Control freewheeling in GM transmissions (4L60-E) 5

[gerhardf]

Hi everybody! I'm more of an electronics guy, so please bear with me here...

I'm trying to shift the gears in a GM 4L60E transmission. I have managed to control the shift and torque converter solenoids, and everything works pretty nicely -- almost. The problem is that with the shift lever in position D, the gears 1, 2 and 3 freewheel. (By this I mean that the motor rpm can drop below the rpm that corresponds to the wheel rotation.) In 4th gear this is not the case, it is coupled tightly between the motor and the wheels.

When the shift lever is in position 3, it is the 3rd gear that's coupled tightly, and gears 1 and 2 freewheel.

What I would like to get to is that all gears are coupled tightly while the shift lever remains in position D, so that I can shift the actual gears with the solenoid valves only and have a behavior that is similar to a stick shift transmission.

Can anybody give me a hint where to start looking for answers here? It seems to me that the only way is to change the control flow in the valve body. Is this correct? It seems that there is a clutch or something in the transmission that controls the freewheeling, and that it can be activated by applying pressure to it. My idea is to find this and add a solenoid to the valve body that controls the freewheeling. Is there a place where I can get a drawing of the hydraulic control flows in the transmission? Or am I completely off base?

Thanks for any help!

 

[trannyman]

The concept is very simple --its much like a bicycle when you peddle it goes forward when you stop it free wheels ---well the trans has a sprag which gm calls the input sprag the way to make the input sprag not freewheel when you let off is to put a sensor on your gas peddle which senses when you are off the gas and what it will need to do is apply the (coast clutches) by moving the coast clutch control valve in the valve body with some sort of electronic acuator. Thats it all you need to do is apply the coast clutches and you have engine braking in all gears --However the coast clutch pack only consists of two clutches that are halfe the sise of the next smallest 6 clutch pack in the unit hence not very durable

 

[crashbox455]

no coast clutches in the 4l60e. see JayMaechtlen's post for a better description of what i was trying to remember

 

[daxcar]

gerhardf- did you ever get your electronic control working without freewheeling? I'm trying to do the same (and failing!). So far simplest solution may be to have a pair of solenoids operating the shift quadrant externally. Goes against the desire to be electronic, of course, but is needed to select reverse and park anyway.

 

[gerhardf]

daxcar - No. From the information I gathered here and by reviewing the transmission manuals, I think that's not possible without either mechanically modifying the transmission (to control the overrun clutch with a valve) or moving the manual valve (so that the built-in overrun clutch control does what I want).

I'm not sure what you mean by "operating the shift quadrant" with a pair of solenoids.

 

[daxcar]

Gerhardf- regarding my post operating the shift quadrant (or shift lever) by solenoids..... I recently saw a commercially available push-pull solenoid/ratchet assembly (or perhaps a stepper motor?) attached to the transmission where the cable or shift rod usually hooks up- i.e. to the OUTSIDE of the transmission. A dash mounted control panel with pushbuttons operated it, allowing you to electronically select which gear the transmission was "mechanically" in. The hot rod builders use them, I guess, to completely get rid of the shifter on the floor. Crude compared to using the internal (fluid) solenoids, but it does avoid your overrun problem. You could still electronically select gears (without engine braking) up to and including the highest that was mechanically selected. A compromise, but that's engineering! I still doubt you could get the same feel and control a stick shift though.

 

[icrman]

In the old 4L60 there is a band that is used for shift down to by pass the second gear sprag clutch. Other wise it coasted above engine rpms.

 

[jballenger]

Engine Braking is determined by the Overrun cluth on the 4L60E. The overrun clutch is not electronically controlled on the 4L60E and therefore engine braking is not electronically controlled on the 4L60E. You can get engine braking in the following scenarios (According to the 4L60E book I have in front of me):

Range Position 1 - First Gear and Second Gear
Range Position 2 - First Gear and Second Gear
Range Position D - Third Gear
Range Position OD - Fourth Gear (overrun clutch is not applied in this position but engine braking is present)

There are two ways to provide engine braking to the 4L60E at all times.

1) Modify or purchase a modified valve body or modify the 4-3 sequence valve to continuously activate the overrun clutch. You could make this actuation electronic if you modified it in the valve body and put a solenoid inline.

2) Purchase a mechanical actuator which will move the Range position based on desired gear. So when you want 1st gear, it will be in Range Position 1, 2nd gear - Range Position 2, 3rd gear - Range Position D, 4th gear - Range Position OD.

I have seen a mechanical acutuator system here:

http://www.mooneyes.com/support2/smartshift.html

Here is an Automatic Transmission Controller that could fully control either of the above situations from Powertrain Control Solutions. I should publicly note that I am associated with this company but I mention our controller becuase it is the only such controller which can easily handle either electronically controlled situation.

This should be less of an issue as the 5L50E and 6LX0E become commonplace as they have electronically selectable engine braking.

The full fluid flow diagrams are available in the Hydra-Matic 4L60-E Technician's Guide, which you can purchase here

http://www.acdelcotds.com/store/default.asp?categoryid=0&scategoryid=&type=Manual

Good luck with your implementation!

 

[icrman]

In my experience the over run clutch, ie either a roller clutch or a sprag. Is grounded at all times and the only thing that turns it on or off is the direction of rotation.
So the only way to turn its fuction off is to lock the member that is rotating by some other means. And in the trans above it is by way of a contracting band.
That has always been the beauty of a sprag or roller (over run) clutch there is no need to have something to control it with.

 

[shootfromthehip]

I really appreciate this thread.

I'm looking for an inexpensive way to control my 4L60E. Most add-on controllers I've seen are in the $700-1200 range. I dabble in electronics, but I'm looking for the easy way out. Does anyone have any options for a simplified controller that wont hurt the pocket book? I thought about digging into my transmission and designing something from scratch, but time is of the essence. I'm not against piecing something together with switches, relays, sensor, and possibly a simple processing board. I really don't need the "programmable" computer-based luxuries. I just want to shift gears at typical intervals and be able to have functional drivability.

If there are no inexpensive controllers available, can I convert my 4L60E into a 4L60?

I would appreciate any information anyone could offer.

 

[gerhardf]

shootfromthehip, a very simple solution (some electronics required):

1) Gear control: Somehow mix current gear, speed and throttle position together to get shift curves that you can live with. This could be done in a very simple manner with a few opamp adding up appropriately scaled inputs. Run the output through a comparator that shifts up or down.

2) TCC control: A simple logic like always fully engaged unless
- in first gear, or
- below a certain speed (say 30 km/h), or
- during a shift (from immediately before shifting until some time after)

3) Pressure (EPC): Always off (full pressure).

This could you get started with some simple electronics. Of course this all could also be done with one off the shelf controller, some I/O circuitry and a bit programming. More flexible, but more work.

Depending on what price you put on your "dabble time", this could get you quickly in the price range of commercial controllers.

 

[daxcar]

Regarding "shoot from the hip"'s desire for a cheap, simple 4L60E controller.

The well-known Megasquirt EFI controller can be programmed to control the transmission instead of EFI. It's known as Megashift, and is supported by a Yahoo group. You can build it for about $150. I doubt a home-grown version would be much cheaper. Haven't looked at it recently, but a year ago it seemed to be thriving. Just search on "Megashift'.

Or even more basic, if you can live with (or want) only manual gear selection you'll only need to set up the gear selection solenoid inputs accordingly; the logic is described earlier in this thread. But you'll still have to control the pressure (PWM) to get the right shift "feel"- to avoid burning up the transmission (too soft) or squealing the tires every shift (too hard), ideally based on the throttle position and revs.

And it will still overrun (freewheel) any gear lower than the one mechanically selected, which is the main gist of this thread.

If you come up with a good solution to any of this please send it to me.

 

[JayMaechtlen]

Did anyone come up with service literature for the 4L60E?
Is the "overrun clutch" indeed a multidisk clutch pack, controlled by hydraulic pressure?
If so, how is it controlled?
If it is controlled by hydraulic logic and not directly by a solenoid, then perhaps some 're-plumbing' is needed, and a solenoid added?
Withought this info, its tough to make usefull suggestions.
Regards
Jay


Jay Maechtlen

 

[gerhardf]

Literature I have:
GM Powertrain: Hydra-Matic 4L60 Technician's Guide
Second Edition, 17001.11-5, HM-4L60-TG

The overrun clutch is a clutch pack controlled by hydraulic pressure. It is controlled by hydraulic logic, mainly through the manual valve.

It seems the consensus of this thread (started by me, before I had this very good literature) is that indeed a modification of the valve body would be needed; an added solenoid that controls the overrun clutch.

 

[icrman]

In the hydramatic 4L60 (THM 700-R4) Technicians Guide.
2nd edition 17001.11-5 HM - 4L60-TG

On Page 20 Figure 21

"The outer cam is held stationary by the lo and reverse clutch support which is spined to the transmission case."

The outer cam being the cam for the roller clutch.
There is no hydraulic clutch that actuates the "LOW Roller Clutch".

 

[JayMaechtlen]

ok, but there are a whole bunch of overrun/roller clutches, and likewise a whole bunch of friction clutche packs.

The "overrun clutch" is probably not the same as the "LOW roller clutch".

At No_bling.com they are developing(?) a controller for the 4L60

http://www.no-bling.com

but the table of powerflow looks wrong to me, so I would be cautious...


Jay Maechtlen

 

[gerhardf]

ircman: Again, I'm not really a transmission engineer and can't say that I've understood all the inner workings of this transmisson... But it seems to me that the main part responsible for freewheeling/coasting is the forward clutch sprag assembly, not the lo roller clutch. And the forward clutch sprag assembly seems to get locked by the (hydraulically applied) overrun clutch.

I don't quite understand what exactly the lo roller clutch does, but from looking at the application charts (it's only applied in first gear) I assume it hasn't much to do with the freewheeling we are talking about. If I'm wrong, I'd be happy to listen to an explanation as to how...

 

[trailingwire]

low roller clutch -function is to allow coasting when you slow down in 2nd or3rd and it down shifts to low. and you are not accelerating. you would get a lunge when it does if it wasnt there. if you dont want to coast you must apply the low and reverse clutches (down in the case in rear)low roller functions in low in d or 3.only
input sprauge(first units used roller but is obsolete) larger used in 87 up. spragues are figure 8 type units instead of rollers between 2 races and lock in one direction only they are installed in the input because you must lock and on lock the power flow to alow the overdrive to alow a approx ratio of .7 to one to exist at that point. the overrun clutches apply paralell to it to cause a lockup over it so it doesent free wheel in 3,2,1
tcc lockup by the solenoid. sol holds pressure against valve which moves and directs pressure to lock up circuit mechinism. this pressure usually is the 3/4 clutch oil but ihave seen some lock up in second.
converters have a large clutch in them to lock them up so they dont function as a torque conv with a rpm loss in them a crusing speed the circuits are design to release sol on engine pulling or deceleration so not to put excess pressure on clutch. if you keep it locked it will stall the engine at idle when you stop vehicle. ihave some ideas on how to do what you want but needs a lot of thought. some trans open tcc when trans shifts. ihope this helps let me know if i can help any more

 

[icrman]

You are correct gerhardf, I was a bit to hasty, about the uncontrolled sprag and roller clutches, I know there are some transmissions that have controlled roller or sprag.
I didn't remember the 4L60 as one of them.
That forward sprag is holding, until overdrive 4th then it's over running. So you really can't just eliminate it if you want 4th overdrive. You have to manual downshift to eliminate coasting.

 

[bakesz28]

I wanted to put in my .02 about downshifting manually with the 4l60. I'm not a mechanic, but I am mechanically inclined. (for those that care). I bought a '93 z28 in '02 with 36,123 miles. Since that day, I was always able to downshift from D to 2nd, then to 1st. And it would grab, (the feeling of a manual). Now with 59,000 miles, for about 2 months now, I have the same problem as posted in the beginning of this thread. There are no mods, only a tranny flush maybe 8-10,000 miles ago. I'm wondering what the hell happened? Was is working properly before or now? I do pound on it from time to time, otherwise the car drives great. Any advice would be great before I start sticking $ into this. Thanx guys, Jake

 

[GregLocock]

You've stretched the bands.



Cheers

Greg Locock

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