4L80E TCC solenoid, revisited

[gmctd]

The FSM's are fraught with unpardonable errors - certainly not the least of which concerns the 4L80E TCC solenoid dc resistance value: indicated value is 20-40ohms - real-life works-fine-lasts-a-long-time value = 10-15ohms - read and heed - also, now would be prime time to correct your books'n'charts, kiddies

Now, a word or several vis a vis the differences in lockup function between the wimpy 4L60E and that HD bad boy, the 4L80E:

4L60E TCC is direct lockup, where +12v is placed on the TCC solenoid to apply the TC clutch for hard lockup - the TCC solenoid is higher impedance at 20-40ohms so as not to overheat and self-destruct with constant applied power - not much torque is being applied thru the hollow input shaft, so this method is entirely functional in the girly-man's 4L60E

4L80E TCC is soft-apply by modulation of the TCC solenoid according to torque requirement, which means the TCC is never fully applied - PCM determines required TCC-apply force by measuring slippage between engine rpm and 4L80E Input Speed Sensor rpm - the TCC solenoid is lower dc resistance to achieve quicker response with the effectively lower voltages applied via the Pulse Width Modulation scheme - PCM applies a fixed frequency, varying the width of the pulses according to torque requirements - narrow pulses = low averaged voltage, TCC is lighty applied - wide pulses = higher averaged voltage, TCC is more firmly applied - there is no hard lockup due to large amounts of torque that can be applied to the hollow input shaft - the 4L80E hollow input shafts have a history of breakage in 3500-series wrecker and dump-truck service, thus the soft-apply scheme

The direct dc solenoids are 20-40ohms - the modulated solenoids are ~10-15ohms.

So, after that long slow curve, now for the quick pitch - read and heed, kiddies: there are several hard-lockup schemes available, whereby a simple switch applies direct battery power to the low-resistance PWM solenoid - not good, as the resistance is too low for sustained constant +12v service, overheating the solenoid coil - and, hard-apply increases probability of input shaft failure - while there has been some success in using the schemes, you should still be aware of the imminent danger and probability of failure

Basically, by improving the venerable T400 HD 3sp turbohydramatic trans with overdrive and a lockup convertor, engineering created a fatal error by boring several holes (hydraulic fluid passages) in the input shaft in that bad boy for the TCC apply piston - hard evidence of that error is: soft-applied TCC unlocks anytime the driver eases up on the go pedal, any speed, any load

That's my story, and I'm stickin' to it.......................
__________________

 

[Sunshine]

Wow,,,I`m listen-in jd...:smile5:

 

[JiFaire]

I never argue with JD on technical stuff... but here's my side of things.

I wired up my TCC on a 3-way circuit -

a] The TCC line from the tranny is grounded, PCM is out of the circuit (TCC stays locked)
b] The PCM is connected to the TCC line (normal factory function; PCM controls TCC)
c] The TCC line and the PCM line are both out of the circuit (TCC stays unlocked)

OK, what kind of a nut would do that?

I (normally) only lock the TCC when I'm pulling, in the hills and I need engine braking, or when I'm pulling in hot ambients (helps to prevent overheating)

I unlock the TCC only when I need to access that torque-multiplier when pulling (you know, when you're just a little too slow for 4th locked, and yet 3rd locked is a bit too wound up?)... usually, it's just to get over the top of a hill.

Most of the time (like 90%) I leave things in factory position and let the PCM do what GM wanted it to do.

That being said, JD, while I agree with you on the potential for damage to the TCC coil, I think with my 1994 OBD-I, this is a worthwhile mod. I've not yet had cause to worry about it, and I think I'm using it judiciously. Bill Heath has long recommended this mod for OBD-I trucks and used it in his own vehicles, with no issues.

I never did ask him why he didn't use it with OBD-II trucks.

Could it be that your analysis is why the mod isn't functional on OBD-II systems? Are they different in the way you describe?

Jim

 

[gmctd]

Sets too many DTC's in OBD2

As indicated, there are successes, and there are failures - it is imperative that failure awareness is encouraged - I could not suggest that the fix be used by either a 3500 wrecker driver, or a 3500 dumptruck driver - empirical data suggests that general passenger vehicle use would not be so prone to failure - so, may the PWM force be with you...................

 

[daustin]

Not trying to argue, but i thought the modulated TCC started in '94. When my tranny was acting up in my '93 a couple of years ago i took the tranny out and swapped it with a '95 4L80E. The TCC didn't work right, so i took my original and the '95 tranny to my usual tranny guy. We noticed a difference in the 2, solinoids..etc so.. We looked it up in several manuals, and from what we read the earlier 4L80E's were a "hard-lockup" while the '94 and later utilized the modulated variety. We rebuilt it utilizing the "hard-lockup" TCC setup and it's worked fine ever since. I later sold the '95 tranny to another friend who stuffed it in his '96 and it worked flawlessly in it. Odd i as thought they all were the same? My original does exhibit the foot off the pedal unlock like Doc described. Interesting.
Don

 

[JiFaire]

Docdray mentioned in the other thread that his 1994, c3500 4L80e transmission TCC solenoid tests out at 20-40 ohms.

I would go out and test mine, but it's currently -40*c and I don't like y'all enough to go through that.


Don, you sure the trans you tried came out of a '95 and not a '96?

My understanding was that all 1992-1995 trucks with OBD-I had the earlier solenoids, making the 'hard-lockup' mod acceptable, as Bill Heath indicates on his blog.

Certainly, tons of us have done this mod with no issues to date, other than people who forget to unlock things when they come to a stop. Lots of people have tried the mod on OBD-II trucks and had instant issues. I have not yet heard somebody report those same issues with an OBD-I, which does not mean it can't happen.

That being said, it is ALWAYS prudent to be sure you understand the potential for failure, as gmctd suggests; and I would think that using this mod will, over time, cause your transmission to wear more (seems GM did lots of things to hlep prevent wear and tear). Using it prudently is only, well, prudent.

 

[gmctd]

All the '94^ EFI series use the soft-apply TCC with release upon decel - the pre-94 non-EFI series used a stand-alone TCM to control 4L80E functions - the solenoid was referred to as PWM TCC solenoid - having had no personal experience with the early series, I can neither confirm nor deny PWM function

 

[ghitch75]

i have gottin' code 83 ever seance i put TCC lock switch on the burb....can't get rid of it?......i guess JD'S soap box is my trouble?.....ok JD how do we get TOW & HAUL with A 95?

 

[Sunshine]

To cut it short I put question to the suppliers that I brought the TCC solenoid from about a 10-15 Ohm or a 20-40 Ohm....


"Paul, I referred your question to one of my technicians. The resistance of the solenoid can fluctuate heavily due to several factors, including temperature and the windings of the coil wire within the solenoid. They tend to have a +/- factor of 10%. Also when testing a solenoid like this, you have to be careful not to test it too long. It is a on/off solenoid and can be damaged if not cooled with fluid(trans). I would say that part failure of new parts is very rare. Thank, John "

Appreciate all of you chiming in, educational..

/Paul

 

[gmctd]

Correct - to interpolize, +/- 10% of 20-40ohms would then be 18-22 to 36-44ohms - several other 4L80E references indicate the 4L80E TCC solenoid is 10-15ohms, which would be, at 10% = 1-1.5ohms, 9-11 to 13.5-16.5ohms, far cry from 20-40ohms - the on-off solenoids in the valve body are 20-40ohms, the pulsed solenoids are not

Even at that, the FSM states the acceptable range to be 20-40ohms, where the average would be 30ohms - a used version and a new version were both measured at ~10ohms cold - I'd run with that....................

 

[gmctd]

Any of you guys out there with the '92-'93 mech injected 6.5TD and 4L80E: does the TCC unlock when you ease up on the go pedal, at some speed above 45mph?

Watch the tachometer, where available:

- if engine rpm remains steady, dropping slowly as vehicle slows, you have lockup

- if engine rpm drops rapidly to some lower rpm, then dropping slowly as vehicle slows, you have unlock, just like the EFI versions

 

[THEFERMANATOR]

My ATSG lists that the 92-93 still uses PWM, but the solonoid is a different style. The 92-93 ran at a different frequency and used a cleaning cycle that the PCM commanded every 10 seconds or so. In 94 they changed the PCM programming and the frequency at which the solonoid operated and eliminated the cleaning cycle. This was the 93 to 94 changeover in the solonoids. You can use a later model tranny in the early ones it says, but you have to get a modified PROM to run at the different frequency.

 

[daustin]

Docdray mentioned in the other thread that his 1994, c3500 4L80e transmission TCC solenoid tests out at 20-40 ohms.

I would go out and test mine, but it's currently -40*c and I don't like y'all enough to go through that.


Don, you sure the trans you tried came out of a '95 and not a '96?

My understanding was that all 1992-1995 trucks with OBD-I had the earlier solenoids, making the 'hard-lockup' mod acceptable, as Bill Heath indicates on his blog.

Certainly, tons of us have done this mod with no issues to date, other than people who forget to unlock things when they come to a stop. Lots of people have tried the mod on OBD-II trucks and had instant issues. I have not yet heard somebody report those same issues with an OBD-I, which does not mean it can't happen.

That being said, it is ALWAYS prudent to be sure you understand the potential for failure, as gmctd suggests; and I would think that using this mod will, over time, cause your transmission to wear more (seems GM did lots of things to hlep prevent wear and tear). Using it prudently is only, well, prudent.

jFaire,
It may have been a '96 tranny, everything but the lockup worked just fine. When we put it in the later model truck the lockup worked perfectly. I got another for my '93 out of a '92 and the lockup worked prefectly. I read somewhere about the change to a different TCC solionoid in '94 'cause the tranny parts people ask about the build date stampled into the tranny side.
I've got that other '93 in the shop, i'll see about ohm'ing the solinoid out. )
Don

 

[gmctd]

The line pressure solenoid is also pwm - PCM pulses it to full pressure every so often to prevent the shuttle-type valve from sticking in it's bore - over a period of time, as mileage accrues, this can be felt at steady speeds as a slight 'bump' - this does not apply to the TCC solenoid

 

[thedole]

Sooo... If you want to have a TCC lockup on the soft lockup solenoids you would best go with an oscillating circuit with a pulse width(and frequency) that resembles what the pcm puts out at max? Bit more complex then a simple switch but shouldn't be too offputting right?

 

[gmctd]

I had kluged up a 555 timer, fixed 30hz frequency, config'ed for varying pulse-width driving a power FET, but when you get full apply, it's the same as direct +12v to the solenoid - however, you could use it for constant soft-apply, wresting all control from PCM, like with a manual switch on the 4L60E - have the brake-switch interrupt for sudden emergency braking - where PCM applies lockup according to torque requirement as well as torque input, you could set it for max soft-apply anytime your switch is enabled - just keep an eye on the transmission temps and engine rpm slippage - basically, they determined that full lockup is not needed at unloaded cruise, which reduces engine overhead and saves wear and tear on the front pump, improving fuel economy - PCM can compare slip-rates and loading and react infinitely quicker than the driver - the main advantage to manual control would be lockup at lower mph for improved economy with no erratic unlock in traffic conditions - also better for engine braking

 

[thedole]

Approximately what duty cycle would the pcm use under unloaded cruise conditions? I'm thinking this would be a place where it could be a great project to use a little programmable chip that took the pcm signal as input and modifyed it according to some switches and/or pots as inputs. But I have very limited understanding of this whole system so my ideas may be based on erroneous assumptions!

 

[tracy]

gmctd asks: (Any of you guys out there with the '92-'93 mech injected 6.5TD and 4L80E: does the TCC unlock when you ease up on the go pedal, at some speed above 45mph?

Watch the tachometer, where available:

- if engine rpm remains steady, dropping slowly as vehicle slows, you have lockup

- if engine rpm drops rapidly to some lower rpm, then dropping slowly as vehicle slows, you have unlock, just like the EFI version.)

My 93 will drop to neutral if I let off on the acc. pedal, engine goes right back to idle rpm. Zero engine braking, I love being able to lockup TCC for engine braking going down hills also I have no lockup untill 55mph because of the 3.42 gears, that means 3rd is practically without lockup, a real pain in the butt when climbing long grades or pushing a head wind with the camper on. The lockup switch mod has been a real improvement on my truck. I would gladly replace a occasional lockup solinoid for all of it's benefits.

 

[gmctd]

I don't have an OBD2 system, so anyone with Autoenginuity: need to observe TCC pwm percentage at various speeds after lockup, incl mild and aggressive accel without causing unlock, also decel - could also note % of input slip, and might also get line pressure % during all observed events

I noted this stuff on my OBD1, but that was back ~'05-'06, and I've slept some since then - you know what they say about old age: several things start to fade the older we get - one is memory, but I can't remember what the others are................

 

[mamzerook]

I am having issues w/ dtc 39,83. This trans is a fresh rebuild, hard 1-2 shift, floats into third, complete slippage, no command 1st or 2nd holdback. even when I lock TCC switch, I can feel it kinda lock under power and is loose under compression! Looked at all external harness, grounds, ignition power supply, and will have to drop the pan next. the problem is intermittent qas it shifts ok when first started and buggers up soon after.I am going to eliminate the TCC mod and see what happens. Any other suggestions? do you think I burnt the solenoid? If so would it still be intermittent?