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TD20B Power shift transmission problem


tstokes

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I'm currently pushing trees with my bull grader. I installed gauges on the dash to watch clutch pressure, lub pressure and converter bypass pressure. The transmission has been overhauled with new clutches, all Orings, seals and bearings. The overhaul included the torque converter as well. I replaced all the springs in the valve body on all three spool valves that control the above pressures. The symptom, when operating the machine in neutral, all three pressures are normal ( 230 psi clutches, 20 psi lub and 85 psi converter bypass). After the machine operates for about two hours the converter bypass and lub drops to almost zero although clutch pressure stays well above 200 psi. If I shift it to neutral the pressures come back to normal. The charge pump is new. I did the work on the transmission because the machine burnt in a fire and damage the Trans and converter. When the pressure drops, I can not detect any change in performance of the machine. Considering that the lub pressure feeds all four clutch channels in neutral, I can not see where I have a clutch leak as listed in the troubleshooting section. Also, if a clutch channel was leaking, I would think the clutch pressure would drop in that gear or the transmission slip in that gear. I disconnected and plugged the hi-low transmission lockout because I thought the piston might be leaking. You guys gave me some outstanding ideas in the past and I'm back at the well of knowledge.

Thanks

Ted

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If I read this right, even though the pressure drops it has no effect on the proformance under full load?

Whats the transmission temp at?

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If converter pressure drops to zero, how is it the machine still moves and operates alright? I would think with zero oil pressure/flow into the converter, torque transfer and locomotion would stop.

What does the manual say? Does it say to check the converter and lube oil pressures in the manner you are? Those two pressures aren't normally monitored, it may be normal for them to drop outside of the specified pressures after warmup. Seems unlikely, but just trying to jog some "theories." ;) Are you tapping the pressures in the appropriate locations?

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I tapped into the test ports that were originally under the floor. The manual,does not say anything about pressure drop during testing although it does want the transmission at operating temperature. The transmission gauge shows between 130-140 degrees F. The temperature pickup is in the outlet from the converter. Also, if you do not watch the gauge you can not tell any difference in pushing performance. I have not been into the rear frame and was wondering if the pivot brake lub could be effecting the lub pressure. The lub pressure and converter bypass pressure effect each other during operation. The converter bypass pressure is not a measurement of the converter fill. The converter is filled directly from main pump pressure according to the hydraulic schematic. Another point, all the filters in the system are new to include the hoses. All lines were removed flushed and painted during the rebuild.

Thanks

Ted

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I'm currently pushing trees with my bull grader. I installed gauges on the dash to watch clutch pressure, lub pressure and converter bypass pressure. The transmission has been overhauled with new clutches, all Orings, seals and bearings. The overhaul included the torque converter as well. I replaced all the springs in the valve body on all three spool valves that control the above pressures. The symptom, when operating the machine in neutral, all three pressures are normal ( 230 psi clutches, 20 psi lub and 85 psi converter bypass). After the machine operates for about two hours the converter bypass and lub drops to almost zero although clutch pressure stays well above 200 psi. If I shift it to neutral the pressures come back to normal. The charge pump is new. I did the work on the transmission because the machine burnt in a fire and damage the Trans and converter. When the pressure drops, I can not detect any change in performance of the machine. Considering that the lub pressure feeds all four clutch channels in neutral, I can not see where I have a clutch leak as listed in the troubleshooting section. Also, if a clutch channel was leaking, I would think the clutch pressure would drop in that gear or the transmission slip in that gear. I disconnected and plugged the hi-low transmission lockout because I thought the piston might be leaking. You guys gave me some outstanding ideas in the past and I'm back at the well of knowledge.

Thanks

Ted

Check the suction filter (screen).
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I checked my manual, maybe the pressure valve?

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Ted,

It's been a long time but I'll try explain the transmission hyd system as I remember it.

IH called it a Cascade system. The pump picked up oil from the main frame through a suction filter, on to a pressure filter and to the pressure regulating valve. I don't think the pump sent any oil directly to the converter. The main pressure (clutch pressure) needed to be satisfied first then the spool opened and sent what's left to the converter spool and then to the lub spool. If the pump and internal leakage could not build enough back pressure to shift the main pressure spool then the down stream systems would not get what was needed. As I remember conv press went up and down with rpm but main only fell slightly at lower rpms

Your diagnosis sounds like the pump is not providing enough flow when the oil is hot to over come internal leakage and maintain main pressure, which at 230 sounds high to me but I am without reference material now.

If it were mine I would remove any extra shims, if there are any, in the main pressure spool, I think you need at least one, and drop the pressure to around 200 and see if the pump can keep up with demand, open the main spool and send more oil to conv and lub.

The only other place that main pressure goes as I recall is the steering boosters which were very trouble free as far as pressures.

IH used this same system in all the dozers, loaders, and some Hough loaders back then that were power shift.

Just some food for thought Ted. Won't cost anything to try it.

good luck

Dennis

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Farmalldr might be onto something. I have a 150 (based on the TD9B dozer) which may be a little different than a TD20B, but my manual says the clutch pressure should be between 170-190 psig. If the TD9B and TD20B trans design is similar as Farmalldr says (which would make sense), it could be the 230 psig you have dialed in on the regulated clutch pressure is too high, and this may result in the other downstream pressures getting skewed lower in the way he described.

If 230psig is well above what it should be, it may be causing excess leakage past the clutch pack seals, especially after the oil and seals get hot and more flexible. Excess leakage past the seals may consume more of the volumetric flow from the pump, making less available for the converter and lube system. The pump can only provide so much pressure and so much volume at the same time, even when it's brand new. When the shifter is in neutral, the volume required goes down to zero on the clutch pack side, which would agree with you seeing normal pressures on all three in neutral even after it's hot. But once it's put into gear the volumetric demands on the clutch side may be too much for it to also provide the appropriately regulated pressure and flow required for the other two. Although I still don't understand how the converter could keep transferring torque with zero pressure - and hence zero flow - as you describe.

I would do exactly as Farmalldr suggested and try lowering the clutch pressure to 190 or so. What does your manual say the clutch pressure should be? I would also think about adjusting the other two up (by adding shim(s)), but I would only do that after you see what happens to the other two in response to lowering clutch pressure first. It could be the whole thing gets sorted out simply after bringing clutch pressure into a lower range. You also mentioned that you replaced all the springs in the regulator; make sure they're not stiffer or weaker than the originals because that'll throw off your pressures just like adding or removing shims when they're not needed. Good luck...

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OK, ya made me go get my manual. To check pressures you were in the right 3 ports; first port toward the front of the tractor is main pressure, middle is convertor inlet pressure and back is lube. All are to be tested with full throttle and should be check in low and high forward, same in reverse and neutral.

Main 140-160 in all positions, 150-170 in neutral

Convertor 50-80 in all, 70-110 in neutral

Lube 20-30 in all

This is for a 20C with power shift, also have for gear drive.

Let me know after you follow above.

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My TD20B manual lists the pressures at 200-230 for Main, 60-90 for converter by-pass and 10-25 for lub. Those specs are from the troubleshooting section. I will try to add a picture of the hydraulic circuit to this post. It shows, 200-230, 50 and 10-25 psi in the diagram.

I removed the valve body previously because all the pressures would drop to zero after pushing it hard. I found all three valves were sticking open in the bores when hot. I have corrected that problem but still show the current problem of the drop on just the bypass and lub pressures. I can not tell any difference in performance of the machine. I do not think the valves are currently sticking because the pressures are normal in neutral even when hot. They only drop when placed in either forward or reverse gears.

All the springs in the valvebody are factory new as well as the charge pump. I rebuilt both steering boosters and the pressure for them comes from the pressure filter although controlled by the main regulator valve. I stand corrected, I miss read the hydraulic schematic and the converter is not fed directly from the main clutch pressure. When looking at the schematic, my pressure taps are on the valvebody not in the various areas as shown in the schematic (e.g. clutch pressure measured before the pressure filterin the schematic and I measure it at the valvebody as called out in the troubleshooting area of the manual).

I'll drop the main line down with removal of washer (I think there are only two in the valve body under the main regulator).

I slowed down working the transmission problem because I had to change the blade hydraulic pump. While pushing, the hydraulic pump for the blade split wide open from end to end. I have tested the pressure regulator on the blade pump and it is controlling the pump at 1000-1200 psi max and the pump is rated at 2250 psi continiously. The failure may have been caused by my round with the engine, remember the Sick DT429. It's is the same machine and the pump caught a lot of unregulated pressure. Also, I'm not sure of it's age. The pump is new and working fine.

thanks

Ted

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Ya your schematic is way different then mine so never mind my numbers. From what I see and you have said, only 2 places left to look, selector valve or hydraulic decelerator valve whatever that is.

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The Hydraulic deaccelerator has been removed and I capped the line going to the hi-lo shift lock on the transmission (same circuit). The deaccelerator would drop engine rpm if the transmission is shifted into neutral. I do plan on putting one back on the machine later. I wonder about the selector valve housing because pressure does not drop on the main line in any of the four gear positions although lub pressure feeds those channels in neutral and any gear position. I do plan on dropping the main line pressure to test the cascade from an earlier post. It maybe next week before I can test the hypothesis.

Thanks

Ted

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Hello Ted,

I remember your engine issues and sorry to hear about your hyd pump failure.

I wouldn't expect a problem in the transmission selector valve. You problably had it apart already during your rebuild. As you problably know there is just a brass wiper with an oring around it to line up with what ever port you move it to. When in neutral, main pressure is dead headed in the selector valve so the main pressure demand is not there hence your pressures come up to where they should be. If it was bypassing in the selector valve I would think lube press would be up because that is where it would bypass to. The selector valve has lube pressure in it at all times which feeds the clutch shafts.

When you installed the pump were both o rings installed around the housing? One fits in a groove in the converter housing and if missing could bypass pressure oil into the flywheel housing.

I am back to more internal leakage than what the pump can keep up with at the high end of the main pressure scale. Because everything is the same no matter which gear it is in I doubt it is an internal leakage problem unless the same problem is with both clutch shafts.

Your clutches will probably fry if run without lube pressure.

My memory is a little vague on this one but seems like in later years, 15C / 20C that they went to a larger volume pump like from 20gpm to 30gpm.

You'll have to research this to be sure. I know that the 25's and 30's had a larger pump, I believe 30gpm but their clutches and demand was a little more. I don't know if a TD25 or TD30 pump would fit a TD20B, I never tried it.

Good luck and keep us posted on progress

Dennis

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The engine decelerator is hydraulic? That's a new one on me. It's a little hard to read but isn't the selector fed with both lube and high pressure? My guess this is for safety so you can't shift hi/lo without being in neutral but a place I would still look since it's one of a very few places there is both pressures. Here's another idea; what's the date on your manual, I ask because a friend bought a new early model B and had all kinds of problems with the trans and after extensive work ended up re-plumbing something, I can't tell you what it was as the friend was a competitor and I didn't care, he has since died. This fix ended up being done on all early B's and if you have an original manual it may not have the updates, in the front it should have the year. I do believe the problem is flow and not pressure but this check takes a lot of hoses, fittings and a special gauge.

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  • 3 weeks later...

The pressure in all three circuits are to spec when I have the machine is under load. Currently, only when I let it idles in gear, the bypass and lub pressure fall to almost zero. The main clutch pressure remains constant either in gear or neutral regardless of engine rpm. I'm thinking the control valves maybe sticking in the valve body. I will check the age on my manual. It seems to fit my machine when working in other areas. My machine is in the 5000-6000 serial number range from looking at other areas of the machine, (my data plate melted in the fire).

I have slowed down on the transmission because since the last 20 operating hours, the engine oil pressure has dropped to 20 psi cold and 15 psi hot (idle or load rpm). The book shows nominal 44 psi and has been in the range of 50 to 60 psi since my engine nightmare. I'm going to pull the oil filters and cut them open to see if something is coming apart internally. I checked the pressure regulator when I fixed a small oil leak on the side of the engine.

Thanks

Ted

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On my machine the trans oil pressure gage will jump up to normal range at idle in neutral a few moments after starting. Once the machine is put into gear - but kept at idle - the pressure momentarily drops off and then builds back up to normal again. The gage on the dash only measures clutch pressure, so I can't tell what lube and converter pressure are. But I would think they're almost nil at idle when the machine is put into gear. The pump isn't spinning fast enough at idle to supply pressurized oil (regulated within normal ranges) to all three systems simultaneously - especially while in gear so that the clutch is siphoning off what little capacity it has at idle. Once the engine is accelerated to operating rpm, the pump is more able to provide full pressurized flow to all systems. So unless your manual says all three systems should have fully pressurized trans oil in all 3 systems at idle while it's in gear? I wouldn't think anything is wrong - especially if the machine otherwise runs strong at normal operating engine rpm.

Sorry to hear about the engine oil pressure loss. Hard to say what's going on, but I would also get another oil pressure gage and temporarily plug it in directly on the engine to ensure you don't have a bad gage and/or kinked oil line leading to the gage. I'd also listen closely for a rod that may have had its bolts come loose. If it's possible to remove the oil pan without pulling the motor, that would be the best bet and see if something has come loose since the rebuild (oil pump bolts, pickup tube, rod bolts etc). Good luck.

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Ted,

Sorry to hear about your engine pressure problems especially after what you have gone through with it already. Good luck with it.

Checking your filters and making sure your gauge is accurate are good places to start especially if this is something that came on quickly.

As far as your manual goes, I don't recall any significant changes in the 20B from start to finish especially in the running gear dept, so you are probably fine with what you have.

As I remember the trans/conv pressure specs were at a high rpm, your book may say that. I do remember the clutch press staying up and nearly the same no matter what rpm or neutral or in gear. However, I remember the converter bypass and lube going up and down with the throttle to a point.

But I can't remember if they dropped to nothing at idle.

If you decide to try another pressure reg valve I believe the 9B, 15B & C, 20B & C and 150 ,175 & 250 loaders were all the same. There are also some Hough loaders that used the same but the specs may have been a little different on them.

Your machine having been in a fire may be playing a part in your valve issues. Depend on how hot it got.

Good luck and keep us posted

Dennis

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I plan to pull the engine oil filters this weekend and also try a different gauge. Since my machine burnt in the fire, all my panel has new gauges, switches and wiring. All my lines to the panel are new steel lines. My machine got hot enough to melt the aluminum suction filter into a pile of ash. My icon is a picture of the machine since rebuild, it took four years (part time) to get it back into operation.

Has anyone seen the heat exchanger plug up and restrict engine oil flow? It looks like the oil circuit starts at the pump in the pan, then flows through the oil/water heat exchanger then around the back of the engine to the oil filters. It flows from the filter into the oil gallery to feed the moving parts. There are two pressure regulators, one at the pump and the other at the oil gallery. I have pulled the one in the gallery inlet and it is clean and functional.

Thanks

Ted

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Be very very careful here, there are tiny lube tubes that shoot oil onto the wrist pins, doesn't take much to plug, once that happens doesn't take long to stick the pin, this will ruin your day. (voice of experience) Mine was a little sliver of silicone.

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