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Another torque converter thread... but different (I think)

Monster Mopar

Monster Mopar

NAXJA Forum User
Location
Moses Lake, WA
My torque converter in my 89 AW4 seems to work properly under most circumstances. Except after being put under a heavy load it will not lock up again until the jeep sits for an extended period of time.

I've found 2 situations that will cause this to happen:

1. When driving at highway speeds and fighting a strong headwind for an extended period of time where my transmission has to consistantly down and up shift to maintain speed (We get really strong winds here). Once I'm out of the wind the torque converter no longer locks up, until it sits for several hours.

2. Sunday I was playing in the sand dunes for a few hours (a side trip after a job interview) Once I hit the highway my torque converter did not lock up. But When I drove it to work on Monday it was fine.

Thoughts?

Now hitting the brake switch doesn't cause the converter to unlock so I went ahead a picked up a new switch. But I don't think this is causing my problem, it seems more heat related.
 
I would try and adjust your brake switch first. That was the issue in mine when it wanted to stay locked years ago. Could also be a bad solenoid in the trans itself. When was the last filter and fluid change you did. If it's due might as well test them while the pan is off.
 
Monster Mopar said:
My torque converter in my 89 AW4 seems to work properly under most circumstances. Except after being put under a heavy load it will not lock up again until the jeep sits for an extended period of time.

I've found 2 situations that will cause this to happen:

1. When driving at highway speeds and fighting a strong headwind for an extended period of time where my transmission has to consistantly down and up shift to maintain speed (We get really strong winds here). Once I'm out of the wind the torque converter no longer locks up, until it sits for several hours.

2. Sunday I was playing in the sand dunes for a few hours (a side trip after a job interview) Once I hit the highway my torque converter did not lock up. But When I drove it to work on Monday it was fine.
Click to expand...
This sounds like a loose connection or dirty switch contact, because it is intermittent. I would go for the dirty switch contact first, since it seems to be heat related. Have you done any modifications to the brake booster or master cylinder?

Monster Mopar said:
Now hitting the brake switch doesn't cause the converter to unlock so I went ahead a picked up a new switch. But I don't think this is causing my problem, it seems more heat related.
Click to expand...

This symptom is the opposite of what you first described. It is most likely the switch out of adjustment. Have you messed with the white switch yet?

The RENIX era XJ has two separate switches on the brake pedal. Since Chrysler took over the engineering work, beginning in 1991, this is all done with one switch. With RENIX, one switch is for the brake lights. The other switch (white in color) is to unlock the torque converter and turn off the cruise control. This white switch also has a valve in it to dump vacuum from the cruise servo (vacuum hose attached). That is the switch you need to troubleshoot, NOT the brake light switch. This white switch can easily be taken apart and the contacts cleaned.

The wiring to this white switch is quite interesting. The switch is wired to apply a ground to the TCU through a NO set of contacts. The switch is actuated when the pedal is up. If this ground is missing at the TCU for any reason (adjustment, bad connection, defective switch, dirty contacts), the TCU thinks the driver has his foot on the brake, and will NOT lock the torque converter. You need to make voltage checks at the TCU while the problem is active.

I had a similar problem to yours in my 1987 XJ. This circuit is discussed in detail here:
http://www.naxja.org/forum/showthread.php?p=245489676#post245489676

MoFo
 
magimerlin said:
I would try and adjust your brake switch first. That was the issue in mine when it wanted to stay locked years ago. Could also be a bad solenoid in the trans itself. When was the last filter and fluid change you did. If it's due might as well test them while the pan is off.
Click to expand...

The problem with testing the solenoid is it only does it under certain conditions. So if I dropped the pan I'd have to do it right after I parked the Jeep when I was having the problem. But by the time the oil drained and the pan was off there is no way to be certain that the failing condition is still present.

I think the way to do it is to monitor the signal to the solenoid. If the TCU is commanding TC lock up and it is not locked then I know it's probably a solenoid issue.
 
MoFo said:
This sounds like a loose connection or dirty switch contact, because it is intermittent. I would go for the dirty switch contact first, since it seems to be heat related. Have you done any modifications to the brake booster or master cylinder?
Click to expand...

I haven't but I'm not sure if the previous owner has. Is there any common mods that are easy to distinguish?



MoFo said:
This symptom is the opposite of what you first described. It is most likely the switch out of adjustment. Have you messed with the white switch yet?
Click to expand...

Yea, I figured it was 2 different problems. To clarify I was describing how hitting the brake did not unlock the TC when I'm not experiencing my no lock issue

MoFo said:
The RENIX era XJ has two separate switches on the brake pedal. Since Chrysler took over the engineering work, beginning in 1991, this is all done with one switch. With RENIX, one switch is for the brake lights. The other switch (white in color) is to unlock the torque converter and turn off the cruise control. This white switch also has a valve in it to dump vacuum from the cruise servo (vacuum hose attached). That is the switch you need to troubleshoot, NOT the brake light switch. This white switch can easily be taken apart and the contacts cleaned.

The wiring to this white switch is quite interesting. The switch is wired to apply a ground to the TCU through a NO set of contacts. The switch is actuated when the pedal is up. If this ground is missing at the TCU for any reason (adjustment, bad connection, defective switch, dirty contacts), the TCU thinks the driver has his foot on the brake, and will NOT lock the torque converter. You need to make voltage checks at the TCU while the problem is active.

I had a similar problem to yours in my 1987 XJ. This circuit is discussed in detail here:
http://www.naxja.org/forum/showthread.php?p=245489676#post245489676

MoFo
Click to expand...

Thanks for the info.... and apparently I bought the wrong switch, haha... On a side note. The previous owner removed all the cruise control components from the jeep. I wonder if the switch was removed as well?? I guess I need to go have a look
 
MoFo said:
This sounds like a loose connection or dirty switch contact, because it is intermittent. I would go for the dirty switch contact first, since it seems to be heat related. Have you done any modifications to the brake booster or master cylinder?



This symptom is the opposite of what you first described. It is most likely the switch out of adjustment. Have you messed with the white switch yet?

The RENIX era XJ has two separate switches on the brake pedal. Since Chrysler took over the engineering work, beginning in 1991, this is all done with one switch. With RENIX, one switch is for the brake lights. The other switch (white in color) is to unlock the torque converter and turn off the cruise control. This white switch also has a valve in it to dump vacuum from the cruise servo (vacuum hose attached). That is the switch you need to troubleshoot, NOT the brake light switch. This white switch can easily be taken apart and the contacts cleaned.

The wiring to this white switch is quite interesting. The switch is wired to apply a ground to the TCU through a NO set of contacts. The switch is actuated when the pedal is up. If this ground is missing at the TCU for any reason (adjustment, bad connection, defective switch, dirty contacts), the TCU thinks the driver has his foot on the brake, and will NOT lock the torque converter. You need to make voltage checks at the TCU while the problem is active.

I had a similar problem to yours in my 1987 XJ. This circuit is discussed in detail here:
http://www.naxja.org/forum/showthread.php?p=245489676#post245489676

MoFo
Click to expand...

I had a knock down drag out debate about 12-18 months ago about this topic with Cruiser 54 hrer, not long ago, and when the dust cleared we all agreed the white dual pneumatic-electric switch only controls the cruise control, and not the TC lock up. It is the second pair of wires on the brake switch itself that tells the TCU to unlock the TC, and tells the TCU if the brakes are off and if it is OK to lock the TC. I also, IIRC, found a bleed diode in the wires from the brake switch to the TCU that may be involved as well!!!!
 
Ecomike said:
I had a knock down drag out debate about 12-18 months ago about this topic with Cruiser 54 hrer, not long ago, and when the dust cleared we all agreed the white dual pneumatic-electric switch only controls the cruise control, and not the TC lock up. It is the second pair of wires on the brake switch itself that tells the TCU to unlock the TC, and tells the TCU if the brakes are off and if it is OK to lock the TC. I also, IIRC, found a bleed diode in the wires from the brake switch to the TCU that may be involved as well!!!!
Click to expand...

hmm interesting.... I'm not familiar of the function of a bleed diode. What would it's purpose be? I'm familiar with diodes, just not bleeding ones, haha.
 
Monster Mopar said:
hmm interesting.... I'm not familiar of the function of a bleed diode. What would it's purpose be? I'm familiar with diodes, just not bleeding ones, haha.
Click to expand...


I am not sure if it is a diode or resistor. Also not sure yet, what its purpose is. All I know is I found one end of it grounded, and the other end tied into the brake switch power feeding the TCU brake power signal. And it seemed to be leaving a small standing voltage of about .2 to .5 volts on the wire in the off position, and 12-13 volts in the on position on mine. I never figured out why it is there, or what its proper state is. I just know I found it hiding in the dash wiring harness near the TCU in the lines from the brake switch to the TCU on my 87. The fact that the voltage never dropped to 0.0 in the off position made me think it might be a diode, as a resistor (bleed resistor) would eventually take the standing voltage to zero? But the TCU is a block box too, with no schematics, so it I don't know, what I don't know, LOL, like is the TCU sending voltage into the same wire? Or was my brake switch bad, and sending a trace voltage into the wire at the time. I never got that deep into those wires since.
 
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