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!

 

[bakesz28]

Thanx Greg. In my Chilton manual it reads: "There are no band adjustments possible or required". Can I continue to drive the car with this problem? It does shift fine 1-2-3-4, 4-3-2-1 in OD, just the manual shifting 3-2-1 issue.... If not, what's the best way to fix this? Thanx, Jake.

 

[GregLocock]

New bands are the only fix, you'll probably find all your shifts are bit soft. I don't think you'll damage it, but if a band breaks the results can be a bit odd (wrong gear selected etc).



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[modistran]

What are you trying to do,what is your application? Shift control can be rigged with toggle switches.Then is the issue of the lock-up.What year are we working with? Later units have a pulse-modulated t/c instead of a on/off design.

 

[trailingwire]

i know 4l60 in and out. run trans shop. build h/d ones for towing. if you want to know more let me know

 

[bakesz28]

Thanx trailingwire....scroll up a page or two and read my initial post. So far I've had some suggestions to what my prob. is: Stretched bands, stuck 4-3 sequence valve, clogged valve body, over-run clutch failure(cracked apply piston or clutch). Kind of a variety, still not sure whats going on here. Any input could hopefully weigh the scales a little more. Thanx again!!!

 

[trailingwire]

TO BRAKES Z28 AND ALL INTERESTED
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.

 

[trailingwire]

BRAKES Z28 ON YOUR 321 SHIFT MANUALLY IT SHOULD HOLD BACK IN 2,1 POSITION DOES IT SHIFT TO 1 FROM 2 IT SHOUD NOT TILL APPROX 20 OR LESS APPROX IF IT DONT HOLD IN ANY GEAR THE THE OVERRUN ARE NOT HOLDING IF YOU DID THIS SHIFTING A LOT AS SOMEONE SAID YOU MAY HAVE TOOK THEM OUT YOU DONT HAVE TO HAVE THEM BUT THE RESIDUE CAN CAUSE A LOT OF PROBLEMS.MOST TRANS IN CARS THESE CLUTCHES LOOK LIKE NEW IF DRIVEN IN OD. THIS IS A GOOD TRANNY IF BUILT PROPERLY

 

[bakesz28]

trailingwire..........since I had the car, in 3rd I could manually shift to 2nd at about 40 mph or so. It would grab the gear (and chirp if going too fast), and the same for 1st gear at about 20mph. Now, when I drop to 2nd, the tach drops as if I'm holding in a clutch. But it does sound like it is downshifting (as if it were in OD without man. shift) coming to a stop. I can man. shift 1-2-3-4 no prob.

 

[daxcar]

Trailingwire: thanks for the great tutorial. So can you figure out a way to get the 4l60E not to overrrun in Drive when it downshifts? (The original thread question). Can changes be made to the hydraulic circuits? What many of us are trying to do is have manual electronic control of the gears, much like a stickshift, but without having to downshift using the manual valve when we want to "hold" the car on the overrun (eg down a hill). Can it be done? (Obviously the elex would need to be smart enough to control the shift firmness, but no-one yet has come up with a way around the overrrun problem, other than a manual control valve downshift).

 

[trailingwire]

BRAKES Z28 STILL BELIEVE OVER RUN CLUTCHES BURNT OR STRIPT.
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 ???

 

[trailingwire]

daxcar i havent had time to think a lot about the overrun clutches but think about this avenue of thought use a solenoid to feed ovr run circuit and have it applied but cut off electrical with a small circuit which would reconize the voltages appied to the 2 solenoids that give o/d u might have to also use a second one to bleed the circuit down. I am tied up severely and havent had time to look the passages etc up but thought this might help.
iwill look up some more soon as ican

 

[pileoford]

Hello,
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