86 Auto E4N71B not downshifting when slowing/coming to a stop
09-15-2024, 10:52 PM
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86 Auto E4N71B not downshifting when slowing/coming to a stop
86 300ZX N/A Automatic,
Symptom: Trans is intermittently not "releasing out of gear when slowing down (no 3-2, 2-1, etc)-- such as when coming to a stop ("Decel" downshifting)...
Way to replicate:
-drive normally; gears change up just fine thru normal driving,
-But then come to a stoplight, and as you slow down, trans intermittently remains in say... "3" (so acceleration from the stoplight then becomes very sluggish as you'd expect from a higher gear).
When this happens, you can *override* and move the selector down to "1", and that corrects it instantly and will force the trans "fine" into 1st gear for proper takeoff and subsequent upshifting gear changes.
But 3-2-1 is Intermittantly not functioning "on its own".
----
150K miles, fluid just changed (was older fluid in there originally but smelled ok, bottom of pan looked fine- and no notable debris). Very well maintained, always-garaged car otherwise, with gentle driving since the late '80's.
Car has been driven sparsely in the last 10 years (about 9k miles).
I was curious what trans part(s) likely play a role in "decel" downshifting on the E4N71B; and might it be fixable?.. (Big items like valve body? Governor? Vacuum? TCU/computer?)
I saw a mention in diagrams of an external mounted "downshift" (lockdown) solenoid - on the side of the trans case -- as well as a vacuum modulator... (?)
Trans does shift fine otherwise -- no slipping, etc. through any of the gears… It is just this decel symptom, "clinging" to last-used gear, instead of downshifting on its own during decel/slowing down.
For what it's worth, if it is related at all – the digital speedo recently reads zero when driving – I attribute this likely to a speedometer cable /transducer problem, but perhaps maybe there is some relationship to some sort of speed sensor input the trans uses? (might be coincidental but figured I'd mention)
Might the trunk mounted TCU Computer control downshifts? or is this part of operation strictly all hydraulic on the E4N71B?
Opinions welcome!
-Miles
-86 300ZX 150K miles
Symptom: Trans is intermittently not "releasing out of gear when slowing down (no 3-2, 2-1, etc)-- such as when coming to a stop ("Decel" downshifting)...
Way to replicate:
-drive normally; gears change up just fine thru normal driving,
-But then come to a stoplight, and as you slow down, trans intermittently remains in say... "3" (so acceleration from the stoplight then becomes very sluggish as you'd expect from a higher gear).
When this happens, you can *override* and move the selector down to "1", and that corrects it instantly and will force the trans "fine" into 1st gear for proper takeoff and subsequent upshifting gear changes.
But 3-2-1 is Intermittantly not functioning "on its own".
----
150K miles, fluid just changed (was older fluid in there originally but smelled ok, bottom of pan looked fine- and no notable debris). Very well maintained, always-garaged car otherwise, with gentle driving since the late '80's.
Car has been driven sparsely in the last 10 years (about 9k miles).
I was curious what trans part(s) likely play a role in "decel" downshifting on the E4N71B; and might it be fixable?.. (Big items like valve body? Governor? Vacuum? TCU/computer?)
I saw a mention in diagrams of an external mounted "downshift" (lockdown) solenoid - on the side of the trans case -- as well as a vacuum modulator... (?)
Trans does shift fine otherwise -- no slipping, etc. through any of the gears… It is just this decel symptom, "clinging" to last-used gear, instead of downshifting on its own during decel/slowing down.
For what it's worth, if it is related at all – the digital speedo recently reads zero when driving – I attribute this likely to a speedometer cable /transducer problem, but perhaps maybe there is some relationship to some sort of speed sensor input the trans uses? (might be coincidental but figured I'd mention)
Might the trunk mounted TCU Computer control downshifts? or is this part of operation strictly all hydraulic on the E4N71B?
Opinions welcome!
-Miles
-86 300ZX 150K miles
Last edited by milesPDX; 09-15-2024 at 10:56 PM.
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