Komatsu D155A-1 Dozer wont move

[chriskarnaze]

I have an old Komatsu D155A-1 dozer (serial 10508) that wont move when shifted into gear (forward or reverse) after it has been moving. It usually moves initially after sitting a while, but in order to get it to move after that, I have to bleed air out of the transmission filter compartment (tapered screw). It appears that a lot of air is getting in, and the transmission dip stick is bubbly. The drive shaft is spinning in sync with the engine speed. I appreciate any suggestion.

 

[Dave Neubert]

check your suction side of pump trace piping if it has a magnetic screen check seal on lid or pump seals are bad causing air to be sucked in. not familiar with this machine

 

[epirbalex]

I have an old Komatsu D155A-1 dozer (serial 10508) that wont move when shifted into gear (forward or reverse) after it has been moving. It usually moves initially after sitting a while, but in order to get it to move after that, I have to bleed air out of the transmission filter compartment (tapered screw). It appears that a lot of air is getting in, and the transmission dip stick is bubbly. The drive shaft is spinning in sync with the engine speed. I appreciate any suggestion.

Sounds like its sucking air , that tapered screw should be testing port . There is a screen on the bottom of the torque converter facing the transmission held on by 3 bolts slightly to the left side . Not an easy screen/filter to get at so is left when it should be serviced that may need attention . The transmission guard may have a trap door just for the job . Is there water in the oil ?

 

[chriskarnaze]

The filter below the torque converter is dirty, as you suspected! I'll clean it and order a new one. Are there other hidden filters impeading the circulation of trans oil that I should check? Does anything need to be pre-filled when replacing trans oil? I lost a few gallons in the torque converter. There doesn't appear to be water in the trans oil. Thanks for your help.

 

[epirbalex]

The filter below the torque converter is dirty, as you suspected! I'll clean it and order a new one. Are there other hidden filters impeading the circulation of trans oil that I should check? Does anything need to be pre-filled when replacing trans oil? I lost a few gallons in the torque converter. There doesn't appear to be water in the trans oil. Thanks for your help.

As far as I can see there are two filters side by side just below the floor plates , yours may have just the one . This must be where you bled the air out . And the screen you cleaned , that should not need replacing unless its damaged . I have not seen in the workshop manual or the service manual that filters for the transmission should be prefilled . I think you will have to go over all the lines and check the retaining bolts to see none are lose or the pipes are cracked thats letting in air . Because you have been able to get her to work it does not sound like the pump has failed .

 

[chriskarnaze]

I'm not having much success in finding where the problem is. It is difficult to find out where air is entering the system. On a recommendation, I've tried using shaving cream, but I'm not sure that it will leave a hole for the air passage and then maintain that hole. Someone recommended putting compressed air into the system when the machine is off so that it would easy to find leaks using soapy water. But I'm not sure about that approach, since it might hurt some seals in the pump or leak out of the oil spout or dip stick. Finding leaks where air is escaping a system (e.g swimming pool) is pretty easy, but what is the recommend approach to find leaks when air is entering a system?

 

[Dave Neubert]

The only place you can get air is the suction side check all hoses and clamps from the pick up tube in the trans to the trans pump/ a bad seal on the pump shaft can also do this. It is best to take everything off and go over it replace all suction hoses and inspect and reseal pump

 

[nicky 68a]

Once you’ve done all the above,it would do no harm to overfill the transmission by 5 to 10 gallons in a 155.
It’s obviously an old tractor that sits around a lot.All those seals are probably hardened and porous.
Your problem is only on the suction side,so just reseal it from the bottom up.Thats not really a bad job and costs pennies for seals.Clean all screens and overfill with oil.
Once completed,start machine on low idle and leave it half an hour before attempting to engage tranny.
Patience and overfilling with oil often keeps these big old tractors running

 

[nicky 68a]

The problem I find with these old,seldom used tractors is that operators don’t bother checking the tranny oil,fire them up,then go and feel for the gears straight away.This envariably trashes the pump in seconds.
When sitting for long periods,oil often weeps into the finals or out onto the floor unnoticed.This is the main problem.Overfill by 5 or 10 gallons before attempting to fire it up,then let it idle for half an hour (if it’s been sitting for weeks or months).
Under no circumstances should you try to engage tranny at this time.
If you do this in future,you could easily get away without replacing all the suction seals as they tend to hold the pressure once they’ve been working again.
I do wonder if you’ve trashed your pump though during your efforts to engage the transmission.
Hopefully not.

 

[chriskarnaze]

I took everything apart from the transmission to the transmission pump on the suction side, and replaced everything that wasn't in perfect condition including the pump seal. But nothing was in bad enough shape to cause the problem. Now I am going to take everything apart from the output of the pump back to the transmission. There is one more bit of information that is very odd - Bleeding air out of the transmission filter case the 1st time, causes the necessary pressure to rise within 1 minute; but it takes several minutes to gain pressure when bleeding air out of the transmission filter case the 2nd time.

 

[epirbalex]

Thats not a bleeding port , there should be 15-20 kg a cm @ low revs with oil temp 75 degrees C
20- 25 kg cm at high revs , same temp . 20 kg cm == 284 lb . As you look at the torque converter from the rear of the dozer there is another pressure port on the right half way up ,
full speed 3--5 kg cm
low revs 2 -3 and at stall between both high rev pressure and above lowest number . Pressure spec's are for 5501 and up .

There is no way in hell I'd remove the filter port with the dozer running .

 

[chriskarnaze]

There is a magnetic filter that services both the transmission and steering and is connected to the transmission case. The transmission pump sucks from that magnetic filter and pushes oil into the transmission screen/filter, out of it, and then into a box (don't have the manual hany for the name, but it deals with shifting). I have a pressure gage right before that box. If I don't bleed air (slowly) out of the transmission screen/filter case, the pressure on that gage remains 0. If I bleed air out of the transmission screen/filter case slowly, the pressure on that gage gets up to the point where shifting and dozer movement can occur. At that point I no longer bleed air, closing the test port. The pressure remains non zero for 30 seconds. After 30 seconds, I cannot move the dozer. If I try this experiment a second time, it takes several minutes to get the pressure up and the dozer to move. My problem is trying to figure out why the pressure drops to 0 after 30 seconds. There are several test ports I could bleed or put a pressure gage on, but what I have set up indicates a problem maintaining pressure. And since the suction side is now in perfect condition (and was in very good condition before), I guess I need to open up that box and whatever else comes after that.

 

[epirbalex]

There is a magnetic filter that services both the transmission and steering and is connected to the transmission case. The transmission pump sucks from that magnetic filter and pushes oil into the transmission screen/filter, out of it, and then into a box (don't have the manual hany for the name, but it deals with shifting). I have a pressure gage right before that box. If I don't bleed air (slowly) out of the transmission screen/filter case, the pressure on that gage remains 0. If I bleed air out of the transmission screen/filter case slowly, the pressure on that gage gets up to the point where shifting and dozer movement can occur. At that point I no longer bleed air, closing the test port. The pressure remains non zero for 30 seconds. After 30 seconds, I cannot move the dozer. If I try this experiment a second time, it takes several minutes to get the pressure up and the dozer to move. My problem is trying to figure out why the pressure drops to 0 after 30 seconds. There are several test ports I could bleed or put a pressure gage on, but what I have set up indicates a problem maintaining pressure. And since the suction side is now in perfect condition (and was in very good condition before), I guess I need to open up that box and whatever else comes after that.

There is one point of entry between the pump and steering case line , the return from the transmission lube relief valve . If all is well at the relief valve the problem could be the pump .

 

[chriskarnaze]

I un-bolted the hose going from the trans filter/screen to the box on top of the trans and ran for a minute. Oil was being pumped around 2 gallons a minute. I suspect there was still air in the lines. I bolted it back but un-bolted the hose coming out of the box. I ran for a minute and nothing came out of the box where the hose was un-bolted. I think this indicates a problem inside the box where pressure may either be getting lost or oil is just being dumped into the trans and bypassing the shifting. The box looks very intimidating.

 

[chriskarnaze]

But I'm not sure if this experiment is correct. I dont think i can really measure the pressure correctly from the pump going into the box. I sealed off the opening going into the box and the pressure didn't go much above about 5 psi. At that point the oil had nowhere to go, so i loosened the bolts to let some oil escape and the pressure didn't change much. I guess the problem could still be a weak pump even though it has a new seal and the gears look fine. Any ideas on how i could be certain about the condition of the pump?

 

[chriskarnaze]

Could my problem be with steering suction instead of transmission suction? (1) I power washed the dozer's belly, and now I cannot get it to move by applying my trick of bleeding air from the transmission screen compartment; mabye some gunk that was helping my cause got removed. (2) The steering screen compartment (next to the trans screen compartment) has a lot of air in it, and I cannot bleed it all out after several minutes. But if the steering system is putting a lot of air back into the transmission, wouldn't it rise to the top so that when the transmisison pump sucked, it would not get that air?

 

[epirbalex]

I un-bolted the hose going from the trans filter/screen to the box on top of the trans and ran for a minute. Oil was being pumped around 2 gallons a minute. I suspect there was still air in the lines. I bolted it back but un-bolted the hose coming out of the box. I ran for a minute and nothing came out of the box where the hose was un-bolted. I think this indicates a problem inside the box where pressure may either be getting lost or oil is just being dumped into the trans and bypassing the shifting. The box looks very intimidating.

Box is 900 KG's , the easy bits first would be the pump . Getting it checked to see if its up to spec must be a first step surely . If you do have to replace it , keep the old one . Mark it so you know it yours .

 

[chriskarnaze]

After taking almost everything apart in the transmission and steering, replacing a lot of o-rings, and waiting several months for back ordered parts (that didn't make a lot of difference), I am starting to think that the original advice of replacing the transmission pump ($3500) is correct. This is contrary to the advice given by the guy I hired to help me take things apart; He used a flow meter and said the pump was ok. Here are some related data points. I have only been using the dozer for about a week.

I over filled the transmission to see if there were any leaks that could account for air being sucked in. After 40 gallons of over fill, I stopped, and the dozer ran fine. However after about 45 minutes, the converter temperature started heading in the red zone. I drained 20 gallons, and the dozer could run for 2 hours without the converter temperature getting hot. 2 hours is about all I can handle in a single stretch, so I was fairly happy until yesterday, for the 1st time, I pointed the dozer with the rear end down hill. Right after that, the dozer wouldn't move. I bled the air out of the transmission filter test port (the oil was filled with a lot of air) and haven't pointed the dozer in that direction since.

So, it sounds like when the dozer's rear end is pointed downhill, the pump may have to do more work and can't handle it. But I want to make sure there isn't something else I can try before handing over $3500 for a new pump. I am still wondering how much oil I would have to add to get it to overflow and if that would show signs of leakage anywhere.

 

[Dave Neubert]

After all you have done I'm betting on the pump I think that maybe you over filling the trans that much also has caused the oil level in the torque to be high causing it to heat One more thing did you check flow when it was not operating correctly with air in the oil?

 

[chriskarnaze]

When it wouldn't move, the pressure after the transmission pump would drop to zero. Initially, without overfilling the oil, the air could easily be bled out of the transmission filter enclosure, and then the pressure after the transmission pump would hold for a few seconds before dropping to zero. After it dropped to zero, it would take a very long time to blead the air out again and get it to move. Over filling the oil solved both problems if the dozer was on level ground or pointing downhill. I'm not sure if that answers the question.