From: John De Armond
Subject: Re: Torque Converter Lockup
Date: Thu, 11 Oct 2001 15:08:18 -0400
"R.J.(Bob) Evans" wrote:
> On Sat, 06 Oct 2001 22:31:13 GMT "William Miller"
> <firstname.lastname@example.org> wrote:
> >let off the accelerator - if the tach drops almost to idle, you're not
> >locked up
> Actually that may indicate a faulty coast clutch or one that is
> disengaged. Better test is as an earlier poster has indicated - goose
> the pedal and watch the tach - if it jumps without a corresponding
> increase in ground speed then you are unlocked.
The problem with this technique is that non-computer controlled
(older) lockup converters and some modern ones will unlock when
doing this. The transmission control algorithm looks at, among
other things, the throttle position (or equiv diesel signal) rate of
change and unlocks the converter to give better feeling throttle
> For deceleration you are right, if the tach doesn't drop to zero then
> the coast clutch and the TC are locked up. However the converse isn't
> necessarily true - if the tach drops to zero there are several
> possible causes.
The most reliable way that I've found to detect converter lockup is
to watch the tach while cruising at constant speed on essentially
flat roadway. Momentarily accelerating, which will positively
unlock the converter, followed by neutral throttle cruise will cause
the converter to relock and that causes a small decrease in engine
RPM. The tach will show a steady pre-lock RPM and then drop a few
hundred RPM when the converter locks.