Leftover O-Rings
A couple of months ago Wayne Colonna went
into detail on a concern that was commonly overlooked on the
4L80-E: problems with the No. 7 and 11 checkball capsules in
the valve body (Technically Speaking®,
September 2005). Many times those capsules would not get
cleaned thoroughly, and that could cause either a slip in
reverse or no reverse. He also talked about the sleeve for the
No. 11 ball capsule and the
O-ring at the end closer to the 3-4 shift valve and how hardening of this O-ring would cause leaks in the actuator-feed-limit circuit, resulting in a 3-4 neutral when the transmission was hot. Many technicians did not even know that there was an O-ring in that location!
O-ring at the end closer to the 3-4 shift valve and how hardening of this O-ring would cause leaks in the actuator-feed-limit circuit, resulting in a 3-4 neutral when the transmission was hot. Many technicians did not even know that there was an O-ring in that location!
This article is about a similar situation.
This time it pertains to the 4T65-E and a complaint of a
torque-converter-clutch (TCC) surging sensation between 40 and
60 mph and/or a P0741 diagnostic trouble code before or after
overhaul. This complaint seems to be more prevalent on
2000-and-up models. The scenario goes like this: While
you’re driving the vehicle between 45 and 50 mph, TCC
slip bounces from 175 rpm down to 50 rpm, back up to 150 rpm
and back down to 35 rpm. The TCC-slip speed seems to come down
to about 25 rpm around 60 mph, although the slip speed will
begin to go up again when the vehicle begins to climb a small
grade.
We notice when monitoring the duty cycle
for the TCC PWM solenoid that the duty cycle seems to be lower
than on other models that we have road tested and that it seems
to cap out around 60%-68% at 60 mph, whereas previous models
would cap out around 75%. This lower duty cycle seems to send
many technicians down the wrong road, the road full of computer
reflashes and engine-load-device repair and/or costly
replacement. You guessed it – this is a normal duty-cycle
percentage; what is abnormal is the slip amount. TCC slip
should be between 0 and 20 rpm at 60%-68% duty cycle.
The root cause of this problem is, of
course, again related to the converter regulator valve but in
this situation may not be a wear-out condition as in the
4L60-E. Figure 1 shows a partial hydraulic schematic of the TCC
apply circuit. Notice that the TCC-regulator-valve line-up has
a bore plug with an O-ring. This O-ring , also shown in Figure
2, when rock hard can cause a significant pressure loss in the
TCC-signal circuit. (For those of you with valve-body testers,
this O-ring also can cause the dreaded “red ATF
underwear.”)
This, in turn, is what creates the surging
sensation. The loss of pressure in the TCC-signal circuit and
lower duty cycle for the TCC PWM solenoid allow the TCC
regulator valve to move to the left, causing insufficient TCC
apply pressure, which may cause engine surging or a DTC P0741
(TCC stuck off). This also may answer the question,
“Where does this O-ring that is left over in the kit bag
go?”
I hope this will help you in your
diagnosis on 4T65-E TCC problems, and we are hoping to see all
of you in the 2006 seminar. I thank Jim Blatt of Lee Myles for
enlightening us on this problem. 
©2005 Transmission Digest
