how exactly does the engaging of the overrun clutch (that helps support the input sprag) make the trans "stronger"? by how much could that be? 2%, 20% of torque capability?

do i understand correctly, that the oc is engaged in second and drive/3. gear only (stock)? starting a pull in second and shifting to drive and let the trans shift is a good strategy then?

 

stock form, 4l60e, D3 appiles the overrun only in 3rd gear.
So if you have shifter in D3, and the trans is in first or 2nd...no overruns

Racing in D3 with a stock valve body is actually worse than OD position because when you shift to 3rd, the overrun clutch has to apply with the 3/4 clutch so it robs oil during the shift and makes it crappy. Like an accumulator of sorts.

 

To try to answer your first question, I'll let one of the experts correct me, but since the overrun clutch has 2 plates while the forward clutch has 5 plates, I would estimate that the overrun clutch can hold about 40% of the torque capability.

This is another good thread on the overrun clutch which helps answer your 2nd question:
https://ls1tech.com/forums/automatic...d-3-2-1-a.html

 

The overun clutch when on acts as not only aditional support but also a shock absorber. The sprag iis a one way clutch acting not so different to a ratchet. Thing is when its not holding it it free wheeling and thus allow the engine to return close to idle when coasting, Good for economy but with a sudden throtte hit such as lets say roll racing . drifting, towing the engine spins up and slams it hard catching up to the drive train the effect is not so different than a less agresssive neutral drop. This can roll or shatter te sprag particularly with high power and or hi stalls.
Keeping the OVERUN on prevents this and keep the input shaft runnning with the drive train so you do not get that shock in those situations while also serving as extra support on an allready stressed part of the trans on lauches>
But as Marronmonster stated in the stock set up its not particulary benificial and may be deterimental coming on with the 2-3 shift in D3 as it take line away from the 3-4 clucth apply.
However when the VB is modified to keep it on such as with the Sonnax valve for D3 function or modified to keep it on in all gears except actual 4th gear it is a game changer,
Before I figured out how to do this when I was with PB our biggest issue with the L3 and Black edition was breaking sprags in very hi power situations 750 rwhp plus. Once that was incorporated 0 input sprag failures even at 1000 RWHP PLUS. It was the single biggest step forward at putting those two builds over the top .
In fact I presently use it with all my builds as its such a simple mod.
The only downside is some depending on build and tuning do experience a downshift bump that can be more or less aggressive as they coast to a stop on the 3-2 shift, but most times its nothing really bothersome to performance and heavy-duty drivers and even then, some tuning can address it such as lowering when that coast downshift happens.
How much does it improve durability and hold I would guess 50 percent or more but short of putting on a high torque power DYNO that could apply the levels of torque to actualy test and make the comparison no way to be exact. I can only speak to the results before and after in real world on the many units we put out with the FT OVERUN mods at my former employer and the sprag went from Number 1 mechanical failure point in very high HP application to in fact 0 FAILURE POINT.
I do prefer the FT OVERUN mod over the sonax valve for 1 simple reason, seriously who actually drives around in D3 or remembers to do the downshift on a sudden hit driving around.
Sorry if to wordy ,
Frank Formerly of PerformaBuilt

 

The Idea for using the D3 Gear-Selector Position for better protecting the Transmission...

Came from the THM700-R4 Transmission/ design (Overrun Clutch Applied at all times except for in the D4/ OD Gear-Selector Position).


I would guess that most people just assumed the 4L60E Transmission was designed the identical way.

 

Yup, and the 4L60E ATSG manual incorrectly shows it applied for all gears in D3. That doesn't help as many treat that book as their definitive reference.

In older threads, I and others often suggested racing in D3 to reduce load on the sprag. Guess you can't win with the stock trans. You chose between immediate failure of the sprag or excessive wear on the 3/4 clutch.

 

Yes my first year working with the 60e I had it wrong from looking at the manual, But when actually studying the valve configuration and channels figured out it could not be on in 1st and 2nd and thus I learned not to trust in what the book says always. Check and verify . the GM manual also has it wrong.

 

thank you so much for the answers everybody. frank, the more you write the more i learn.

so i understand (and correct me where im wrong):

1. the overrun clutch blocks the input sprag, prevents it from fluttering/shocks and ands to its torque capability under load.
2. the 2 overrun clutch steels/plates add to the torque capability of the 5 forward clutches/plates when under load. so the difference is massive.
3. with stock trans it is advisable to make a pull in 4d rather than 3d, because in 3d the overrun clutch comming on "robs the 2-3 shift of oil"

questions:

a) how debatable is (3.) above? what difference in pressure could it make, as during the 2-3 shift so many thing are happening anyway (2. servo, 3. gear oil pushes off band, 3/4 piston fills, what else)? what might a pressure gauge show?

b) how does (2.) above concretely work? in my imagination the sprag and forward clutch are "in series" (where the weakes link would set torque capability). it seems the overrun clutch is not "in series" with the forward clutch but rather added to it somehow. the overrun clutches move againts the forward clutch apply plate (to rear of car) when applied. that plate moves to the rear against the forward clutch backing plate for the forward clutches to apply. what makes the overrun clutches not disengage? (i can read and look at pics and vids all day, as long as i have not seen the inside of the trans in real life it diffucult to understand.)

c) please confirm my shifting strategy (mentioned in #1) is correct: start pull in 2d, shift to 3d and let trans make the shift. on my car 1. gear is useless, but same would hold for: start pull in 1d, shift to 2d, let trans make shift, shift to 3d, let trans make shift. overrun clutch stays engaged all the time, right? maybe anything else "wrong" with doing this?

d) as the overrun clutch is never engaged in 4. gear, should i ever reach a crazy speed and feed max torque into the trans, it has good chances to let go, right? (here max speed limit is 120 kmh, but its not too far to germany to a stretch of autobahn with no speed limit. you have to go at night though, iv not done it yet.)

edit: two unlerated questions: is the fill plug on the pan really a plain m12 (12x1.75)? how much fluid comes out if you remove it with engine not running?

 

Your first paragraph is correct, As for the rest I will address or someone else may? when i get some time the needed explanations will be in depth and honestly would be better done with video or verbal explanation but can be done in text just will take considerable time I do not have today. I have chores and a trans to build lol.

 

If you remove the plug with the engine running...you'll have quite a bad time. Yes it's just a plain jane drain plug...you'll get anywhere from 3-5 qts likely if you just drain it

 

This seems like a new concept to many of you...

But other Transmission Models from other Brands (Ford, Dodge, Etc) sometimes do this differently from the GM Units that are Common on this Site.
(D3, D2, and D1... the Overrun Clutch is applied... just like in the THM700-R4).

My THM200-4R, THM700-R4, 4L60E, and 4L80E... ALL operate this way, and have for a Long time now.
And all also are offered with the Overrun Clutch applied at all times (except in OD/D4 while in the 4th-Gear).

My Performance Built Transmissions have NO NEED for a Fuel Economy Feature (such as un-applying the Overrun Clutch).


Fortunately for all you guys with a 4L60E Family of Transmission...
Applying the Overrun Clutch at all times (except in OD/D4 while in the 4th-Gear) is the most simply Transmission Model to do (of the GM Models that I listed).

 

Of note the full time overrun D4 mod can be done to the 700r4 also, I have not looked at the 200r4 to see but imagine it can be.
In the 700 and 2004r some might thing pointless since they already do it in D3 but again who drives around in D3 or remembers to pull down in a quick spur of the moment dash on the street.

 

"The input sprag isn't engaged in 4th gear. It's overrunning.": i had no idea. so is the the trans weaker in 4. gear or not? compared to 3. with overrun clutch engaged?

"The overrun clutch does not add to the fwd capacity.": confused now. not adding to forward capacity would mean it doesnt help propelling the car, doesnt strenghten the trans?

(btw, shifting "manually" like i describe is second nature with me, i do it on all my automatic cars for wot. even if driving my amg limousine and wanting to pass i shift into the appropriate gear on a country road. i dont want to wait for it shifting after i floor it. i even did a mod on the cherokee for the trans to never shift into 1. gear when i pull in into d1/2 for that purpose.)

 

Since Sonnax Sells a Product for the 4L80E (an Auxiliary Valve-Body)...
Applying the Overrun Clutch at all times (except in OD/D4 while in the 4th-Gear).

I figured I would Post showing what they did, just in case any of the Members here would like to try and create their own Method of doing so.
I will not be sharing my Method at this time (maybe in the Future).

The Images below show what Sonnax did by tapping into 3 Circuits for their Auxiliary Valve-Body using One Valve and Spring:

 

@tayto

Any luck?
It's not as convenient/ simple of a Modification as the 4L60E...

But it can be done a few ways.

 

If I get some time later I will find the diagrams I made and post, Basically you do the same as the 4l60e , block two holes then feed fwd clutch oil to the overrun at the 3-4 sequence valve, This will give you full time overun in 1-2-3 even in d4 position and the sequence valve will dump it on the 3-4 shift,
Note when doing this mod to the 700R4 the 3-2 downshift at coast is a good bit more aggressive than the 60e because of the way pressure control works, So if doing this on a customers trans be sure and let them know they will feel a very distinct downshift braking on that downshift , Some find it unpleasant particularly with lower gears in rear, But everything always a trade off in high performance any real enthusiast knows that .

 

Basically you have to block the D3 oil from the overrun and connect fwd clutch oil instead at the 4-3 relay valve. I had found pretty simple way to do it just need to look at case channel diagrams to remember , Havent done it in a while as I do not do many 700r4 now days .

 

Hi Mr. Frank
Just for the sake of knowledge, The question might sound silly for pro's but why overruns cant be used in 4th?

 

This is already done in more than one of the valve bodies I make.
I've got Overrun applied in all shifter positions, even reverse, with 4 gear oil shuttling the overruns off.
Just like the sonnax deal, but without a bulky add on...all self contained in the VB

I'm 99% sure I am the first to do this without a valve body add on like sonnax

 

If the overruns stay applied in 4th...the transmission will lock up
It's the whole reason there is even a sprag and a clutch pack there in the first place...beacuse it HAS to overrun for you to get 4th (and reverse)

The overruns don't add to the capacity of the FORWARD clutch either.
It just supports the input sprag. So it does make the transmission as a unit more durable, but it's not making the fwd clutch itself any better