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KATOOM

NP241 DHD tailshaft bushing part number

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Does anyone know the part number for the NP241 DHD tailshaft bushing?  I've been to the parts stores and the dealer but neither could help.  I've seen a few versions online but I'm hoping to have the correct part delivered the first time.

 

The reason I'm doing this is because I've replaced the seal three times.  The last time I researched and researched and determined the correct one since all have slightly different shaft size ID which is weird but nonetheless...  So after installing the seal I thought was best the leak was gone for a long time.  Then...as usual, I took the 5th wheel out for a camping trip and once again the tailshaft started puking like a stuck pig, spewing fluid spray all over the underside of the truck.

 

I measured the slip yoke play and its very minimal, but must be enough to allow deflection of the seal under power with 14k behind me.

Thanks guys... :thumb1:

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Posted (edited)

Are you just talking about the rear seal where the yoke goes into the t-case? 

I can get the whole set up here for like 20$. I use these guys all the time, awesome people too! 

20190705_230904.jpg

Edited by Stanley

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Posted (edited)

No, not the output shaft seal.  I'm looking for the brass (or ? material) sleeve bushing located inside the rear portion of the tailshaft housing extension.  It should have rifling groves and be about 2" long and what the slip yoke rides on.

I've seen diagrams which identify it for the 231 but strangely there's no recognized part on a diagram for the 241.  And yes, I looked through the R&R article but unless I overlooked it, there was nothing about that bushing.

 

With the rear seal obviously not wanting to seal over time, replacing this bushing is my last option fixing this problem.

Edited by KATOOM

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If I remember correctly, I called the guys at quad4x4.com out of Montana and they had the bushing. Needed it when I rebuilt the t-case in my truck.

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If you are near a Six states they usually are very good about this type of thing.   Here they sometimes know the part # right off the top of their head and usually in stock.  At least that's how it happened with my '67 W200.  I would think this would be easier.

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Where are you getting your seals? I wonder if aftermarket is not quite right. I have replaced several also.

 

This is the current offering from NP/NV.

 

https://torqueking.com/product/10896/qu10896-np241dhd-rear-output-seal-1996-2002-dodge-transfer-cases/ 

 

It supersedes this one.

 

https://torqueking.com/product/50171/qu50171-rear-o-p-shaft-seal/

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@KATOOM I have been getting ready for this bushing replacement myself. I have been looking at the same bushing @NIsaacs listed. 

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Would love to know the outcome, I've been debating if I want to change that bushing for few years now. Mine is just a drip though. I got my bushing from local tranny guy, it was just wrapped in paper no box, he probably gets them in a case or something. No part number, what's posted above seems to be the right one. I suppose you checked the vent and it's not over filled. 

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2 hours ago, Dieselfuture said:

 I've been debating if I want to change that bushing for few years now. Mine is just a drip though.

You're not the only one :lmao:

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As much as I dont want to have to change the bushing, I'm also questioning if this will even fix the problem.  Here me out...

 

As I stated before, I changed the seal and it was leak free.  This has generally been the case except when I used a cheaper seal which I know was too loose of an ID surface.  That one leaked right away.

 

Any leaking always takes place during towing conditions and continues to do so until I replace the seal.  I've checked the clearance of the slip yoke movement and its very minimal.  I'll upload a video when I get to a better internet connection so you can see what I mean.

 

Knowing that a short bed truck will have more driveshaft movement due to the angle of the shaft, I'm wondering if the yoke is being shoved too far into the seal while towing and damaging it when there's weight on the truck. :think:

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24 minutes ago, KATOOM said:

I'm wondering if the yoke is being shoved too far into the seal while towing and damaging it when there's weight on the truck. :think:

Not a bad guess, may have to polish up that unused surface 

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Here's a short video I took of the tailshaft bushing movement.  I'm not claiming to be right but I've handled more than a few tailshafts checking for excess play and this one seems to be in great shape.  You can see that the slight amount of movement doesnt even cause the boot to move.

Tell me what you think... :thumb1:

 

 

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Posted (edited)
2 hours ago, KATOOM said:

 Tell me what you think... 

Gremlins, looks just fine. Mine is same that's why I haven't changed anything yet. I've sliped new bushing over yoke when I had drive shaft out to re balance, because I thought maybe it was out of balance causing the leak. Btw my leak started after I removed drive shaft to do rear pinion seal, I did not change transfer case seal at that time, it was not leaking then. About a week later after the rear pinion seal and new u joints and driveshaft rebalance it started to drip. So I changed the seal in tcase, still dripped. Then I went and bought a bushing and another seal at the same time I took the driveshaft back to have it rebalanced just to be sure, it was with in spec but the guy took weights off and rebalanced it anyway. Still dripping today. That's my story.

 

The only other thing I can think off, is when you slide drive shaft in, the lip of the seal may roll inwords we can't see it because of the protection boot. I had same thing happen on my Honda after changing timing belt I also changed all the seals, within a week I was dripping oil, took it all apart and started looking, at first glance looked fine because you can't really see oil seal behind dust seal. After I took it out it was obvious the lip rolled outward when I pushed it over crankshaft. So what I did is used pvc pipe same size 1/12 I believe, put seal on pvc then held it against crankshaft and slid it on, it had no way of rolling wrong. 

OK I'm done for now. :thankyou:

Edited by Dieselfuture
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If it didnt entail a lot of effort and money, I'd love to convert the TC tailshaft to a fixed yoke with a slip joint driveshaft.  I've never been a fan of these slip yoke tailshafts.

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Katoom,

 

One thought is could your TC vent be pinched or plugged?   (it should be on the firewall near the vacuum lines that go to the TC for the CAD to operate)   

 

Another thought,  I need to do some more research, but some cross sections of radial seals (seal designs) are limited to very small shaft to bore mis-alignment ( as low as 0.005")  and total dynamic runouts of as little as 0.003"    I agree  New Ventures engineers should not have used a design that needed to be that precise, but.....

 

If it is not the vent, and the surface of the yoke is good and not damaging the seal, and you are not dragging foreign materials into the seal to damage it, it has to be "runout" killing it.  I agree at any instant in time, it is not run-out, but loaded vs unloaded is forcing it to operate in different locations, so your shaft to bore misalignment is a constantly changing number, based on ride height and load being applied.  (this means while pulling the camper up the hill it operates in one position, coming down the hill it is operating in a totally different position. 

 

I truely believe that if you have ruled out the other items, it has to be the inability of the bushing to hold the yoke centered. 

 

HTH
 

Hag

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Posted (edited)

Haggar, thank you for the detailed response...

 

Yes the vent is clear and has always been as I've checked it before thinking it could be the culprit.  The runout as you described it makes perfect sense, and would be sad if thats how intolerant NP was with their design specs.

 

Let me throw this in the mix of my problem though...  Instead of doing anything right away, I washed the underside of the truck and took it for a 20 mile drive yesterday.  Strangely the seal is NOT leaking.  This tells me that:

1) I didnt drive far enough, but I cant imagine since it was leaking enough to leave spray droplets all over under the truck while towing.  Or 2) the fluid level is too low to push fluid up against the seal (cant imagine since its almost perfectly full). Or 3) there's something going on associated with towing and either the weight of the trailer changing the driveline position or the amount of load the driveline is placed under while towing that heavy.  Also noting that the driveline runs very smooth and has been balanced.

 

I've checked the driveshaft wear patterns and it doesnt seem that the rougher portion of the shaft is making it that far into the boot.  Also, to help reduce rough corrosion from collecting, I grease the back portion of the slip yoke.  Not sure how much it helps though.

Edited by KATOOM

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Katoom,

 

Dang it.  I was hoping vent really.  That would be easily explained with operating temps unloaded vs loaded.  so nix that one.

 

The NVs usually have a pump in the TC that spray oil to the tail shaft bushing.  (I only know this from the GM NV t/c's but I assume (and they refer to it in our FSM) they have the same on ours.)  So only if you are really low on fluid, would there not be oil circulating to the tailshaft bushing. 

 

So I think that circles us back to loading (or torque application) changing the position of the yoke in the tail housing. 

 

Since you are a short bed, are you running a 1 piece or 2 piece drive shaft?

 

GL

 

Hag

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How is the condition of the transmission mount? Could it be deteriorating and allowing too much flex causing the yoke to bind against the bushing and flex the seal?

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11 hours ago, Haggar said:

Since you are a short bed, are you running a 1 piece or 2 piece drive shaft?

 

One piece...and its straight and balanced.

 

8 hours ago, NIsaacs said:

During seal install, are you getting the weep hole in the down position?

 

https://torqueking.com/product/50171/qu50171-booted-rear-output-seal-for-98-02-np241dhd-transfer-cases/#note1

 

I've installed it both ways.  Didnt seem to matter...

 

6 hours ago, BBHD said:

How is the condition of the transmission mount? Could it be deteriorating and allowing too much flex causing the yoke to bind against the bushing and flex the seal?

 

Good thinking...but everything is tight.

 

Just for sake of knowing, this truck only has 125k on it.

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Katoom,

 

I figured it was a one piece.  You have a significantly larger wear area on the yoke from the seal than I do.  In a one piece shaft your tail shaft bearing plays a more significant role in yoke location (and more important the instant center during rotation). 

 

One also has to remember, due to the gear ratio (torque multiplication) the pinion would much rather rotate AROUND the ring gear than turn the ring gear.  Yes picture that.  un-restrained, the tires would sit still and the axle housing would spin around the ring gear.  Our rear suspension prevents the axle housing for doing this, but the forces that want to do this are still in the system and must resolve themselves. Some of this force is in the upward and downward movement of the nose of the rear axle. (upward during acceleration or carrying the load, downward under off throttle unloaded decel etc)

 

Now picture the side view of the rear axle, driveshaft and TC output.   Begin rotating the rear axle about the wheel center line.  What does the yoke do?  It has to move out of the TC.  Depending on how you imagined the relative relationship of the TC and pinion yoke (you should have imagined them in a parallel offset configuration) the yoke not only slid in and out, but it rotated up or down a little bit about its own physical center. (the yoke tries to move in only a lateral line, but there is an angular component that is unresolved.)  In your mind picture pulling a pin out of a tight hole.  The best way is to pull it straight.  If you pull it at an angle, what is the pin going to try to do, it will try and pivot in the hole to meet the direction of force and "drag" on a side.  This is how the tail shaft bushing wears out.

image.png.558fa9757fddc216ce7521fde51261c0.png

 

 

In a carrier bearing drive shaft (now it has a bunch of its other problems)  the tail shaft AND the output yoke have the same reference to the frame.   so  any movement of the yoke is closer to straight in and out.  The carrier bearing is what sees the brunt of the angular issues and reduces the wear on the tail shaft bushing. 

 

image.png.d7ab40ca4f1949ac18bf4e884b074b66.png

This picture doesn't show it, but there is a slip joint near the middle working angle on our 2 piece drive shafts.  So most of our torque thrust and angular issues are resolved there, leaving the tail shaft bearing to only support the weight and keep it in line.

 

The reason I brought this discussion up, is to explain why you would have a tail shaft bushing issue MANY moons before I should (and I have already replaced mine).  Your tail-shaft sees much more work than mine in exactly the same conditions.  The reason you don't have a vibrational issue that you can feel yet is the item you are displacing is the TC output shaft.  The output shaft's radius of gyration and associated mass in the system is extremely small.  (the drive shaft is the elephant in the room)  Since the drive shaft is well balanced, the fact that the instant center during thrust is different is not enough to disturb the rotational balance. 

 

If you need to, hook the go-pro to the frame and run some video of the pinion and then some of the TC output during the same loop on the road.  I have used that in the past to solve some vibration issues before.  Its kinda neat. 

 

I hope this made sense and helps....

 

Hag

 

 

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Posted (edited)

Again, lots of good info. :thumb1:

 

In years past I've set up drivelines on my trucks and I've preferred the stationary yoke instead of a slip yoke.  I also used a double cardan joint on a rear driveshaft to offer better u-joint angles on a lifted truck.

 

So I guess I can understand what you mean by the slip yoke absorbing more abuse than that of a two piece shaft.  I'm just getting bored of this since its leaked for years.  Maybe I should just try replacing the bushing and see if that does anything...  I'm guessing it wont but I have no other options at this point.

 

I talked to a tech from Quad 4x4 about allowable movement in the yoke and his response was "there should be no movement".  I said I've never seen one have no movement.  I had a hard time with his response since it would be very difficult to install a driveshaft inside a bushing with tolerances so tight that there would be zero movement.

Edited by KATOOM

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Katoom,

 

I agree, the "no movement" is a non-sequiter.   (no movement would be just that it wouldn't move.)  I have looked many times for true clearances for yoke and bushing for our application.  I have found it no where.  (even for the old power slide...  no one goes into enough detail to give the dimensions in 3 or 4 decimals.)

 

Here is a standard chart for plain bearing / shaft running clearances.

image.png.d48ba626a1b392e6281c1db6026ad258.png

Our application is dead on the 0.003" Diametral line.  a bit over 2" yoke diameter (i think its considered 2.2) and nearly 3000 rpm (ok a bit more in OD.  call total clearance 0.00325")   So it should be approximately 0.0015" clearance per side.  ( this chart may get modified later for thermals and other things, but this is a good starting point.)

 

So I can kind of see an answer of "no movement" by someone that is not into machine design.  A better non answer would have been almost none.

 

You presently have more than 0.0015" to 0.0020" per side clearance. 

 

HTH GL

Hag

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