NP241 DHD tailshaft bushing part number

[BBHD]

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?

[KATOOM]

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.

[Haggar]

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.

 

 

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. 

 

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

 

 

[KATOOM]

Again, lots of good info.

 

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 July 10, 2019 by KATOOM

[Haggar]

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.

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

[KATOOM]

7 hours ago, Haggar said:

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.

 

I totally agree...

And I too have tried looking up what the bushing clearance should be but strangely there's nothing.  How are people supposed to know whats "within spec"???

[Dieselfuture]

When it leaks it's out of spec 

[KATOOM]

20 minutes ago, Dieselfuture said:

When it leaks it's out of spec 

 

Genius...

[dripley]

3 hours ago, KATOOM said:

 

Genius...

@Dieselfuture's head is now to big to fit thru a normal door opening.

[Dieselfuture]

Ok I'm about to start crying. Took the tail housing off after I remembered the snap ring  got the bushing pressed out and decided to measure old and new before I installed it. Well new is .010 bigger I'd,  old bushing is better then new. Now I'm stuck with it till I find a right bushing, this one I got from local tranny guy that's been doing it for 40 years, hard to believe he'd make a mistake. Unless when it gets pressed in housing it shrinks. My bushing had some side wear and looks like tail housing bearing was spinning in the case. May need new case bushing seal and maybe yoke to make it right or I'm just going to slap it all back with new seal and call it a day, tired of it. 

@KATOOM did you ever figure it out.

 

top is where snap ring is split, you can see gold color on the right from torque I'm guessing. And you can see where bearing was spinning righ in front of snap ring is the polished area.

Drove new bushing in and it deformed because of drain hole and did get smaller in I'd, driveshaft fits tight now. Something is wrong, it shouldn't deform like this. But it is tight idk, stupid truck stuff.

[Dieselfuture]

Got it all back and took it for a drive, seems fine no leaks yet, time will tell I guess. That snap ring was fun getting back together, made a little jamming to keep it spread out, worked like a charm.  Need a drink after this, happy Saturday .

[dripley]

47 minutes ago, Dieselfuture said:

Got it all back and took it for a drive, seems fine no leaks yet, time will tell I guess. That snap ring was fun getting back together, made a little jamming to keep it spread out, worked like a charm.  Need a drink after this, happy Saturday .

Good to hear it all went well.

I am lawn mover mechanic this week end. Repainted and rebuilt the deck and now the steering for Sunday. The lawn mower is almost as old as the truck I hauled it home in.

[Dieselfuture]

I'm happy to announce that it's still dripping, going to order another bushing seal and gasket from torque king that @NIsaacs provided

ThI'm happy to announce that it's still dripping, going to order another bushing seal and gasket from torque king that @NIsaacs provided

Thinking it could be a driveshaft out of balance or yoke is bad, although it looks good.

[Dieselfuture]

I'm sorry @KATOOM I keep hijacking your thread. 

Drove the truck some more yesterday and didn't see any drips. Maybe first time I looked was just a residual fluid left from when I installed the drive shaft, I put a bunch on the shaft and the seal. Or maybe it's just empty now, hoping it won't leak for a while. At first I was a bit paranoid about bushing deforming like it did up on install, but the more I think about it, top and bottom were really not a point of contact for the driveshaft, as I could clearly see most of the wear was at 3 o'clock looking from the back of the transfer case. So if the rest of that bushing is still around maybe it will work just fine, I'll make sure to post an update 

[Royal Squire]

For sure it won’t leak if empty

[gerlbaum]

All I can say: I've done new yoke, new bushings (multiple), new u joints, and new carrier bushings. I've not been able to get my t case to never stop dripping out the rear. I have the tool to pull the bushing without removing the tail housing so it only takes a few minutes to replace the bushing.  I'd be happy to try anything. I have a new bushing and seal sitting on my shelf but I'm just not ready to try (and most likely) fail yet again lol.

[Dieselfuture]

3 hours ago, gerlbaum said:

All I can say: I've done new yoke, new bushings (multiple), new u joints, and new carrier bushings. I've not been able to get my t case to never stop dripping out the rear. I have the tool to pull the bushing without removing the tail housing so it only takes a few minutes to replace the bushing.  I'd be happy to try anything. I have a new bushing and seal sitting on my shelf but I'm just not ready to try (and most likely) fail yet again lol.

It looks like the seal got updated mentioned earlier in this post. If mine decides to leak again I might try it. What's weird is even my old seal when I slide it over the yoke it fits tight, not even sure how it can be leaking. Unless the rubber on it is too stiff and it doesn't give much.