I'm rebuilding my first 4l80e. The direct and forward piston return springs are broken.
Is this common? - What can be the probable cause of this?

 

What year model 4L80E?

The spring cages... as in the metal top/ bottom?
Or the actual springs cracked/ broke?

 

It's a 1998. The actual springs are broken - the metal cages are fine

 

I mostly only see this when there has been a major component failure...

Or if the drums were assembled incorrectly (snap-ring for the return springs/ spring cage not fully installed or incorrectly installed).
Or the springs were cocked...
Or if the apply piston is not fully inserted/ crooked...

In the THM400/ 3L80 and 4L80E transmissions... going over 200 Psi of line-pressure can do some serious damage!
Something small like blowing apart return-spring cages; all the way to blowing the case apart at the center support!

This can look very similar to this TH400:

 

I see what's left of a steel direct drum and the piston...who neutral'd their trans at the big end?!

 

LOL!
I wish I knew...

This image is just from a Google search...

Definitely looks like a OEM cast iron drum went into hyper-speed!
Poor stock Direct and Forward drums...
What am I saying??? Look at what they did to the case! LOL!

 

There is no major component failure (that I have found yet) and the direct and forward pistons were installed correctly.
I have not taken the pump or the valve body apart yet, so I guess I will look for a stuck line pressure valve?
Both sets of springs are broken exactly the same way. I will try to post a pic later.

vorteciroc, I am trying to avoid an explosion like that one - LOL

 

 

The most common cause of excessively high line-pressure in a 4L80E transmission (especially in the reverse gear range) is from a worn-out pump pressure regulator boost-valve and sleeve.

This is very commonly worn-out. Replacement upon a rebuild is always recommended.
Sonnax produces a nice after-market replacement part.

 

When measuring line-pressure with a gauge on the line-pressure port...
170 to 180 Psi maximum pressure is great for anything that the stock parts can handle and more.

When the boost-valve is worn badly... it is common to see 300 Psi in the reverse gear range...
This often why 1997+ units have broken Low-Reverse servo pistons.
I horded a kit that Sonnax made for these servos, and make a brass restrictor-orifice for reverse boost fluid if I raise line-pressure significantly...
Reverse boost fluid can be blocked completely if fixed line-pressure is desired.
In regard to the servo piston; a billet replacement piece is available (but this is not fixing the cause... it is fixing the effect).

When you get to the point where the input-shaft fails and you need to upgrade the transmission...
About 180 Psi is where you want to be, up to about 1,000 HP.

200+ is where you do not want to be on a stock unit.
More than 200 Psi can be needed with power at 1,200+ HP... but there are also significant changes made to the transmission at this point.

 

I am not really sure...

I have seen similar results from extreme ATF temps... and from severe rust (your springs do not appear to be rusted).

The springs in your images almost look like they were cut... the springs surface treatment/ tempering was probably off... Defective.

 

Thanks a lot for the guidance as to where to look for the cause.
Yes, they do in fact look cut - and it very well may be a factory defect. No rust on them.
The fluid was not burnt, and the clutches look pretty good (except for the direct clutches which have tiny nicks taken out of them, probably from little pieces of spring flying around in there)
I was told the transmission was in a work truck, with stock engine - and there was no problem with it. For $150 bucks - I suspected a different story once I opened it up...lol.
Thanks again for the help, and I will post the findings as I move forward with this new project...

 

Good luck and have fun!

 

Just want to update on some things I have found so far. One thing to mention this is my first 4l80e, so I am not too familiar with things yet .
I assumed being that this transmission has a green tag on it saying that it is a GM Factory rebuild - and a GM Performance sticker on the bell housing - that the parts inside of this transmission would be installed correctly...
The boost valve had a very tiny 'bump' to it as it rode in the sleeve - kind of sticking. Going to replace with a sonnax.
Pump gears measure ok, but have a very little scoring to them - so replacing gears with new.
Reading up on how thrust puts lots of stress on the rear planets, I installed the ck rollerized planet set up.
I didn't like the way the forward hub rides on the output shaft so I installed the sonnax roller forward hub.
I also rollerized the output shaft. This all seems to make sense to me - and in theory spreads the thrust around.
Rear end play is .009
planetary end play is .002 - rollerized planets
forward to direct is .002 - rollerized front hub
front end play is .012 with a .106 plastic shim.
Seems OK?
Installed all new sprags - the sprag on the direct clutch had strange uneven wear marks on the outer retainers.
Some direct clutches also had strange uneven wear marks in the clutch material, and some had uneven inner spline wear marks.
I thought all was good until I discovered the output shaft bushing - where the rear internal gear rides, had a rear stator bushing installed from the factory rebuild.
Those bushing are similar - but not exact.
I wonder if this contributed to the uneven wear marks I found on some things?
Could have this caused a vibration enough to break the clutch springs - in some way?

 

My replies are in red bold.

 

It is also a good idea to find and use a THM400 carrier silencer ring.

 

My front end play measurement is taken with the gap in the input shaft snap ring taken into consideration. That gap is .020. I pull up - feel that gap take up - and then pull up (much harder) until my dial gauge stops. It stops at .032.... So, .032 minus .020 = .012. Not sure what you mean by pushing the out put shaft forward?

I can easily get .010 on the planets, but the front hub may need some working....

Sprag races are perfect - the marks are on the outer retainers... Thanks again for the info...

 

I should have said 'rollerized reaction carrier' end play (or float) = .002.
It is a Ck performance set up, https://www.ckperformance.com/View/R...ACTION-CARRIER

 

I understood you and know of what you are referring to.

CK has changed their instructions multiple times, regarding that clearance/ end-play/ float.

I recommend 0.003" clearance for the torrington bearing (1.5 thou. for each side of the bearing to have space for oil/ lube) and another 0.004" clearance for the brass thrust-washer between the carrier and the center support.
So, I like a minimum of 0.007" carrier float and a max. of 0.010".
Some of the stock units have over 0.100" float... so reducing it to 0.010" is a massive improvement.

You can run the carrier float that tight... I am sure people have, but I do not recommend it (especially regarding the brass thrust-washer, that actually has contact now).

Good luck.

 

vorteciroc , I owe you a HUGE THANK YOU!
If you didn't mention the tightness of the pinions, or my method of figuring front end play - I would have probably exploded my first 4l80e.

I felt something wasn't right (after your post) so I tore everything down and figured ALL end plays out again.
I found that I did it all wrong - never taking into consideration the rear end play with the front end play - and figuring rear end play with the planets installed.
After re-doing all that - with no planets installed for rear end play, and thinking a lot about the ck methods - here is what I got.
rear end play .012
rear carrier .011 - however it may change (reason at the end of post).
front hub .010
front end play .016 with a .090 pump washer - HUGE difference! I originally did the front end play being .012 TOO TIGHT! Pretty sure that would have been catastrophic!?
Also, upon a second tear down, I noticed the rear planetary pinions seemed loose. I checked the clearance in the pinions and they were over .030 (with a feeler gauge), and one had a little wobble. So, I decided to just rebuild them. The picture is of the 4 pinions - guess which one was the wobbler?
3 pinion shafts measure .443 and the 1 worn one measures .434 - it was only a matter of time. Lesson learned here!!
If it wasn't for your input I would have never found this until after the explosion.... Thanks again!