Freshly rebuilt 4l60e granaded.

[Hipster]

The shop claimed that while my crankshaft tolerance was loose, it was still within spec. I'm guessing they didn't shim it correctly each time because they tell me the tc slammed back into the oil pump and destroy it...? I'll post pics today.

You don't say?......after the fact. You want realistic answers, the best way to get them is posting relevant info. You can't shim for a failed/worn thrust bearing. Shimming would bury the TC into the pump even further.

 

[joesenior79]

You don't say?......after the fact. You want realistic answers, the best way to get them is posting relevant info. You can't shim for a failed/worn thrust bearing. Shimming would bury the TC into the pump even further.

It was definitely shimmed. I don't remember the thickness of each washer, (I'll go out and measure them shortly) but there were three gold washers on each pad so in total 9 washers.

 

[Hipster]

It was definitely shimmed. I don't remember the thickness of each washer, (I'll go out and measure them shortly) but there were three gold washers on each pad so in total 9 washers.

well if they shimmed while the crank was forward, then moved, guess you know what happened and It doesn't lead back to the engine not needing to be addressed or looked at. They already brought forth there's movement at the end of being within spec.

 

[joesenior79]

Not uncommon for either a bad thrust bearing to take out a trans or for a grenaded trans to take out a thrust bearing. You may have found the problem and grenaded trans is just a symptom. 3rd trans. the problem likely elsewhere, like thrust bearing issues letting the converter walk fore and aft and binding trans internals. Fix the crank end play in engine. You're not wearing transmissions out, you're breaking hard parts. if you got a crash /bang shift kit, get rid of it.

This would explain the tc slamming into the pump causing failure. However, from what I can tell, the internals of the transmission are fine. How would the thrust bearing clearance cause the tail end of the housing to explode?

 

[Road Trip]

The shop claimed that while my crankshaft tolerance was loose, it was still within spec. I'm guessing they didn't shim it correctly each time because they tell me the tc slammed back into the oil pump and destroy it...? I'll post pics today.

Let's say for the moment that we're troubleshooting the possibility that the crankshaft
is moving back & forth longitudinally enough to turn the torque converter into a
battering ram on the internals of the tranny?
IF the engine is healthy, then the normal spec is only .005"-.007" of an inch. (!)
This can be easily checked either at the flexplate or the harmonic balancer.
(It ain't much.)

You must be registered for see images attach

Supposedly this has been checked and 'shimmed for' at
least once...but the same failure has re-occurred?

In order to cover all the possibilities, I'd like to put the excess crank play
aside, and instead go towards the other side of the transfer case
for a moment:

Pics as promised:

I'm no professional but from what I can see there is no other damage to the transfer case or driveline.

I just took a careful look at your photos, and according to photos #3 & #4 the witness marks are on the transfer case side?
What are the chances that on the other side of the transfer case that the front and/or rear driveshafts are injecting some
kind of excessive (unexpected) torsional stress from u-joint driveshaft angles and or hammering from a too long driveshaft?

The tahoe is lifted 6". However, it was done before the tranny rebuild. Yes, the same shop did all the work the three times it had to be taken in. They did the removal, rebuild, and install all three times. There is nothing wrong with the transfer case that I can see... which is strange to me.

1) I've never run a 6" lift before. I'm assuming that the driveshaft lengths must be modified in order to bridge the additional distance
between transfer case outputs and differential inputs? If so, did they get these new lengths right? (I'd expect that if there was
some sort of hammering action going on during full suspension compression that there would be interference (witness) marks
at the transfer case?

2) IF the driveshaft lengths are correct for the lift, then how about the u-joint angles? Was the truck vibrating at certain speeds
and/or with different throttle inputs? I know it's standard practice to angle the pinion angle up once a truck is lifted a certain
amount, but if by doing so the front u-joint and the rear u-joint aren't both working at the same angles then you
can aggravate the twice per revolution speedup/slowdown of the driveshaft. If it's bad enough, it's putting a torsional 'ripple'
reaction through the entire system, and it's conceivable that all this stress is concentrating at the weakest link in the chain & causing
the failure you are experiencing? (Here's a 4-minute video demonstrating what I'm trying to describe: (LINK)

****

To summarize, IF the crankshaft <> torque converter interface is wrong then absolutely you will destroy parts.

But if that scenario is checked for & no problem found, then we need to go to the other end & make sure that
everything having to do with the 6" lift/driveshafts were set up as good as the original no-lift (stock) setup was.

For what it's worth. Since I can't lay hands on this directly I'm reduced to wondering aloud. And even if I'm proven
wrong at this side of the mechanical equation, no problem at all -- careful checking is free, and I'm just trying to
cover all the possibilities.

Good luck!

 

[Road Trip]

This would explain the tc slamming into the pump causing failure. However, from what I can tell, the internals of the transmission are fine. How would the thrust bearing clearance cause the tail end of the housing to explode?

Exactly! You posted this while I was composing the previous...

 

[NickTransmissions]

Let's say for the moment that we're troubleshooting the possibility that the crankshaft
is moving back & forth longitudinally enough to turn the torque converter into a
battering ram on the internals of the tranny?
IF the engine is healthy, then the normal spec is only .005"-.007" of an inch. (!)
This can be easily checked either at the flex plate or the harmonic balancer.
(It ain't much.)...

Supposedly this has been checked and 'shimmed for' at
least once...but the same failure has re-occurred?

Nice post, @Road Trip. I'm inclined to agree - this doesn't seem like a problem sourced within/from the engine. I occasionally hear of the transmission actually taking out the main thrust bearing due to converter ballooning in HP applications, usually with TH400s, 4L80Es that run stupid-high pressure pump PR springs and fail to restrict the converter charge orifice in the pump cover and vise versa where the converter/flex plate is not shimmed correctly (shimming is rare to begin with as most applications will have the standard 1/8-3/16 clearance unless somethings wrong like converter not fully engaged w/pump upon marrying engine and trans). Of course I could be wrong (sure as hell wouldn't be the first time, lol). Perhaps an out-of-balance condition due to super worn main bearings could create harmonics that race through the transmission and locate the weakest part of the case, which is that junction between it and the TC adaptor.

I would figure the pump bodies in @joesenior79's transmissions both some scoring, gouging or excessive wear from shimming related errors but don't see how that alone would cause the rear of the case to completely fracture and come apart like that. I see those pumps come apart for numerous reasons like cracked flex plates, TC failures, excessive RPM and plain old 'over-maintenance'. But I have only seen a few 700R4 and 4L60E cases come in cracked at the rear like that. If memory serves, three (3) cases out of over 800+ 4L60Es I've rebuilt in the past 10 years, all early model 4L60Es (93-97) and one was driveline related (can't recall the reasons behind the other two). None of those transmissions came back after their rebuild.

@Hipster mentioned the transmission mount being a possible suspect and I know for a fact worn transmission mounts will actually damage internals including the rear gear train, if it's worn badly enough.. That could be as it's in the right area. Maybe a combo of extremely worn / out of balance engine and worn or different mount (totally spit-balling here).

I feel bad for Joesenior79, sucks this keeps happening but at the same time, hope that he keeps the thread updated and lets us know what he determines the cause(s) to be.

 

[Road Trip]

@joesenior79 ,

I've searched the interwebs a bit more, and here are some trends
that make a cracked 4L60 housing occur more often than average:

* 4WD (has transfer case)
* Bent driveshaft and/or bad u-joints
* Trucks with lifted suspensions (majority but not always)
* Short wheelbase versions of the GMT400s

For example, here's a thread from 2021 in this forum titled "4l60e cracked case for 3rd time":

Hey everybody, I'm in a 1997 GMC Sierra K1500 single cab short box. Within the last 30,000 miles, I have gone through three transmissions. All of these have cracked between the pan and the transfer case adapter. I'm looking for any insight on what is causing this issue. The crack is located in the same place each time. The truck has had the motor mounts replaced and the transmission mount, along with the u joints, are also new. The transfer case has been looked at. The truck has no lift and the torsion bars are adjusted slightly up. They are nowhere near maxed out. Thanks in advance.

well after all this time it was a bent driveshaft. does anybody recommend this driveshaft? or would i be better at getting one made? https://www.summitracing.com/parts/rnb-946-781

Here's another vehicle being discussed in a different forum:

You must be registered for see images attach

(credit: Follow this link.)


Saying this another way, I was unable to find 4L60-E case failure in a 2WD truck. (!) And the short wheelbase
4WD occurred more often than the longer wheelbase K-series trucks. And trucks with suspension lift kits seemed
to be in the mix the majority of the time?

And interestingly, all the failures I was able to locate had the failure in the 4L60-E case and NOT the transfer
case that's in the middle of all this?

The bottom line is that your lifted, short wheel base, 4WD Tahoe ticks 3 out of the 4 boxes that describe
the majority of reported 4L60 case failures. The only box we have yet to tick is the driveshafts...so again,
please really make sure that not only are the U-joints new, but all the other driveshaft parameters are also
in perfect condition. And if you are still running the original (stock) driveshaft with the lifted suspension,
verify that the length is correct, for some threads discussed the fact that a too-short driveshaft can cause
the yoke to pull out far enough that it would momentarily bind at a slight angle instead of sliding, especially
under torque, putting deflecting pressure on the transfer case...which gets coupled through the transfer case
and blammo. (Or, instead of a single catastrophic deflection, smaller deflections work-harden the aluminum
and eventually leads to cracks/connection failure at the same spot.)

Of course there's a fix/upgrade for everything. In this case, a SYE (Slip Yoke Eliminator) is one.

Hope you find this helpful. From here it looks like you need to unstack the variables that, when
lined up exactly wrong, put excess stress in this specific area of the drivetrain.

Good luck. Let us know what you find!

PS - When these case failures occurred, can you remember anything in common? Sudden acceleration?
Or possibly sudden braking? Minor Dukes of Hazzard maneuver over a set of train tracks? Of just driving
gently (like the po-po is following) and it still popped? Anything you can remember occurring at the
moment of failure might help us further narrow down where the root cause lies...

 

[Hipster]

@joesenior79 ,

I've searched the interwebs a bit more, and here are some trends
that make a cracked 4L60 housing occur more often than average:

* 4WD (has transfer case)
* Bent driveshaft and/or bad u-joints
* Trucks with lifted suspensions (majority but not always)
* Short wheelbase versions of the GMT400s

For example, here's a thread from 2021 in this forum titled "4l60e cracked case for 3rd time":





Here's another vehicle being discussed in a different forum:

You must be registered for see images attach

(credit: Follow this link.)


Saying this another way, I was unable to find 4L60-E case failure in a 2WD truck. (!) And the short wheelbase
4WD occurred more often than the longer wheelbase K-series trucks. And trucks with suspension lift kits seemed
to be in the mix the majority of the time?

And interestingly, all the failures I was able to locate had the failure in the 4L60-E case and NOT the transfer
case that's in the middle of all this?

The bottom line is that your lifted, short wheel base, 4WD Tahoe ticks 3 out of the 4 boxes that describe
the majority of reported 4L60 case failures. The only box we have yet to tick is the driveshafts...so again,
please really make sure that not only are the U-joints new, but all the other driveshaft parameters are also
in perfect condition. And if you are still running the original (stock) driveshaft with the lifted suspension,
verify that the length is correct, for some threads discussed the fact that a too-short driveshaft can cause
the yoke to pull out far enough that it would momentarily bind at a slight angle instead of sliding, especially
under torque, putting deflecting pressure on the transfer case...which gets coupled into the transmission adapter
and blammo. (Or, instead of a single catastrophic deflection, smaller deflections work-harden the aluminum
and eventually leads to cracks/connection failure.)

Of course there's a fix/upgrade for everything. In this case, a SYE (Slip Yoke Eliminator) is one.

Hope you find this helpful. From here it looks like you need to unstack the variables that, when
lined up exactly wrong, put excess stress in this specific area of the drivetrain.

Good luck. Let us know what you find!

PS - When these case failures occurred, can you remember anything in common? Sudden acceleration?
Or possibly sudden braking? Minor Dukes of Hazzard maneuver over a set of train tracks? Of just driving
gently (like the po-po is following) and it still popped? Anything you can remember occurring at the
moment of failure might help us further narrow down where the root cause lies...

Was going to something along the line of looking at everything down to use or abuse, but you covered it. I've had a couple short beds and both driveshafts seemed to could have used another inch at stock ride height. The transfer case/yoke bushings were/are a bit sloppy allowing a bit of excess movement in both trucks. Never technically measured either truck for a shaft but 4 inch kits have been known to cause vibration issues in some short wheelbase trucks. I think he said He's @ 6. SYE might be the ticket or maybe CV driveshaft of proper length. I would still want to verify the crank end play number if the info came from the trans guys with no number.

 

[Hipster]

This would explain the tc slamming into the pump causing failure. However, from what I can tell, the internals of the transmission are fine. How would the thrust bearing clearance cause the tail end of the housing to explode?

The front and rear shafts in a trans are set up at a specific endplay number. Off hand I don't remember what that clearance is. You don't want the front shaft beating the back or vice-versa with the yoke bottoming. i don't think you're dealing with a trans build issue. The issue is elsewhere. You didn't build a stadium truck with 15 inches of super compliant energy absorbing suspension travel. landing it like one of the Duke boys, burn outs with wheel hop, washboard roads @ 60mph with all that energy being transferred in the chassis and components Takes it's toll. Harmonics, think of the Harley that cracks it's frame, the bad balancer that breaks a crankshaft into to 2 pieces. It can crate all sorts of nastiness. Also been my experience , once a crank thrust bearing start to go, it goes rather fast, as Nick said TC's hardly ever need shimmed and the trans guys are already pointing to at least one issue that is not their issue.