Caterpillar D7G Bulldozer, Powershift Transmission. S/N 92V6463. Transmission slips on occasion, seems worse on hot days. Normally, clunks into first or reverse fine, good solid clunk, and doesn't slip. When it doesn't slip, delivers plenty of power to finals fine. Machine has 9200 hours on it. Nothing been done to tranny that I know of. I have changed the oil I think three times. Always looks good, replaced with 50 weight gear oil as specified. I have the Cat manuals. Here's my thought: The tranny itself is good (gearing, bearings, clutches) I think. The gear and mode clutches (fwd and rev) are selected by the lever and actuated by servos (pistons with O rings in a hydraulic bank I think). When the machine is cold on startup, etc, seems to clunk in with a vengence, runs good. When hot, just doesn't clunk reliably. Usually, a second try works, but I hate that slipping, that is hard on the clutches. Yesterday I noticed it not only slipped in first which is the only gear I use, but also fwd second and third. And it slipped in reverse also, which I really haven't noticed in past. My thought is the servos are not getting full pressure and flow when hot, and / or O rings are getting tired. Oil level is right on, tranny doesn't leak. I don't think I have changed the trans oil filter in the 700 hours I have put on it. Dealer claims he did when I bought it. Seems elementary, but I haven't. Dirty filter will restrict flow and pressure. I will of course. But that would be too simple and too good to be true. Need your help. Thanks.
As you will note from my previous questions, I give a tip. I really need the answer soon and I need a high level of detail, but I only have $19 in PayPal right now, but I want to get started. If you help me with this, you can imagine how tranny problems can be stressful, I will be more generous. Thanks. Dirck
You seem to be on top of this machine and are very familiar with the workings. Do you have the tools to test pressures? That would be the best place to start.
I would also check the filter and the strainer. Replace the filter and cut open the filter to layout the medium to inspect it for debris. Look for metal and dirt or bronze from the clutches. If you find anything, please let me know or post some pictures of the debris. Pass a magnet over it to see how much is iron.
Look at the suction lines and replace them if they are very stiff. Hard hoses can allow air to enter the oil and this will cause pressure to drop. The oil should also turn foamy on the dipstick.
Monitor the pressure as it warms and note the drop. Check it in each gear to see if any loose more pressure than the others.
Let me know what the pressures are and we can go from there.
Thank you. Good input. I don't have the pressure tools. Is that something I can buy from my Cat dealer? Is there a kit? I do agree, the Manual just goes on and on about checking pressures. I was hoping it would be simpler, although checking pressures shouldn't be that hard. Pressure points might be somewhat inaccessible, not sure. Do have to read Manual again and really understand it.
In order to check the strainer, I have to drop the oil, is that right? I'm pretty sure I checked the strainer when I changed oil last time which was last summer. I keep a log, but I don't see an entry. I couldn't possibly NOT have checked the strainer when the oil was out could I? Unless there is a belly pan in the way. My memory is the strainer housing IS accessible. I will look again under the machine.
Yes, by all means, I will cut open the filter, that's easy, and advise you of findings. There are two on the right side of the machine, right? One real big one and a smaller one next to it. Again, I have to review my Manual. I have the Manuals, must use them. The section on the powershift trans just seems to go on an on. But I will do it and advise.
The dipstick has never showed foaming, that I check all the time, oil is always clean, honey-colored, and smooth, so at least the lines should be good.
Thank you Donnie. I will do some things, and contact you again here. Oh, one more thought. If the pressure or flow or both are dropping when hot, typically wouldn't adding some 90 weight to the 50 weight to increase the viscosity help? Maybe 5 gallons of 90, I think the trans holds 2
Jesus, I keep hitting enter prematurely, sorry. Was saying trans holds 20. Will 90 weight mix with 50 weight? I think the term is miscible. I will experiment with samples before doing anything. I must be tired. Will sign off now and contact you when I have more info. Thanks. XXXXX
I would not mix any oils. I really think 50W is to heavy and could cause problems when the weather turns cold. We always use 30W and don't have any trouble from freezing to 100 degree days.
The large housing near the front of the engine has four bolts in the cover and a port. This is the filter for the transmission that should be cut open and inspected. The port is an easy spot to access pump pressure. It is not the most accurate location but, it is close enough for first tests. The plug is usually a 7/16"-20 "o"-ring boss thread. The pressure in the transmission is below 500 psi so, any gage that will read around 650 psi would be good to test pressures.
Cat dealers have the individual gages needed to test the transmission but, you can get them anywhere. Cat has some "Hanson" type couplers that work great. The manual may have some part numbers for this testing. You don't need a test kit, it is way to expensive and you can do most of these checks with just two. The transmission internal ports are 1/8" pipe tapered threads. This is sometimes easier to do with a pipe nipple to raise the adapter so it will be easy to hold and not drop in the transmission. You can make your tooling work any way you want but, the size of the port is fixed.
The smaller housing has four nuts, this is the magnetic strainer and is located high enough the oil will not need to be drain the inspect it. Pull out the magnets to see how much iron is in the oil.
Note what type of material is in both and how much. Small amounts is normal.
I have see lots of problems with the suction line from the strainer to the bottom of the transmission sump. Bent oil lines, hoses too hard that allowed air to enter and hoses the had failed internally that were restricting flow to the pump. This is something to examine closely before buying a pump.
Interesting on weight of oil. Maybe I should consider 30 weight. I went with 50 only because that is specified. Wow, as I am typing this, you are still answering. Well, I guess I didn't check the strainer if it is up next to the filter. That sure makes life easier. And a pressure port on the filter housing to accept pressure gage sounds easy too. I will check the strainer and filter tomorrow. I won't have a pressure gage for a few days. My Cat dealer is four hours away (H O Penn in Newington CT. I live in Upstate NY near Cooperstown).
The torque convertor has a small screen in the bottom of the housing which would be accessed by dropping the pan. If you find debris in the filter, I would check this screen as well. If you catch more than a couple of gallons of oil when you drain the convertor, this could be a sign the scavenge pump section (part of the transmission pump) is damaged. The screen in the torque convertor is there to prevent large debris getting to the scavenge section and destroying it.
Any part store that makes hoses could make you a hose or may have fittings to adapter to the o-ring boss port and to a gage they have. It does not need to be CAT unless you prefer a better quality gage.
50W oil is fine for very hot climates, I don't think yo need it up there. You don't need to change it back unless it turn cold, then I would definitely change back to 30W
So that gear pump right there on the accessory drive side of the rear engine mount is the trans pump? I've had that apart couple years ago, was leaking badly, failed O ring. The lines to and from look good, one burst last year, but I will be looking again. I keep machine clean and don't work it too hard. I respect machinery.
I dropped the main belly pan couple years ago because I swallowed a valve seat and needed to get at the crankshaft and conn rods. Never put the belly pan back, Risky, but I don't run machine over stumps, rocks, etc (famous last words). So then the converter strainer is accessible? I must have checked it. There is another smaller belly pan under the trans, I have not removed that. Are you referring to the engine belly pan or the trans belly pan.
Yes, it should have a hose that runs directly to the large filter housing(pressure) and a tube from the strainer housing(suction). If pressures are low in all the gears when the oil is hot, check the pump. If it has any heavy scars internally or the bearing are worn down, rebuild or replace it. Old machines like this, be sure to ask for Classic parts and save some money, they are good as original.
The rear pan would need to be dropped to access the torque convertor and the suction line to the sump of the transmission. Most of the later D7Gs had a pivot and could be lowered with out completely removing it. Check the pivots to see if your are still attached, they were often damaged. NEVER lay under the pan without something to support it when removing the bolts. It will be very heavy and deadly.
No, I don't have to have Cat gage. If monitoring the pressure off the filter port is good enough, then I will get on with that. Pump looked real good when I had it apart, no scoring, wear, or other obvious defects. All your comments seem to refer to the pump, filters, weight of oil, lines, pressure check, etc. You have not mentioned the so-called servos or pistons or actuators of the clutch discs. That seems encouraging, because that would be a major teardown to get to the valve bank I call it. Am I interpreting this right? You are being very helpful.
Oops, I don't really want to drop the rear pan. It appears damaged and bent from prior owner, I will look again, but I don't recall pivots. I would not lay under it. Hoping all the other things you mention will prove fruitful. I can't wait to check strainer and filter up on deck level, can't believe I haven't done that before. I trusted dealer (and still do). Did not buy it from H O Penn, but rather a used equip dealer in Texas believe it or not, and had it shipped up here.
I want to start at the begining. Not assume to much before we know the basics of how the machine can perform. If pump test good, then we can move to the transmission pressures and see if something is wrong there. The cover has a small round plate to check the main pressures in the valve. This is were the adaptes with the 1/8" fittings will be needed. Make adapters to connect the gage and hose you fabricate to test the pump with.
That damage could bend the suction tube, inspect it closely to see if it is damaged. I had one a stick got into and nearly colapsed the line and caused low pump pressure.
If yours has the hose, you may need to replace it as a precaution. The oil would need to be removed to do this so, wait to see what the pressures are first. I see a 3P-7170 as the hose part number, the early models had a short tube that is what got damaged on the one I worked on.
I will be off-line for a short time but, I will check back in soon.
Now that's irony. The prior owner in Texas supposedly used the machine for clearing trees. There is a very hefty stick, more like a strong branch or root, stuffed into the trans belly pan that I haven't been able to pull out. I better have a real good look at that. Not sure yet if I have a flex line or hard tube. This machine has always had isolated occurrences of trans slip it seems, but never caused problems because a second try with the shift lever seemed to clunk it in. Don't misconstrue this comment. The slippage has been truly minimal over the 700 hours (ten years) I put on it. But yesterday it was bugging me, wouldn't seem to behave on the second or third or fourth try, so I got frustrated. Like you say, first things first. Inspect strainer and filter and report findings. Then pressure check. Then maybe drop trans pan. Oh me oh my.
That is something to investigate. Had a D7R that the suction hose collapsed and cause two pumps to starve for oil. Low idle pressure was good but, after running at high idle for a long period, a flap dislodged and would restrict flow. Took almost a week to find this problem.
Thanks again. I will be on these recommendations. Cold and rainy today. Tomorrow. Dirck
No problem, just keep me posted each day to keep the link active.
Hi Donnie. Well, rain stopped, first step check low pressure magnetic strainer. Embarrassed to say I don't think I have checked this in the ten years and 700 hours I put on machine. Yeah, I'm on top of it you say, but strainer checks are motherhood. And I don't know if used equip dealer I bought it from did either, altho I would think so. Too long ago to ask him, not sure he's even there. Well, steel first. No steel chunks or chips at all, plenty of fuzz on the magnets, but I would say a normal amount of fuzz for 700 hours or more. I will borrow a digital camera soon, oddly I don't have one, and get you pictures. But I don't thing we have any gear or bearing problems. What I do have is many (maybe 20 or so) chunks of a non-metallic, non-magnetic material that was mostly in the bottom of the housing and some in and around the screen. Black, brittle but fairly strong, one piece about half inch by half inch, several others about quarter inch by quarter inch, all appear to be about 1/8 inch thick. Clutch discs? And couple of them have a bronze coating on one side which I would gather is bronze flame sprayed onto the disc. The chunks again are non-magnetic. What are the discs made of? I certainly will get pictures of these pieces to you, most of the other pieces are small, maybe one eigth by one eigth, and lots of real small pieces, almost particles or sludge. Overall it doesn't seem that bad to me, I surely don't like clutch discs breaking up, but again 700 hours is much too much time between inspections. But be that as it may.
I have not pulled filter yet, and I don't have gage yet. Will try to buy one and some fittings tomorrow. As an aside, the oil in the strainer housing, like the oil in the sump, is clean and smooth and oily.
As another aside, which is further embarrassing, you correctly gleaned that I have some mechanical savvy. Well, ironically, I worked for Sikorsky Aircraft for 47 straight years, that's the helicopter builder in CT. You know, the BlackHawk, the Presidential copter you see on the White House lawn, etc. 47 years. I am a degreed mechanical engineer. Here's the real irony. All 47 years in their transmission design and overhaul departments. If anyone is qualified to look at chips and understand gearboxes, it is me. Oh me oh my. How could I not check the strainer all these years. Checking the strainer on helicopters is standard procedure before and after each flight. And of course, allowable debris is much more stringent than on heavy equipment. And further, and this is the main point, helicopter transmissions have only one speed, one direction, are all direct drive, no torque multipliers, converters, shifters, clutches, nothing but straight connection from engines to rotors with gears, (spur, helical, bevel, and planetaries) bearings, shafts, housings. Point is, I am not familiar with transmissions that shift or select speeds or directions or have servos or actuators or clutches etc. Helo trans just sits there and delivers torque to rotors. They do have lubrication systems, pumps, strainers, filters, oil coolers, magnetic chip detectors, and quite a bit of sophistication.
So that's the first step. I'll try for pictures, but all being said and done, my findings would not have restricted the suction side of the pump as such. But we're not there yet. I don't want to section the filter medium until I have checked the pressure, right? But that debris implies there may also be a lot of fine debris that makes it thru the strainer and the pump itself and is trapped in the filter, and filter could even be bypassing. Stay tuned. Thanks.
Interesting story. I was asked if I wanted to do Helicopter maintenance when I went into the USAF but, I could not see any practical use of that knowledge in the rural area I live. I never thought about living somewhere else but, I often question those decisions and wonder were I would have been if I had chosen a different path. Hindsight is always 20/20 right?
Try scraping the large pieces to see if it is all the same material. The clutch disc are "sintered bronze". I don't know what that means but, it sounded special and better than the paper used in todays transmissions. The separator plates are all steel and only have trouble when the transmission is slipping. They can become warped and cause the machine to move even in neutral. The disc don't fail but, they do wear out. When this happens the stack will be too thin and it will allow the clutch piston to travel out past the seal face and loose pressure. This is normally one gear (often forward) only.
If you don't think it is bronze, apply some heat and watch how it melts. If it is part of a hose, it should burn and melt to oilly goo. Metal would not burn and likely form a bead.
Pressure test before changing the filter will only show how plugged the filter is. It is OK to know this but, it won't change much to the transmission. You're correct about a bypass. It will push the filter down on a spring below the filter and allow the oil to flow over the top bypassing the media. I don't know what the bypass pressure would be but, it is not much because the filter would fail if it didn't bypass.
The strainer design is not much to protect the pump. The pumps do "eat" allot of trash and a simple screen is all that is used, even on todays machines. Since your tractor feels normal cold and weak hot, it could be a pump wear issue. Many other things could be wrong in the valve, I just want to eliminate the simple things first.
I posted a long answer discussing my findings in the strainer, chunks are sintered bronze form clutch discs, hit enter, it went into the back and forth. Where is it now? How do I refresh? Is it lost? Help. I can rewrite it of course, don't understand computers sometimes. It all seemed accepted last night.
What I wrote was I scraped the pieces from the strainer, all 1/8 uniform thickness, charred black, wouldn't burn and wouldn't bend, but would break with a lot of force trying to bend, and after scraping used a ten power glass which really brings it up as you know. Pieces are all definitely sintered bronze. So we have a disc or discs partially breaking up. Sintered bronze is powdered bronze put under very high pressure and temperature (sintering) to form shapes. It is typically used for friction devices like this, Sikorsky uses a lot of it in clutches, thrust washers, bushings, etc. Oilite Bronze with which I am sure you are familiar is sintered bronze impregnated with oil at pressure and temperature again. Oilite is therefore self lubricating. I've been giving this a lot of thought because you mentioned the discs don't usually break, but wear, sometimes so thin the stack allows pistons to come out of their normal travel limits. Well, I surely have been careful that when this maching did slip, I immediately reduced engine speed and kicked into neutral, and tried again. It usually went in. Point is I never just kept pushing while slipping. But if the pieces are so charred, it occurs to me that the prior owner may have been frustrated and just kept working while slipping which would immediately overheat the discs and char them. Like you said, surprised the steel ones aren't warped, but she doesn't ever move in neutral. Prior owner is unknown, but dealer said this machine was just more or less abandoned in Texas, so the owner may not have cared much about anything. Only a thought. But have you seen charred bronze discs in your experience??
Sectioned the filter today, remarkable, pulled the folds apart in the medium. There is not one single piece of anything in that filter. Amazing. No bronze, no steel, no nothing. I would have bet there would be bronze fines. Nothing. And nothing in the filter housing. Nothing anywhere. Just the chips and chunks in the strainer. So I am baffled. Trying to get a pressure gage, I surely will, but not sure yet where or when.
I am suprised too. We will get into the pressures when you get the gauge. I will change this question to Q&A, it will help me be notified when you reply.
You can still reply to this same question. No need to start a new one.
When you get back to test the machine, remove the floor plate and look at the drive shaft. If it is turning and the machine tracks are not moving, the transmission is slipping.
On the top cover of the transmission is a small (usually round) plate. This is were to access the clutch pressures. Use the testing and adjusting section for the location of the pressure taps on the transmission. Don't worry about removing the load plug yet, just check pressures for the direction and the speed for all selections.
No O-rings are used to seal the spools. It is all metal to metal fit. The only o-rings are to cover end caps, not a common problem for them to cause a severe leak.
Inspect the linkage to make sure it is going into gear correctly and not sticking between speeds. Shaking the control rod after selecting a gear is all that is needed to test it.
Pressure form the pump is fine, reliefs are in the transmission valve and the torque convertor. 435 psi is exactly right on the money for pump pressure.
90W oil is way too tight for the transmission, the 20W-50 should be ok.
Please let me know what you find and we can get deeper into this problem.