I believe I hurt the trans last year during AutoX at LSFest and developed a bad vibration doing the drag race which I thought was a bent driveshaft. New driveshaft fixed 80% of the vibes but still occasionally had a vibration on acceleration. The trans also developed a leak I could never pinpoint. Trans seemed to operate normally until a few months ago when it started holding first a little longer with a harder shift to second. I attributed that to fluid level due to the leak. During LS Fest this year it got progressively worse and would not make a 2-3 shift wot. Truck has been parked since September with intentions to pull the trans and go thru it. I knew I was going to try to get on it on Sunday so I took it for a spin around town Saturday night to check out the big car event in town. Trans seemed to operate fine in D3 but shifting to M2, trans would not hold any power. Shift back to D3 and it would hold a little in second but felt like it was slip/grab/slip/grab... Pulled the trans today to go thru it expecting to find a rolled intermediate sprag or burnt intermediate clutches or band.

Well... Looks much worse... Cracked Case!

Cracked 4L80 Case

4L80, lots of clutch material but no metal chunks

Lots of metal sludge on magnet

As can be seen from the pics, there were was lots of material in the pan and fluid but no metal chunks suggesting hard parts failure. I am trying to decide if I want to open it up to see the condition or just go ahead and scrap it. The case is cracked behind the pump so a SFI bellhousing swap is not an option. If the case has already cracked for what ever reason, I presume a weld repair would also crack or the case would crack in another spot.

Any ideas on what would cause the case to crack here? I did a quick Google search an didn't find another one cracked in this location.

 

It depends on wither or not you want to have any extra parts laying around or not.

I rebuild tons of these discontinued transmissions... so I take almost any core... there is always something usable inside.

 

yeah you have to open it up and find out what caused that.

I've had to recase a few transmissions due to my core guy being kind of a hammer-fist. my local hard parts exchange has them for $100 and up depending on year

 

I have seen an out of balance drive shaft crack cases before.

 

Definitely!

But not at the bell-housing of a 4L80E.

During my time at GM, there were two transmission models that often had case failure/ cracking due to drive-line issues...

-The Allison 1000/ 2000
-The New Process Gear Over-Drive/ Over-Run section/ housing for the 48RE transmission.

Some of you may have known, and some may not have...

GM and Chrysler used to share R&D space/ laboratories and engineers from the 1990s up till the 2009 financial crash.
After the crash, a company by the name of Magna purchased all the NPG and NVG products and started producing their own.

GM and Ford also started their own arrangements in 2004 to get the 6L80/ 6R80 transmissions ready for production.
This has now continued into the GM, Allison, and Ford 10-speed transmissions.

 

Most of the bell-housing cracks that I have seen, were from:

-Fully solid suspension and mounts for transmission and engine.
-incorrect engine/ transmission angle (nose of engine up to high).
-Fasteners not properly secured.
-engine way over powers stock transmission casting... especially with solid trans mount.
-Torque-converter failure.
-Miss-aligned engine/ transmission, crankshaft/ torque-converter.

 

Got the trans disassembled just to see where the crack was internally and what condition all the internals were in. The crack along the top is right at the pump shelf sealing surface and as it gets towards the bottom, migrates into the machined surface along the side of the pump. Internally everything looked better than I was expecting. Only damaged hard parts were the direct drum wear from the toasted band and some wear on the input shaft at the pump bushing. Direct band, direct clutches and intermediate clutches are all toast. I was expecting to find the intermediate sprag rolled but it was fine. Two of the forward steels had a very minor hot spot on them but the clutches looked fine. OD assembly looked new but I dont put trans in OD all that often. I presume based on where the crack is at the pump outlet, there was a gross leak and pressure loss causing the burnt clutches/band. Input shaft wear was likely from the slight misalignment behind the pump due to case sagging at the crack.
Now for the carnage pics...
Case crack into the dipstick boss...


Cracked case...


Case crack along pump shelf sealing surface...


Case crack around pump shelf into park pawl void...


Case crack along machined pump surface...


Clutch material in accumulator...


wear on inputshaft from pump bushing due to misalignment...


Sliver of material from direct drum. Looks like casting flash broken off...


Close up of sliver...


Band wear on direct drum...


Burnt direct clutches...


Band completely worn down...


Burnt intermediate clutches...


All laid out and labeled on bench...


So now I am looking for a rebuildable core or a good case to transfer everything to with a new direct drum, clutches band and intermediate clutches.

 

i have purchased cases on ebay in a pinch. usually $150-200 will get you a good type 2 case

 

Picked up a late model core at a local wrecking yard for a good price. Looks like it was in a mud truck and had some water/mud ingestion.


I havent separated the pump yet but a few passages have some mud pack in them.


All the hard parts look ok and the direct drum is good (which I need). However, the Forward and Direct assemblies came out together and I can't seem to get them apart. They separate about 1/4" and have a hard stop. There shouldn't be anything that could catch between the two. I am all ears if any of you guys have an idea. I really don't want to force anything as I need the direct drum for the build as my other is badly worn from the band.

 

Units/ Cores that have had water inside, really have no value to me...
They are usually rusted/ damaged, or too much of a hassle to disassemble and clean.
There are plenty of cores without any water intrusion.

However, since this is a DIY project for you... have at it; just know that finding another cheap core is probably a better route to take.
Being that you had a core already (with a bad case), hopefully you can make the 2 cores into 1 good unit.

I have not looked at the pump photo well enough... but that is most likely the vent passage in the pump that is filled up with debris from the short metal vent tube on top of the transmission case.

With Both the Forward clutch drum and the Direct clutch drum assembled but separated from everything else...
The only major contact is normally between the center of the Direct drum and a brass thrust-washer to the face of the Forward hub of the Forward drum.
...excessive wear hear may have the two drums slightly stuck together.

Pry them apart as necessary... if they are already damaged... you can't really do too much more harm by prying.

 

Thanks for insight. Doesn't look like it has been sitting long as the only internal rust was a small spot on the forward drum.

I will be using most of the hard parts from my old trans. Only thing I need from the core are the case, direct drum and valve body (due to HD2 pressue relief valve). I will try to gently persuade the two drums from each other. Hopefully the direct is not damaged at that thrust surface.

 

its likely the splines from the forward pressure plate have the direct frictions dug into it really deep. hosing wd40 into the gap has helped me. unforunately when they get to that point with water intrusion...usually piston sealing surfaces are the first thing that gets wrecked

 

Ding! Ding! Doug wins the prize! I was able to separate the two assemblies enough to pop out the direct snap ring. The direct clutches were trashed and dug into the forward splines.



Fortunately the direct drum is fine. I believe someone has been thru this trans previously and improper assembly could have been the root cause. Disassembling the forward clutch stack, the wave plate was between the first steel and friction. (so piston>steel>wave>friction) The forward frictions looked ok but the steels had hot spots and the first steel against the wave plate got really hot. I dont recall the order the directs came off the fwd hub but they may have been the same way. This is the first pic after got them apart where you can see the direct wave, friction and steel. Also notice the broken friction teeth emptied out of the direct drum.


As for the clogged pump port, it was the cooler out port. I found larve in the cooler case port so I believe it was something nesting there as the trans sat after being pulled. Inside of the pump looked good with minimal wear. It did have water but no mud/debris so thats good.

 

Excellent Doug!!!
Great point to bring up!

Some of you may be familiar with the Cast-Iron THM400 Forward clutch hub not holding-up to much power... and needing an aftermarket hub in its place...

In most street vehicles the OEM 4L80E Forward clutch pressure-plate (that the Direct friction plates spline/ grab) holds up perfectly...
However, it actually starts to become a problem in the 2,000+ HP builds... and rarely a problem in lower power builds with excessive abuse.

Heavy abuse can cause wear of the teeth on both the Forward pressure-plate and the Direct friction plates at any power level (but is not common at lower power levels)
Which in this core disassembly, seems to be the situation.

In the higher power builds a surface treated steel pressure-plate or a "Billet" Forward pressure-plate is used.
I will also install this upgraded part in heavy trucks/ tow-vehicles/ diesels/ Etc...

Doug, I really enjoy seeing you express the knowledge, that all of your experience has accumulated!
Honestly keep it up!

 

I was not able to view the images...

I suspect that the images are not viewable to anyone on the forum currently... can you please check this on your end?

 

I neglected to share the photos before linking directly to Google Pics. Should work now. Here is the entire album if anyone is interested... https://photos.app.goo.gl/1RSPXtZ8h6fuKTXF9

 

At what point does the engine/trans angle become a problem ( I have assumed 2-4 degrees is appropriate) and is there any way to measure the engine/trans alignment and what would be a safe +/- zone. I have done it for manual transmissions and have wondered about the automatics.

 

+/zone is the wrong way to phrase it but from the topic I assume you understand the question. It is getting late for me.