Function of transfer case pump?

[JayArr]

Here's a question. I see a "pump" on both the transfer case drawings above. What's it for? I read a theory of operation from an older trailvoy site that said the electric motor drives the forks for the clutch and for the hi/lo selection.

What does the pump do?

 

[mrrsm]

This is for a different model (...but same family) of Transfer Case... but the "Pump" design problems, tear down, diagnosis and repairs of the problems are well described:

...and in THIS Model... The "Thin Gerotor Pump" broke at its Locking Tang and spun itself out of the Oil Pick Up Tube as it self-destructed the Pump.

 

[JayArr]

Thanks mrrsm but that's not what I was asking for. I'm not looking for problems with the pump, I'm looking for it's function - what does it do? Why is it there?

In the transmission a pump produces hydraulic pressure that is directed and regulated through the valve body to push pistons and engage clutches and run the TC. In the NP226 the clutch is actuated by an electric motor so why the need for a pump?

The two units in your videos don't match the Envoy and the function of the pump is not explained.

 

[mrrsm]

The closest thing I can find to bear out an explanation is this "Beefed Up" After-Market TC Pump R&R which shows the R&R and Dis-Assembly of the OEM Pump... including showing where the Screened Off Pick Up Tube collects the Transfer Case Fluid way down in the interior of the Case suctions Fluid up into the Pump using a Gerotor-Like Mechanism.

This Pump probably pressurizes enough fluid to pass through inside of the Hollow Drive Shaft and Lubricates not only the inner Needle Bearings and Planetary Gears needing Pin Support Bearing Lubrication... but also flows inside of the Clutch Plate Pack as well to prevent excessive friction while removing-flushing loose clutch plate debris and transferring any Heat into the Moving Fluid. This Dude sells an Improved Version of this Pump Cover:

The Wide Chain also distributes Case Oil throughout the exposed gears as it dips down into the Fluid and carries the stuff around, slinging it hither and yon under centrifugal force. Between these two modes... the "inner" areas remain lubricated enough to avoid "Dry-Pack Friction" and the Roller and Needle Race Bearings have the Gerotor Pump to keep them "Wet" at all times during the Power Take Off as the unit is driven by the Transmission and Engine Power:

Jimmy from the "1Road" YT Channel shows just How Much Debris and Dirt is collected into the Transfer Case and demonstrates the many reasons why regular fluid changes becomes so important with a Transfer Case being stressed by so many parts coming into friction contact while working in its various modes:

And Finally... Eric "O" from South Main Auto (SMA) gives One, Pretty Damned Good (almost elegant) Explanation of what happened when somebody either failed to clean the Two Case Halves sufficiently to remove the 'Old Silly-Cone" Gasket Material as he often calls "The Stuff" and he points out what happened when the Transfer Case Oil Pick Up Tube became so badly Glommed and Clogged Up with Black Silicone Sealant that Oil Starvation followed along... Leashed in Like a Hell Hound!

Follow Eric's gestures and motions indicating precisely WHERE that Gerotor Oil Pump is Directing the Oil Flow Under Pressure ...ALL the way out to the place in that Narrow Case Neck where the TC Drive Shaft Thrust Bearing lives (or in THIS "Case" DIES) for Lack of Having Proper Lubrication. So, hopefully these Videos will clear up any lingering mysteries about these Ubiquitous GM 4-Wheel Drive Units. :>) And... Also, Way Cool... No Clutch Packs in THIS Model...

 

[Mooseman]

Moved to its own thread as it was off-topic.

 

[mrrsm]

This is Important... For Owner's of 1998-2007 Vehicles with Transfer Cases:

One last "Thing Worth Mentioning..." is that for ALL Owners of AWD or 4WD Systems... The Mystery of "Where Did ALL the Transfer Case Blue Oil GO?" is solved upon any Post R&R tearing down such outer Magnesium Case Segments and locating the Rectangular Cavities in the spaces where the TC Oil Pump TANGS will assiduously POUND OUT PIN HOLES into those interior thin metal casting areas situated in at least three locations. Catastrophic Transfer Case Failure CAN be avoided by making a Very Close Inspection of those areas around the Outer Take Off Case where there are ANY signs of oil weeping out and collecting Dirt and Detritus... and NO leakage from around the Take Off Shaft Oil Seal.

You might ask, "How is this even possible...?" The answer is simple:

(1) Consider the active presence of Newton's Third Law of Motion at play here:

For Every ACTION...There is an Opposite and Equal Reaction.

(2) And Look at how MASSIVE the Chain Drive and Drive Cogs are that Capture and Transmit the Energy of Rotational Torque from the Engine and Transmission ... onto the Tiny Outer Gerotor Oil Pump Aluminum Housing Tangs.

(3) Then... Look at how Small and Thin the GM OEM Aluminum Outer Gerotor Free Floating Transfer Case Oil Pump Housing Tangs are that react and restrain the RECEIVING END of that Oppositional Reaction Force!

(4) As the Transfer Case activates under Acceleration as the Drive Power during 2L, 2H, 4L and 4H activities...they also RELAX during Deceleration.

(5) Thus, the Outer Transfer Case Gerotor Oil Pump Plate TANGS will move RAPIDLY Forwards and then Backwards within their Outer Case Cavity spaces of confinement SLAMMING against the Inner Corners of those Magnesium Casement cavities... Thousands of Times during Years of normal vehicle operations.

(6) Gradually... Pin Hole "wounds" will appear in multiple locations from these actions...and perhaps NOT so gradually... Gravity and Oil under "sling" and under pressure will ultimately Drain the Transfer Case Oil BONE DRY. If YOURS displays such damage, the Outer Casement will have to be replaced:

(7) So by ALL means... DO look for any Failed Driveshaft Seals on the Transfer Case Drive Shaft points... but also include a Further Inspection of the Outer Magnesium Case Housing spots adjacent the TC Gerotor Oil Pump Housing areas looking for signs of "Oil Weeping". When caught EARLY enough... There is a Repair Kit that can be installed to Prevent Further Damage to the Case:

Amazon.com

Amazon.com

 

[Mooseman]

Maybe helps with cooling?

 

[mrrsm]

A Magnesium Fire?

Uh-Oh Brother ... BIG Problems...

Magnesium has a Low Ignition Temperature of under 1,000 Degrees F
Magnesium is Highly Flammable & once it ignites, Burns at over 5,000 Degrees F
Magnesium can Burn WITHOUT ANY OXYGEN & uses Atmospheric Nitrogen instead.
Magnesium Fires must Burn Themselves Out or be Buried in Sand as they cannot be Extinguished.

Magnesium - Wikipedia

en.wikipedia.org

Flammability:

Magnesium is highly flammable, especially when powdered or shaved into thin strips, though it is difficult to ignite in mass or bulk. Flame temperatures of magnesium and magnesium alloys can reach 3,100 °C (5,610 °F),[19] although flame height above the burning metal is usually less than 300 mm (12 in).[20] Once ignited, such fires are difficult to extinguish, because combustion continues in nitrogen (forming magnesium nitride), carbon dioxide (forming magnesium oxide and carbon), and water (forming magnesium oxide and hydrogen, which also combusts due to heat in the presence of additional oxygen). This property was used in incendiary weapons during the firebombing of cities in World War II, where the only practical civil defense was to smother a burning flare under dry sand to exclude atmosphere from the combustion. Magnesium may also be used as an igniter for thermite, a mixture of aluminum and iron oxide powder that ignites only at a very high temperature.

You cannot Extinguish a Magnesium Fire using WATER (Observe @ 1:11 into the Video):

 

[Fred M.]

Here's a question. I see a "pump" on both the transfer case drawings above. What's it for? I read a theory of operation from an older trailvoy site that said the electric motor drives the forks for the clutch and for the hi/lo selection.

What does the pump do?

When the TC is placed in neutral, and towed, the pump supplies lubricant to the front bearings and Clutch Pack so they don't go dry. These areas normally get their lubrication from rotating parts driven by the Transmission.

 

[JayArr]

Thank You Fred!

That makes sense as soon as you hear it.

Mystery Solved.

 

[mrrsm]

That theory comes under much suspicion when you consider that since the Transfer Case Gerotor Fluid Pump is directly connected to the Large Drive Chain and thus, permanently powered by it... its Outer Pump Housing Flange persistently manages to pound out three distinct holes, right through the Magnesium Outer Housing over time.

This phenomena would never happen if the ONLY time that the TC Gerotor Fluid Pump was theoretically "at work" by getting engaged in Neutral and then only be applied during Towing. Ask yourself... Which is the more likely cause of such a condition to damage the case?

(1) Whenever the Transmission is deliberately being shifted into Neutral...and therefore under NO LOAD.... the Gerotor Oil Pump engages to lubricate.

or...
.
(2) The NV design of Transfer Case Gerotor Fluid Pump is NOT adjudicated by means of any special clutch feature and thus, it is always in constant motion and Pumping Fluid whether the Engine & Transmission Torque is being applied Full On during Hard Acceleration or to a lesser extent as soon as the Gas Pedal is let Off. The damage phenomena occurs to the case because of these innumerable events because the Load is either being Added or Relaxed whenever the Accelerator Pedal is either Applied or Let Off...but the Pump prevails pumping fluid, regardless of the Volume of the Fluid being moved..

The Two most prevalent causes of Catastrophic GM Transfer Case Failure BOTH involve the Failure of the Gerotor Fluid Pump:

(A) A Total Drainage or Loss of Transfer Case Fluid due to the Three Hole Damage to the Outer Magnesium Housing after being impacted by the Gerotor Fluid Pump Outer Plate.

(B) A Catastrophic Destruction of the Transfer Case Gerotor Fluid Pump where either the two halves are ruined with the base rotation around and tearing out the TC Fluid Pick Up Tube resulting in a Complete Loss of Gerotor Pump Fluid Pressure.

This is a supporting article (with photos) from, "Bob' IS The Oil Guy" showing the actual points on the case that become damaged for the nearly constant pounding from the Transfer Case Gerotor Fluid Pump:

GMC transfer case pump rub fix

Hopefully this will help someone avoid an expensive repair in the future. This problem affects the 1500, 2500, and 3500 series trucks but I'm not 100% certain which year models. In November I noticed my truck started to "thump" when I let off the brakes after coming to a stop and sometimes as...

bobistheoilguy.com

One last observation. All Gerotor Oil (Fluid) Pumps are made such that they will only function when a constant supply of oil is present. This is due to the requisite establishment of a Post-Prime Vacuum in order to draw fluid into the Dual Rotors of the Gerotor Oil Pump and allow the fluid to be constantly moved along either at a Greater or Lesser Volume.

If you require more evidence of this... please visit the images of my Gerotor Oil Pump Autopsy to see these requirements in more detail:

GM Atlas 4.2L LL8 Engine Gerotor Oil Pump

This Album shows Images of the Autopsy of a Late Model GM 4.2L LL8 Gerotor Oil Pump.

www.flickr.com

The NV Transfer Case Gerotor Oil Pump follows this identical design and like the "Blue" Viton "O" Ring is necessary to maintain a permanent suction from the Oil Pick Up Tube Screen in the base of the 4.2L Engine, likewise the TC Gerotor Fluid Pump uses a Special "O" Ring Seal around the Tube leading down to the Screened Rectangular Oil Pick Up Tube where it is buried in the bottom of the Case where hopefully, the Blue ACDelco TC Fluid resides in sufficient quantity and must do so in order to maintain a Solid Fluid Column from bottom to top. Breaking this up action with any intermediate mechanism might risk Catastrophic Air Cavitation if the TC Fluid Pump were to Lose its Fluid Prime.

In the case of the GM 4.2L Motor... from the moment the engine turns over, the Mechanical Gerotor Oil Pump instantly applies Oil Pressure. So too does the Gerotor Fluid Pump inside the NV Transfer Case whenever the Main Drive Chain is in motion. Neither one can afford NOT to be working at all times when anything is moving down there and any mechanical parts are in motion, regardless of whether the Engine Torque Loads are increased or decreased.

Please supply any additional source information that might improve our understanding.

Note: Casing manufacture nomenclature distinctions are:

NV = "New Venture"
NP = "New Process"

 

[JayArr]

OK, I pulled my paper service manual off the shelf to see if I could sort all this out.

First thing I see is that the pump pumps all the time, it's connected to the "output shaft rear" so anytime the rear driveshaft is spinning the pump is pumping. That includes but is not limited to towing.

From the diagrams the chain only moves when the clutch is engaged. The output-shaft-rear spins the clutch hub which spins the clutch pack. When the apply plate is engaged by the electric motor the clutch housing spins which makes the drive sprocket rotate which drives the chain. The chain is idle in 2WD.

The manual explains the pump as follows: "An oil pump, driven by the rear output shaft, pumps the fluid through the rear output shaft oil gallery to the clutch and bearings."

No other information in the manual, I'm guessing GM never intended their mechanics to rebuild these, they were an outsourced part to be replaced only. I'd be interested to see how the oil pump output is directed and exactly where but it would seem that it's needed all the time, not just in tow mode.

An interesting note: "The NVG 226 case halves are high-pressure die-cast aluminum..."
This is a 2005 authentic GM service manual.

I went back and looked at the other links in this thread and I notice they refer to Silverados and larger trucks. I also notice they list other transfer cases and not the NVG 126 or 226. The kits do not list our NVG 226 as an application either.

I think we may have been wrong to think that our TCs have the same problem as the other platforms. This magnesium pinhole thing may be a problem that happens on other GM 4WD platforms but not on the TB/Envoy/Rainer platform. We've got Aluminum castings baby!

 

[mrrsm]

Interesting... Good Follow Up...

However... This excerpt from another On Topic Article mentions:

Wear in Magnesium Transfer-Case Housings - Transmission Digest

One OEM supplier estimates that 2 million transfer-case housings have been made from magnesium1. In the aftermarket, these parts have been working their way into transmission shops at an ever-increasing rate. The questions I discuss here are why magnesium transfer-case housings wear so...

www.transmissiondigest.com

"Transfer cases with magnesium housings include but are not limited to the Ford/Borg Warner 4405 and 4411 and the 1999 and newer GM/New Venture 136, 149, 236, 246, 261 and 263 models. The type of magnesium alloy dealt with here is AZ91D, which is commonly used in these and other automotive applications. Wear in the Ford/BorgWarner (BW) typically causes engagement issues and rear-seal leaks; the GM/New Venture (NV) units show up with pinhole leaks in the housing and a loss of fluid. Magnesium transfer cases can be identified by the letters “Mg” inside a triangle cast on the outside of the housing."

That Mg "Ear Mark" would be a Good Thing To Know & Look For by anyone uncertain of... or perhaps unaware of the AL vs. Mg Case Controversy...and having Bone Dry Transfer Case Issues. :>)

 

[JayArr]

Good info, I'll check for that mg next time I'm under. It doesn't list our 126 or 226 so we may have dodged a bullet but you never know.

 

[TJBaker57]

From the diagrams the chain only moves when the clutch is engaged. The output-shaft-rear spins the clutch hub which spins the clutch pack. When the apply plate is engaged by the electric motor the clutch housing spins which makes the drive sprocket rotate which drives the chain. The chain is idle in 2WD.

Thought I would interject this.....

I have means of monitoring the front propshaft speed with Torque Pro or Car Scanner ELM OBD2 or equivalent. I have done a lot of monitoring this and related parameters and can say that even in 2WD the front propshaft is spinning quite a bit. More so when cold than when hot but even then we are talking like 700 something rpm when hot and a road speed of 65 mph, and in the neighborhood of 1200 rpm when cold at the same road speed.

I judge this to a combination of factors mostly the accumulated frictions of the TC clutch plates and components in the front differential as well as the splined axle disconnect.

 

[JayArr]

Maybe this is due to that 5% preload I've read about. I forget where but I read that the clutch is kept preloaded so the engagement isn't so sudden.

I wonder if you pulled the wires off the motor that engages the clutch and re-ran the test would the rotation stop?

 

[mrrsm]

I remember when I was making THIS Video that at around the 3:27 mark... I focused my Lens on the Rear 4.2L Crankshaft Seal Housing Plate... memorializing the TRIANGLE with the "AL" Manufacturing Mark Identifying that part as having been Cast from AL 380 Aluminum (..an Aluminum-Silicate Alloy),

This information is relevant HERE because if THIS Triangle with an "AL" Marking inside appears on the Outer Housing of anyone's Transfer Case... then it will be made of SAE 380 (AL) Aluminum (Periodic Table Id'd as AL) rather than (Mg) Magnesium (Periodic Table Id'd as Mg). Thus, this distinction makes any other "Pin Hole" Leakage issues, considerations or concerns about having a case made from Magnesium become... academic:



Source:

 

[mrrsm]

This Video is PERFECT as an "On Topic" indicator of what happens inside when the Outer Gerotor Fluid Pump manages to Bang Back and Forth and eventually "Punch its Way OUT" of the Magnesium Case and allow it to Darin DRY::