Speedo/Cruis Problems '93 Explorer

[billymcgates]

Hi Guys,
I have a bit of an issue with my stock '93 Explorer XLT 4x4. A few months ago I started to have an issue with my cruise control not shutting off when I hit the break. I didn't think much of it, and just turned off cruise manually when I didn't want it anymore. Then, the other night, I turned on my truck and went for a ride, when I noticed that out of nowhere my speedo was bouncing. It would be fine up until about 50mph, then it would start jumping erratically in spurts of 10mph. Last night it stopped jumping constantly, but I noticed that it's off 10mph consistently above 50mph with the occasional jump. This literally happened between turning it off to go into a meeting, then back on a few hours later.

I've been doing some reading, and it seems like a toss up between changing the speed sensor, the speedo gear, and the speedo cable. It doesn't appear particularly expensive to do either or, but I'd like to be more targeted so I'm not replacing the entire system at once.

I've also been looking around, and while I've been doing my own work on it for a while, I'm still not terribly knowledgeable on where everything is (e.g. the transfer case). Any help the community could throw my way would be a tremendous help. She's got 220k on her and runs like a champ.

Thanks!

 

[arco777]

The speedo in these trucks is mechanical so it's not related to your cruise issue. The Ford speedo of this era is simple and pretty reliable but can be a pain when it fails. Basically a gear is driven off the transfer case (bolted to back of transmission) or on the trans tailshaft on a 2WD. It spins a cable inside a sheath which can hang up if it is not greased or is kinked. The cable spins a magnet inside the speedometer assembly which is surrounded by a cylinder. The magnet's field "grabs" the cylinder without touching it, which spins and winds up your speedometer needle. There's a small wind-up spring to return the needle to the stop (zero mph) when it's not being spun.

Bounces in the speedometer are usually caused by quick changes in the cable's speed, caused by kinks or lack of grease letting it wind up and then release its energy. Another thing that sometimes happens is a hot exhaust part near the cable melts the outer sheath, burns off the grease and the cable scrapes on the damaged sheath.

Sometimes however, the speedo itself goes bad. The tight tolerance between the spinning magnet and the cylinder can go out of alignment, and the magnet can physically touch the cylinder, causing needle bounce. Had it happen on a 90 Mustang which is built the same way. This assembly's tolerances are too small for a person to easily fix it so I'd suggest a junkyard speedometer replacement. You can identify this kind of damage by spinning the cable head (where the cable enters the speedometer guts) by hand and watching the needle and the magnet/cylinder assembly. If a steady hand-turn of the speedometer input causes a bouncing needle, the speedo itself is bad.

On to your cruise issue. There's a switch or two attached to the brake pedal. I don't know exact layout on an Explorer, but there is often a switch for the brake lights, a switch to cancel the cruise control, and in some cases a dump valve for brake vacuum. Check for a non-functional brake light or cruise cancel switch. They are actuated simply by pressing the pedal. Check that they're working correctly - you can test function with a multimeter.

Otherwise, I'm not sure... I've had issues with cruise control not working at all, and replacing the amplifier module (a small box behind glove box) fixed it.

 

[billymcgates]

The speedo in these trucks is mechanical so it's not related to your cruise issue. The Ford speedo of this era is simple and pretty reliable but can be a pain when it fails. Basically a gear is driven off the transfer case (bolted to back of transmission) or on the trans tailshaft on a 2WD. It spins a cable inside a sheath which can hang up if it is not greased or is kinked. The cable spins a magnet inside the speedometer assembly which is surrounded by a cylinder. The magnet's field "grabs" the cylinder without touching it, which spins and winds up your speedometer needle. There's a small wind-up spring to return the needle to the stop (zero mph) when it's not being spun.

Bounces in the speedometer are usually caused by quick changes in the cable's speed, caused by kinks or lack of grease letting it wind up and then release its energy. Another thing that sometimes happens is a hot exhaust part near the cable melts the outer sheath, burns off the grease and the cable scrapes on the damaged sheath.

Sometimes however, the speedo itself goes bad. The tight tolerance between the spinning magnet and the cylinder can go out of alignment, and the magnet can physically touch the cylinder, causing needle bounce. Had it happen on a 90 Mustang which is built the same way. This assembly's tolerances are too small for a person to easily fix it so I'd suggest a junkyard speedometer replacement. You can identify this kind of damage by spinning the cable head (where the cable enters the speedometer guts) by hand and watching the needle and the magnet/cylinder assembly. If a steady hand-turn of the speedometer input causes a bouncing needle, the speedo itself is bad.

On to your cruise issue. There's a switch or two attached to the brake pedal. I don't know exact layout on an Explorer, but there is often a switch for the brake lights, a switch to cancel the cruise control, and in some cases a dump valve for brake vacuum. Check for a non-functional brake light or cruise cancel switch. They are actuated simply by pressing the pedal. Check that they're working correctly - you can test function with a multimeter.

Otherwise, I'm not sure... I've had issues with cruise control not working at all, and replacing the amplifier module (a small box behind glove box) fixed it.

Is it possible to grease the cable at all? I was hoping it would be a simple fix. Given the ridiculous nature of my schedule, fixes that take more than a day often take a VERY long time to do. I have a speedometer on my nav, but cruise is worthless with a bouncing needle. I'm more concerned that the erratic needle is affecting other parts of the motor in a negative way. How urgent would you say this is?

Thanks for your very detailed and knowledgeable help!

 

[arco777]

The speedo cable/needle has no effect on anything else but the mechanical speedometer. It is not an urgent fix at all.

The cable can be greased with the proper stuff, but I'll be honest - I've chased down several speedometer problems and it was never due to a lack of grease. Check for physical damage to the cable first or kinks. But you can try it. I believe molybdenum grease is correct for it. I have seen white lithium used as well, graphite lube, and others. Not sure exactly which is correct, I'll research it.

It is possible that your speedometer driven gear is damaged. But again not real likely. There's a gear at the driveline end of the speedometer cable. It sticks into the hole in the t-case/tailshaft and meshes with an internal speedometer drive gear. The gear is replaceable and the number of teeth on it actually varies depending on your rear axle ratio (to calibrate speedometer they can be changed). Let me know if you need a schematic and I'll try to post some up.

EDIT: Also there's a Vehicle Speed Sensor attached inline with the speedo drive gear - check that it spins freely.

 

[arco777]

Info dump! Should be four pictures attached.

 

[arco777]

here's the legend for the technical drawing above

 

[billymcgates]

Wow, that's amazing! Thank you!

 

[arco777]

Wow, that's amazing! Thank you!

You're welcome, let us know how it turns out and if you need anything else.

 

[billymcgates]

Ok, so either I am having an all out catastrophic failure, or I'm seeing symptoms of a single problem. Leaving the cruise thing out of it (this started a long time ago), here is what's happened so far.

Speedo was working fine the other night when I turned the Explorer off. Came back out three hours later, it was jumping like a mad man after the needle hit 55. Turned on gps to see what my speed was, and speed was 5mph faster than indicated starting at 40, and 10mph faster at the 65 mark and above. Accurate until about 35.

I'm not sure of this is because I have an automatic, but I've noticed with the speedo off, my gears aren't shifting in the usual place, and I am often running at higher than usual rpm. In overdrive, between 1500 and 2000 rpm, the engine runs rough, like it can't decide whether or not to shift. Either slowing or speeding up on its own. Doesn't happen in drive.

Within the same week, while in the car wash, I caught my abs light blinking a code at me. I caught it halfway through, and wasn't able to find much based on what I did catch. Abs is now disabled.

I know my year has an abs speed sensor in it. I don't know if it would affect the speedo, or if they're in any way related. I don't know if the position of the speedo has anything to do with the automatic gear shift either. Now that I have more information, I wanted to share and see what you thought.

Thanks!

 

[arco777]

The speedometer itself is just a mechanical unit. The VSS at its base is the only part that has an effect on anything else.

The only shifts that are electronically controlled are 3-4 and 4-3, which are controlled by the PCM through a 3-4 shift solenoid and a torque converter clutch (TCC) solenoid. These solenoids can go bad; I have heard of the TCC solenoid going bad on these transmissions before.

As I understand it, the ABS diagnostic connector is the exact same as the engine diagnostic connector, and codes are stored (and can be pulled) in the same way. I will attach a how-to on pulling ABS codes using the light-flash technique but you can also use a cheap code reader. The connector for the ABS is on the drivers side fender and is covered with a red protector. The PCM test connector is on the passengers side between the airbox and the blower motor.

In addition I would suggest running a KOEO test and a KOER test on the PCM to see if any trouble codes have been set in past by malfunctioning sensors, and if any problems are detected. If the shift solenoid is malfunctioning or a speed sensor is bad, it may have a code for it stored in memory.

The light flash method works fine if you have the patience for counting the flashes. If not, a Ford OBD-I code reader is pretty cheap at your local parts store. Mine is made by Innova and cost $30; just hook it up, key on, push the button and it reads all the codes (you can even watch the light flash at the same time to practice). It also has a memory feature which saves the codes on the unit. You will have to look the codes up, but that's what http://oldfuelinjection.com/ works well for.

 

[arco777]

Check out your VSS (Vehicle Speed Sensor). See if it is not spinning freely. It is at the base of the speedometer cable and is usually held into the transmission/t-case with one bolt clamping it. It goes in-line with the speedometer cable. Picture is attached of the sensor.

The signal the VSS generates goes to the PCM to tell it vehicle speed. It can affect your 3-4/4-3 shift and torque converter lockup.

Maybe your VSS is going bad; if the signal it generates is bad it would cause problems similar to what you describe of shift hunting. If the sensor's bearings are bad or it is not spinning freely for whatever reason you may see that in the speedometer as well.

While you are in there, check the condition of the gear on the end of the VSS, and the corresponding gear inside the transmission/t-case.

 

[arco777]

One more thing to check out - this relates to your ABS issue as well. The rear speed sensor, mounted on the diff housing.

 

[arco777]

Something to note - don't just automatically buy new parts to replace all these possible culprits. Find out what sensor/solenoid is most likely bad, indicated by trouble codes or symptoms, and let us know the results. If you have a multimeter there may be an established test procedure for the component such as checking its internal resistance. That way you can tell for sure that a part's bad.

 

[billymcgates]

Dude you are a Cornucopia of knowledge. I'll check all this out tomorrow and let you know what I find. I appreciate the time you took to break this down for me.

 

[billymcgates]

Ok, update time!

Went ahead and yanked out the VSS. Turns out part of the shaft had broken off inside the gear it connects to inside the transmission. That's a definite issue! I bought a new one from O'Reilly for a paltry $16.99, and got to work installing it. After I got everything tightened down, I went ahead and took it for a test drive. It went very well and jump free for about 15 minutes. Speed was once again accurate. Yay!

Downside. At the end of those 15 minutes the needle started to do a small bounce, about 1/8 of an inch back and forth. Speed remains accurate, and it doesn't appear to affect cruise. Shifting is correct, and the engine is running smooth. Any thoughts on our little bounce?

Thanks!

 

[arco777]

Glad to hear you got it figured.

As for the speedo bounce, does it do it at all speeds, or low speeds only?

The fact that it was fine for 15 minutes and then started bouncing sounds like a lubrication issue.

 

[billymcgates]

The bounce is present at all speeds. I'm going to be putting new shocks on the old girl in the next few hours, so if you think it's something as simple as lubrication, let me know what and I'm all over it.

 

[billymcgates]

Well, I just took it on a half hour drive to the next ton over, and it looks to be getting progressively worse. I'm exploring the possibility that the sensor I got is bad, or the gear it attaches to is a little worn. Going to try a replacement real quick and see what happens.

 

[Suicide77]

arco777, Great responses and write up! I don't have any speedo issues but I have to say it was a great read and now I think I could attack it if I ever do! Thanks again for the thoughtful responses!

 

[arco777]

Well, I just took it on a half hour drive to the next ton over, and it looks to be getting progressively worse. I'm exploring the possibility that the sensor I got is bad, or the gear it attaches to is a little worn. Going to try a replacement real quick and see what happens.

If the sensor spins smoothly then it wouldn't be hanging up and causing speedometer bounce. The cable may need to be greased, or the sheath may have physical damage or a kink at some point on its travel. Also the cable itself can stretch out over time.

I suggest you take out the instrument cluster when you have time and try spinning the speedometer input by hand (as described in my first reply); if the speedometer needle bounces when you turn its input at a steady speed, the speedometer itself is probably bad.