Over the next few days, I've got the job of overhauling a Cat 953B HPCU. The 943, 953, 963 and 973 B series and earlier are all much the same. Anyway, due to the fact that these machines are getting scarce in front line work nowadays, and the relatively high cost of repair I think this may be the last one I ever get to do. If anyone has any interest, I'll post some photos showing the the insides of one of these mystery boxes and what goes into rebuilding them.
Yes for sure, would be very interested in following you in the rebuild of a hydrostatic.
Count me in
I will be looking too, Cmark, and a toast to you. on a great idea.
Me too, I have a 953.
You are right Cmark, haven't seen them in exchange stock for years. Maybe you could put it together and get it filed by it's self so it's easy to find in the future. Post it here and it will get lost as time goes on. Later Bob
I would love to follow a rebuild. I may end up with one of the pre electronic machines someday. Shawn
So here we go. Due to an unfortunate incident involving an Iphone and a puddle, pics of the teardown and start of the rebuild are lost to mankind forever. We join the action as the second pump is being built up. We've already installed the new swash plate bearings and set up the end-float, and the same with the pump drive shafts. The new pistons are being installed. I'll comment as we go along. Any questions, just ask and I'll try my best to answer. These are the main damaged parts. One of the slippers came off a piston and the retraction plate broke free. Normally you'd suspect some sort of cavitation scenario, but in this case the machine has high hours and was reported to be working normally before the fault suddenly happend, so we're calling it an old age thing. We have to measure the clearance between the slippers and the swash plate using feeler gauges and adjust it with shim packs under the retraction bearings. The spec is .003"+-.001". For something like this, I like to set up a go/no go scenario, so we're using a .05mm and .1mm feeler gauge. (My tiny set of feeler gauges are metric). If the small gauge slips in the gap and the big one doesn't, we're good. The swash plate and pistons finished. Next. Cylinder barrel.
Installing the spring into the barrel. The spring keeps the barrel pushed against the port plate. And the barrel installed onto the pistons. Can't get an action shot of it happening as it's a three-handed job on a good day The yellow cover is just for protection. The barrel face is precision finished and any damage or scratches is a big no no. This is the LH pump, by the way. Inside of the case where the LH pump will go. Here the case is laid down and we are seeing at it as if we were stood at the front of the machine looking towards the cab. The RH pump already installed. Next, installing the pump.
The shaft goes up from the botton and the bearing cone is installed on the top end We screw an eyebolt into the shaft and hang the pump from the crane. This is one of the servo cylinders. Just a simple double acting hydraulic cylinder that swings the swash plate back and forth. We already stripped and resealed these. The hoses can be a cause of trouble, especially if the machine has been allowed to run hot. They're a bugger to change when the thing's assembled so they always get renewed on a rebuild. Servo cylinder attached to the swash plate. The black O ring is just to keep the thing under control as it's being dropped into the case. Lowering the LH pump into the case.
Swashplate bottom bearing. Swashplate top bearing. Swashplate top bearing housing installed. Swashplate endfloat is adjusted with shim packs under the top and bottom bearing housings. We adjusted this previously. Both pumps installled. Gasket in place ready for the pump head. Note the long guide-bolts. Probably the cheapest tools you can make and they make jobs like this soooo easy. More to follow. Probably tomorrow.
Cmark, Thank you for sharing that information with us, I have always wanted to see what that procedure looked like.
Thank you very much for sharing this. Would you mind if I put a like to this thread on my website so it can help others out too? Thank you, Chris Hill http://ihmusedparts.com
Nicely done. I use loctite gasket eliminator 515 and 520. I am curious what you use. Shawn
Personally, I've got no objection to you linking this, but I think you should probably get the go ahead from Steve or one of the mods first.
It's Cat 6V6640 which is Loctite 38364 high temperature flange sealant. The gasket is steel coated with plastic. (anyone know what the plastic is? Teflon maybe, or some sort of graphite compound?) so strictly speaking, gasket eliminator shouldn't be necessary, and normally I don't use any where the build doesn't call for it. However, once the unit is installed in the machine, an oil leak here would be a disaster of biblical proportions, so it's just a little extra insurance, to be sure, to be sure.........
I had my numbers wrong. It is 510 high temp. rigid castings ect.. 515 flexible both anaerobic. A fellow helping me used Dow Corning 111 a heavy silicone grease on a 10 psi bearing cover (very rigid stationary pump). Very easy to clean up when you need to go back in for future work. Anyhow thanks for letting us follow along. Shawn
I have had the pleasure of changing those servo hoses in the machine before, not fun, it was a rebuilt unit with low hours from another state, hoses were twisted when tightened up and rubbed through. something I learned from someone else's error. Hope it helps someone
Thanks for the tip. I'll pay extra attention when I hook them up.
Thank you for the feedback.
Thanks for documenting this Cmark. Lots of WOW's and OMG's here. The precision, cleanliness, and the cost to make parts like this is amazing to me.
We put grease on the back of the port plates to stick them to the head while it's hanging upside down. And then tie them on for safety. You can just see the little loops of string through the holes. The one on the right has fallen off already. Good thing we had the string! As per the barrels, dings or scratches on the port plates are unacceptable. And the head's bolted down. A pin anchors the servo cylinder barrel. And a cap goes in the hole.
A couple of parts to go into the head next. First the oil cooler bypass valve. And then the charge pressure relief valve. Bottom plate and a few baffles. And the sump. And it's ready for the transfer gears
Transfer gears and housing go for a spin. Flip it on its back, install the drive gears and tighten the retaining nuts to 500lbf. Install the oil cup thingys.
The input gear is a little corroded so we spin it in the lathe and hit it with the scotchbrite. And make sure all the abrasive is washed off. The little pie oven we use for heating up bearings (and pies). And put the cones on the input gear.
Forgot to mention the sump is one area where there is a difference between the models. Some have a large one like this, some have a small one simillar to the top cover. I've not done any extensive research on this or anything, but I know that I've seen a lot with a small sump and the working oil level almost to the top of the HPCU. I'm guessing that this caused problems with the rotating components being submerged in oil (power loss, overheating maybe?) so they went to the bigger sump and lower oil level.
You do some great work
Cmark you have a 953 HPCU there. Large lower pan to increase oil capacity with lower oil level as the 943 has. Filling case as the 963&73 would sap too much power from the 3204. Later Bob
I can admire this work , professional , clean the way I like to see things done. Now I know what's under that valve cover looking thing.
looks like a GREAT JOB thanks
Edit. Double post.
Shrink the input gear bearing cups and install them, but not the seals at this stage. Install the housing without sealant. And check the endfloat of the input gear. Adjustment is with a shim under the cup in the housing. And when we're happy with the endfloat, take it apart again, install the seals and fit the housing. No gasket here, just the Loctite sealer.
Now we move on to the other components which go to make the thing work. These are what Cat call the replenishing valves. There's one for the right side and one for the left. They handle all the high pressure side of things after the main drive pumps. They're both identical apart from the component on the bottom left. This component is on the RH valve only. Its job it to allow some oil to bleed between the two circuits when the drive pressure is low which helps to keep the machine going in a straight line when needed. The LH valve (pic 4) has a needle valve in this position which is used to disable the function during certain tests. The main function of the valve is to "replenish" the oil in the drive loop. That's handled by the spool (right) which also allows the main relief valve (top) to sense drive pressure in both fwd and rev. Note the long thing on the left with a plug on the end. This is found on later machines. Earlier ones had a spool valve with some extra exlernal lines instead. This allowed to the machine to be towed once the parking brakes were released. It can lead to specific problems with the drive which aren't covered in any of the Cat troubleshooting. In later machines such as this, this plug has to be removed instead. In practise, it's 100000% easier to just pull the drive shafts if you need to tow it. This is the LH replenishing valve. Note the tube sticking out on the right of the picture. It connects both valves together. This tube is a later example with two O rings and backup rings at each end. The early ones only had one. This is a favourite source of leaks on the early machines. If you ever find yourself in the position of removing the replenishing valves to fix a leak here, I suggest you upgrade to the two-O-ring tube. I hope you're all keeping up. There'll be a quiz later
This is the charge pump. Nothing very sexy going on here, just a simple gear pump, but.... It's direct driven at engine speed which means its output flow is directly proportional to engine speed. The system senses this flow (note flow, NOT pressure) to tell how fast the engine is running and prevent the drive system from stalling the engine. More on this to follow......
One word of CAUTION here if you pull the sun gear shafts for towing. Take out the end cover thrust plugs and put in your tool box. They have a habit of falling out and ruining the planetary gear set. Upon pulling a shaft the planet bearings should be checked as well. The planets will stay in mesh with the sun gear installed with failed bearings but get out of mesh by themselves and break the ring gear. Later Bob
Yeap, count me in as well, sounds interesting for sure. Never too ole a dog to learn a thing or two. Ty
Yair . . . Cmark . Fascinating stuff. About what expectation of hours do you expect from such a transmission assuming proper maintenance? Cheers.
Cmark, Good stuff, very interesting and well done thread. Did you go thru the track motors as well?
Hey Scrub. IMO these transmissions should last tens of thousands of hours, given proper maintenance. But as your question implied, proper maintenance is sometimes a subjective thing. This particular machine is getting on a bit. To be kind, I would call the hourmeter reading "unreliable", but looking at the overall condition, I would say it's around the 15 - 20k mark. This is not the first time somone has been inside the HPCU as it has someone else's paint marks are in there. This customer runs several hystat track loaders and with routine oil and filter changes I think he gets excellent reliability out of them. We've been looking after his gear for around 8 years and this is only the second major tranny problem we have seen.
Yes we always strip and inspect the motors in a situation like this. In this case, luckily, the motors were OK. Just wear commensurate with age to the port plates. The main bearings in these motors are, IMO, very large for the size of the motor and the wear was negligible. We simply rebuilt the motors with lapped port plates.
The next component of interest is the main control valve. (Front view) (Back view). There's several things going on in here including neutral start function, braking and and couple of pressure controls. What interests us though is....... This component with the two O rings. It's the venturi. It takes the flow from the charge pump and (as we all know from high school physics class, duuh) the pressure at a venturi is lower than the pressure upstream of the venturi and the faster the flow, the lower the pressure at the venturi. This provides us with two pressures. The difference between the pressures (delta pressure) is directly proportional to the flow and, because the flow is provided by the charge pump, the delta pressure is directly proportional to the engine speed. BTW, apologies to any physicists reading. I'm only a diesel fitter and if my take on any of the fundamentals is way off, please let me know.
Yair . . . Cmark . Thanks for reply to my query re hours upthread . . . and I reckon you oughta drop the "only" tag from your job description. (big grin) Cheers.
Back view of the replenishing valves. And the replenishing valves in place. Main control valve manifold. And the main control valve in place.
Next we install the servo valve housings and connect the servo cylinder lines. At this stage, it's vitaly important for your sanity that you don't drop anything down the sides
This is the next component in the load sensing system. It's callled the underspeed valve. It takes the two different pressures created by the venturi and uses them to vary the ratio of input from the FNR lever to the amount of movement at the servo control valves. Or let's put it this way. See the shaft sticking out on the right? That's directly connected to the FNR lever. The silvery thing in the centre is actualy the back of a ball joint which is connected to the servo control valves. If the engine is idling, we have a low delta pressure and if we move the FNR lever 100% FWD, none of the movement gets sent to the servo valves. However, if the engine is at high idle and we move the FNR lever 100% FWD , the underspeed valve sends all that movement to the servo valves and both pumps go to full stroke FWD. When the machine comes under load, the drive pressures increase and the engine slows down. This causes a drop in the delta pressure and the underspeed valve reduces the command to the servo valves, the pumps destroke a little and the load on the engine decreases. This is what allows the operator to drive into a load and not ease back on the FNR. If an operator finds he has to modulate the FNR to reduce the load on the engine, there's a problem. This is also why it's important to run the engine at full RPM. Also note the load on the engine doesn't have to come from the transmission. If the implement hydraulics slow the engine down, that will also cause the transmission to destroke. The whole set up is designed to keep the engine RPM from dropping below about 2000 RPM (depending on model). But what if we want to move the machine slowly, around the yard, or loading it onto a truck? We don't want to run the engine at full throttle, do we? We need to override the underspeed system somehow. OK, so let's put in an underspeed-override valve, just like this one. This partially dumps one side of the delta pressure to artificially raise it when the governor lever is not set wide open. It is mechanically connected to the governor lever and is the reason why a faulty machine will sometimes increase ground speed when the governor lever is moved back towards idle; the underspeed override valve has opened and raised the delta pressure. Here's the underspeed valve in its position.
These are the servo valves and the associated linkages that keep the two sides synchronised and allow each side to be independently slowed down for steering. The only common wear points here are the two bronze bushes in the plate at the bottom of the picture. These are the bearings for the steering linkages. If all the external linkages are correctly adjusted and the machine won't counter rotate, wear in these bearings is a possibility. The servo valves and linkages all built up. And installed in the case. Note FNR input top left, underspeed valve left, underspeed override valve bottom left, top of the two servo valves middle of picture and steering input levers and linkages top right.
And the back side built up. You can see the charge pump in the centre and the filter housing top right. Early models had a different filter housing that stood vertically. Both do the same thing but the later ones like this can be serviced without having to lift the cab. You can just make out a brass valve below the filter. This is to drain the housing before servicing. It's important to do this because if you don't, oil from the dirty side can enter the clean side when the filter is removed. Anyway, that's about it. I hope someone found it to be useful or of interest. :thumbsup
This was great Cmark very well done. Many thanks
Yes very informative and pic's of parts rarely seen by most people. Thanks Cmark. Later Bob
Great thread
Are you kidding? Now, if only I can get my jaw back to where it belongs. :notworthy
My question is what all is different on the new ones and u will pry say they are all electrically controlled with solenoid valves and computers so they wont have all the linkages is that right? Thanks for posting all this it is very interesting and mind boggling to me if you don't do them very often how I would remember all that! Was gonna say that we have 850J deere dozer so that why I was wondering what difference was if 850 looked at all like that on the inside?
The Cat C series use two "off the shelf" hydraulic pumps, driven by a simple splitter box and controlled by solenoids and an ECM. I haven't got a clue about Deere dozers I'm afraid, but I would guess they work on a similar principle to the C series. I haven't seen anything else ever in the world in space that looks anything like one of the Cat HPCUs.
still learn'n. The deere isn't even close although the principles are the same. Its very close to this http://powersolutions.danfoss.com/s...ons/documents/product_literature/520l0603.pdf It is two pumps for the tracks one behind the other, one for each side and then an another series 45 for the hydraulics. Cmark. Really liked reading this, its nice to see another mousetrap.
Cmark, Looks like lots of fun! Do you ever have someone ask, "Why are you so fussy about getting every thing so clean?" Had a guy ask us that once when we were rebuilding an Allison 6 speed CLBT 5860 transmission That guy is now a superintendent at one of our smaller plants. Could never understand why just because this equipment works in the dirt they have to be covered with dirt all the time.
Yair . . . Excellent comprehensible thread and pictures Cmark . A beautiful bit of gear but you would really have to wonder about the designer who first got his head around the concept and put it down on paper . . . it makes my head ache just thinking about it. Cheers.
I had the good fortune to meet one of the engineer's (Hugh Piper) involved in the later stages of their development. According to him the concept was from the 1960's worked on then put on the shelf. Hugh got involved when the got out the drawings in the late 70's. They took the linkage drawings and built large scale cardboard copy's of the parts, assembled them together and worked them back and forth to perfect things. Then they built parts from steel. A large fleet of the bigger ones worked near here and provided much research and development information. Later Bob
And I thought that was just the way guys like me figured things out, cardboard or scraps of plywood to design brackets and such?
That's interesting. I'd love to chat with the designers and find out how this thing came to being. What doesn't come across in the pictures is the weight of the components. Every item is solid and heavy as billyo. It must have cost a fortune to tool up to produce the things. Seeing as how, to the best of my knowledge, they were only fitted in the track loaders, I wonder if Cat ever made their money back?
I have noticed the D6K finals are very similar in appearance to a 953. I wonder if the 2 machine share the same hydrostat , engine setup. I never understood why they didn't use the 53 drive on a dozer. Not to sidetrack this thread but if this happened earlier on there would have been a hydro dozer in the late 80s. I ran a Case 1550 which operates almost identical as a 953. I was always told they had issues with cross contamination and failures in the drive system. But this machine could have been the Achilles heel if it had proven out. Cmark I guarantee CAT made there money back. My neighbor is an engineer , has his own dozer , we talk about equipment a lot , he has told me its so much cheaper to do pilots over conventional linkage these days. I think most of the switches are made in China or over seas in cheap labor areas.
The story I heard was the 943 and 53 was very profitable and dependable. The 963 was less so and the 973 was a very Expensive Learning Curve. If you look at the four HPCU's side by side and then look at the horsepower going through them you can understand why. Heat is the problem and the 73's had two speed motors. The rotating group was mounted on trunion bearings with swivels carrying the oil. If the bearings flexed the swivels would leak and trans overheat. That was one problem that was overcome but motor leakage was biggest problem next to shock loads breaking the internal drive shafts. Later Bob
Bob, we used to see alot of 973's here in the northeast, mid eights till mid 2000, used in stripping overburden in bluestone quarrys, operators would bang back and fourth peeling cap rock, worn trunions and broken shafts were the common, they were real money makers if you liked crawlin through the mud and oil from blown drive hoses, once the belly pans were smashed in.
Cmark, very well presented, nice work,
Hi , just wondering , what sort of cost is it to do a full overhaul like this? Thanks for the full rundown on this , it's really good to see .
Bearing in mind this is a public forum, out of respect for our customer I'd rather not discuss costs if that's OK with everyone. However if anyone wants to discuss price of repair from a business point of view, they can certainly PM me.
Ok all good, we don't see many track loaders over here, a few older ones 955/941 and a few 953/943s ,so haven't had much to do with rebuild prices of the hystat system , often thought about a 943 but as they are getting older now worry about the cost to keep going( to a good state not just "going") .
That's the thing about the hystats. They either go (with little problems along the way) or they don't....bigtime. Their biggest downfall was the high pressure drive lines from the HPCU to the motors. The entire thing is crowbarred into the chassis with maybe 3/8" to spare either side to remove and install hoses like iron bars. Difficult enough to replace in a clean machine but in the field, keeping dirt out of the system was much like the recreational pursuit of walkng through mountains. Impossible. If you happen to buy a used one that runs for a few hundred hours without trouble, you've probably got a winner. If you blow a hose however, be ready to spend an extra hour cleaning things down before you even begin to remove the old one. It will be time well spent. (This applies to all hydraulic systems of course, except most hydraulic systems don't take an hour of cleaning)
Looks like a very professional overhaul. I presume from this and your other previous posts that you work for a Cat dealer? Are these type of jobs just given to anybody who works there and expect them to follow the book and produce a reliable rebuild? Or are they only given to the best techs who are capable of doing as good a job as you have here? The reason I ask, is I have worked with some Cat trained mechanics and some ex-Cat trained mechanics who would not be capable of doing a job like this, and it has always made me wonder what standard of repair I would get if I ever sent a component to a Cat dealer for a rebuild.
Sorry to dissapoint PF, I'm an independent contractor. However father ran an earthmoving business all his working life. I left school in '83 and have worked a steady 50+hrs/week purely as a HE mechanic since then (That's a lot of bolts tightened. ) and I've spannered everything for Aveling-Barford to Zamboni. I've worked for Cat dealers, TEPS dealers, contractors, subbies, dreamers, wannabes, chancers, carnies, gyppos and myself. I'd be lying if I said access to SIS wasn't essential to doing a good job on Cat equipment, but bear in mind the yellow/black stripe over the door doesn't guarantee a good job if the people sitting under it aren't up to scratch.
No disappointment at all. That's what I was getting at. I guess that means I am not the only one who is concerned about it.
My thoughts exactly, some clever people out there, wonder how many hours it took to iron the bugs out of the prototypes? Ex tractor fan
that was a brilliant layout an explanation..i wish i had a Cat
What Cmark has to say is spot on. Your local Cat dealer has field mechanics, shop mechanics, truck mechanics, and specialized mechanics. The guys who do overhauls like these are the ones who have the knack and special training, not to mention the equipment to do the job correctly. However he got it, Cmark has this training, and the facilities required to do this work correctly. When a shop or field mechanic removes this transmission, he delivers it to the specialization shop for overhaul. I'm not saying that this work cannot be performed in your garage or shed, but you do need the proper tools, information, parts, and cleaning capability before you start. Oh, did I mention money? Regards, Clark
Very informative thread Cmark! There are still quite a few of these old machines running out there and many of us who own them appreciate the time and information you have shared here! Thanks!
I'll second that , great thread. Cmark along with a few others are full of valuable information. I appreciate the fact that they take time to share.
I would also like to see the internals of one too please
Cmark, did you have to use the proper CAT tools to adjust the linkages or is there another way