic fluid into the transmission. All the suggestions above are right on and need to be addressed. That you have gotten this far with this machine is spectacular. With that comes all the internal wear points of all the hydraulic system and the associated problems you are likely to encounter. Maybe its time to check the utilization of the machine and consider a replacement in the not distant future.
John, I agree with evrything you said with just one comment. Being able to drive through the park brake in 1st gear is a designed safety feature just in case the park brake can't be released for whatever reason. It will as you say burn up the brake but that's the way the design works. I suppose burning up a brake is preferable to losing the whole machine in an emergency. I also thought that if you shifted from neutral into 1st twice in quick succession the 2nd time you did it the transmission would actually go into gear. That's how Cat machines work, no idea about the Dark Side. Also the axles with wet brakes now call out an anti-squeal additive. Along with SAE50 TO-4 oil it works a treat
The drive through in first is right on, the FNR linkage had a neutralizer in it. Lose brake pressure and the cyl would collapse and the claws would force the trans into neutral but not so much it couldn't be forced into gear and moved in emergency. That housing had two switches, one warned of brake on in gear and the other controlled the back up alarm. Nige could you look carefully at the brake lines and see if they don't have a smaller slack adjuster on front and back. I am sure there is one. They are designed for the piston to return with a measured amount of oil to release the brakes. If the seals leak and the pistons don't move, oil will go through the adjuster check valve and the brake will be locked on. Later Bob
Bob, I've looked at both the SysOp and Parts Manual and there is no slack adjuster. I couldn't remember one but it is so many years since I had my hands on a 50W machine I began to wonder if my memory was playing tricks on me. The key thing on the service brakes of this type as far as I'm concerned is the accumulator. If it's not charged correctly (or worse still not charged at all) then the brake pump alone does not have the force to apply the brakes. Strange thing is though that the piston-type accumulators such as the 50W machine has are generally pretty reliable, but on a machine that is probably getting on for 30 years old who knows what state the seals are in. I personally would go for the accumulator first then move on to the brake pump (taking a look at the steering section of the pump at the same time) and then to the service brake control valve before moving on to each of the brake packs in turn (blanking the other 3) to test for brake piston seal integrity.
I believe you're thinking about this kind of thing Bob? I've come across them on various machines over the years, but I don't remember them giving any trouble. Obviously that doesn't mean they can't give trouble. Saying that, I don't see anything like that listed on a 50W.
I'm aware that there was an option of ground powered steering on Cat loaders but of the dozens I have worked on, 966's, 980's and 988's, none had that option installed.
Cmark, This is the version I'm familiar with, off a 988 87A vintage machine: I've searched quite a bit on SIS and have not come across on of any style used in the 988B's. If I remember I can see if I have any old parts books or manuals at work to see if anything shows that way.
Appreciate everyone's input, I will be with the machine tomorrow and check the accumulator valve first then move on to the pumps. Will keep you all updated. Thanks for the help.
I would say that in addition to checking the accumulator valve you also want to check the precharge pressure. Even if you do not have a gauge that can do this you can use the procedure that Bob/Ont gave in post #2 on Page 1 regarding pumping the brake pedal until the alarm goes off. Of course that kind of assumes your low accumulator pressure alarm is actually working...........maybe that's something you need to check as well. Typically if the machine has been left overnight or over the weekend the alarm will sound and the light on the panel will flash when you first turn the key because the accumulator(s) will have bled down during that time. So if there is no visual/audible alarm on the dash panel for the brakes at that time I would suggest you probably need to investigate the low pressure alarm before going any further. The brake pressure warning light is the next-to-bottom light on the LH side of the 2 columns of lights on the Monitor Panel.
kshansen, I went back to an old service manual that does not show the ground power steering. I had to pull some old brain cells back out of moth balls and seem to remember that emergency steering became a required system on machines that could coast with the engine off in the State of Oregon. There are plenty of machines with these systems on the west coast but usually only on the 988 and larger. I only specifically remember the slack adjusters on Komatsu machines but never worked on A model 988s. My old book doesn't show any on the 988B. I don't recall them on the Volvo loaders but got away from them as quickly as I could. It's also kind of odd that I've never had to work on brakes or steering on a Hough 560. I guess there is something to be said about the durability of dinosaurs. I agree with Nige on the troubleshooting progression. Do the quick on the accumulator at start up. I also seem to remember you could shut down the engine, leave the parking brake released and then cycle the service brake to full on and off till the parking brake sets. I seem to remember that three cycles was minimum. After that you will have to plug in a gauge at the pump and see what is going on.
Those are the ones I was thinking of CMark but must have been on a different model. They will give trouble if the piston doesn't move and the oil goes through the check valve. The piston must move first then return to reduce the volume of oil in he brakes, if it doesn't the brakes will stay locked up. Later Bob
So I was able to check the accumulator valve today and I do not think there is anything wrong with it. I performed the check exactly as Bob mentioned and all six applications came on. Is there any other way to see if the accumulator valve is not functioning properly? Also performed some other checks today. The parking brake is working fine and stopped the machine completely on a slope. The emergency brake is working just like its supposed to as well. The normal brake stops the machine over a long distance and the steering is still very stiff. There are no leaks or anything, have never experienced anything like this before so its starting to bother me now. I read everyone's input and there is nothing else wrong with the machine to give me an indication as to where the fault might be. Could it be that the replacement pump I installed is not functioning properly?
You do not mention brake system (hydraulic) pressures so I assume you have not checked them, maybe because you don't have the tooling. Please confirm this. If you have a piston seal failed in one of the four brake packs you will be losing hydraulic oil with no apparent leak. Are you topping up hydraulic oil on a regular basis..? Are the oil levels in the axles correct or are they too high..? Does the axle oil appear to be "thin" - another sign that 10W brake oil is getting into the 50 oil in the axle. I think as a next step I would be looking to get a pressure gauge, blank off the lines to the 4 service brake packs (1 on each wheel) and see what pressure you are getting in the brake system with all the brakes isolated. IIRC a dime works perfectly as a blanking plate in those brake lines. That will give you an idea of how the brake pump and control valve are performing. The fact you say that brakes AND steering are problematic would lead me to suspect the pump (or maybe even the suction lines to the pump from the tank), because it's basically 2 sections of the same pump that are supplying both brake and steering oil. Was the pump you installed a new one, and did you check any pressures after installation..?
The steering requires pilot pressure from the hand metering unit to move the spool, this pressure can be cut off by the limiting valves that shut off the flow before you hit the stops. Check the limiting valves are not seized. Then check the steering pressure with the center locking bar in place. Check at high and low throttle. Later Bob
One idea to try to see if there is oil leaking somewhere internal could be to build up brake pressure and then kill engine. Turn key back on and apply and hold the brake peddle down. Couple things, if it's quite you might hear the oil flowing somewhere also if the low brake pressure comes on after holding down for some time it means the oil IS going somewhere. One other thing did you see my question about bleeding the brakes?
can anyone show me how autolube system works in cat 740b