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

 

Take the TCU out and send it to me to be repaired. More than likely the TCU isn't allowing the Lockup to Disengage and it will burn up the transmission if it's left go. Also Replace the Filter and fluid because I am sure its starting to get burnt.

XenonZcar
17 South Willow Street
Mount Carmel, PA 17851

 

Hi Xenon--

I would be interested in potentially sending the TCU to you to get recapped/repaired/etc.
might you have an approx cost for this?

thanks so much,

Miles

86 NA 300ZX

 

He said that he already replaced the fluid.
Did your downshifting problem start when the speedo stopped working?
My Z was a 5 speed so I never had to dig into a Z auto tranny.
My current street rod has a 4L65E that does use speed as one of the indicators for shifting.

 

I've attached the Workshop Manual for ATs. As usual, the Troubleshooting portion is at the end. You can test the ECU, see how to test/replace kickdown solenoid, etc.

The remaining Workshop Manuals can be found here.

 

Nice info GWZ.

MilesPDX, the speed sensor is used. Check out these pages, AT14, 15, 17, 73, and troubleshooting AT-75 to the end.
Stepping on the brake should release the converter lock up.