94 Plymouth Voyager transmission

94 Plymouth Voyager 3.3L

When coasting downhill at 50 MPH or so in overdrive the engine speed
drops below 1000 RPM and then the transmission jerks into 3rd gear.
Shop replaced transmission with a used one but it started doing the
same thing in a few days. Seems like there must be an external cause
such as bad info going into transmission computer. Does this
transmission have any vacuum control at all?

Otherwise it is fairly smooth, accelerates fine, no worn out disc
symptoms. Problem virtually goes away in sub-freezing weather even
driving 40+ miles.

Your thoughts please.

Thanks,

john


When coasting downhill at 50 MPH or so in overdrive the engine speed
drops below 1000 RPM and then the transmission jerks into 3rd gear.
Shop replaced transmission with a used one but it started doing the
same thing in a few days. Seems like there must be an external cause
such as bad info going into transmission computer. Does this
transmission have any vacuum control at all?

Otherwise it is fairly smooth, accelerates fine, no worn out disc
symptoms. Problem virtually goes away in sub-freezing weather even
driving 40+ miles.

Your thoughts please.

Thanks,

john

 

Are you using the Cruise Control when this happens?

 

Sounds like the transmission may be going into "limp home" mode. Your
description of it "jerking into third gear" could well be when it actually
reverts to second gear in the limp home mode (not third). The transmission
controller is programmed to revert to second when it is either not working
properly, or (more likely, especially in this case) when it is not receiving
one of several signals it needs to determine the proper gear ratio. Two of
the signals used are the engine and axle speeds measured in instantaneous
revolutions per minute in order to calculate the appropriate gear ratio to
be used. If the input speed sensor (measure engine speed) or output speed
sensor (measures wheel speed) are failing, then it will go into second gear.
The clue here is that you do not mention if the speedometer goes to zero or
stays at the correct speed. The speedometer receives its signal from the
output speed sensor, so if it is reading correctly, it could be the input
sensor that is failing.

The bottom line here is that it would appear that the shop you used may have
replaced the transmission prematurely when all that was needed is a $30
speed sensor. Take the vehicle to a shop that can read Chrysler
transmission codes and has real experience working with Chrysler electronic
transmissions.

Good luck.

Bob

 

Thanks Bob!

jh

 

Sorry, didn't see your post at first. Cruise control was on but not
engaged.

jh

 

Selected 3 and accelerated up to 50 MPH. RPM indicated was same as
when it jerks down from 50-55 mph coasting. So I would guess it is not
going to "limp home" mode.

 

O.K. Thought it was downshifting and using the engine as a brake to slow
down.