Speedometer jumping around...What gives?

Speedo sits at 125

This is an old thread, but it has the best pictures of the likely problem part.

A few months after buying my 89 5-spd, the speedo pegged to 125 while I was driving it. A couple days later it worked fine, then went out again while driving it. Now is just pegs to 125 at start up and sits there.

I have already had the IC out for previous issues and I'm confident all the connections are good. The odometer is still working as well, or at least it is still turning and seems accurate for the mileage I have driven since the problem, which is very low. Overall the car has 70K miles, no rust, and is very clean.

My best guess is the speed sensor has gone bad. I have found the replacement sensor at Rock Auto. I'm wondering how hard it is to change out, and how I get at the sensor. I am not a mechanic, but willing to learn and give it shot before taking it in to my local shop. I'm also wondering what the likelihood is that the plastic gear inside the trans is the problem. That would probably be a real pain to fix.

Given I won't be driving the car much until spring, I have time to sort this out. It's no fun to drive without a speedo. The GPS readout on my traffic app keeps me out of trouble, but it's just not right to look down at an unmoving speedo.

Thx,
MP
 
One wiring connector and one bolt on the clamp/retainer. The connector is aged, so be gentle with the ears so you don't snap them off.
4

Unless it's gummed up and chemically welded, it should pop out with a slight twist/pull, I'd think. Have the new one ready in case fluid tries to escape. Pay attention to the orientation so you don't have to fight the connector going back on.

Good luck, but if it were me, I'd suspect the gears in the speedo head first. Is the trip meter stuck on 0000?
 
One wiring connector and one bolt on the clamp/retainer. The connector is aged, so be gentle with the ears so you don't snap them off.
4

Unless it's gummed up and chemically welded, it should pop out with a slight twist/pull, I'd think. Have the new one ready in case fluid tries to escape. Pay attention to the orientation so you don't have to fight the connector going back on.

Good luck, but if it were me, I'd suspect the gears in the speedo head first. Is the trip meter stuck on 0000?

The odometer and trip meter are both working. I don't see anything in the Ford shop manual or pics of the odometer gears that indicates they are connected to the speedo. The EVTM troubleshooting guide just says to replace the speedo, which I would rather not do unless it's the only option. Of course if the odometer is working that would seem to indicate the speed sensor is sending a signal, so that isn't a very likely fix either. I'm mostly guessing at a fix at this point.

But replacing the odometer gears is good idea for preventative maintenance regardless, so I'll probably do that.

Thanks,
MP
 
The sensor is held in with a single 10mm bolt if my memory is any good. You can get to the sensor pretty easily by jacking the car up mid door on the drivers side...no harder than changing a light bulb.

-Tim
 
The sensor is held in with a single 10mm bolt if my memory is any good. You can get to the sensor pretty easily by jacking the car up mid door on the drivers side...no harder than changing a light bulb.

-Tim

Thanks, that helps. I just wish I was confident this would fix the problem.
 
I just wish I was confident this would fix the problem.


You can always just pull the connector, then live test to see if the speedo rests at zero instead of 125. If the head unit itself is borked, it shouldn't make any difference.
 
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There's a second part. The VSS signal drives the odo and the speedo off the same feed; if the odometers are working properly, most likely the VSS is OK and it's internal to the speedometer.

Third part. Does the VMM, if so equipped, call for oil and filter changes early? That is, at say 1500 miles not 3000 miles? If it calls early, it may be a bad VSS or a bad shield in the wiring from there to the cluster; if not, again, the VSS is probably OK and it's in the speedometer.

RwP
 
Thanks, I'll look at those options to narrow down the problem.

The VMM hasn't called for any changes. I have put about 3000 miles on the car total, but only a couple hundred since the speedo went out.

MP
 
New speedo fixed problem, but came with bad odometer

Update:

I decided the sensor must be good since the odometer was working just fine so I picked up a new IP. The speedo now works, but the IP came with a bad odometer. Plus the check gage light is on just for fun. No light with the original IP. I think I'll track down a new speedo for the original IP, upgrade the odometer gears, and put that IP back in. We'll see if that fixes everything.

Of course now the heat and AC don't work, but that's a separate thread.

MP
 
Mine jumps around when I'm stopped and even in park. Ill be sitting there and it will jump up to 100mph to as far as it will go. It doesn't work but the odometer still works.
 
You can swap the speedo from the new cluster into the original, it just pulls out from the front of the assembly and while you have it out odometergears.com has the replacement gears.
 
New speedo

I ended up going with a new speedo in the original IP cluster. Got a nice 140mph unit from TBSC shop with new odo gears and set to the proper mileage. I assume the original dead speedo has no real value, unless someone tells me otherwise. I have the other IP for a back up for now.

On to the next repair.
 
does any one have the dash wiring diagram?
is there a place in the dash or under the dash to be able to get the vss signal with a fq counter?

1990 sc low miles. show car.
speedo jumps all over the place when stopped at idle.

almost like a bad ground or power supply issue...
 
They used the same sensor body on cable driven earlier cars and trucks ...Ford didn't want to re-tool everything to make a separate sensor so they just used the same body and put a dummy plug in it...Check your gear to see if it's apple- cored..if it is either the gear is worn or the bushing or bearing,(depending on your transmission) in the rear of the case is bad
 
The plug in the pic.. Thr one you thought broke of or came out of the speed sensor is that either an o2 sensor or knock sensor? Is it on the drivers side or passenger side?
 
the odometer and trip odometer is working.
do you have a pin out on the speedo cluster?
a bump do you have a pin out on the speedo cluster?
and does any one have the signal charts for the vss output to the cluster?
i just ordered the manuals set from super coup...
I hope they are like the gm manuals and have the exact specs for a fq counter.

i suspect a bad solder joint or bad ground in the speedo its self.
 
New speedo

I ended up going with a new speedo in the original IP cluster. Got a nice 140mph unit from TBSC shop with new odo gears and set to the proper mileage. I assume the original dead speedo has no real value, unless someone tells me otherwise. I have the other IP for a back up for now.

On to the next repair.
hey 91 T do you still have the old unit that does not work?
i would like to take a look at it!
 
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