What’s wrong with my nv4500s?

[joshuak]

If no damage to the 208 slip extension housing I doubt the u-joint caused that. How could the entire t-case escape damage and then the 5th gear housing on the trans take the hit?

Even if let’s say the rear driveshaft was too long and it jammed into the back of the t-case as the suspension compressed. The damage would have been in the tail shaft and back half of the 208 before the 4500 would have got hurt.

I think there are some 4BT specific harmanonics or resonant frequency vibration that killed that 5th gear housing. Keep this in mind gm put a harmonic balancer type deal in the 5th gear housing on 4500’s used behind 6.5 diesels. And a 6.5 is inherently way smoother than a 4BT could be on its best day.

Thanks for the intel. This Isuzu isn’t as bad as the 4bt, but still rougher than the 6.5.

To me it stands to reason that I would use what I could to calm that down in addition to using the cast iron 5th gear housing.

I assume a solid rubber isolator mounted at an angle would help in this regard more so than a quality liquid filled one mounted flat, correct?

Sorry for asking to be spoon fed, just trying to avoid making the ass out of me part of assuming. Again.

 

[imiceman44]

U joint stayed in the slip yoke portion, looks to be in good shape.

View attachment 449299

Driveshaft side missing a cap and that ear shows signs of banging around.

View attachment 449300

View attachment 449301

View attachment 449298

That looks like one cap got damaged and it was banging around making the noise you described

 

[imiceman44]

If no damage to the 208 slip extension housing I doubt the u-joint caused that. How could the entire t-case escape damage and then the 5th gear housing on the trans take the hit?

Even if let’s say the rear driveshaft was too long and it jammed into the back of the t-case as the suspension compressed. The damage would have been in the tail shaft and back half of the 208 before the 4500 would have got hurt.

I think there are some 4BT specific harmanonics or resonant frequency vibration that killed that 5th gear housing. Keep this in mind gm put a harmonic balancer type deal in the 5th gear housing on 4500’s used behind 6.5 diesels. And a 6.5 is inherently way smoother than a 4BT could be on its best day. To me it stands to reason that I would use what I could to calm that down in addition to using the cast iron 5th gear housing.

I agree with that.
For some reason I forgot about the tcase in between.
But still the Ujoint self destroyed itself probably simultaneously.
It was banging for a while on that yoke

 

[joshuak]

That looks like one cap got damaged and it was banging around making the noise you described

Damaged or MIA, no snap ring, no cap. No sign of foul play either, possibly installed incorrectly (me).

 

[ZooMad75]

I agree 100% with that train of thought. Thinking about it, guy I know put one of those Cummins r2.8 things in his Jeep with a nv3550 and it vibrated the transmission apart. Twice!

I’m no engineer, but well versed enough in GM logic that if they used a vibration damper on diesel trucks they did it for a reason.

If my old school service engineer buddy I worked with was still alive he’d probably go down the rabbit hole explaining a first or second order vibration that is causing the issue.

This is a different animal than if the transmission was an automatic. The torque converter would have absorbed a lot of the vibration until it went into lockup. But since the manual trans has a hard connection transmitting the power the vibration/resonant frequency goes right on down the line.

Resonant frequency is the same concept that allows an opera singer sing the right note and shatter a wine glass. The sound waves happen to be at the right frequency for the glass and it starts vibrating in sync. Then it shatters.

Every item has a specific frequency they resonate at. The problem comes when something puts out the same frequency. Stuff goes wrong, usually in a big way. Buildings, bridges anything.

Different materials like aluminum or cast iron have different resonant frequencies which is one reason why a cast 5th gear housing is more likely to survive in this situation. But I bet if you look at 4500’s in dodge trucks behind 6bt 12 valve’s probably had the cast housing and some kind of dampener. I’m not a dodge guy so that’s purely a guess. Somebody fill me in.

 

[imiceman44]

Damaged or MIA, no snap ring, no cap. No sign of foul play either, possibly installed incorrectly (me).

If the Grove for the snap ring doesn't show damage then yeah you probably didn't get it in good enough.
That is usually not the first thing I assume when looking at trucks here so I didn't say

 

[imiceman44]

I’m no engineer, but well versed enough in GM logic that if they used a vibration damper on diesel trucks they did it for a reason.

If my old school service engineer buddy I worked with was still alive he’d probably go down the rabbit hole explaining a first or second order vibration that is causing the issue.

This is a different animal than if the transmission was an automatic. The torque converter would have absorbed a lot of the vibration until it went into lockup. But since the manual trans has a hard connection transmitting the power the vibration/resonant frequency goes right on down the line.

Resonant frequency is the same concept that allows an opera singer sing the right note and shatter a wine glass. The sound waves happen to be at the right frequency for the glass and it starts vibrating in sync. Then it shatters.

Every item has a specific frequency they resonate at. The problem comes when something puts out the same frequency. Stuff goes wrong, usually in a big way. Buildings, bridges anything.

Different materials like aluminum or cast iron have different resonant frequencies which is one reason why a cast 5th gear housing is more likely to survive in this situation. But I bet if you look at 4500’s in dodge trucks behind 6bt 12 valve’s probably had the cast housing and some kind of dampener. I’m not a dodge guy so that’s purely a guess. Somebody fill me in.

I remember my 2wd van with the 6.2 had a big damper on the tail housing not sure if that was the purpose.
My gasser didn't have any

 

[joshuak]

If the Grove for the snap ring doesn't show damage then yeah you probably didn't get it in good enough.
That is usually not the first thing I assume when looking at trucks here so I didn't say

I appreciate you reserving your judgement, but no worries a spade is a spade as far as I’m concerned. It is what it is.

 

[joshuak]

If no damage to the 208 slip extension housing I doubt the u-joint caused that. How could the entire t-case escape damage and then the 5th gear housing on the trans take the hit?

Just for conversation sake and obviously I’m a neophyte, but that gear housing especially where it snapped is a lot thinner than any part of the 208 including the tail shaft housing IMO.

Possibly the tail wagged the dog and this was the result?

 

[eodcoduto]

Lots of good info from various sources here, my guess would be the u-joint added with the motor mounts and transmission mounts being different materials. The harmonics didn’t have a common path to travel through and they found a way out.

 

[ZooMad75]

Just for conversation sake and obviously I’m a neophyte, but that gear housing especially where it snapped is a lot thinner than any part of the 208 including the tail shaft housing IMO.

Possibly the tail wagged the dog and this was the result?

I don't think it's any thinner than a 208 or 241. I've got a lot of miles on my 4500/241 combo without any issue at the 5th gear housing. Now if you hang a cast iron 205 or doubler off the back of a 4500, I'd invest in the cast iron housing.

 

[Fastereddie]

Just for conversation sake and obviously I’m a neophyte, but that gear housing especially where it snapped is a lot thinner than any part of the 208 including the tail shaft housing IMO.

Possibly the tail wagged the dog and this was the result?

Very possibly

 

[1-ton]

Not the case here.

The only description you have are the engine and transmission mounts holding everything in place. That is not enough to keep anything in alignment. My V3500 crew cab truck has stabilizing brackets at both motor mounts to inspection cover, and one that bolts from the side of my NP205 to the bell housing.

 

[KB6Chris]

I'm going with the u-joint failure scenario.

My theory is that the U joint began to seize up and started to induce a levering or cranking action into the transfer case. Using the transfer case essentially as a long lever to pry and eventually break the 5th gear housing forward of the transmission mount. True the tcase is also made out of aluminum, but the force exerted on it at the output slip may not have been enough to damage the output of the tcase. When you magnify the distance from the output of the tcase to the middle of the 5th gear housing there is quite a of pry on the transmission. The transmission mount essentially acted as the pivot point for all that force and the weak link ahead of it was the aluminum 5th gear housing.

This is all considering that the transmission itself and t-case were all in working order.

Another theory to consider is drivetrain mounting out of alignment. Looking at your first picture I notice the casting doesn't line up with the broken section appearing to be clocked from the forward section. Could the difference in the engine mounts and trans-mount have created an abnormal amount of torsional load on the components?

The "clocked" look may just be the weight of the case hanging off that side or just the way it laid after the break. One way to check this is with your engine bolted in see how your transmission sits on your trans mount. Is there a large gap on one side or is it sitting on it flat?

There are lots of possibilities and a lot of good ideas in here

 

[tarussell]

To add to this multi-CSI discussion my vote is that you had a combo perfect storm kind of a deal happening.
First culprit is the weird harmonics that happen with a brute 4-banger diesel ( worse than a 6BT ).
Second is the part/component victim is the well known weak O/D housing - the better cast iron version is much better but might still need some assistance in living behind a 4BT.
Third a good idea would be to add some T-case to bell housing area bracing that has an angle from one point to another for rigidity. The later square GM motor mount to converter inspection cover bracing and side brace were all to help save the bell area from forming cracks. You would be doing the same but just a little further down the line.

The harmonic balancer device used on other applications is a good idea but I would suggest getting one from a P-series “Bread truck” that came with a 4BT so that it is compatible with the shak’n and jiggl’n that goes with the dance that the 4BT grooves to.

My guess is that the u-joint was a victim of the harmonics and O/D housing breakage and not the cause of it ( if a retaining clip was not installed correctly that most likely aided in this event ) . It might have been the cause of the sound when it all let loose but it would have some serious markings on the trunion and yoke if it were to have locked up enough to jack the housing up like that and like said earlier would have most likely taken out the 208’s tail housing as well.

Something to consider is that there is a better retention method used on the Dodge diesel 5th gear now days ( aftermarket stuff ) because the harmonics on the 6BT was causing such havoc - just imagine what a 4BT will do…
The gas burner Dodges never had this issue and neither did GM stuff - apparently the 6.2/6.5 Detroits didn’t wiggle enough to cause this issue.

This is all just an opinion - could be wrong…

 

[joshuak]

...

This is all considering that the transmission itself and t-case were all in working order....

Have not checked output shaft runout as suggested by FasterEddie yet, but trans output spins fine, shifts into all gears and no weird debris or chunks on the bottom of the case. I took the side inspection cover off and cleaned as best I could. Transfer case shifts into the different ranges without weird noises when rotating by hand.

Another theory to consider is drivetrain mounting out of alignment. Looking at your first picture I notice the casting doesn't line up with the broken section appearing to be clocked from the forward section. Could the difference in the engine mounts and trans-mount have created an abnormal amount of torsional load on the components?

The "clocked" look may just be the weight of the case hanging off that side or just the way it laid after the break. One way to check this is with your engine bolted in see how your transmission sits on your trans mount. Is there a large gap on one side or is it sitting on it flat?

I'm thinking it's the weight of the transfer case pulling that way. For giggles, when the new 5th gear housing shows up I will do that.

There are lots of possibilities and a lot of good ideas in here

Really appreciative of everyone's input, there are some bright bulbs around here. Thanks for shinning some light.

 

[joshuak]

To add to this multi-CSI discussion my vote is that you had a combo perfect storm kind of a deal happening.

Agreed, thankful it hit when it did.

First culprit is the weird harmonics that happen with a brute 4-banger diesel ( worse than a 6BT ).

Hoping solid mounts keep the beast a little calmer, like this CFM frame motor mount bracket and isuzu isolator and block bracket?

Second is the part/component victim is the well known weak O/D housing - the better cast iron version is much better but might still need some assistance in living behind a 4BT.

10-4. It's incoming.

Third a good idea would be to add some T-case to bell housing area bracing that has an angle from one point to another for rigidity. The later square GM motor mount to converter inspection cover bracing and side brace were all to help save the bell area from forming cracks. You would be doing the same but just a little further down the line.

The harmonic balancer device used on other applications is a good idea but I would suggest getting one from a P-series “Bread truck” that came with a 4BT so that it is compatible with the shak’n and jiggl’n that goes with the dance that the 4BT grooves to.

This?

My guess is that the u-joint was a victim of the harmonics and O/D housing breakage and not the cause of it ( if a retaining clip was not installed correctly that most likely aided in this event ) . It might have been the cause of the sound when it all let loose but it would have some serious markings on the trunion and yoke if it were to have locked up enough to jack the housing up like that and like said earlier would have most likely taken out the 208’s tail housing as well.

Something to consider is that there is a better retention method used on the Dodge diesel 5th gear now days ( aftermarket stuff ) because the harmonics on the 6BT was causing such havoc - just imagine what a 4BT will do…
The gas burner Dodges never had this issue and neither did GM stuff - apparently the 6.2/6.5 Detroits didn’t wiggle enough to cause this issue.

Tranny has the 1 3/8" Dodge input shaft and gm output shaft, would hope they used the "upgraded" 5th gear nut during the rebuild. But I'll verify.

This is all just an opinion …

And thank you for sharing it.

 

[tarussell]

Agreed, thankful it hit when it did.



Hoping solid mounts keep the beast a little calmer, like this CFM frame motor mount bracket and isuzu isolator and block bracket?

View attachment 449447



10-4. It's incoming.



This?

View attachment 449450



Tranny has the 1 3/8" Dodge input shaft and gm output shaft, would hope they used the "upgraded" 5th gear nut during the rebuild. But I'll verify.



And thank you for sharing it.

Yep - that’s it !

 

[bp71k5]

I’ve got a gas version but my mounting setup is similar, though I have urethane motor mounts and have two smaller donut mounts on the aluminum tail housing, a 205 and magnum box, No other torque rods or braces. But my mount points are on the magnum box instead of the tailhousing.



Those specific style motor mounts have given me trouble on other vehicles and so if those go, or move more than expected because it’s a diesel that might be where I’d place a bet. I’d also maybe find a mount for the trans that would for sure flex more just for insurance.

 

[joshuak]

For giggles (lbs)…