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Discussion Starter · #1 ·
Hi everyone. I have a 99 SE with a duratec and AX4N transmission with 132k miles that has the hesitation shifting between 1st and 2nd. It only happens after the car has warmed up (been driven 20 miles or so), and it only occurs randomly but does it a lot more in stop and go traffic and much more in summer compared to winter. It feels like it shifts into neutral for a few seconds and the lurches back into 2nd. I also noticed that it does not have this problem when using Drive to start out and then shifting to overdrive after the 1st to 2nd shift.

The car has been doing this for a while, however, I finally got tired of it and took it to my mechanic, but he didn't find any codes and couldn't replicate the problem. He suggested that the trans is slipping, however, based on other posts here, I think it could be the vehicle speed sensor (VSS). Trans shifts perfectly otherwise and does not burn or use any fluid. I had the trans fluid and filter changed but it did not help.

Can the VSS have issues in overdrive but not drive? Also, does a bad VSS always cause a code to show up? My mechanic doesn't want to replace the VSS because he doesn't think it is broken, but I am hoping to convince him to replace it.

Does anyone have any thoughts? Any help would be appreciated. I have researched other posts, but could not find any mention on the code issue. Thanks.
 

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Hi!

Is your speedometer functional? Does it register the proper speed or does it flutter around or not register a speed at all?
Not all VSS failures will trigger a MIL illumination. Mine did not. However the problem would be present in any gear on the tree.

The why the VSS works in the AX4N specifically (the 1996 AX4N to be exact, mine) is a plastic gear attached to a shaft spins basically a motor. The VSS unit has an electrical plug attached to it. The signal is sent to the PCM thru the wire and the PCM controls the transmission using the data from the VSS. The speedometer is also controlled in the same way, although some models used a cable driven speedometer design.

Newer AX4N transmissions do (and other models im sure) do not have a VSS. The vehicle speed is obtained thru the ABS sensors.

What you are describing does not sound like a VSS failure to me. I feel your mechanic is probably right to be weary of replacing parts. it's great you have someone honest enough to not just throw parts at it.

If you could supply a little more info about your car perhaps we can get a better idea of what may be happening. Year, Mileage, the usual :p

Good luck, please be sure to post back and keep us updated as the work progresses on your vehicle!
 

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Discussion Starter · #3 ·
Yes - speedo is correct (agrees to mph per my gps). The car is a 1999 and has 132,000 miles but it does not have ABS. No ABS means no ABS sensors, right? I have not tried to look for the VSS since the duratec engine compartment is so tight.

It has been doing this for at least a year - I guess I have just gotten used to it but I am doing more city driving now and it is starting to get annoying. Like I said, the really strange part is that is doesn't hesitate when I start out in drive, but will do it when starting out in overdrive.

Transmission has no other problems, uses no fluid, and shifts great except when this happens. I have had the fluid changed every 20-30k miles. I was hoping this was an easy fix and the car doesn't need a trans rebuild.

Given that it has been doing this for a while with no other driveability problems, any other thoughts on what it could be?
 

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You could start with the VSS. Otherwise, I think the trans is starting to go. If you do need to get a rebuild, have your old trans rebuilt, with the upgrade parts. Getting a shift kit while they are in there is also a good idea.
 

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Discussion Starter · #5 ·
I am going to try replacing the VSS this week. Will let everyone know how it goes. If it doesn't solve the problem, I will have to consider getting the trans looked at.
 

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My 99 taurus does the exact same thing as yours. Slips 1st to 2nd when warm, not in Drive just OD. Please let me know what happens with the VSS or anything else. Thank You.
 

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The speedometer can act normal when the VSS goes out. I have a digital dash and it didn't misread at all, but my transmission would suddenly downshift or shift late. It ended up being the VSS, and i broke all sorts of exhaust bolts getting to it. Good luck!
 

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not trying to hijack thread

my speedometer is dead does not work at all stays at zero and shifting has changed like starting off !st gear shift like around 2k and know it bucks a little then shifts at like 4k could it be the vss and what does that stand for
 

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my speedometer is dead does not work at all stays at zero and shifting has changed like starting off !st gear shift like around 2k and know it bucks a little then shifts at like 4k could it be the vss and what does that stand for
I had the same problem with my (now wrecked) '99 Taurus, 3.0 DOHC engine. The VSS is hard to get to on this engine! I took it to my friend's transmission shop and got it replaced for $50.00 labor cost.
He removed the right motor mount, through the wheel well. Access is not terrible after the mount is removed. The symptoms were: No speedometer reading (obvious), The engine control module goes ape-s**t when there's no reference to speed, and shifts at a very high RPM, downshifts erratically and all sorts of weird actions.
After replacing the VSS, it goes back to slow shifting actuation of the solenoids in the transmission.
I did a lot of checking using a Ford shop manual (wiring diagrams) and found the following.
All the wiring to the various components are correct. The transmission control module shows up as a "box" with nothing ID'd, so you're stuck with guessing which wire does what, backtracking the wire to the component. ALL of the grounds are not correctly documented. They just show the ground symbol. In actuality, the various ground wires go into the wiring harness on the left side of the engine. When you check for where they come out of the harness, you find only one wire, going to the left inner fender panel. What they did in the harness was connect all the grounds, with ring terminals, to one wire, with it's own ring terminal. They used a rivet for the connector.
The solution: Find the connector in the harness (cut the tape and un-wrap it), and check continuity with a ohmmeter. If there's any movement of the ring terminals, the rivet is not tight enough and you get intermittent bad grounds, causing sporadic weird reactions of the solenoids in the transmission.
I replaced all the ring terminals with a made-up (by me) soldered harness of several wires into one, clipped all the wires and used butt connectors to attach the made-up harness to the ground wires.
That gets rid of the bad electrical connections. Now, going back to the symptoms!
When accelerating from a stop, if you accelerate slowly, (as you would when in traffic), and the shift points are around 2000 RPM, you probably get a slow shift from one gear to the next. If you acclerate more aggressively, (no traffic to slow you down), and the shift points are around 3500 RPM, I'll bet the shifts are a lot more positive without a 1 to 2 second delay between gears. I've toyed with the idea of a complete transmission oil change and using synthetic transmission fluid.
The only problem is, the car is now in a boneyard. If my 2003 Taurus starts giving me the same symptoms, I'm going to try the oil change first!
 

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I had the same problem with my (now wrecked) '99 Taurus, 3.0 DOHC engine. The VSS is hard to get to on this engine! I took it to my friend's transmission shop and got it replaced for $50.00 labor cost.
He removed the right motor mount, through the wheel well. Access is not terrible after the mount is removed. The symptoms were: No speedometer reading (obvious), The engine control module goes ape-s**t when there's no reference to speed, and shifts at a very high RPM, downshifts erratically and all sorts of weird actions.
After replacing the VSS, it goes back to slow shifting actuation of the solenoids in the transmission.
I did a lot of checking using a Ford shop manual (wiring diagrams) and found the following.
All the wiring to the various components are correct. The transmission control module shows up as a "box" with nothing ID'd, so you're stuck with guessing which wire does what, backtracking the wire to the component. ALL of the grounds are not correctly documented. They just show the ground symbol. In actuality, the various ground wires go into the wiring harness on the left side of the engine. When you check for where they come out of the harness, you find only one wire, going to the left inner fender panel. What they did in the harness was connect all the grounds, with ring terminals, to one wire, with it's own ring terminal. They used a rivet for the connector.
The solution: Find the connector in the harness (cut the tape and un-wrap it), and check continuity with a ohmmeter. If there's any movement of the ring terminals, the rivet is not tight enough and you get intermittent bad grounds, causing sporadic weird reactions of the solenoids in the transmission.
I replaced all the ring terminals with a made-up (by me) soldered harness of several wires into one, clipped all the wires and used butt connectors to attach the made-up harness to the ground wires.
That gets rid of the bad electrical connections. Now, going back to the symptoms!
When accelerating from a stop, if you accelerate slowly, (as you would when in traffic), and the shift points are around 2000 RPM, you probably get a slow shift from one gear to the next. If you acclerate more aggressively, (no traffic to slow you down), and the shift points are around 3500 RPM, I'll bet the shifts are a lot more positive without a 1 to 2 second delay between gears. I've toyed with the idea of a complete transmission oil change and using synthetic transmission fluid.
The only problem is, the car is now in a boneyard. If my 2003 Taurus starts giving me the same symptoms, I'm going to try the oil change first!
\
i am thinking it could be a lose wire due to i just pulled the hole motor / sub frame out of car and put it back together three days ago and i have a few ghost i have to take care off it has new fluids tranny filter ect so i am hoping it is the connector if not i will change the vss (i hope)
 
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