Hi, i'm new here and my english is as bad as my dozer technical condition right now. Dozer D6N LGP, serial DJY00951. So, all starded when i felt strange gear shifting- short break between, for example, 3 to 4 gear while moving in reverse. And i notice quiet noise from transmission hydraulic pump- buzzing sound at full engine rpm. Then i turned down engine and started again and noise was gone and gears shifted smooth for 10 mins. Now dozer is not moving in first gear properly- when i switch forward, it moves a bit and stops immediately and then moves again. After a while of not moving in first gear it shows Serv Code 673.02 or sometimes 671.02. Other gears shift +/- normally. As i know those Serv Codes means problem with speed sensors. Is it possible that all this trouble is because sensor or wiring failure? What should i do next? Thanks in advance!
You are correct that 673.02 & 671.02 are related to the tranmission output speed sensors. HOWEVER the speed sensor Diagnostic Codes could be the symptom of a different problem, especially when you say that they are only intermittent. The buzzing sound you heard could be transmission pump cavitation. Without hearing the noise it is impossible to tell but it is a possibility. This could be caused by either low transmission oil level or a partially blocked oil suction line between the transmission case and the pump inlet port. There is a screen in that line - see Step 3 below. I suggest that you should first do some basic checks: - 1. Check for correct transmission oil level with the dozer on level ground, oil warm, engine idling, & transmission in neutral 2. Transmission oil colour & smell. Is it dark and cloudy rather than being clear and bright? Does it smell burned? 3. If the oil is dark or smells burned you should drain it. Change the transmission filter and cut open the old one to inspect for particles (there are plenty of "how to" videos on YouTube). Also you need to remove and inspect/clean the transmission magnetic suction screen for metallic & non-metallic particles. The location of the screen will be shown in your Operation & Maintenance manual. 4. If you find particles in either the filter or the screen, please take photos & post them here. 5. I would suggest that you don't refill the transmission with oil immediately. Depending on the findings of steps 2, 3, & 4 above it may have to be removed for repairs.
i forgot to mention that i bought this dozer a couple month ago and changed all fluids and filters right after, included OEM transmission oil. Now i have worked about 50 hours. Oil level seems a bit above max level, oil looks clear. Old oil was fine- bright, yellowish color. Didnt check filter inside. I didnt know how many hours was that oil worked. I dont have proper operation manual yet. What is exact transmission oil change procedure? I consulted with the dealer about what to do, and he told that it is this simple- drain old oil, change filter, fill in new one. Is that really it? Where is transmission magnetic suction screen located? what is the purpose of these two screws?
the picture did not come through so no idea on that but see attached file for the magnetic filter:
If you need manuals check out this link: https://www.servicemanualpro.com/?page=Products&searchbox=DJY00951
You can download a pdf Operation & Maintenance manual from Cat for $49. Go to - https://catpublications.com/ Click on the "Continue as Guest" option. Type in SEBU8124 in the box and click the Search button. The illustration below should appear. If you buy a pdf download you can have it available in 5 minutes or less. (for CD or paper versions you also have to factor in shipping time.)
Regarding the suction screen it is just before the pump. See the attachment "Power Train oil lines". It is circled. There is also a suction screen in the torque converter housing. See the other attachment "converter housing".
Please confirm that you are checking the oil level with the machine warm, engine idling, and the transmission in neutral..?
Another thought. While you are removing the screen #11/12 you should make sure the hose #33 is in good condition and that the hose clamps #13 are tight. If those connections are loose or the hose is in bad condition it will pull air into the transmission pump.
Now i double checked- transmission oil level is between min/max under conditions you mentioned. Buzzing sound is exactly the same as when hydraulic oil level is way too low. Tomorrow i'll check both suction screen.
Please make sure to check that hose and the hose clips that I mentioned above while you are in the screen.
Yes air in oil going through a pump can make some strange noises and also is not good for the pump!
while I'm preparing for the suction screen test. is it possible that this case affects the operation of the transmission so much?
If the suction screen is partially blocked the transmission pump will be struggling to suck oil from the transmission case (which is effectively the oil pan). If there is anything in the suction side (e.g. a clamp, O-Ring, hose, etc) that is in the slightest way defective the pump will suck air in through that point rather than suck oil. That could be the cause of the pump cavitation noise you are hearing. If the pump is sucking any air at all the transmission will not function correctly. A suggestion of looking for suction air leaks - make a strong mixture of household dishwashing liquid & water, then put it in a hand-operated spray bottle like below. Spray the foam from the bottle on every joint in the suction lines while the engine is running. If you see the foam disappearing into the joint you have found your air leak. There is a distinct possibility that you may find some sort of problem while you are looking at the screen. For example the O-rings #65 & 71 in the illustration above, or maybe the bent tube #20 or the O-rings that seal it. You really don't know what you might find until you remove the floor plates in the cab and start looking around. Before you start cleaning anything take a good look for oil leaks, because if oil is leaking out when the engine is stopped then it is possible that air is leaking in.
So i removed the suction screen and it looks like this. there was a lot of dirt inside, but I didn't find any large or significant particles. However, I have no idea when it was last cleaned. The suction hose is hard as rock, but I did not find any leaks. I will clear the suction screen and put on a new tube. However, what to do next - pour back the oil and try to test, or is it already clear that the fault is elsewhere? Btw, i bought the operation manual and learned some important things.
That "dirt" is most likely burned clutch friction material. Not knowing when the screen was removed last it's impossible to know if it got there recently or has been there for a long time. If it is a long time since it was last cleaned the quantity of material is not that alarming. Personally I would clean the screen, install a new suction hose and new clamps to replace the "hard as rock" existing one (it could be that hose is cracked and sucking air through the hose itself, not at the clamps), put back the oil that you drained and give it a try. At this point you have nothing to lose. As various people said before the cavitation sounds that you reported from the pump are an indication that it is not performing as it should. There are two possible reasons for this, blockage in the suction screen or air leaking into the system - or even both at the same time. The hard suction hose may be an indication that the transmission system has been very hot at some time in the past. Oh, and when you replace the cover for the screen I suggest to use a new O-Ring. The old one is proably hard by now.
Agree while the amount of stuff in that screen is not good but if it's been several thousand hours since it was cleaned not that surprising! Not familiar with the D6N but seem to recall on the D6C I worked on shortly be for retiring in 2015 that there was also a screen in the torque converter or am I thinking of a D8?
The D6N has one also. See the file "converter housing" attached to post #7 above. I did recommend to remove and clean it while the oil was drained. Thinking a little more about the material in the screen. I think that if it was from a failure that is in progress right now the transmission oil ought to be dark and smell burned, not clear with no smell as the OP has described it.
So, i was not as lucky this morning as expected and the test drive turned out to be unsuccessful. What exactly did i do these days - I visually inspected the transmission from both the bottom and the top, clean both suction screens, put on a new suction pipe and clamps, check for oil leaks and oil levels. The result - the bulldozer moved slightly at first speed and high idle and stopped immediately. Driving normally at other speeds. The same thing happens in reverse. If I start in second gear and switch to first gear, the bulldozer stops in the same way as the brakes are applied quickly. When i try to drive at first gear but it doesn't move, then appear Serv code- 113 671.02 and 673.02. The errors disappear if i just drive at some other gear. The buzzing sound seems to be gone, only slightly noise when steering. ps. since the first day I worked with this dozer- when switching from the second gear to the first at high load, there is a small break / knock and then traction reappears. Break was just 0.5 second long, but i felt it was probably not a good thing. Small or medium load= no problemo. i thought of a solenoid problem. Is it worth watching, or have I won a ticket to remove the transmission?
Unfortunately it appears as though you have. It looks as though the speed clutch for 1st speed, which works for both forward & reverse, has failed. The only guaranteed way to confirm it is by checking the clutch pressures using a pressure gauge capable of measuring at least 500psi. It would pay you to measure the clutch pressure in all five clutches.
Have you tried swapping the first speed modulation valve with 3rd speed?
No but i could give it a try. Before i do that i need to know what is what and what to change places.
Following Mobiltech's suggestion you should interchange Modulating Valves "G" (1st speed) and "E" (3rd speed).
i swapped these two places but nothing changed. Sorry for the stupid question, but how exactly do speeds work. i mean, there's 1.5-> 2-> 2.5-> 3-> 3.5 possible shifting gear, but as far as i understand there are 3 solenoids and 3 clutch discs for gears. How it is possible that when clutch disc collapse, the bulldozer first (1.5) speed suddenly does not work at all, but all others operate normally. (2/2.5/3/3.5) how exactly does it work?
There are actually 5 clutches in the transmission, each one of which is controlled by a separate solenoid valve. To select any gear in the transmission two clutches have to be engaged. A direction clutch (forward or reverse) and a speed clutch (1st, 2nd, 3rd). The clutch numbers and what they do are listed below. #1 - Reverse #2 - Forward #3 - 3rd speed #4 - 2nd speed #5 - 1st speed You have no 1st speed in either forward or reverse which is consistent with a problem in #5 clutch. You interchanged the solenoid valves for clutches 3 & 5 with no difference, so it cannot be a solenoid valve problem. the conclusion is that #5 clutch has burned out and the next step is to remove the transmission for repair.
There are really only 3 transmission speeds or ratios. The 1.5 and 2.5 are achieved by automatic engine speed limitation. In other words smoke and mirrors. It does sound like you have internal problems. The good thing is if you have no winch on this you can have the transmission out and tore down before lunch!
the gearbox has been successfully removed. The biggest trouble was that I didn't know about the third axis. * facepalm * Anyway, I visually looked at the gearbox and didn't notice anything special. As far as i understand the condition of the clutch discs is determined by their thickness. How much should be? Would it be wiser to change all at once? What else needs to be done / replaced so that the gearbox problems can be forgotten for a while?
Before attempting to answer the “what to replace?” question, how many total hours are on the machine and does it look as though the transmission has ever been removed before.?
About 15100h. Almost all the screws that needed to be unscrewed were with damaged paint and everything showed that it had already been done before.
In that case a lot will depend on what you find inside the planetary transmission when you disassemble it. There are two kits (aatached) available for the transmission:- 345-9110 Bearing Kit 345-9112 Gasket Kit Also attached a parts breakdown of the transmission and the control valve.
Here is a Disassembly & Assembly procedure for the transmission. My thoughts about what you should consider replacing as an absolute minimum:- 1. Clutch piston seals in all 5 clutches. 2. Friction discs/separator plates in #2 & #5 clutches. The clutches are for forward direction and 1st speed. 3. Friction discs in reverse (#1) & 2nd speed (#4) clutches. 3. Every gasket & seal. 4. Every bearing. Check condition of - and replace if they do not meet specification. (Specifications are attached.) 1. 3rd speed (#3) clutch friction discs/separator plates (3rd gear doesn't get used that much) 2. Reverse (#1) & 2nd speed (#4) clutch separator plates. Replace if they show any signs of heat (blue colour) Hopefully others will offer their opinions as to how you should move forward on this, but remember that nobody apart from you can see the condition of the parts that you are removing.
Good morning, I dismantled the planetary gear of the transmission and found the damage. There was a horrible view and I could only wonder how I could do it at all and how I got out of the pond on my own. Attached pictures. I don't really know why the disc springs broke (mby heat?). The first gear fiction discs are in critical condition, but the dozer was still able to drive. The first gear disappeared due to damage to the piston seal and loss of pressure. Other fiction discs look like new, with minimal wear. Thank you very much Nige for the information which was very helpful to me. I am currently waiting for the spare parts to be delivered and then to be able to put them together.
A couple of suggestions after seeing the damage in your photos. 1. Check all the piston housings (and especially the 1st speed one) for scoring or anything that could cause a piston seal to fail. You should consider the possibility that a piston seal failure might have been the cause of the clutch failure. It is not unknown for the housing to be damaged when a clutch fails like that because the piston travels too far and literally "falls out of the end" of the housing bore. 2. I would personally still replace the discs/plates in both the 1st speed & forward direction clutches. 1st speed forward is when the machine does most of its hard work. 3. How did the disc/plate stacks for 2nd, 3rd, & reverse clutches compare to specification and are you planning to renew anything in any of those three clutches other than piston seals.?
I checked the piston housing and did not notice any damage or wear. However, the piston is badly damaged and I will put it new along with piston seals, rotating rings (?), All first speed friction discs, seperator plates and disc springs. i measured the other disc / plate stacks. Carefully cleaned the discs before measuring. Forward stack- 40.1 mm, Reverse 40.2 mm, 3rd gear 24.3 mm, 2nd gear 15.9mm. Forward stack had one slightly bluish points on disc plate. Think of replacing this from 3rd gear. My colleague and I could not agree on whether it is possible that these discs have been changed before. i don't want to believe they could last 15k engine hours and wear so little. We figured out how to save on expensive gearbox costs by placing a gear pressure gauge in the cab. Or the pressure should be measured regularly for preventive purposes. As far as i know there are no sensor for each gear, only main pressure sensor.
I think based on your reports of their condition then it is almost certain they have been changed before. As you said earlier there were signs that the transmission had been removed previously. Others may have a different opinion but I think placing a pressure guage in the cab is going to achieve very little. You also need to be careful that the tube you use to take the pressure from the transmission cannot get damaged somehow and fail. That would dump all your transmission oil on the ground. To take pressures on a regular basis by hooking up an external gauge when doing maintenance might be a good idea.
I would put all new plates (and discs) in the forward clutch and lleave the exisitng ones in the 3rd gear clutch. As mentioned previously the 1st speed and forward direction clutches are the ones that take the most load and are used most frequently.
Just thinking out loud. Is it possible the failure you have now is the result of someone who repaired the transmission previously "trying to cut corners" and save a few dollars on the cost of parts by re-using stuff that was not really fit to re-use.? If that is potentially the case are you in danger of falling into the same trap by trying to do the same thing.? You can either do it right or do it cheap. If you do it cheap you run the risk of having to do it again in the near future.
The old "Pay me now or Pay me latter" deal! What will suck is that some of the things you replaced the first time will need replacing again the second time. And this does not even take into account the labor and down time!
I will replace all parts that are worn, scratched, or otherwise damaged and all rubber / plastic parts. As well as parts that Nige recommended to replace - forward discs / plates. I also consulted with the dealer and they could not recommend anything else. I also don't think it would be wise to change the parts for good luck, which costs a lot of money. I also do not have any clue as to why this damage occurred. It is possible that the previous owner made careless repairs. It is possible that this is simply a failure. I'll measure the pressure from time to time and hope for the best. There is nothing more I can do right now. I have been working in agriculture for a long time, I use different brands of equipment and sometimes it just breaks for no reason. New or old- doesn't matter.
Also make sure you inspect the friction discs for wear in the tooth are not just thickness. Check steel plates for wear at the dowel pin contact area. When replacing planetary gear needle bearings also replace the rubber/steel retainer pins.
Transmission problem no more! I successfully put together a dozer and worked for a little over a week. Everything seems to be working well, after a while the pressure in the transmission should be measured. You were right, the transmission can be removed, disassembled and reassembled all in one day if you know how to do it. Not as complicated as I expected. If someone else is confused, like me (unlikely) the display of D6N gears then- 1.5- 1st gear, high rpm 2.- 2nd gear, low rpm 2.5- 2nd gear, high rpm 3.- 3rd gear, low rpm 3.5- 3rd gear, high rpm. The question is, what is affected by the "pressure accumulator" above the transmission housing and what are the signs if it has lost pressure?
The purpose of the accumulator is to supply additional oil flow in the power train system in any case where the pump is supplying insufficient flow. To measure the nitrogen pre-charge pressure you will need a charging kit. See attached.