tranny erratic shift down / info

[tums]

For information, quite interesting, trouble shooting still in progress:

Symptom: after warm up the gears shift erraticly back to 2nd, especially when coasting.

It started at the end of an 8h drive home, mostly doing 80 when coasting to app. 60 , with a sudden shift down (and rev up). After the first shock gone we decided to go home another 80 miles or so spending the gas on on a "constant 4000rpm" drive.

Back home and for half a year nothing happend, all normal (all short-range).
However I detected I slight flicker in the reading light on idle and - after a generator failure the year before I installed a clock with voltage indication - on each starting the clock jumped back to 12. Cheap chinese... but wait, why did it work before? And why a bearly hearable hiss in the radio now?

Next came a trip of another 700 miles highway, all normal except periodic cycling of the torque converter clutch, as before.

The way back started in heavy traffic, speed 40-50. After 20 mi suddenly shift down. We paused 20 min and went on. This time within a few minutes the same erratic shifting. We paused a few times more, and always at the beginning normal again, then shift-down. We decided to take a shortcut off the highway - a completely wrong decision as on each slowdown there was a rude shiftdown not to be recovered.
Back on the highway with some "feeling" and luck I manged to get in third gear occasionally and you should note, that if you get above 60 there is a hydraulik lock blocking shiftdown - this way we did the rest of the trip.

Home and cold: all normal.

Now what , no DTC either?

I started with the generator and put a museum-like oszilloskope on B+. Result: some Oszillations that look not strange, but not like textbook either. I checked the manual, disconnected B+ und the regulator (car on battery) and they were still there, with spikes of a few volts across the battery! To begin with, that explains the set back of the clock possibly. That explains the radionoise.

That may explain to some extend the trouble with the tranny - has to be checked.
Fact is, that could only be ignition and as I installed new ignition cables and plugs 3000 mi ago it looks like the coil, dont ask me why and how, as the secondary circuit should be closed by design, but I will install cheap spares and plugs to test that.

As one might see, you always find things if looking there where you not looking

[Windstartled]

Originally Posted by tums

After the first shock gone we decided to go home another 80 miles or so spending the gas on on a "constant 4000rpm" drive.

Holy Schmolly that would have made me apprehensive to say the least. Was the OD OFF indicator flashing during this time?

Anyway what you describe is often caused by a faulty ABS sensor on one of the front wheels or a defective VSS. But since you seem to be experiencing electrical system issues the "fault" could simply be due to those sensors not being powered adequately. I guess you have little choice but to fix the electrical problems first and then see if everything falls back to normal.

[tums]

Frankly, I cant remember, anyway I was busy watching the outside, just in case ...but I think -- no OD.

Ahem, how to tell you , the ABS is off since years. I had three cases with a low speed release were I was happy the others gave way, and since then I dont miss it really.
It should be something failing when getting hot, more or less the rest of the engine.

[Windstartled]

Originally Posted by tums

Ahem, how to tell you , the ABS is off since years. I had three cases with a low speed release were I was happy the others gave way, and since then I dont miss it really.

The front ABS sensors are not limited to the ABS system only. In fact their actual name is wheel speed sensor and as the name implies they are what tells your speedometer how fast you're going. Not only that but they also feed this info to the PCM via the VSS , and the PCM uses this value to manage shifting. Even if the ABS module is turned off the front sensors are still being used, just not for braking.

The best way of telling if one of those sensors is shot is when the speed reading on the speedometer does not appear to match the actual speed of the vehicle. You can tell this by using a GPS which will report your true speed and then compare it to the speedo reading. Or you can simply use a multimeter to measure sensor resistance at the connector between the sensor cable and the main cable, which should be roughly 1.8K ohms. Even if the multimeter has auto-range set it manually to 2K ohms. The connector is at the top of the wheel well. This requires you lie down under the van so it's a bit messy but it's a very simple procedure. Personally I fixed what I had been told was a major transmission problem by simply replacing one of the front sensors, they cost less than $20 here (Canada/USA) maybe a little more in Europe but shouldn't be by much.

[tums]

That could be very valuable information as the speed sensor indicator (thats acc. Ford the name of ring with the teeth) is broken from rust building below (neverless still holding in place) and both front are due for exchange - they are already on shelv but there is just always this other job to be done ... and the fuse is out anyway ...

All other is new when doing the brakes (sensors too, the old ones ok but the insulation of the wire cracked) nevertheless I should check if there is a change to worse. However that would in my opinion not correspond to short-distance very normal behaviour, if I have to guess I would go for malfunction on getting hot like oil (old, bubbles? tranny was rebuild 3000mi before) or electric reasons.
Of course, in the end, it could be a bad job on the tranny, but in my feeling it is mechanicaly much more sturdy than its reputation. This car I own now for 16 years, pulling trailer most of the time.
Coil is ordered, garage swept, story to be continued ...

[12Ounce]

You did not mention the mileage on the transmission or its general condition, but general wear on the transmission friction plates will increase the tendency of pressure to fall below necessary levels, especially as fluid warms, to maintain the upper gears. It has been my experience that once detected, the wear-down escalates until there is wholesale failure ... I hope you have a different experience.

EDIT: I now read your most recent posting where you mention the mileage on the tranny. I would guess you are due a re-build/re-placement of tranny or friction plates and seals.

[Windstartled]

Ah yes, the ring with teeth. That is indeed what the abs sensors, which are optical devices, use to measure speed. Around here we often just call it a cogwheel. It is true that dirt and rust can interfere but like you say this should not only happen when the engine is hot. You may have a wire that's gotten loose and is rubbing against a part that causes the cable's shield to melt when it gets hot which could lead to a short once the inner wire contacts metal.

I had not realized you had a first-generation Winnie, I'm not 100% sure but I don't think those use the wheel speed sensors for the speedo because that trend only started during the late 90's after the industry figured that using a purely electronic approach to speed gauging would greatly improve communication between the PCM and the transmission. Prior to that I believe the turbine shaft speed sensor was used as the source for speed data, which needed to be converted from analog to digital before reaching the PCM. It does make sense that a system (the ABS) that requires constant wheel speed monitoring would eventually also become the main source of digital speed data. While this only marginally improves speedometer accuracy it is significantly less costly and more efficient as far as the PCM is concerned. Unfortunately it is also less sturdy and highly dependent on the abs sensors working properly because a sensor failure will lead to shifting issues. This may explain why some consider the Winnie's transmission as somewhat problematic when in fact the cause is elsewhere. Minivans in general, especially the earlier ones, had more transmission issues than cars and light trucks because that's what happens when engineers slap on a car tranny in a much heavier vehicle without proper adjustment.

[tums]

To sort things out :
it is a 1996 3,8 GL with an engine and transmission overhaul 3000 miles ago, the engine myself, the tranny a shop. When leaving they told me they almost never see their jobs a second time (what I believe, from my impression of the people, the place (and their marvelous old Guzzis ).
This model has a speedometer pick up on top, both mechanical and electrical, that had be changed (a set together with the cable).
The sensors are inductive type, hence the teeth. The ring breaks because its seat is corroded from beneath, thus expands by rusting until it "pops" in one place to relieve tension, by this (most probably) disturbing geometry and thus the signal to ABS with the effect of the warning light, but after some move only.
The 20s cycling of the torque converter clutch (the rpm needle to be watched closely) is acc. Fords manual:
Section 07-01: Transaxle, Automatic—AX4S
Ignition coil
Symptoms: Harsh engagement and shifts, late WOT shift and no torque converter clutch engagement
and
Throttle Position (TP) Sensor 9B989:
Symptoms: Harsh engagements, firm shift feel, abnormal shift schedule, torque converter clutch does not engage, torque converter clutch cycling.


Alright: that is also guessing, but it corresponds to the immidate shiftdown on taking back the pedal when coasting: because the only apparent change is compression (beside the movement of TP) and thus change of load in the secondary circuitry (changed resistance for spark due less compression), thus a changed potential of interference, aided by a hot condition - and that may well "disturb" the torque converter clutch program at higher speeds when shiftdown is inhibited by hydraulic ( more than 60).
As said: parts are on their way.

[tums]

waiting for the spares I started changing oil. Somewhat bewildered from reading instructions I took the wrong side of the line , but luckily that splashed into the container too. Where I saw bubbles, rather foam.
Could that be the dirty pan?
Well, I drained like the book told me to, where I left that procedure to see inside the oilpan. Thought it is empty, but it is still FULL, so be aware when it is getting loose. Checked oil, it was a brownish red. Compared it. Checked with a microsope and saw a lot of particels, but all tiny, obvious wear, however I had also an impression of halos, like tiny small airbubbles. Checked magnet, fine metalpowder, should be normal. Pulled off filter and pured it into pan: result: foam.


So much for 3000 miles after overhaul. Wonder what they used (or if I forgot to change oil, cant remember), however, guessing I would say that could possibly be the wear (dust) which could have changed the oil to a condition like adding soap, faoming more easily.

Here I may have to correct myself: when filling new Hightec 8000 I experienced that type of bubbles in the funnel and moreover in the (new) oil being drained by the engine acc. to procedure

I am somewhat convinced I found the main source for the problems in the oil. Would correspond to the main symptoms: only when hot, sometimes sluggish shifting only when hot, gone after pausing.

Great maintenance manual Ford made, I am impressed. Dont believe, check. Obviously the oil had detoriated in very short time beyond any expectation.

t.b.c.

[wiswind]

The pictures that the link in my signature takes you to includes a series of pictures showing the transmission fluid exchange, pan removal & filter change.
It is worth noting the comments I put about the gasket on the filter neck of the OLD filter getting stuck up in the hole.....preventing the new filter from seating correctly....which can cause you to draw air....which will be compounded by even slightly low fluid level.

I would also verify that your radiator fans are working correctly.
To do this.....with the engine running at idle......Gear select in PARK, turn the AC ON.
Get out and physically look to see if the radiator fans are running.....and stay running....(not just a pulse while the compressor is on).
If they are NOT running....then you likely have a broken/defective radiator low speed fan dropping resistor.
This defect can cause your transmission fluid to not cool as well when you are sitting still (like in traffic).....which will cause your transmission to run hotter....and your transmission fluid to break down quickly.
In stop & go traffic....I like to have my AC on to force the radiator fans to run....keeping the engine and transmission cooler.

Also...if your transmission was rebuilt......did they verify that the fluid flow through the in-radiator cooler is sufficient?
A failed transmission can create chunks of junk that become lodged inside the in-radiator transmission cooler....restricting....or even completely blocking the fluid flow through the cooler.....causing the transmission to overheat.

I added a auxillary transmission cooler to my windstar....fluid flows from the transmission, through the in-radiator cooler, then through the auxillary cooler, then back into the transmission.

I also added a Magnefine filter to the fluid line going INTO the transmission.

[tums]

I followed your link, excellent pics and advise, that answered my question how to continue "out of routine" oil change

Originally Posted by wiswind

...which can cause you to draw air....which will be compounded by even slightly low fluid level.

When that happend first thing I checked the level, which was near to high mark. Also there had not been a problem before, so I do not expect drawing air.

...that your radiator fans are working correctly.

indeed, the AC is cycling which puzzles me, I should check the fans, but normally I would expect an increase of temperature that I could not see. I did the resistor on engine overhaul, nevertheless I will check that again.

This defect can cause your transmission fluid to not cool as well when you are sitting still (like in traffic)...and your transmission fluid to break down quickly.

corresponds with the symptoms

A failed transmission can create chunks of junk that become lodged inside the in-radiator transmission cooler....restricting....or even completely blocking the fluid flow through the cooler....

after using the wrong side for draining I can rule that one out, oil splashing out through the cooler like a fountain and reason for overhaul was detoriation, not a broken tranny

I added a auxillary transmission cooler

on shelfe, I just dont know where to put that thing ...and then they said, it is not needed really, if all is healthy, but after all I should install it.

[tums]

First results after changing all ignition parts (new:spark plugs, the cheapest 765, wires sentec and the coil).
Unfortunatly I deleted the old pics and was only able to recover them partly, thus the quality. Nevertheless you will see on pic 1 spikes of a few volts (if not more, that is an old oszilloskope with a tracing-tube) and the generator regulator was obviously reacting on that spiking voltage and thus the flicker.

Now look after installing the new parts: the selector for the scale is now not on 1V but on 50mV , and switching to display the voltage in total(without generator, battery only) the line shows a steady left to right, not like rolling waves on the beach before.

Now I am curious whats with the tranny.

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I did not have a chance for extensive driving yet - but it makes a fine impression so far. The clock, that made me think about the electronic issue, had only a bad battery - still waiting for other spares .