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doctorcorey 
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Location: S. KC Missouri
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 Topic: Hd7G Trans Lube pressure
Posted: 21 Nov 2011 at 9:40am |
A couple of things here. On my machine, the "trans clutch" gauge reading drops down after some time running, requiring higher engine rpm to maintain pressure. This is, I gather, the trans lube circuit, providing cooling and lube for the trans gears and clutches? Can anyone here give me a heads up on isolating the cause of this problem. My first step will be to verify that the gauge is correct. I will be changing the pickup screen in the tranny and filter. My trans oil pressure (high pressure) is OK. When the "trans clutch' pressure drops, there is no noticable drop in tractor power or performance; that leads me to believe it to be a gauge or regulator problem, like debris in the trans selector valve or such. One more question: What is the accepted Safe method for extreme cold start such as ethyr? I will try to preheat with a torpedo type heater, but this is only so effective in the open air. 
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mdtractormechanic
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Joined: 26 May 2011
Location: MD
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Posted: 21 Nov 2011 at 11:33am |
Do you see the eng. or/trans. temp rise? How much of a pressure drop? What are the weather conditions?
I had costumers use torpedo heaters. They blow the heat in from the rear with a piece of plywood covering the lower front of the machine. Heard no complaints with that method for outside use. If you are near an electrical source use a block heater overnight.
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Joe's 1939 Model WC, 1940 Model RC, 1944 & 1950 Model C's, B-125 PU
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Mactractor
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Joined: 20 Jun 2011
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Posted: 21 Nov 2011 at 11:33am |
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Doc , your clutch pressure gauge is for just that - it shows the pressure holding the trans clutches engaged, not the lube pressure, but one pump does both circuits. The pump on my 11EP (almost same setup) is tired and pressure drops in both circuits when temp comes up, but you operate power shift tractors at high revs, so up there, pressure is ok for clutches. Dont want clutches to slip, it destoys the plates. If your lube pressure is not affected, your pump maybe ok and trans losing clutch pressure thru worn parts. Clean ATF 10W and filter may help. The electric glow element in inlet manifold is the preferable starting aid. Only use eather in desperation very sparingly unless an engine is near shot. Mac
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doctorcorey
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Posted: 21 Nov 2011 at 11:42am |
 mdtractormechanic wrote:
Do you see the eng. or/trans. temp rise? How much of a pressure drop? What are the weather conditions?
I had costumers use torpedo heaters. They blow the heat in from the rear with a piece of plywood covering the lower front of the machine. Heard no complaints with that method for outside use. If you are near an electrical source use a block heater overnight. |
No temp rise. It was upper 40's and colder the next day. I hadn't noticed the pressure drop last weekend when it was 70 outside. My fluid is still new but not the filter.
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doctorcorey
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Posted: 21 Nov 2011 at 11:47am |
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OK thanks. I'll use an external gauge to verify tractor gauge, then change the filters and blow out the screen. Is it possible to blow out the sump screen through the inlet hose by blowing compressed air through it? I'd like to avoid draining all that fluid. I have been using a tractor trans/hydraulic fluid but am adding atf as it leaks out.
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Mactractor
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Posted: 22 Nov 2011 at 12:24am |
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Better to drain your oil into clean cans to reuse it, then unbolt bottom plate from trans and get strainer out or clean it there with trans drained. HD7G and HD6EP (same converter, trans, and rear end) have trans and bevel gear/steer clutch housings all using one oil resevoir. With the oil shared by all these compartments, you have to take extra precautions to prevent steer clutch lining fragments accumulating in your trans oil. Dont let your steer clutch linings get to the fragmentation stage, and keep your oil, filters, and suction screens clean. Dont use oil any heavier than 10W. If you do, trans clutches can try to engage with the shifter in neutral. Some ATFs are now heavier than 10, and have caused the tractors to go off to work while the operator is at the door of his truck with a coffee in hand letting the tractor warm up! While your trans is drained, also clean your steer clutch pump suction screen thoroughly. Thats a crucial one that can cause havoc with your steering if not cleaned regularly. I will look up the book for clutch pressure specs Doc
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doctorcorey
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Posted: 22 Nov 2011 at 3:00pm |
Good advice I'll consider. It's a shame my 3 inch thick service manual makes no mention of the location and servicing of these critical screens. I don't even know what they look like. I envisioned some type of fan shaped device attached to the pump inlet hose inside the trans case. I assume it's some type of wire mesh strainer? Anyway I'll get to that this weekend. I'm making myself a makeshift shallow 'pit" in the clay to drive over and give myself a bit more wiggle room under there. I'll just drain the trans case and change/clean all the screens. Sounds like a heck of a mess! 
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Mactractor
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Posted: 23 Nov 2011 at 2:32am |
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Doc, book says 4 bolt flange bottom right side of case has the screen in it. Steering line tees off that line so shares that screen. Under right footplate, above driveshaft, oil collector in front of forward gear clutch shaft has 2 pipe thread stoppers on it. Plug a gauge into the lower one to test clutch pressure in low forward gear. the other port is for high forward. At about 1000 engine rpm with trans up to operating temp, pressure should be 140 - 150psi
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doctorcorey
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Posted: 23 Nov 2011 at 9:34am |
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Thanks. I'll get to that Friday. I've got a huge fuel injection test kit. Do you know what size fitting are the test ports? I had another thought last night whilst leafing through the service manual; last week, I adjusted the range shifter linkage to center it in the sector better. My tractor has a speed governor (disconnected) and a push start pump. I wonder if, while adjusting the shift linkage, if I may have somehow disturbed or engaged the governor or push start pump. Until last week, I didn't have any pressure problems. Another mystery! Well, again thanks for the heads-up.
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doctorcorey
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Posted: 27 Nov 2011 at 10:28am |
 Well, after laying in a stream of freezing water in a rainstorm, I changed my trans filter and checked the trans pump scavenge screen. Both looked clean and newer. I think it would take a pound of wood chips to clog that screen, it's so big! My trans readings on lube and main are just above the yellow, that is 120 on main and 5 lb on lube pressure. Now, if I engage the push start pump, pressures climb some into the greens, especially at a low idle. I didn't remove the main strainer as the weather made it impossible, it's a sob to reach. With the hose to pump disconnected, fluid pours out of the fitting. If p start pump uses same screen, then I wouldn't expect a pressure/flow rise by engaging it if the screen is clogged. Anyway, I'm changing to straight ATF versus the tractor hydraulic fluid: that could make some difference. What kind of dash gauge readings do you other 7G owners see? This is mid forties for temp, oil warm not hot. BTW, main pressure doesn't drop when put in any gear. Lube pressure will drop when in gear. Tractor pulls hard and runs great. I appreciate your advice as always. Next weekend I'll have better weather and can do some pinpoint pressure checks.
Edited by doctorcorey - 28 Nov 2011 at 11:45am
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