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Wes (VA) 
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Location: Elkton, VA
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 Topic: 7GB wont go forward
Posted: 09 Aug 2021 at 1:09pm |
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Hi all, got my 7GB going that I bought back in the winter. Loader hydraulics work good, linkage is a little stiff, little PB or fluid film should help that. Anyway, wont go forward in either 1 or 2, pushing brakes in just about any combination, all it does is jerk for a split second like it tries to go. Reverse- no problem there. Steers fine that way too. Wondering if the shift body is like the 7000 series tractors with spool valves in there. I see where the linkage from the shifter ends up on the side of transmission. (The floor pans are gone) Read another post here where the seals in the trans clutch packs were shot causing a similar issue?
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DMiller
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Joined: 14 Sep 2009
Location: Hermann, Mo
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Posted: 09 Aug 2021 at 6:03pm |
Same trans and shift quadrant style assembly as the 7G series.
Rev is on one shaft, Forward the other, likely the accumulator seals on the end of the shaft are gone.
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Wes (VA)
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Posted: 10 Aug 2021 at 11:06am |
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Are they accessed somewhat easily? Or does this require removal of rhe transmission?
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Wes (VA)
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Posted: 10 Aug 2021 at 1:41pm |
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Pulled up parts book. I see the accumulator housings. Gonna dig in to see what I find.
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DMiller
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Posted: 10 Aug 2021 at 6:41pm |
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Best off to drag the box OUT. Sadly the Accumulator seals were least of my 7G trans issues. Find my posts on Fat Allis, are some p/ns in there that any Hydraulic shop can achieve. This is NOT for a amateur to attack but a decent mechanic with enough tooling can fix. Caution as remove the accumulator housings, are the shaft bearing retainers also and are shimmed for proper tension on the ball bearings.
Edited by DMiller - 10 Aug 2021 at 6:42pm
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Wes (VA)
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Posted: 13 Aug 2021 at 2:37pm |
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I cant seem to find a source for the seals 70624691. Tried calling minnpar a couple times, never got through.
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DMiller
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Posted: 13 Aug 2021 at 5:46pm |
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What I ended up doing is removing one seal in decent shape, took that and the clutch shaft to a hydraulics shop that rebuilds EVERYTHING, went into old Hercules Seal catalogs and bought by dimension which were Cylinder Shaft Wiper Seals. This is reasonably LOW pressure so would not be a issue. Next up the clutch pack Piston to Shell seal is completely Obsolete as a O-ring .260 o-ring, can get .250(too small no seal) and .265(Too LARGE cannot get into housings) NOT the .260. So went with a Teflon Seal and smaller diameter quad ring support ring to keep the seal against the bore, essentially a LARGE Piston to Cylinder seal as on Dump Trucks. Sent ALL the old paperwork with the new owner and have NADA for this as to reference other than remember Hercules Seal Company.
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Wes (VA)
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Posted: 14 Aug 2021 at 10:20am |
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That helps. Thanks! Sounds like the same deal on the pto clutch in a straight 7000 tractor, where sandy lake implement bores out the housing and puts in a new seal.
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DMiller
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Posted: 14 Aug 2021 at 11:30am |
Dragged out tax records and found the receipts for the seals.
the accumulator seals by dimension were 1 5/8" od, 1 3/8" id 3/16" thick, the item code is [U12-1.37-18D], Not certain if they used the Hercules number or not. These had a backup o-ring inside the V-seal lip of the seal that I removed for flexibility to get the shafts in.
The Piston Seals were 17-4053 and I do not remember whose p/n that was.
Bought from E&E Hydraulic Union MO, in 2017.
The seals have a pertinent position in the housings and have to seal Oil to the two ports, IIRC the Center of the three seals faced away from the install hole to port oil into the shaft. This is ONE of the two shafts The Upper, can see where the three seals ride at ported end:
This is a shaft disassembled to install the Piston seal
Will need a LOT of specialized snap ring pliers and a service manual to show how to get this far. The Teflon seal and reinforcing ring will install in that slotted rim at center of the shaft, will need THIN sheet aluminum and hose clamps to fashion a ring compressor to get the drum back on.
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DMiller
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Posted: 14 Aug 2021 at 11:34am |
The seals
My make shift ring compressor
compared to the .250 OE O-ring:
Edited by DMiller - 14 Aug 2021 at 11:45am
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DMiller
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Posted: 16 Aug 2021 at 5:25am |
Will explain how these transmissions actually function. The shift oil is passed thru the accumulator housing either thru the end of the shaft port or the side if the shaft port(Separate feeds) and applies oil to the side of the Shift Piston(Shaft, fixed piston) where the 'Tube' of the shift cylinder(Aluminum unit in the above photo) slides and compresses the clutch pack. ALL the oil to shift and keep the trans engaged is fed thru the accumulator ports. These are very simple yet complex in the values of hydraulic pressure required.
Leakage as in bypass flowing oil thru a bad seal will either stop trans shifts or in case the center accumulator seal fails, engages Both Hi and Lo gears same time and does not engage at all. Bypass flow at Piston seal will give soft and slipping shifts or just no engagement as oil flows from pressure side to exhaust side and does no work.
The bolt holes in the plate by the small seals are 1/2".
Edited by DMiller - 16 Aug 2021 at 5:28am
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Wes (VA)
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Posted: 19 Aug 2021 at 8:25am |
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Thanks again Dave! Very good information here. I didn't pull the transmission, but was able to get the accumulator housings off while still in the machine. I'm going to apply air to the ports in the transmission shafts to test for leakage in the clutch packs. So for forward motion oil is applied to the upper shaft in one port for low, then the second port for high? Opposite shaft for reverse?
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DMiller
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Posted: 20 Aug 2021 at 4:20am |
Correct, with trans drained if hear air passing inside the trans or if exhausts from the other port the trans will have to come out. There is only one place can leak from at that point, and that is at the piston.
If had not looked, the 'Space Saver Head' bolts that hold the trans in place are 1/2" 12 point head 1/2" uss thread, only way to remove most is by Hand Wrench and there are shorter ones for the tighter side boltings, get the side bolts out first then save the top (IIRC 5) for last.
Edited by DMiller - 20 Aug 2021 at 4:23am
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