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speedo problem

johnbender

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September 10, 2013
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Year, Model & Trim Level
1991 ford explorer xlt
Hello my mom recently gave me a 1991 automatic 4wd explorer. It had been sitting on the side of her house for about 7 years. less than a year before she stopped driving it she had the engine and transmission rebuilt then then about 4 months later it would not gear unless she warmed it up. That's why she stopped driving it. so before i tried to start it i changed all the fluids and filters
then started it up and pulled the codes then replaced some sensors and all was going well (Oh yeah i replaced the entire steering and suspension systems as well). soon after that i noticed that the speedometer was reading about 10mph faster than i was actually going. so i did some research and found out that the tires she had on it where to big (which would make the speedo read slow right?) so i swapped them for the right size tires and i did not really affect anything much. after that i put in a new speed sensor and cable and everything when down hill. when i drive it the speedo seems to work for about 10-15min but it is not accurate then i will let off the gas and still be traveling the same speed and the needle drops to zero. then i press on the gas again and it jumps back up and when i drive over any small bumps the needle jumps around. idk it just kinda has a mind of its own sometimes it will just stay at zero no matter how fast im going. sometimes it just jumps all over the place. and every time i hit a bump and the needle jumps the explorer will rev up or something like it just cant figure out how fast its supposed to be going. and i cannot get into 4th gear. i have been trying to fix this on and off for months. i have taken it all apart and put it back together even with the old vss (i threw away the cable though so i couldn't try the old cable). I have pulled out the vss and pulled the worm gear off and hooked up a drill to the vss and i have sat there and held the drill at a constant rpm for 25min seemed to work perfectly and then i sat there and held the drill for 25 more min changing the rpm every couple min still seemed to work fine. i have inspected the worm gear very closely and it is in pristine condition even the square slot the vss goes in (it is not worn its perfectly square). I have stuck my fingers in the hole on the transfer case the vss goes into and the drive gear does not feel worn at all but it does spin freely absolutely no resistance (is this normal?) i can only find side veiw pictures of the drive gear so i cant see what it looks like on the inside (im wondering if the inside what ever catches on the drive shaft is worn out and is not spinning the drive shaft properly). I keep wondering if there is something wrong with the cable then i keep doing the drill test. Im ripping my hair out. this sucks. i lubed the cable and everything. the first time i put the new speedo in i torqued it down to tight cause when i took it out i noticed the metal bracket the bolt goes through was i bit bent not much but the gears looked fine after that. ppl look at me like i dont know how to drive cause the explorer is reving like it has a mind of its own. i put die electric grease on the electrical connector on the vss. Also for some reason i cant tell if my ATF is too high or low cause i warm the car up and check it and i cant really see a line of ATF its kinda just spatted on the dip stick. Oh yeah i forgot to say when she gave it to me i changed to ATF and filter and the 5min warm up problem where it would not go into gear went away completely. sorry for the bad grammar and thanks in advanced for all the help.
 



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my problem is kind of like yours but also not, i own a 94' sport, 5 speed, and mine goes from my speed then will jump around anywhere from 0 to my speed or over then back to my speed and is a few mph off, and on bumps it will kind of jump around. I have heard a few things on a speed sensor in the transmission that might be at fault but im not sure.
 






Okay like the inside of the drive gear? Not the part that groves in with the worm gear. That's kind of what I thought. Thanks for the reply all you guys are awesome. I am definitely going to pay to become an elite member as soon as I can (Sorry as of right now I am a broke 22yr old looking for part time employment cause I am just starting school) you guys have saved me many times. I am very grateful.
 






Check this link: http://www.explorerforum.com/forums/showpost.php?p=1478573&postcount=17
Case.jpg
 












Okay so I finally pulled the drive shaft off today and used speedo hole to push the drive gear out the back of the t-case but the drive gear seems fine the nylon is not worn down at all. I found out the drive gear is magnetically driven. the inside of the gear is smooth (no notches that are supposed to mesh with other notches). So now I am really confused and disappointed that I have not found my problem. Is it possible that I just need to replace the magnet in the t-case?
 






I just realized the vss I bought was motorcraft with mechanical instrumentation. They also had a motorcraft vss with electronic instrumentation. My t-case is a BW1354 which is a electric shift case. They also have the BW1354 which is mechanical shift correct? So I am wondering if I got the vss for the wrong t-case. Should I have got the electronic vss?
 






Your case is 1354, not 1345. I doubt it makes a difference if it's manual or electric shift.
Where did you find out the gear is magnetically driven? I don't believe that is true. I think vss started on the 1995 Ex.
 






I think it is magnetically driven because it is smooth on the inside as is the shaft it goes on. Also the shaft the gear slides on is magnetic my tools stick to it. I don't see how else it would work since the gear just slides on nothing holds it in place on the shaft. It just spins freely. You are right BW1354 sorry typo.
 






Sorry if I am wrong. I am not trying to spread misinformation. thank you for the reply.
 






Hmm, okay. I've never been inside a t-case so I gotta believe you.
Did you get that vss at the dealer? Could you just go back and double check the two parts numbers, to find out if you got the right one for you?
 












The part that has a built in magnet is a different type of sensor. It uses the Hall Effect to provide a variable signal from the collapsing & expanding magnetic field just like ABS & ignition distributor sensors.
 












Look inside the transfer case to see if it has a plastic worm gear or a steel ring gear. It should have a worm gear like the photo in post # 5. The smooth sensor is usually at the top of a diffferential, and not in a transfer case. Maybe your transfer case has the wrong sensor?
 






It looks exactly the same as the picture in post #5 . It has a steel ring gear with nylon on the outside. I thought the worm gear was the gear that clipped onto the end of the vss that meshes in with the steel/nylon drive gear.
 












I will see if I can take some decent pictures tomorrow morning. Thank you for all your reply's.
 



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Yeah I have read about that. So the gear on the vss is just the driven gear and the drive gear is also called the worm gear?
 






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