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Thread: Some LT1 4L60E transmission tuning observations (8051)

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    Some LT1 4L60E transmission tuning observations (8051)

    I promised lionelhutz I'd start a thread on what I'd learned about 4L60E tuning in 8051 LT1 cars, specifically B-cars. Some of this is my own learning, and much of it is what I've gleaned from others who wish to remain anonymous. To all those who have helped me, thank you.

    Let's start with some hydraulic theory:
    1. The 4L60E builds pressure via a variable displacement vane pump located in the front of the trans, just behind the torque converter, and driven by the torque converter shell. If the engine is running, the pump is running.
    2. Line pressure is regulated via a balance circuit. Two small springs push the vane pump's outer ring (the "slide") offcenter which increases the displacement. Line pressure pushes back on the other side, trying to put the ring back on center, reducing pump displacement. The Electronic Pressure Control (EPC) solenoid (also known as a force motor) runs on a duty cycle (pulsewidth-modulated) which, when deactivated, allows leakage out of this circuit which then lets the springs win and more line pressure is generated. At idle, the EPC solenoid is fully on, fully closed, and the trans is making min line pressure except for in reverse, which has a separate boost valve to give more clamping power. It should be noted that the stock pump slide springs tend to give way to centrifugal force around 5500rpm, softening the shifts at or above this RPM. I think this is a built-in safety feature for stock vehicles but would not be good for peaky motors making lots of power above here. Sonnax makes a stronger spring, and for racing applications, some builders will physically block the pump slide all the way over for max pressure no matter what.
    3. GM built the 4L60E so in the event of an electrical problem or electrical power failure to the trans, the transmission automatically defaults to max line pressure and still has manual 2nd, 3rd, and reverse. People call this "limp mode" but the only time I can ever find that GM used that lingo was with the Northstar engines during a catastrophic coolant loss event. Pull the codes and fix the problem and you're back in business.
    4. The 4L60E has no built-in pressure sensor to provide feedback to the PCM, so all it can do is gauge shift quality based on time it takes to complete a shift. Ebay seller cmbclalb sells a good one that I've used for a long time. A healthy 4L60E will have around 70psi at idle in Park, Neutral or Drive, and climb to around 150psi in reverse. You should see over 200psi at WOT at some point in 1st gear.
    5. The 4L60E is a bit of a hybrid transmission in that the shift solenoids command the START of the shifts, but the actual shifting is still completed by hydraulic valves, unlike something like the Chrysler 41TE where the solenoids directly fill the hydraulic circuits with no additional valves. Sometimes these shifts take a long time to complete, so if you're hitting the rev limiter and you have sufficient line pressure during the shifts, you need to reduce the shift MPH to get the shift to complete on time. A looser converter, numerically lower rear axle, more engine torque, and more vehicle weight will all exacerbate this late shift behavior.
    6. Shifting harder IS shifting faster, and vice versa. It's really a balance point. For modded vehicles, the only way to get your 4L60E shifting perfect assuming it's in good mechanical health is to dial it in over the course of a datalogging/tuning session, or in my case, a road trip. Avoid hard shifts, period. It is needlessly shock-loading the transmission and driveline. The clutches are there for a reason, and smooth quick shifting will not wear the clutches at any appreciable rate.
    7. The 4L60E is now a mature transmission since it's been out for so long. Sonnax and others make many upgraded parts for it. There is no longer any excuse for an unreliable 4L60E. If your builder can't keep the 3-4 clutchpack together and you have tuned it for good 2-3 shifts, it is HIS fault, period. If your builder thinks Sonnax is crap, then you need to find another builder as I have found no one else who has explored the real reason for 3-4 clutchpack failures (input housing distortion and valvebody hydraulic leaks) more thoroughly than Sonnax. I do not work for Sonnax and never have, but I have spoken at length with their lead 4L60E parts developer and he knows his stuff.
    8. There have been various electronic shift improvers marketed throughout the years. These are basically resistors spliced in series with the EPC solenoid, reducing current and thus shifting line pressure up across the board. It "feels" firmer, but you've also needlessly raised line pressure at idle and part throttle while doing nothing for WOT. Avoid these components.
    9. A couple of quick notes on valvebodies, accumulators, bushings, and hole drilling.
    A. Valvebodies, especially ones with higher mileage, are very likely to have more leaks around the valves. Pay attention to this, and a good rule of thumb is that if Sonnax makes an aftermarket valve for a particular spot in the valvebody, they did so for a reason.
    B. Accumulators are basically fluid shock absorbers that work only at part throttle (at WOT they are slammed against the end of the bore and they don't have much effect). It was fashionable for a time to block accumulators in place in high-power applications. I would not recommend this for any street car as there is no way to dial out enough pressure to soften the shifts enough to compensate. This is especially true for the 2nd accumulator (1-2 shift). If you have taken out all the line pressure from the 1-2 shift, I would check the accumulator first; then check the 1-2 feedhole to see if it got drilled real big, then the servo to see if someone put in a bigger servo, and finally the 2-4 band to see if someone installed a wider band.
    C. Anytime you have a 4L60E rebuilt, have all the bushings replaced, and install any upgraded Sonnax bushing Sonnax makes. This is the number one way you can help avoid internal leaks and maximize fluid control.
    D. Be real cautious about big hole drilling. A little goes a long way. Also, don't let anyone convince you to enlarge the shift solenoid feedhole. If you do, it'll actually take MORE TIME to complete the shifts because those circuits are a feed-bleed setup that requires the feed and bleed orifices to have certain relative sizes.
    10. ALL of the 4l60E electronics can be accessed and replaced without dropping the transmission.


    Tuning suggestions:
    1. Just like engine tuning, the transmission MUST be in good health before you tune it. If it's got low line rise, fix that first before you tune. Commanding max pressure is a fool's errand if the trans is only generating 150psi at WOT and you really need 200+ to get good shifts in the vehicle/powertrain setup you have.
    2. Line pressure is calculated by adding up the various line pressure tables and then dividing that by the "max line pressure" value to get a % duty cycle for the EPC solenoid. DO NOT RAISE THE MAX LINE PRESSURE value. You would effectively be lowering pressure across the board by doing so. BTW the units are wrong - it's not psi. It's just counts.
    3. Think of line pressure tuning as two separate regions; during shifts, and between shifts. If the trans is not slipping in gear, then leave the line pressure tables alone and ONLY reduce the "Shift time (sec) vs. TPS vs. shift." In the last LT1/4L60E I tuned, the WOT shifts were perfect at 0.600 sec for 1-2 and 0.875 sec for 2-3. Leave the 3-4 shift at 0.00 seconds because the 4th gear apply piston is small and needs no softening. That 1-2 shift value gave me just a slight chirp from the rear tires. I tried 0.400 sec but it was too harsh and barked the tires. 0.800 sec wasn't firm enough and was actually cutting pressure during the shift according to the logger.
    3. I would only up line pressure if you think it's slipping, OR if you installed a larger throttle body which is causing more engine torque to be applied for a given TPS. If anything, lower line pressure during cruise will give you better fuel economy because the pump isn't working as hard.
    4. TCC tuning is a bit of an art. Lots of useful flags in the 8051 binfiles for keeping the TCC locked during various TPS% events, downshifts, etc. I've tried a lot and personally I like the way GM setup the stock TCC behavior. The TC serves as a rotational shock absorber; shifts without the TCC unlocked are jerky and unpleasant.
    5. The '93-94 4L60Es did not have a PCM-controlled TCC apply rate. That came in 1995, with the PWM-controlled apply solenoid & valve. The valve tended to wear the valvebody and cause leaks (the P1870 code in '96-up). You can disable this in the PCM by setting all the TCC apply/release rates to 100% and 0%. If you have a '95 4L60E, strongly consider repairing the valve correctly via a Sonnax kit (either find a shop that has the $$$ reamer and take the valvebody to them to do it, or just buy the reamer and rEbay it when you're done). Don't just block the TCC regulator valve in place at full open, because this will put max line pressure into the torque converter, ballooning it during WOT and possibly damaging the crankshaft thrust bearing in the process.

    I would strongly suggest going for a drive with a real line pressure gauge hooked up to the trans and a datalogger going, monitoring the actual line pressure versus commanded line pressure, in gear, at idle, during shifts, and at WOT, BEFORE doing any tweaks to the tune. You will learn volumes about what the PCM is doing.
    Last edited by sherlock9c1; 08-21-2014 at 07:13 PM.

  2. #2
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    BTW this thread has a lot of good information for $0D tuning:
    http://www.gearhead-efi.com/Fuel-Inj...mission+tuning

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    4L60E transmissions are JUNK in the worst way possible. If you are making any power at all and/or have a heavy vehicle 4L80E all the way! I use .300 for commanded shift times on both the 4L60E and 4L80E (.600 is WAY TOO LONG for a hot rod type setup), only way to keep things from burning up when you are making torque. The turbo 4L80E guys go with 0.00 command shift times. 1-2 shift should chirp the tires otherwise you will cook the 2nd gear band, not a matter of it happening, but when.

    For comparisons purposes, both are the same vehicle. Both transmissions were modified with a Transgo HD2 shift kit prior to being tuned. A stock 4L80E with a shift kit will hold far more power than the best built 4L60E.

    Stock "Black box" 4L60E
    https://www.youtube.com/watch?v=WydwLghk_yw

    Tuned "Black box" 4L60E
    https://www.youtube.com/watch?v=7SgptElOCpY

    Tuned "Silver box 0411" 4L60E
    https://www.youtube.com/watch?v=NPHR6mzCDoY

    Stock "Silver box 0411" 4L80E
    https://www.youtube.com/watch?v=2CqkRkABKk4

    Tuned "Silver box 0411" 4L80E
    https://www.youtube.com/watch?v=yXTXqMCkF34
    Last edited by Fast355; 08-19-2014 at 04:42 PM.

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    I'm not trying to start a debate here; and there's no question that a stock 4L80E will handle more input torque than a stock 4L60E. All I'm trying to do is offer some LT1/4L60E tuning tips. After I rebuilt and beefed up the 4L60E in my car, I've put over 50k on it, drag raced (close to 200 runs), road raced for nearly 5 hours in one day, road tripped, everything, and the pan stayed clean the whole time. AFTER all that (and regular fluid changes), the ideal 1-2 shift time was 0.600 seconds. That trans had good line pressure so I didn't need tiny shift times to make it shift good. Other 4L60Es, especially stock ones with high miles, will likely need shorter shift times. It's really going to come down to the individual vehicle and combination.

    FWIW, the 8051 PCM can control a 4L80E with nothing other than programming changes (and maybe modifying the trans harness connector pinout).

    What I don't want to see is people needlessly raising line pressure in the main tables or raising the "max line pressure" scalar without realizing what they're actually doing.

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    Quote Originally Posted by sherlock9c1 View Post
    I'm not trying to start a debate here; and there's no question that a stock 4L80E will handle more input torque than a stock 4L60E. All I'm trying to do is offer some LT1/4L60E tuning tips. After I rebuilt and beefed up the 4L60E in my car, I've put over 50k on it, drag raced (close to 200 runs), road raced for nearly 5 hours in one day, road tripped, everything, and the pan stayed clean the whole time. AFTER all that (and regular fluid changes), the ideal 1-2 shift time was 0.600 seconds. That trans had good line pressure so I didn't need tiny shift times to make it shift good. Other 4L60Es, especially stock ones with high miles, will likely need shorter shift times. It's really going to come down to the individual vehicle and combination.

    FWIW, the 8051 PCM can control a 4L80E with nothing other than programming changes (and maybe modifying the trans harness connector pinout).

    What I don't want to see is people needlessly raising line pressure in the main tables or raising the "max line pressure" scalar without realizing what they're actually doing.
    I understand on the line pressure thing. There are multiple feed holes that need to be enlarged and numerous accumulator springs that need to be stiffer to get a good shift feel.

    You do realize if you are still using torque management and the corresponding timing retard that you are also retarding the timing for 600 mseconds at each shift. On a car that is going to be used Street/Strip I have no problem running 0.00 commanded shift times on ALL shifts to keep the PCM from trying to reduce line pressure. With the 0411 its pretty easy to adjust command shift times and line pressure to give maximum line pressure at high torque production since all the tables are referenced against engine torque. Also keep in mind that a higher stall converter has a cushioning effect on the driveline and to get the same sharp shifting at WOT and more so at part-throttle it will need a quicker shift timing and more line pressure at part-throttle.

    My stock as the general built it and tuned it 4L60E lasted about 38,000 miles. Rebuilt with a properly setup Transgo HD2 to 4L65E specs and had a decent tune in the PCM to keep the clutches from smoking and it lasted 44K before hard parts failure. At 82K I swapped a 100K mile used 4L80E in it after installing a Transgo HD2 and B82 4.3 converter.
    Last edited by Fast355; 08-19-2014 at 05:11 PM.

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    The last 4L60E I tuned has a firm 1-2 shift that occasionally spins the tires a little, yet glides around town pretty smoothly despite a somewhat loose 2,700 rpm converter. This transmission is on borrowed time however. Has relatively high miles (85K on rebuild) and sits behind a 330-340 HP L31 that is making somewhere close to 400 ft/lbs of torque and its in a heavy 1999 Suburban.

    https://www.youtube.com/watch?v=3RAqXKq1e9Y
    Last edited by Fast355; 08-19-2014 at 05:16 PM.

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    Yeah, the TransGo HD2 kit was good. I really like the Sonnax 4L60E-HP-01 kit even better. It's pricier but it's got a lot more good parts in it.

    BTW the 8051 does not have torque management as far as I'm aware.

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    Quote Originally Posted by sherlock9c1 View Post
    Yeah, the TransGo HD2 kit was good. I really like the Sonnax 4L60E-HP-01 kit even better. It's pricier but it's got a lot more good parts in it.

    BTW the 8051 does not have torque management as far as I'm aware.
    It may have a 1-line type of torque management, similar to the older TBI PCMs. To my knowledge they all have abuse mode torque management that is active under certain conditions. Such as reving the engine above 1,500 rpm and moving the gear selector, such as when rocking a vehicle stuck in snow.

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    Huh. I assume nobody's discovered this? (where's steveo) I know the 4L60E itself has "abuse valves" in the forward and reverse apply circuits which bypass the normal apply process under heavy load conditions and provide much more power to the clutch applies to avoid slipping them during these sorts of applications. If those valves get stuck in the open positions in the bore (been there experienced that), you get really harsh shifts into gear from P/N.

    FWIW, if you're stuck in snow, don't bother shifting. Automatic transmissions take too long to shift. Just use the gas pedal to rock the vehicle back and forth, but leave it in one gear. Worked every time for me when I was in the snowbelt.

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    Quote Originally Posted by sherlock9c1 View Post
    Huh. I assume nobody's discovered this? (where's steveo) I know the 4L60E itself has "abuse valves" in the forward and reverse apply circuits which bypass the normal apply process under heavy load conditions and provide much more power to the clutch applies to avoid slipping them during these sorts of applications. If those valves get stuck in the open positions in the bore (been there experienced that), you get really harsh shifts into gear from P/N.

    FWIW, if you're stuck in snow, don't bother shifting. Automatic transmissions take too long to shift. Just use the gas pedal to rock the vehicle back and forth, but leave it in one gear. Worked every time for me when I was in the snowbelt.
    I use 2nd gear start to rock it enough to move. No issue driving around with the limited ice days we have here. Can't stop people from doing dumb things so GM had to find a way to counter them.

    I also seem to remember the older TBI PCM cutting timing if you manually shifted the transmission above the factory shift points. I guess the PCM saw that as "abuse"

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    (where's steveo)
    even if i had an lt1 to work on; i've never worked on the automatic stuff, i'm a gear jammer. besides a tiny bit of cleanup and confirmation on the xdf, that is.

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    This is great info. Hopefully it helps people understand how the line pressure tables work. I knew the "psi" units were BS but hadn't spend enough time testing things to know how it worked yet.

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    Just my 2 cents worth, please don't mistake a harsh shift for a positive shift. I've been in the transmission repair industry for almost 20 years and harsh shifts are to be avoided. Imagine what abuse you are subjecting the internal components to when you chirp the tires. Generally, when the transmission changes gears, you have several parts rotating at different speeds which must stop at an "instant" during the shift. Have you ever been drilling a hole and hit a spot where the drill wants to stop and break your wrist. This is similar to what happens during a shift.

    The 4L60E is not generally considered a performance transmission due mainly to the 3-4 clutch failure. As stated above they can be built to handle quite a bit of torque. But that is relative to your budget(go figure). I don't have any experience with the 8051 but I do have tons with the 4L60 lol. Enough of my ranting, have a great day everyone.

    Buddrow

    edit: OP's info is great keep it coming.
    If it don't fit force it, if it don't force fit f&%@ it!

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    Quote Originally Posted by buddrow View Post
    Just my 2 cents worth, please don't mistake a harsh shift for a positive shift. I've been in the transmission repair industry for almost 20 years and harsh shifts are to be avoided. Imagine what abuse you are subjecting the internal components to when you chirp the tires. Generally, when the transmission changes gears, you have several parts rotating at different speeds which must stop at an "instant" during the shift. Have you ever been drilling a hole and hit a spot where the drill wants to stop and break your wrist. This is similar to what happens during a shift.
    Agreed x 1000. When people brag "my car chirps the tires at 20% throttle" on a stock sunshell and stock u-joints I just cringe.

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    Quote Originally Posted by sherlock9c1 View Post
    Agreed x 1000. When people brag "my car chirps the tires at 20% throttle" on a stock sunshell and stock u-joints I just cringe.
    Thats not the kind of shift I am talking about. Just a nice, quick, solid, firm shift that sometimes chirps the tires. I have a 4L80E, spicer solids and a 9.5" corporate 14-bolt. With the Transgo HD2 I had to put some torque management back in it to keep the shifts from barking the tires @ 50% throttle.

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