What’s wrong with my nv4500s?

[joshuak]

Greetings folks, have a couple trannies acting up, this is a thread about them. Hoping y’all post up if you’ve been down this path before or have helpful advice to offer.


Details on the first, reman from High Impact. Less than 500 miles on a 4bd1t/nv4500/208 combo, this in k30 with service body in back.

Drivetrain held in place at three locations. Driver and passenger side motor mounts, then one at the transmission crossmember. Motor mounts are liquid filled and oem at the crossmember.

Obviously not OEM installation, but the angles all jived and there was no driveline vibration or indication of not being happy before it broke. It broke going down a straight, flat section of rd. in 4th gear at about 50. Rhythmic knocking, I put in neutral, then rear seemed to lock up, then aimed for ditch. This in about 5 sec.

Pics…





Ujoint at transfer case broke too.



So first question, to further diagnose I was going to drop the tranny. Now I’m debating doing that or not. In place I can take the inspection cover off, rotate the output shaft, verify it goes into all gears, drain what little juice it has left and look for slivers or junk.

My reasoning is, I wouldn’t do anything different if I separated them. Thoughts?

Second, what would you do differently to increase drivetrain support? If you think it’s needed. I understand there is a cast iron upgrade to the tailshaft housing. But golly day, I’ve treated her very gently.

 

[Bent77]

Is that a rubber mount at the transmission?

Generally the rule is solid mounts are ok only at the engine, not trans
Additionally, that is compounded if the engine mounts have to much give, that stress will be witnessed at the transmission either directionally or through torsion

 

[joshuak]

Yes rubber, oem (Anchor brand) rear transmission mount for the 4500.

Generic pic.




What you say makes sense though and the motor mounts do have give, part of their attraction I guess.

 

[imiceman44]

Greetings folks, have a couple trannies acting up, this is a thread about them. Hoping y’all post up if you’ve been down this path before or have helpful advice to offer.


Details on the first, reman from High Impact. Less than 500 miles on a 4bd1t/nv4500/208 combo, this in k30 with service body in back.

Drivetrain held in place at three locations. Driver and passenger side motor mounts, then one at the transmission crossmember. Motor mounts are liquid filled and oem at the crossmember.

Obviously not OEM installation, but the angles all jived and there was no driveline vibration or indication of not being happy before it broke. It broke going down a straight, flat section of rd. in 4th gear at about 50. Rhythmic knocking, I put in neutral, then rear seemed to lock up, then aimed for ditch. This in about 5 sec.

Pics…

View attachment 449281

View attachment 449282

Ujoint at transfer case broke too.

View attachment 449284

So first question, to further diagnose I was going to drop the tranny. Now I’m debating doing that or not. In place I can take the inspection cover off, rotate the output shaft, verify it goes into all gears, drain what little juice it has left and look for slivers or junk.

My reasoning is, I wouldn’t do anything different if I separated them. Thoughts?

Second, what would you do differently to increase drivetrain support? If you think it’s needed. I understand there is a cast iron upgrade to the tailshaft housing. But golly day, I’ve treated her very gently.

I would say more likely that ujoint went out and took the transmission with it

Ujoint could easily be defective and didn't last.
That feeling and sound you heard just before it went is why I think that.
It happened to me and took out my tailshaft housing

 

[joshuak]

I want to think that’s what happened, because that would mean least amount of $.

So, replace tailshaft housing and u joint then reassemble, double/triple check driveline angles and run it?

Upgrade tailshaft housing or replace with similar as known weak link?

 

[imiceman44]

I want to think that’s what happened, because that would mean least amount of $.

So, replace tailshaft housing and u joint then reassemble, double/triple check driveline angles and run it?

Upgrade tailshaft housing or replace with similar as known weak link?

Well you need to inspect your Ujoint and see what happened.
There should be signs if it self destructed or it was destroyed from the outside like bent ears or something.
If it did self destruct, then just replace broken parts on the transmission and call it good

 

[Bent77]

Could also be that the engine trans combo was just trying to fall out of the truck. The two broken sections on the bottom of the trans may be a display of it trying to open up like an accordion

 

[Capt Ron]

Rhythmic knocking, I put in neutral, then rear seemed to lock up

I'm going with u-joint failure also, as soon as you "unloaded" and went into coast mode the transfer of power direction caused hair in the biscuits.

 

[imiceman44]

I'm going with u-joint failure also, as soon as you "unloaded" and went into coast mode the transfer of power direction caused hair in the biscuits.

Exactly.
That rhythmic knocking also happened on my brother's 73 k5, the front cv was binding and if it weren't for the cast iron np203 that would have happened too.
Instead we just pulled over then repaired the driveshaft and we were good.
There is something to be said about cast iron, not needed in normal duty but in catastrophic failure they come in handy.

 

[Fastereddie]

I don’t think the unjoint caused that. I find that hard to believe because the joint is back in the slip of the t-case which is also aluminum and also way behind the mount. Could have been a flawed casting. I guess the u joint could of gave the ghost and that pushed it over the edge. I would leave the trans in, and idle it in gear to check that the output shaft didn’t get bent during ejecto. Since you now need a new housing I would definitely get the aftermarket cast iron one. I’m a little worried about your engine mounts saying they are liquid filled. Those probably let that engine torque quite a bit and your trans mount may not.

 

[obijuank5]

I’m on the high quality engine mount and low quality trans mount train.
With a ujoint failure I’d expect the tail cone to have an injury.
I think this because of the circumferential cracking just before the isolator.

 

[1-ton]

This looks like the kind of thing that happens when you drive around in 4-wheel drive without a support bracket attached to the transfer case, in order to keep the transfer case in alignment with the transmission.

 

[joshuak]

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



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

 

[joshuak]

Could also be that the engine trans combo was just trying to fall out of the truck. The two broken sections on the bottom of the trans may be a display of it trying to open up like an accordion

I think I understand what your saying, but I’m not running any crazy adapters that would lengthen the combo to an excessive length, IMO. Add a support somewhere?

 

[joshuak]

… I would leave the trans in, and idle it in gear to check that the output shaft didn’t get bent during ejecto. Since you now need a new housing I would definitely get the aftermarket cast iron one. …

10-4.

I’m a little worried about your engine mounts saying they are liquid filled. Those probably let that engine torque quite a bit and your trans mount may not.

I hear you, they do flex a bit, OEM in the Chevy bread trucks that had 4bt.

If they suck, they suck though and I’ll replace.

I’m on the high quality engine mount and low quality trans mount train.
With a ujoint failure I’d expect the tail cone to have an injury.
I think this because of the circumferential cracking just before the isolator.

Low quality rubber isolator or cast aluminum (?) tailhousing? Or both lol?

If isolator, do you have a recommendation?

Tailhousing, cast iron got it.

 

[joshuak]

This looks like the kind of thing that happens when you drive around in 4-wheel drive without a support bracket attached to the transfer case, in order to keep the transfer case in alignment with the transmission.

Not the case here.

 

[obijuank5]

10-4.



I hear you, they do flex a bit, OEM in the Chevy bread trucks that had 4bt.

If they suck, they suck though and I’ll replace.




Low quality rubber isolator or cast aluminum (?) tailhousing? Or both lol?

If isolator, do you have a recommendation?

Tailhousing, cast iron got it.

Anchor brand is not known for its superior performance.
I’m not positive it would work but I think you can keep the soft 4b oe ones with a single pivot mount like on 2wds.




This would put all the flex on the mount stud and not the wider bolt spacing like it had.

What I think happened was the engine is flexing more up front and the twisting was happening at the thinnest point in the adapter instead of the isolator.

An iron housing would potentially just move the problem to the bellhousing.

 

[joshuak]

Anchor brand is not known for its superior performance.

Well fork .

My motor mounts are Anchor 2859 and I can attest to that, have already had to replace one. I was “hoping” that was a fluke. I honestly thought I was doing something with Anchor, lol.

I’m not positive it would work but I think you can keep the soft 4b oe ones with a single pivot mount like on 2wds.

View attachment 449316


This would put all the flex on the mount stud and not the wider bolt spacing like it had.

Thank you.

What I think happened was the engine is flexing more up front and the twisting was happening at the thinnest point in the adapter instead of the isolator.

An iron housing would potentially just move the problem to the bellhousing.

Not trying to send the problem upstream.

Do you think the issue would be mitigated with better quality liquid filled motor mounts? Or just quit already and do solid rubber.

Parker Lord has a somewhat similar option that would require less reworking of the motor mount brackets. Expensive but easier than starting over.

For giggles:

 

[ZooMad75]

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.

 

[Fastereddie]

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 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!