What is the difference between AT Gear Slippage and Torque Convertor Lock-up?

[outrun]

When my 4L60E is driven after about an hour a weird thing happens.

I am going between the 2-3gear upshift at 1,500 and approximately 45-50mph and then the tachometer will start "dancing" flucuating up an down during the part throttle shift. If i put the pedal down the the trans will shift and everything is ok again.

This happens every so often. I would take it to the dealer but i have the gut instinct that as the problem is so intermittent and hard to replicate they will not be able to duplicate the problem.

Thanks, at this time i have no intention of a rebuil or buying a new reman unit. Propably going to save up here for the Holden GTO or an LS1 transplant for my car

 

[S2000driver]

Does your car have a cable going from the throttle to the transmission? If you do, consider having it adjusted... usually "tighter" is what's necessary. One of my cars has this cable, and the rule is that there should be just enough tension that moving the throttle off it's stop makes the transmission lever at the other end of the cable come off it's stop. When I got the car it was sloppy, adjusting it made the transmission shift just like it should.

On a car that uses a throttle position sensor to electronically control the tranny, the TPS adjustment would be an equavalent thing to check.

 

[MolaKule]

At that speed and rpm, the TCV should be locked-up. It sounds as if the computer is "hunting," trying to make a decision whether to shift or not. I am not sure there is a TS cable from the TBI to the transmission, depends on the year of the vehicle. The 4L60E is supposed to be the electronic version of the 700R4, although I have seen some transition models with both the 4L60E and the TS cables. Check the TBI and see if there is a cable running from it to the tranny. If there is a cable, adjust it by pressing down on a flat lever (toward the firewall) and moving the cable forward or backward about 1/8" each time. You may have to do some experimenting to get the right shift point.

Gear's dont slip but bands do, caused by insufficient hydraulic pressure. It sounds as if something is confusing the computer's decision making software, assuming the shift point is controlled by the ECU. You may have to go as far having a pressure check done on the transmission.

 

[novadude]

GM & Ford both use PWM (pulse width modulation) strategy where the pulse the lock-up clutch apply fluid to slip the clutch in 3rd gear.

When the friction modifiers get depleted in the oil, this results in shudder, a real problem in Fords, and the whole reason they introduced Mercon V.

Sounds like you may be seeing the effects of the PWM converter control, as the clutch is being applied/released. Maybe fresh fluid would replace friction modifiers and allow for smoother operation?

 

[novadude]

Oh... BTW... I think GM went to PWM on '95 cars (for LT1's, anyway). I not positive, but I think this is true.

'94 4L60E *may* have used the traditional on/off converter clutch apply strategy.

 

[MolaKule]

Thanks NovaDude,

I have a '92 Sub 4X4 with a 350 V8 and it has a 700R4 with both a TS cable and electronic control, one of those transition models. Here's the kicker - the shop manual shows a 4L60E layout but the ID tags on the actual tranny show that its a 700R4, but it has all of the 4L60E cables from the ECU going to it.

I use Schaeffer's #204S ATF and have had good luck with that fluid. Very smooth shifting.

[ February 08, 2003, 01:07 AM: Message edited by: MolaKule ]