G wizz
Elite Veteran
Date registered: Apr 2006
Location: Uk
Vehicle(s): Dont own a G anymore, Too expensive!!!!
Posts: 686
| RE: Front Drivesharft removal
4x4abc - 6/22/2007 2:51 PM
Ian,
I raised that same question some time ago (thread about whether the first T-cases had an ol pump at all) whether the common knowledge (run in SA when front shaft removed) was indeed correct as I found as well that the oil pump was on the rear shaft. Nobody responded, so I let it die.
This is the bit im confused with. The pump must work directly from the input shaft from the gearbox. It has to be otherwise the pump would not be doing its job when the PTO was engaged, which is why they introduce it on the VG080. |
hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| Re: Front Drivesharft removal
dai - 6/22/2007 9:37 AM It may not be directly related to the pump, I think that when the front is run without a driveshaft and without SA selected, the oil is starved to some components because of the way oil is flung off gears and routed to critical areas. There are channels inside the T-case that flow oil where it needs to go. Whether it comes from the pump or tossed off of gears and rerouted, the bottom line is that more than one gearbox has been damaged by not running in 4WD with a front shaft removed. I have a lot of miles with my front shaft removed, driving in SA without a problem. Happy box. Nothing negative doing this. -Dai There are actually two "pumps" helping ot oil the bearings on the front input shaft of the transfer case. Oil is flung from teh gears and gathered in a little tray in the top of the box. From that tray oil flows into a passage above the tail end of the front output shaft in the area that's covered by the speedo drive. The rear cover of the transfer case in that area is machined in a way that the spinning front output shaft creates hydraulic pressure that's relieved through a hole leading to the rear output shaft. This machining of the rear cover is the first "pump" in the oil supply chain. This is the one that does not work properly unless the front output shaft is driven. The pump that one finds in the EPC and in the workshop manuals is the "second" pump. This one is fed by the first one. The second or main oil pump is in fact on the rear output shaft and is driven by that shaft spinning, so it's actually driven all the time, no matter which drving mode the shifter is in, or which output shafts are attached. I think this is where some confusion comes from. People who look into it a little deepr think, "Well there's the oil pump, it's on the rear output shaft, not the front, so I can disconnect the front without worry." But in fact, that pump can't function without the first one feeding it, and the first one is just some machined grooves and holes, so it doesn't show up on any parts list. The second pump takes that oil fed to it from the first pump and moves the oil up a hole in the center of the front input shaft. The bearing near the front end of the input shaft is the low range input gear bearing. That's the one that suffers when iol feed begins to falter. Since you don't drive in low range a lot, that bearing can be damaged by oil starvation when the front shaft is removed, but not show up until you later run in GA a while and try to load that damaged bearing. Or if the damage is bad enough it can break up just from un-loaded running since the gear and shaft are running at differnet speeds any time the box is in S or SA mode. There are lots of other threads to be searched here and on BWF with pictures, etc if anyone's interested in more info. -Dave G. |
hipine
Date registered: Jul 2006
Location: US, CO, Bailey
Vehicle(s): 460 1980 280GE w. 617A
| Re: Front Drivesharft removal
dai - 6/22/2007 4:43 PM Thanks Dave, excellent explaination. Some of those passages are pretty small and high quality gear oil like lightweight Super Shockproof or MT-90 will help keep the syncros happy and flow oil through those tiny places to keep the thing spinning. -Dai Totally agree. Mine gets the Superlight Shockproof, but other good synthetics work just as well I think. -Dave |
