redvet99

Has anyone had problems with their torque converter lockup clutch slipping when they switched to synthetic?

Rebuilt my tranny couple of months ago. Back to stock tune with Protorque (recently refreshed by them) 3,000 stall lockup converter.

No knock retard, and brake pedal TCC switch is newly replaced and shows OK in PCMCOMM (have lt1-edit)...BTW, this is in my 95 Lt-1 Corvette Coupe.

Converter clutch slips above 65 mph or so when above 197F when throttle barely pushed past cruise speed to go a little faster....seems to hunt on-off-on-off. Pushing fluid temps higher than I'd like 230F at 93F ambient.

Help

Gilbert@Ace Racing

I have not experienced a TCC slippage, chatter condition when using synthetic fluids. We ran Royal Purple in the test Mule vehicle for a long time... mainly because of the temps we were taking it to hot lapping it at the track last summer.

That being said, can you tell us if it is being commanded to lock and unlock when it is symptomatic... I'm pretty sure you would have mentioned that... so I would say no it is not. But please verify that! It is paramount to this discussion, I don't like to take things for granted, thanks.

Was this an issue before the rebuild? Most converter shops "rebond" the converter clutch disc linings themselves... it might be a good idea to ask those guys if they did so on your converter, if they did ask them if tey used a "paper" material or a "fiber" material. It could easily be the clutch material itself!

If that's the case, ask them what fluid they would recommend, try changing fluids and see what happens then.

Good Luck.

g

performabuilt

iTrader: (25)

Well Im not sure from your description "hunting" that slipping would be the proper term sounds more like its turnng off and on and PWM may be functional which will give what I am assuming is a small diameter converter a messy feel for lack of a better word. Or would suggest some time with a scanner with data to see what the PCM is telling the converter to do under those conditions. Was a shift kit of any type installed and if so what was it. I am concerned with PWM because the ratios of slip or pecentage allowed is based on a full diameter converter clutch with a specific clutch surface area.When you reduce this area as with a small diameter converter you will get more slip with the same settings. And I noted you have the stock tune.
As for synthetic verses natural we have and we have customers running both and have not noted any issues with either. Some people however I have seen post on this forum over the past year say they have however.

jimmyblue

iTrader: (11)

I don't know if the LT1 does the same lock/unlock for
detected misfires as the LS1s do. But if it's cycling
and it feels like a hard on/off this would be my bet.
A clutch slip problem is a softer, pedal-proportional
flare (unless you get right up to the tune lock TPS/
MPH point).

I am one who's had fluid related TCC slip problems
but these were more like howling under light load
apply, and slip up grades. Not locking/unlocking.
That, I got on converter #2 and I see this as a
balance issue (also have some increased vibration
I can feel).

Balance in converters seems to be something few
builders care to talk about, except for TCI who
claimed at one point that all their converters were
machine balanced. Small shops may just measure
or maybe static-balance things. How do you know
it's good? Not until after install and the light don't
blink and the converter don't unlock randomly.

joecar

As spoken above by Gilbert, Perfomabuilt (sorry, I don't remember your first name) and Jimmy, there's a few aspects to be looked into:
- what is the PCM commanding for the TCC solenoid (on constant, or on/off cycling);
- what is the PCM commanding for the TCC PWM solenoid (what % duty cycle);
- are any misfire codes being set (I believe LT1 does do misfire detection);
- if the TCC is truly slipping, then any of the following may be possible:
a. the TCC PWM solenoid may be faulty,
b. the TCC friction surface may have damage,
c. pressure is lost somewhere (leaky/sticky valve/solenoid, missing turbine shaft o-ring...)...

If you try different ATF as suggested, be sure to drain all the ATF from the TC, otherwise you would be mixing fluids (4 qts new fluid to 8 qts old fluid); to drain TC, disconnect cooler return line, and while ATF pumps out you add new fluid (may stop engine every 2 qts to catchup on filling); takes 12 qts total, or more if you have deep pan and/or cooler.

joecar

Ah, I just remembered the earlier 4L60E's only had one of those solenoids, I forget which one (I think the first one?).

redvet99

I've pretty much always had this slippage problem with this smaller diameter converter, but only when the tranny fluid gets above 196F or so.

TCC goes into and out of lockup fine. It just seems to start slipping when pressing accelerator pedal just a little more than cruise at highway speeds of approximately 60 mph + in 4th w/lockup, and definately on a highway grade when pushing pedal to keep speed constant.

I don't think it's a missfire problem as the engine pulls fine and with PCMComm there's 0.00 degrees knock retard shown and TCC shows as in constant lockup command.

Is there a tuner program that will allow changing the duty cycle of the TCCPMS ? Think its slipping cause the stock converters a 12" and this is only a 9" and has alot less lockup clutch surface area, so I want to raise the duty cycle to increase TCC lockup pressure....can't do that in LT-1 edit that I'm aware of.

performabuilt

iTrader: (25)

Thats a question I cannot answer. It does sound like your on the right track though. I have limited knowledge of LS1 tuning and none of LT-1 early stuff though its likley you can also you might consider doing away with PWM completey mechanically making lockup a simple on off operation would be another possible option.

redvet99

Dear Performabuilt,

I'm a Corvette Forum member and have a simultaneous thread over their about the TCC apply in a 95 4l60E....does this look right to you?


As far as I've read (I'm no expert) the TCC Solenoid is a simple on/off type solenoid valve located in the pump body that is normally open, when the PCM enegizes this solenoid blocking converter clutch signal fluid from exhausting, this creates pressure in the TCC signal fluid circuit. This pressure causes the converter clutch apply valve to move against spring force and into the apply position. Then basically this valve simultaneously exhausts fluid from behind the TCC pressure plate and applies fluid pressure to the torque converter thus applying the TCC.....WOW

Now, the TCC Pressure Wave Modulation (PWM) solenoid ( a pulsed not on/off solenoid) regulates the amount of fluid flow to the converter side of the TCC.....the apply fluid actually leaks past the clutch surface to cool it and exhausts through the turbine shaft via past that little check ball valve you see in the end of the input shaft when the converter is taken off the tranny (BTW, that ball seats when the TCC valve vents fluid from behind the clutch apply plate and this slows the venting and makes for a smooth clutch apply...that's why if you remove that checkball from the end of the shaft the TCC apply will be very harsh).

So, the TCC solenoid applies the TCC through the TCC Valve and the TCC PWM solenoid varies the pressure on the TCC. Otherwise you wouldn't need a TCCPWM solenoid.....IMO they should never have added one in the first place......

At least that's what I can make of it....I didn't go to tranny school you know

joecar

Yep, that looks right...

TCC solenoid enables the TCC apply;
TCC PWM solenoid regulates/controls the TCC apply pressure;

BTW: PWM = Pulse Width Modulation

Unlike the 4L60E, the 4L80E only has one: the TCC PWM solenoid only.

performabuilt

iTrader: (25)

You hit it right on the head pety much . PWM (plused with modulation) or controllled converter slip was in my opinion never a good idea.
Now on that check ball in the end of the shaft we actually remove it on all our units it will not make TCC apply feel to harsh more like a weak shift into another gears , And its removal can dramatically increase the life of small diameter converter clutches since you dont want them to even think about slipping .

redvet99

And now you tell me about that little check ball...where were you 5 months ago when I was rebuilding the tranny ?

Trade secret

Now all I have to do is find a program that will adjust the TCCPWM solenoid duty cycle and I'm cured !

Any takers?

performabuilt

iTrader: (25)

That or you could go into the valve body mechanically disable PWM.

redvet99

Could you email me on what you actually do to it to modify it?

performabuilt

iTrader: (25)

Yes send me and email at performabuilt@yahoo.com And I will reply with several ways you can address it

redvet99

Emailed you last night, but no reply yet

performabuilt

iTrader: (25)

Sorry been really busy today will have that to you this eve sometime .

redvet99

Well I have to hand it to Frank at Performabuilt

He was nice enough to explain how to mechanically lock out my TCC valve.

I got into my tranny today and walla, no more TCC slippage.

Works perfectly now.

That was really nice of him

performabuilt

iTrader: (25)

You are welcome anytime I am always glad to help anyone when I can.