6L80E Won't go into forward gears-Reverse is fine

[First c10]

Hello all,
my sons 1970 has a 2011 5.3 Aluminum LC9 with a 6L80E transmission.
he backed it out of the shop and put it in drive and nothing but a small roll forward.

After a little research on the ole' interwebs I found that the 6L80E has a problem with a plastic check ball in the valve body shrinks and gets stuck in the plate.
I will be checking codes later today to see if there is anything like the below explanation.

Has anyone had this problem on here? I figured I would start a repair thread on this issue....any help is appreciated.


From www.trucktransdiag.com---
Complaint: Transmission slips in forward range, first gear take off. P2723 P2728
Cause: Possible codes P2723 Sol 5 stuck off or P2728 Sol 5 performance, Very possible that the number one check ball in the valve body has shrunken and wont seal or is missing. This ball can be replaced with the 1/4 inch Chrysler check ball from a 47RE or 48RE etc part #
52118261 this ball is much more durable and wont shrink or disappear.

[First c10]

6L80E check ball problem video

[BR3W CITY]

I'll wait here until Clinebarger can just give us the skinny on this.

[Clyde65]

Br3w said what I was gonna say! Cline's your man!

[First c10]

I totally agree with you guys!

[clinebarger]

Originally Posted by BR3W CITY

I'll wait here until Clinebarger can just give us the skinny on this.

Double check Fluid Level & check for codes FIRST! Solenoid/Electrical faults can cause no movement issues on 6-speed units! P0700 in the ECM means there are specific codes in the TCM!

It's very possible that the #1 Checkball is stuck in the plate.....Blocking the 1-6 Feed, If the Checkball is stuck, Pulling the shifter down into L1 will bypass the 1-6 Feed & supply the 1-2-3-4 Clutch with Drive Brake Oil.
Some/Most 6L80E's do not have have a L1 position.....So this may not be possible, But for it to get stuck in the the 1-6 Feed the trans had to be in a First Gear with Engine Braking condition (1-2-3-4 Clutch & Low Reverse Clutch Applied)...Probably through the "Tap-Shift" feature that was on the truck the trans came from, If your swap vehicle doesn't have "Tap Shift", You will need a capable scan tool to activate L1. This is just a test to see if the trans can move forward & that it IS a Control issue & not a Burnt Clutch or other mechanical issues....Besides A blown Lo-Roller Clutch that will cause loss of forward gears, Usually makes noise though.


If the Checkball has shrunk to the point it passed trough the plate.....It will not move forward no matter what you do. You will have to pull the Valve Body & tear it apart to see if the Checkball is missing, If it's not.....The trans will need to be torn down to inspect the clutch packs.

#1 Checkball issue's generally cause Solenoid codes, But I have learned the hard way that it is NOT 100% true on all units/programming.

D1 Diagram, 1-2-3-4 Clutch & Lo Roller Clutch Holding, #1 Checkball blocking Drive Brake Feed #36a.


L1 Diagram, 1-2-3-4 Clutch & Low/Reverse Clutch Hoding, #1 Checkball Blocking 1-6 Feed #21e.


Plate Diagram, #1 Checkball Shuttles back & forth between holes #36a #21e.


[SIZE="4"]Checkball Functions & Valve Body Locations.

[First c10]

Thank you cline. I have printed the pictures you posted above. I haven't been able to check codes yet. I did try to put in L1 but no L1. I tried to shut it off and restart a few times strong reverse but no real forward gear. It does start to move forward but like a idle only no difference if you give it fuel.
I will check for codes and report back.

[First c10]

Ok ran to my shop. No codes on the truck and it won't go in a forward gear. Reverse No problem shift on it firm. Fluid level is good and doesn't have a noticeable burnt smell.
The weird thing is we pulled it into the shop a few weeks ago and went to pull it out this weekend and no forward gear. Not like we were beating on it around town when it failed.

[First c10]

Sorry these are the codes but this should not be an issue with the trans could it?
And could I do the solinoid check with HP tuners?

[clinebarger]

Can you obtain Trans Data? Watch Pressure Switch #3 State.....Open= 1-2-3-4 Clutch Pressure, Closed= NO 1-2-3-4 Clutch Pressure.

[First c10]

What's the best way to get that info? Can I get that from hp tuners? Or do I need a special scan tool?

[clinebarger]

Originally Posted by First c10

What's the best way to get that info? Can I get that from hp tuners? Or do I need a special scan tool?

I don't think HPTuners will display pressure switch states, But I could be wrong as I don't use the Scanner part very often because I have a GM Tech 2.....I would be guessing about any other scanner as well.

[First c10]

Ok I am going to see if I can borrow a snap-on scanner from my work. I read somewhere that it will allow you to open close solenoids. .

[First c10]

Still trying to locate someone with the correct scan tool. May just be easier for me to pull the valve body and replace the check balls.

clinebarger, what it the reason for the 8th check ball kit i have read about?

[Hart_Rod]

Originally Posted by clinebarger

I don't think HPTuners will display pressure switch states, But I could be wrong as I don't use the Scanner part very often because I have a GM Tech 2.....I would be guessing about any other scanner as well.

You can log"PCS 1-5 Cmd switch pressure" in HPTuners. Is that what you are talking about?

[clinebarger]

Originally Posted by First c10

Still trying to locate someone with the correct scan tool. May just be easier for me to pull the valve body and replace the check balls.

clinebarger, what it the reason for the 8th check ball kit i have read about?

An 8th checkball was added to slow the release of the Lo/Reverse Clutch, This is a Non-Issue, Without the checkball....You may notice/feel a "clunk" as the Lo/Reverse clutch comes off. I personally like the clutch to come off as soon as possible.

This reminds me of the TH400's in the 60's & 70's......The Cadillac's/Buick's/Oldsmobile's had a restricted orifice at the Lo/Reverse Band feed to soften apply & slow the release of the band. The truck TH400's did not have the orifice because Plowing/Backing Trailers/Getting stuck could quickly burn the band up if the operator did not allow time for the band to come off or come on.

[clinebarger]

Originally Posted by Hart_Rod

You can log"PCS 1-5 Cmd switch pressure" in HPTuners. Is that what you are talking about?

Hey Rob, How are you sir?

My gut feeling is that PCS 1-5 Cmd is the Pressure Control Solenoid (Clutch Pressure Trim) commanded state. We are after the Transmission Fluid Pressure Switch state (TFP Switch 3 Hi/Low or Open/Closed) Hi/Open meaning the 1-2-3-4 clutch has pressure. Do not confuse Internal Mode Switch (IMS) states with TPF switches.

For someone that has been reading data on a Tech 2 for the last 18 years.....Reading HPTuners data is like reading a different language, Their acronyms for some things are baffling to me or just flat wrong....For example on some 4L80E data that I recently went through on the HPT scanner the 1-2 shift solenoid (A) is labeled 1-2 shift solenoid which is correct, The 2-3 shift solenoid (B) is labeled 3-4 shift solenoid, Alas.....It also had no data for the TFP switches.

Tech 2 Trans data list (engine running/Trans in park), TPF switches highlighted in red

[First c10]

Well since I could not get with the guy that had the scanner i went ahead and pulled the valve body and checked the check balls...... well all looked good. check balls were all the same size.
What is the next route??? Pull the damn thing and have it built???

[First c10]

Clineberger help!

[First c10]

Good morning guys.
With football season finished up. now its time to get this truck on the road.

I am going to pull it and rebuild it. Can someone let me know the best place to order the parts I need for a 6L80e transmission?

[First c10]

Ok guys
I got the 6L80E out of my sons 70 c10. I ordered all the parts to rebuild it myself.
This is my first automatic trans rebuild so wish me luck.
I will try and take pictures as I go.
The first order of business is to disassemble and find the problem.
More to come when I tear it down tonight.

[First c10]

Well when I got home last night I had a box of transmission parts.
So tonight I thought I would dive in. I got as far as the big C clip.
So I thought I would make the tool to remove it.
Got a chance to use my lathe. I turned down some 3/8” round stock and used some 3/8” x 1” flat stock for the arms. 1/2 hour for 10 seconds to remove it. Worked like a charm.

Ok so after I got it all removed. I started to tear into each clutch pack. Starting with the 1-2-3-4 drum and clutches

[First c10]

Ok so while getting the clutch packs out I found a bunch of clutch material in the drum.
Found 1 clutch with no material on it.
All caused by the piston with the crack I would assume. It maybe hard to see but it’s there.

[First c10]

I do have a few questions if anyone know if this will be ok? The race looks like a little bit of clutch material go under the bearing.
Will it be ok?

[First c10]

1 more thing. This large drum(I can’t remember which one it is right now) has a small pin holl. You can see it lite up from the backside. Is that right?