crazy speedometer

[dnalley]

I lost a 2002 F250 to local flooding back in  september of last year.  Later found a very clean 250 with low miles with 7.3 engine because I was afraid of the later 6.0 engine.  I have been disappointed with fuel milage on the replacement truck but everything mechanically seems fine so far.  Long story short, my wife and I were driving down the road last week and she mentioned that the speedometer was acting up again.  I had never noticed it but when you start from a dead stop the speedometer doesn't register until the truck gets up to around 30 miles an hour, then it springs up and works like it should.  Same thing slowing down; get down to around 25-30 mph and it just drops down to zero.  Nothing registers at these times, no speed, no mileage.

Anybody ever seen anything like this??  Haven't said anything to the dealer because after all it is a used truck.  Sure makes it hard to determine when to change oil and such.  Sure burst my bubble and now I'm wondering just how many miles does it have on it?  I know "you pays your money and takes your chances" but maybe someone will have some ideas.  Anybody???

[Roxie]

My 1986 Oldsmobile Cutlass Sierra GT Coupe (which I purchased new), developed a speedometer problem about two years after I bought it.  One day I was driving and glanced down just as the speedometer dropped dead from 50 to 0.  It stayed there just limp and hanging for a few months.  I made an appointment with the mechanic for an oil change and mentioned to him that I'd like him to take a look at the speedometer problem.  No kidding, on my way to the mechanic's, the needle jumped up and started working, and never had another problem.   :

DanG thing made me look like a liar.  However, in my case, the mileage didn't stop being recorded when the speedometer wasn't working. 

Doesn't help you any, but you aren't crazy. 

[dnalley]

Thanks Roxie....however I do have my moments :D

[fishpharmer]

dnalley,sometimes I drive a f450 fish delivery truck with  the 7.3l  diesel.  Occasionally, the speedometer acts up on it and just dies.  I found that if you shift into neutral, turn the key off and then back on, the speedometer comes back to life.  Can't explain why, but that usually fixes it until the next time.  That makes me think its some kind of electrical glitch.  Someday I will track it down :D.

[roger 4400]

HI ! I had this kind of problem 2 years ago on my 2000 250, When this occurs have you notice that your  overdrive (on-off) signal on the arm on the steering wheel is ** blinking**( I mean going on and off I,m french talking so sometime I do not use the right terms, sorry)   and my speedometer was going to zero and then comming back, It was the speedometer sensor in the rear axel ( gears turn and every time it passes by that sensor it gives a message converting to the speed you are going) It is magnetic so if there are some little metal parts that grip on it, it gives a wrong message and go wild, Really easy to fix, go over your rear axel (on the axel) on top there is a **plug** ,(looks like a bolt) unscrew it and clean it there must be some metal shavings on it, it is usually the cause and things might come back to normal. Give us news about it. Good luck. Roger
By the way if it comes back often, it could mean that a gear **is sick** in the axel. It is good to have your axel oil flushed at +- 100,000 km or 60,000 miles because the clutch in the axel (if so equiped) are polluting your oil. Have a nice day ;)

[dnalley]

Thanks Fishfarmer and roger.  I'm going to try y'alls solutions and see how it comes out, but i sure hope it's not "sick" gears in the chunk   roger your french is at  least as clear as my redneck lingo.  Thanks again   ( BTW, have you ever seen a used car dealer that would actually tell you a lie :)

[roger 4400]

Hey Dnalley......I wrote rear axel by error....you should read rear differential,  (the big bowl in the middle of the axel :D :D told you my english was bad sometimes :D) the bolt over the differential , sorry for my mistake. Good luck. Roger

[celliott]

On my VW, when the temperature gets well below zero here, occasionally my tachometer will start randomly dancing all over the place, go to the redline, down to zero, jumping all over, with no change in engine speed.  Speedo has not done it. could it be a temperature, or moisture issue?  And, didnt chevy have speedo issues with some of their HD pickups? seems like I know of at least a few people with speedos not working on those trucks.

[Patty]

My 2007 suburban did the same thing occasionally, along with the dash lights going out and all sorts of intermittent glitches. They finally tracked down the problem to a short in the electrical system up in the dash. One of the screws was grounding out against a piece of metal now and then causing all the problems. It took Chevy about a year to track down the problem.  :

[ellmoe]

  And, didnt chevy have speedo issues with some of their HD pickups? seems like I know of at least a few people with speedos not working on those trucks.

   I've got a 2003 Chevy HD 2500. I haven't had a speedometer in so long that I forget to look at the speedometer in other vehicles I drive. Speedometer went out, gas gauge is sporatic, and oil pressure gauge shows  zero when it's cold out. Supposed to be the computer, Chevy had a recall, but my mileage was too high, then GM went into the toilet. I received a speeding ticket as the speedometer was failing (I didn't realize what was happening at that time), but none since it quit completely. Proves the old adage, better to not have something ( or someone), than to have something that's not dependable).

Mark

[Bobus2003]

Your Speedometer problems are caused by a faulty VSS (Vehicle Speed Sensor) Located on the Rear Diffrential. Up above the Pinion. Had one go bad on my '99 F350 at about 237K miles, easy fix may take you 5min (if your handy with a wrench). The turning the Key off then back on will work for a while, but eventually the sensor will get bad enough that it will stop picking up and reading.

Deffinatly cant go wrong with the 7.3l, Much more reliable than the 6.0l (Though they are good engines too when the known problem areas are fixed).. What year is your "new" 7.3l? manual or auto tranny?.. what kinda mileage do you get? Any modifacations to the old truck or new truck that could account for the mileage drop?

[Captain]

To ellmoe and others .... the GM instrument panel clusters that failed are actually pretty cheap to exchange for a reman unit at your local GM store.  Way cheaper than speeding tickets. (at least in this part of he country)

Captain

[dnalley]

Thanks Bobus.  My "new" to me truck is a 1999, automatic trans, basically the same as the 2002 but without the Lariat package.  About 60,000 miles less than the'02 but I paid well for it.  Not sure about the rear axle gear ratios but a trip this weekend to the "Tail of the dragon" in the N C mountains averaged 18 miles per gallon, altho a lot of those miles on the dragon and other twisty curvy roads didn't register at all (well maybe not a lot, but some anyhow).  Much more pleased than I thought!  Gonna get under there tomorrow and check out this sensor.  It really amazes me the knowledge lurking in the b
ackground on this forum, and the helpful attitude of all y'all.  Thanks so much....Dwight

PS -forgot-this truck doesn't have shift on the fly....gotta lock the hubs BEFORE you get in the middle of that mudhole ;D

[ely]

my gm insturment cluster is doing the same thing, the speedometer is ok but all the rest of em are give or take. i will look into getting a new one.05 hd 2500.

also be careful when messing with those sensors under the newer trucks. as i understand some of them are actually using ac voltages to tranfer the info to the guages. i may be wrong on this, if so someone correct me. i was told you can get quite the shock in certain circumstances.