Control freewheeling in GM transmissions (4L60-E)
Control freewheeling in GM transmissions (4L60-E)
(OP)
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!
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!





RE: Control freewheeling in GM transmissions (4L60-E)
Word of warning - hard shifts are a quick way to stretch your band brakes.
Cheers
Greg Locock
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
Cheers
Greg Locock
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
Automatic transmissions seem to generally freewheel and only provide engine braking in the highest gear that is possible in any position of the shift lever. This is usually the desired behavior when shifting automatically, but it's not in my case.
I'm not sure what the overrun clutch does. In any case, it seem to be something that can be controlled through hydraulics, because the shift lever controls it through the manual valve.
RE: Control freewheeling in GM transmissions (4L60-E)
Cheers
Greg Locock
RE: Control freewheeling in GM transmissions (4L60-E)
In 4th gear (in D position) with the TCC engaged, the rpm is tied to the wheel speed like with a manual transmission. Very little slip in either direction. This is what I would like to have in the other gears, too.
I'm pretty sure it's not the torque converter that's causing the freewheeling. When the TCC is disengaged, the TC allows the engine to run at higher rpm than the wheels would require, creating additional torque. When it is engaged, this doesn't happen. That's how it's supposed to be, according to my understanding. But no matter whether the TCC is engaged or not, the transmission allows the engine to run at lower rpm than the wheel rotation would require (in gears 1, 2 and 3), and so there is no engine braking in those gears.
In the recent trucks with a "tow/haul" switch that sets the shift points higher, you can feel that freewheeling in 2nd and 3rd gears (always talking about the D position). With the normal shift points, you usually don't get to feel it, because it shifts in the higher gears before you really feel any freewheeling.
RE: Control freewheeling in GM transmissions (4L60-E)
Next, I would say you may just be on to something, as I know the old TH400's did the same thing, yet the TH400 I have in my current car will freewheel in both 1st and 2nd, with the only major change to the Transmission being a reverse pattern transbrake valve body. Just how they accomplish that however, I do not know. Perhaps you could contact one of the Major aftermarket Transmission people ( B&M, TCI, JW Performance, etc.) and find out how they accomplish it.
Greg, on my 4L80E in my Truck, I do have engine braking in 3rd, obviously without TC lockup, are you sure about having to have the TC clutch locked?
RE: Control freewheeling in GM transmissions (4L60-E)
Our gearbox has at least two one way clutches in. These are called OWCs. Again I don't understand their function, I've never had to mess with them. I suspect they control the free wheeling.
Cheers
Greg Locock
RE: Control freewheeling in GM transmissions (4L60-E)
maybe you could "MacGuyver up" some stepper motor control for the manual spool valve?
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
Crashbox, this is not quite correct, in two respects. It is not the transmission that controls the TCC, it is the PCM. At least in the Tahoe, the PCM engages the TCC in 3rd gear when the shift lever is in the 3 position. This basically can be summarized in saying that they engage the TCC only in the highest gear available. (And that's always only above a certain speed, around 35-40 mph.)
I think there's nothing that says that they couldn't engage in in the lower gears, too -- it's just that they didn't go that extra mile in complexity in the PCM, probably figuring that the time the car spends in the lower gears is too short to worry about. This might not be true though for towing, for example, or for extended uphills (which they don't have in Detroit :).
RE: Control freewheeling in GM transmissions (4L60-E)
Cheers
Greg Locock
RE: Control freewheeling in GM transmissions (4L60-E)
i forgot about TCC in manual 3rd, but no, you cannot say that it "will engage in highest gear possible". 3rd and 4th only. the point of my statement is that you don't need TCC lockup to have the gears "coupled tightly", you need to actuate the manual 1st thru 3rd options, so as to lock up the overrunning clutch and input sprag. so the internal workings of the trans portion of the PCM don't really mean diddly.
i realize this post sounds a bit snotty, but it's because i'm in a hurry and typing fast. i hope my input was worth something.
RE: Control freewheeling in GM transmissions (4L60-E)
I think I get to a drawing of the hydraulic control flow soon, and I'll check out the overrun clutch and input sprag controls. (I'll also try to understand what exactly they do :) Is this all that's related to the freewheeling?
PS What means "MacGuyver up"? I've been thinking about the stepper thing, but if I can add just a little solenoid that applies pressure to a clutch or sprag, that could be easier.
RE: Control freewheeling in GM transmissions (4L60-E)
for example, when my throttle cable broke on my camaro, i pulled out one of my shoelaces, and used it to move the throttle by pulling it through my driver's side window. that was a 'MacGuyver'.
as for the input sprag and overrunning clutch, they are opposites in effect on the transmission. the input sprag allows the engine to put torque through the transmission, while letting the engine idle during deceleration- if you know what a "sprag" clutch does, it should be obvious. the overrunning clutch is the opposite, when engaged, it keeps the output from "overrunning", which means it keeps the engien from idling under decelleration, which means ENGINE BRAKING. they are opposite in direction, and in "DRIVE" or "D", only the input is engaged. in manual 1st thru 3rd, they are both engaged, which gives you engine braking. the overrunning clutch is only available through the "manual valve", which is actuated by the shifter. this is why you can't get "tightly coupled" gears using only the solenoids.
i assume from the 'MacGuyver' question that you are not from the US, so hopefully i am crossing the language gap effectively. let me know if you need any clarifications.
RE: Control freewheeling in GM transmissions (4L60-E)
You're right, I'm not originally from the US (I'm from Germany), but I've been here long enough that the language gap is not the real problem anymore -- except for such things like the MacGuyver show. I haven't been around long enough to know about it :)
RE: Control freewheeling in GM transmissions (4L60-E)
A large part of the reason one way clutches are used is to simplify the act of shifting gears. As patdaly noted above, you can't have two gears of different ratios engaged at the same time without risking a very quick stop. This implies that each gear ratio needs a clutch so it can be individually engaged. In a manual transmission, that would be the synchronizer or a dog clutch. In a planetary automatic (gotta be specific these days, what with all the powershift and automated manuals out there), you have friction clutches (plates or brake bands) and one-way clutches. Until recently, the OEMs have had great difficulty in making shifts from one friction clutch to another smoothly. Too much delay between release of the lower clutch and engagement of the higher ratio clutch, and you're in neutral (engine flare). Not enough delay, and you're back to the two-gears-at-once scenario (tie-up).
However, if you put an overrunning clutch on the lower ratio, then you can engage the friction clutch for the higher ratio without releasing the friction clutch for the lower ratio, because the overrunning clutch will effectively release the lower ratio gear when the higher ratio gear takes up the torque.
When you're looking through the service manual, you want to find the "clutch schedule". This is a text chart that will show the gear selections on one axis, individual clutches on the other, and the field will indicate which clutch is involved in selecting which gear. There's often an adjacent chart that indicates the status of the one-way clutches under engine braking. Once you understand what's needed mechanically, then you can go hunting through the worm trails to figure out how to make it happen.
Happy trails!
RE: Control freewheeling in GM transmissions (4L60-E)
I suspect the power flow/shift scheme is similar to the 4L series...
In Drive range: first gear, the input clutch and 1-2 band are both applied, and the input sprag is holding. Release the gas, the input sprag will overrun.
In Manual Lo, the input clutch and third clutch are applied, along with the 1-2 band.
So, for engine braking in first, you need the third clutch applied.
In Drive range, second gear: input clutch, 1-2 band, and second clutch are all applied.
In manual 2nd, you have the same. (???) that means that we should have engine braking in Drive range second gear- but it would normally just upshift instead...
In Drive range, third gear: - input clutch and 1-2 band are both now released, and you have second clutch and third clutch applied.
In manual 3rd: second clutch, third clutch, and input clutch are applied. hmm- so apply input clutch for engine braking in 3rd?
In Drive range 4th gear- the fourth clutch, third clutch, and second clutches are applied.
This is from the GM Service Manual for the vehicle (which was mine until a few months ago...) Beautiful full color hydraulic circuit diagrams, full description of shift swquences, etc. Hopfully you can find one like this for your vehicle!
happy hunting.
jay
Jay Maechtlen
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
I'm not sure what you mean by "operating the shift quadrant" with a pair of solenoids.
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
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://ww
Good luck with your implementation!
RE: Control freewheeling in GM transmissions (4L60-E)
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.
RE: Control freewheeling in GM transmissions (4L60-E)
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.
RE: Control freewheeling in GM transmissions (4L60-E)
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.
RE: Control freewheeling in GM transmissions (4L60-E)
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.
RE: Control freewheeling in GM transmissions (4L60-E)
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
RE: Control freewheeling in GM transmissions (4L60-E)
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.
RE: Control freewheeling in GM transmissions (4L60-E)
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".
RE: Control freewheeling in GM transmissions (4L60-E)
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
RE: Control freewheeling in GM transmissions (4L60-E)
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... :)
RE: Control freewheeling in GM transmissions (4L60-E)
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
RE: Control freewheeling in GM transmissions (4L60-E)
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.
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
IS IT 4L60 OR 4L6OE COLD BE EITHER IN 93 BOTH WORK THE SAME EXCEPT ELECTRONIC CONTROLL OF VALVES AND PRESSURE REGULATOR. OD POS STARTS IN LOW LOW ROLLER CLUTCH HOLDING WITH FORWARD CLUTCH HOLDING INPUT SPRAGUE HOLDINGPOWER FLOW IS THRU FOWARD CLUTCH AND SPRAGUE TO GET SECOND BAND APPLIES(INTERMIDIATE)THIS CHANGES ROTATION OF LOW ROLLER CLUTCH AND IT DOESNT NEED TO HOLD IT IS STILL THERE THO.THE BAND IS APPLIED BY THE INT. PISTON 0N THE SMALLER SIZE TOWARD THE COVER THE OUTER PISTON IS USED FOR OD APPLY.TOSHIFT TO 3RD WHEN CONTROLS CALL FOR IT THE SAME PRESSURE THAT APPLIES 3/4 CLUTCHES APLLIES TO THE INNER SIDE OF THE INT PISTON THICH IS MUCH BIGGER THAN THE APPLY SIDE PRESSURE BEING THE SAME BUT THE SQUARE INCHS BEING LARGER THE PISTON RELEASES THE BAND THE 3/4 CLUTCHES ARE STILL ON . WE NOW NEED 4TH GEAR SO THE OD PISTON HOOKED TO THE SAME BAND IS APPLIED BE PUSHING THE APPY PIN THRU THE RELEASED INT PISTON AND APPLIES THE BAND WHICH BRINGS A PLANET INTO PLAY TO GET OD THE INPUT HOUSING WHICH IS DRIVEN DIRECTLY FROM THE CONVERTER IS HOOKED TO THE REACTION SHELL KEEPS THINGS TURNING AND THE FORWARD CLUTCHES ARE RELEASED. THE INPUT SPRAGUE IS RELEASED TO PREVENT A TIE UP TO DOWN SHIFT OD PISTON IS RELEASED TO DOWN SHIFT FROM 3RD THE 3/4 CLUTCHES ARE RELEASED THIS REMOVES THE HOLD OFF PRESSURE ON INT PISTON TO APPLY INT BAND BEING THE APPLY PRESSURE HAS ALWAYS BEEN THERE. TOGO TO LOW THE INT BAND PRESSURE IS RELEASED AND THE L/R ROLLER CLUTCH IS THERE WAITING TO LOCK UP AS THE DIRECTION IS NOW REVERSED. WHEN USING (d) OVERRUN CLUTCHES PARALELL INPUT SPRAGUE SO IT CANT FREE WHEEL IN 3 AND 2 AND 1 BUT THE ROLLER CLUTCH MUST BE LOCKED IN LOW WHICH IS DONE BY SHIFTING TO 1 POSITION WHICH BRINGS ON THE LOW AND REVERSE CLUTCHES IN THE CASE. USING MANUAL LOW AND SECOND ALSO RAISES THE PRESSURE. IN D POS IT WILL STILL FREWHEEL; IN SECOND BECAUSE OF L/R ROLLER WHICH LETS YOU SLOW DOWN TO A STOP WITHOUT A LUNGE WHEN IT SHIFTS TO LOW.
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
RE: Control freewheeling in GM transmissions (4L60-E)
DAXCAR HAVE TO DUE MORE THINKING ON A WAY TO DO THIS SIMPLE. OLD EDSEL HAD PUSH BUTTON ELECTICAL SHIFT POSITION IN THE CENTER OF STEERING WHEEL. I WAS FORD SVC MNGR AND DIDNT WORK ON THESE BUT IBELIEVE IT HAD SOME KIND OF MOTOR AT THE TRAN. ICAN FIND OUT FOR YOU. THE MODEL T WAS A MANUALY CONTROLD PLANETARY TRAN WITH CLUTCHES AND BANDS ???
RE: Control freewheeling in GM transmissions (4L60-E)
iwill look up some more soon as ican
RE: Control freewheeling in GM transmissions (4L60-E)
I also build trans for a living, and have my own shop.
The sprags, or roller clutches are there to allow a higher ratio (lower gear) to freewheel, as stated, to avoid a tie up. The real reason it comes on in manual low is to add more holding power for towing, plowing, etc. The overrun clutch, also known as a coast clutch should be on in manual 3,2,1. As stated above, it is comprised of only two frictions. It is pretty wimpy.
Now, if the four- three sequence valve gets stuck, the clutch will not come on... this should give a clue how to turn it on/off.
As far as possibilities that caused your problem, it is not the bands. You have no coast clutch operation. The 4-3 valve could be stuck on, the stator support sealing rings could be bad, you could have cracked the coast clutch piston, burned the seals, or burned the frictions. It sounds as if you have been into the valve body, so I would start there. Other possibilities include: checkballs in turbine shaft not sealing or missing, or the checkball in the piston not sealing (worn out seat).
As far as a good hydraulic flow diagram, I have a copy of MOTORS domestic trans manual, fourth ed. It does not cover the 4l60e, but has the 700 r-4, or 4l60. Hydraulicly, they are identical, in that the two are mechanically very similar. If you really want a good diagram, get a fifth edition.
Good Luck!
chris