I have a D-6 H LGP with a powershift transmission. After operating for about 20 minutes, when the oil is warmed to operating temp the left side will not drive, I at first thought it was the Sterring clutch but when I engage the lever the track tightened. When I pull the left lever the right track drives fine and steers but when I pull the right lever the left side will not drive or steer. Are the left and right sides independently driven in the trans? there are four axles, Two inside and 2 outside. Filters where clean, screen was clear, oil looked clean and not burnt. No alarms or temp increases,Lube pressure was 305 psi.When I pulled the axles and started the machine and put it in gear, I looked inside the azle openings and the right side of the trans was turning but the left side was not. Is there a right and left side cltuch pack for this trans.? Could a piston seal be blown on the left side only? Before I pull this trans can anyone give me some suggestions or a test I can do to narrow the problem down. on what this might be. Thanks Billy:Banghead
Welcome to Heavy Equipment Forums wrench2556! :drinkup
Thank ya Thanx:drinkup
On each side you have a brake clutch and a steering clutch In order to get movement oilpressure has to be applied to both. It seems that when the oil gets tinner either the pressure to the steering clutch falls letting it slip or the brake clutch engages. there should be pressure taps for each of these clutches already installed on the steering and brake valve housing so it's easy to connect a gauge and see what's going on. With machine running, no levers touched and parking brake released it should have 335psi in the steering clutches and 410psi in the brake. I think you might have a problem with the steering clutch, it transfers enough power to tighten the track but can't drive the machine.
I agree with Mr. Ericksson. It sounds to me as tho the left steering brake is not getting enough oil pressure to release properly hot, whereas it does when cold. This has been a common problem with High-sprocket Cats for years. Two fixes; one is to check the oil pressures as he recommended, if left brake release oil pressure is low, first check the steering/brake linkage from control lever to control valve. This often comes loose, out of adjustment, or the ball joints wear out. Any repair has to make sure the dimensions are carefully adjusted as they are critical. Hmmm, the linkage bearings also have a tendency to stick with rust and dirt or dried out grease. If the steering and brake valve does not move the correct amount, the steering and brake won't work as they are supposed to, sometimes sticking open. The other involves getting inside the final drive to the steering clutch/brake module. If it comes to this, look for bad seals in the brake piston, also groves worn into the chamber, with sometimes a collection of debris on the bottom side. These parts have to be replaced if that situation is found, though they can be repaired by a machine shop. But that is usually not worth the trouble. Usually a set of seals and some new friction plates and steels are all that's required. But, if you are going to do one final, you should do the other as trouble with these critters usually runs in pairs. I suppose one could pull the steering/brake control valve and look at it after checking the linkage, and if you do the finals I'd recommend it. But these are simple and fairly hardy and I've never had much trouble with them. Good Luck!
D-6H LGP sterring or trans O.k. Guys,Thanx for the response I really appreciate it, I pulled the final drive and sterring clutches and brakes off. Went into the sterring clutches and inspected everything, Found nothing wrong, disc miked out good, plates were not discolored or warped, checked all bearings and seals, Piston seals looked a little worn but tested them with air and no leaks. resealed everything, and put together. Filled with oil started unit and let warm up. Started operating and after 20 minutes, same thing, Left side will not move, I swear I think it is in the transmission, Do the left and right axles drive independently and could the left drive side of the trans be losing pressure from oil by-passing around the seals in the trans. I checked the linkage and steering valve, Had to put one rod end on, everything working fine, Sterring cltuch pressures good. Like I said before, If you pull all the axles and look in the tubes, Put trans in gear at medium rpm, the gears on the right side are turning but the gears on the left side are not. Man I hate calling a dealer, All the old techs have retired and the new guys just want to change parts or send it to the shop and then you get a $4o,000 bill.:Banghead Billy
Maybe I got this backwards but... This is a 'newer' CAT to me so bear with me if I got this wrong... Aren't the steering clutch and brakes both spring applied and pressure released on these dozers? If so when driving ahead/brake released there should be pressure releasing the brakes but no pressure at the steering clutches? When steering the selected clutch pressure should rise to release the clutch and the brake pressure should drop to apply the brake? What are your pressures in neutral, parking brake off?
From the transmission you have transfer gears that bring the power up to the bevelgear that's bolted to a SOLID shaft that has 2 splines in it, one for the left axle and one for the right axle, not much that can go wrong there, all solid steel. What pressures did you have to the 2 left clutches? If the steering clutch gets the correct pressure and the brake clutch doesn't it will hold the inneraxle and thus the bevelgear aswell stopping the right side too so it has to be something funky with the steering clutch and since you picked it apart and found nothing abnormal oilpressure to it is the only thing left. Only the brake clutch is applied by springforce, steeringclutch is applied by oilpressure. Straight travel has full pressure to both clutches When steering you modulate pressure to the steering clutch with the steering valve to get different rate of turning. When doing a sharp turn it drops steering clutch pressure to zero and then relieves the brake oilpressure to zero holding the finaldrive stationary what's your serial?
The serial is a 6FC00609, I will get back to you on pressures, I have them wrote down at the shop, What really throws me off is, When I ran it today, It ran fine for 20 minutes, Then started losing power on the left track, I let it run in neutral for about 5 minutes and it worked fine again for about 10 minutes. I put a block under the drawbar and raised the tracks off the ground, Put trans in first gear and the right track turned but the left track wanted to but was very slow, When I pulled to engage just the clutches the track tightened up and when I released them the track got loose like it was working properly. I am very gratefull for all the input from everyone and will pull assembly back off again to see if there is a hairline crack in one of the pistons or housing, I am so glad cat made the high sprocket, At least it is not that hard of a job. As for the trans being solid steel from the bevel gear up, Why is only one spline turning if bevel drives them both? . I am going to pull axles in the morning and see if both inner splines in trans are turning when oil is cold. Thanks again for all the assistance, Hopefully I can help someone else one day with a problem, Billy:beatsme
You may have to run the machine with pressure gauges attached and watch them closely to see what happens as the oil warms up. Assuming that the bevel gear turns both right and left sides equally, than there is no problem in that area. The problem has to be in the left steering clutch, as the brake is spring applied and seems to be working fine. The problem really is most likely not in the clutch directly, but in the amount of oil that the clutch receives and uses. This would account for the fact that the clutch seems to operate fine for the twenty minutes or so you report, then slacks off. This can be caused by hot oil opening up a crack in a valve, maybe the piston or chamber, or thinner oil slipping past seals where cold oil will not. Using the gauges longer may help. Good Luck!
Good advice... Ideally you would have four gauges marked left clutch, left brake, right clutch, right brake with hose extensions long enough to hang them inside the cab during machine operation. Write down the pressures in neutral, during forward/reverse operation and note what happens to the pressures when you steer. When the problem manifests itself you will hopefully see a change in one of the gauges between left/right or brake/clutch.
D6-H sterring problem Thanx to all those who responded to my problem with the steering issue. I took pressure readings with it cold and never touched a lever, Pressures were equal at 285psi on L+R clutches. After 20 minutes the left side droped to 40 psi. I took the steering brake valve out and I found the bearings and pins and clip that holds the needle valve in place broke. I guess this is the pressure drop. Ordered parts tonight and will repair tommorow. Hope this solves the problem. Thanx again to everyone:notworthy Billy:drinkup
Glad we could help. This was a difficult problem to detect the cause of. Shows the value of using gauges to troubleshoot. Good job!