Another topic that I have been receiving questions about recently, would be the 4L80E OverDrive one way roller-clutch.

Like most GM automatic transmissions, the 4L80E received regular updates annually.
Mostly small updates/ changes... and a few years consisting of significant changes.
Some updates/ changes were improvements... and some, well... not so much.

From the 4L80E transmissions start in 1990 for the 1991 model year through the 1996 model year; the 4L80E went mostly unchanged.
However the 1997 model year would bring about significant changes for the next two more model years that followed.

The first/ original 4L80E OverDrive one way roller-clutch looked as it appears in the images below:









This is a 12-Element One Way Roller-Clutch.
It is responsible for handling the forces placed upon the transmissions input-shaft and transferring it along through the transmission.
The 4L80E OverDrive one way roller-clutch (or input one way roller-clutch) has a very difficult job to do...
And most of the time, the OverDrive roller-clutch is doing this job on its own (compared to having the addition support of the OverRun clutch).
When the 4L80E is being operated in any of the three manual gear-ranges (meaning not using the OverDrive gear-range)... the OverRun clutch is applied and aiding the OverDrive roller-clutch.

Prior to the 1997 model year, the 4L80E had very little issues.
The 4L80E was being used with many of GMs Gasoline engines and with the 6.5L Detroit-Diesel Engine.
At this time a more powerful and more modern design diesel engine that would replace the 6.5L diesel, was almost ready to go into production.
The Engineers at HydraMatic (which had become part of the GM PowerTrain Division) has concerns over the 4L80E not being reliable with a more powerful diesel engine.
Also at this time, a new model Allison transmission was almost ready to go into production for GMs medium-duty trucks (4500 series through 7500 series).
Ironically, the biggest factor for the changes made to the 4L80E, would never come to be...
In 2001 the new Allison 1000 transmission would replace the 4L80E in light-duty trucks, such as the 3500 series.
The 4L80E would not be put behind the new 6.6L diesel DuraMax engine after all.

The 4L80E was about to go through some major changes with the possibility of a new more powerful diesel engine coming.
As most of you know, the 4L80E would be changed to the "late" style "Center-Lube" version for the 1997 model year.
We will not be getting into all the changes made to the 4L80E (most of you know them already)...
Getting back to the OverDrive roller-clutch.

For the planned upcoming 1997 - 1999 model year changes... there were to be 3 sprag/ one way roller-clutch changes.
These changes were largely decided on by Engineers from Borg-Warner that wished to make some more profits in redesigning the corresponding parts for these sprags and roller-clutches.
Borg-Warner Engineers worked with GM HydraMatic Engineers to make the needed redesigns for the proposed sprag and roller-clutch changes.

The first is very simple and actually required no corresponding parts changes...
The Intermediate Sprag was changed from a 16-Element sprag, and upgraded to a 34-Element sprag.
Unfortunately, out of the three changes... this one was the only actual "upgrade".
Early 16-Element Intermediate sprag:


Late version:



The second change was to the one way roller-clutch used in an optional "heavy-duty" torque-converter for the stator.
This torque-converter used a "double-row" roller-clutch.
I do not have any images of the actual part, however it would have looked like this:

The late version was supposed to be an upgrade, but unfortunately it was not:



Last, and finally there is the late style OverDrive roller-clutch.
This is where most of the concern was in regard to handling a new more powerful diesel engine.
The original OverDrive roller-clutch was NOT a problem... it did however not last as long or handle as much power in testing, as GM wanted.
Borg-Warner sold GM on the design that would be used for the remainder of production for the 4L80E.
The reason that the late design OverDrive roller-clutch was chosen... is because Borg-Warner told GM that a similar roller-clutch of the same design, tested significantly better.
This was the design used in the Ford 4R100 transmission for the OverDrive roller-clutch.
Here are images of the late design 4L80E OverDrive roller-clutch:





This OverDrive roller-clutch was not an upgrade compared to the early design.
There is one significant reason why the OverDrive roller-clutch in the Ford 4R100 transmission tested better than the early 4L80E OverDrive roller-clutch.
It has nothing to do with the actual roller-clutch itself.
The Ford transmission has a far better OverRun clutch strategy than the 4L80E!

In both of these transmissions, the OverRun clutch aids/ supports the OverDrive roller-clutch in handling the forces that are placed upon it/ the input-shaft.
The ONLY times that the 4L80E OverDrive roller-clutch has the help of the OverRun clutch is in the manual gear-ranges.
Most people, most of the time are driving/ operating the transmission in the OverDrive gear-range... where the OverRun clutch is never used in the 4L80E.
The 4L80E OverDrive roller-clutch is essentially working all on its own taking all the stresses that the engine/ vehicle places upon the transmission.

Ford however did not use the same OverRun clutch strategy that the 4L80E uses.
Ford made a far more intelligent decision in its OverRun clutch strategy.
The Ford 4R100 always uses the OverRun clutch unless the transmission has shifted into OverDrive.
The gear-range does not matter... OverDrive or any of the manual gear-ranges will use the OverRun clutch.
The OverRun clutch is even applied with the transmission in Reverse.
The Ford 4R100 with the gear-selector in OverDrive will use the OverRun clutch until the transmission shifts into OverDrive.
The OverDrive roller-clutch has the aid/ support of the OverRun clutch the MAJORITY of the time.
This is the ONLY reason that this design roller-clutch tested better in the 4R100 than the original 4L80E roller-clutch.

Borg-Warner never disclosed this to GM... by the time that the GM engineers had implemented the new design parts/ completed testing...
It was too late!
A massive amount of money was spent to bring this new design OverDrive roller-clutch to production... so it was not going anywhere.
Sadly the 1997+ models had far more issues than the early units... the new OverDrive roller-clutch was just another reason to add to the list.
Don't get me wrong... the new part did its job... it just was never as good as the original.
Lube issues, planetary issues, bushing issues... all new problems that did not exist in the early units!

What a shame!
Note: anyone looking to build a 4L80E in the higher HP numbers... it is beneficial to switch from a Late OverDrive section to the early style to use the early roller-clutch.
The entire OverDrive section must be swapped!
Also Sonnax produces a kit to make the OverRun clutch act just like the Ford 4R100!
If you have a 1991 - 1996 core... this kit will interfere with the Lube-Pipe fitment somewhat... but it works!

 

Good info, and 100% accurate!

Ford was able to use the overrun (Ford calls it a "coast" clutch) with this strategy because they have a dedicated solenoid to control it, whereas the 4L80E overrun is brought on hydraulically in the three lower manual ranges. If the overrun and the OD clutches were on at the same time (in either the 4L80E or the 4R100), it would tie up the gear train, and not be pretty. Without a solenoid to control the overrun, GM is limited to the manual ranges that hydraulically block the OD clutch from coming on. Ford just simply turns off the overrun (coast clutch) solenoid right before the OD is commanded on, regardless of which manual range it is in.

One irony is that the Allison that replaced the 4L80E in HD applications has no sprags whatsoever (except in the torque converter, of course). It helped to lead us into the "clutch to clutch" era.

 

For both early and late, if you race your car in D3/D2/D1 where the overrun clutch is on...you'll rip the splines out of the OD carrier before you have roller clutch issues

Yes, the early is certainly stronger. But if you're a competent driver...you won't have issues

As for the lube changes...THAT's a path we should go down vortec...some GM engineers need a stern talking to for those changes!

 

You think I should go over the Lube circuit changes?
I can do that!

 

I think you should go over the changes
and also send a nasty email to the guys that approved the "upgrades" hahaha

 

Something that I did not mention in all of this... is that there is a division hierarchy.

For example, Corvette is it's own division separate from Chevrolet.
Chevrolet is very far down within this hierarchy... but Corvette is very high up.

I mention this because Detroit-Diesel (now the DuraMax and Allison division) is also very high up.
When Detroit-Diesel told GM they wanted something... GM usually complies.
When Detroit-Diesel said that they needed the 4L80E transmission to be changed...
They got what they wanted, along with help from Borg-Warner... regardless of what the majority of Engineers at HydraMatic said.

 

LOL! Nice!

I'll work on it tonight!