Have you tried tightening the nut on the output shaft of the tcase? IIRC its around 220 ft/lbs. The rubi uses a tone ring and hall sensor. If the ring is loose it will give erratic readings
X2. This is where I would start.
I also found this on another forum. It's a lot more in-depth:
Step 1: Define the problem
A. Goal is to find out if it Is just a speedometer problem or not
B. Notice if other gauges are affected such as RPM, fuel level, temp and so on.
C. If they are not skip to step 2
D. If they are this is either CCD bus, PCM or instrument cluster
E. Instrument cluster can be isolated in step 2 below
F. Side note: CCD bus is what controls the gauges for RPM, speedometer, fuel, temp, oil, voltmeter
G. Side note 2: On the back on the instrument cluster is a 2 connections C1, C2
a. C1, pin 1 goes to CCD (-)
b. C1, pin 2 goes to CCD(+)
c. C1, pin 9 goes to ground
d. CCD (-) goes to C1 connection on PCM (grey plug on PCM), pin C28 (white/black)wire
e. CDD (+) goes to C1 on PCM pin C30 (red/Light Green)wire
H. Side note 3: If your gauges don’t work when the air bag light is on there was a recall for this the reason for this:
a. Is because the air bag module taps into the CCD bus, which causes the CCD bus to be off, if the airbag module is over loading it.
I. Side not 4: All the pins on the back on the instrument cluster are as follows:
a. C1 connection:
1. Pin 1 = CCD (-)
2. Pin 2 = CCD (+)
3. Pin 3 = Rear window defogger relay
4. Pin 4 = Rear window defogger switch sense
5. Pin 5 = 4WD
6. Pin 6 = right turn signal
7. Pin 7 =
8. Pin 8 = Key-in switch
9. Pin 9 = Ground
10. Pin 10 = Seat belt
b. C2 connection:
1. Pin 1 =
2. Pin 2 = Red Brake warning
3. Pin 3 = Fuse box/ Lamp dimmer switch
4. Pin 4 = ABS warning
5. Pin 5 = High Beam
6. Pin 6 = Ground
7. Pin 7 =
8. Pin 8 = Fused ignition switch (start/run)
9. Pin 9 = Fused b+
10. Pin 10 = Left turn signal
Step 2: If just Speedometer Isolate the instrument cluster:
A. The instrument cluster is 98 Jeep Wrangler can be isolated by doing a diags test on the cluster.
1. With the engine off hold the trip button on the cluster
2. Turn the key to on, do not crank the engine
3. Let go of the trip button
4. When you release all the cluster lights should go off and the gauges needles should move
a. The speedometer should move 1/4, 1/2, 3/4 and all the way full and back the opposite way 3/4, 1/2, 1/4, back to zero
b. This is the same for all other gauges as well
5. If it fails bad cluster
6. If it passes then it is a grounding problem with the 5V power going to VSS or data wire going to the VSS, or bad VSS.
Step 2: Isolate the VSS (Vehicle Speed Sensor)
A. Unplug VSS, VSS is located in the transfer case held on one 1/2” bolt with a 3 pin power connection, the plug is on the backside the transfer case
B. Drive around
C. Does the speedometer still jump?
1. If not test the 5V VSS power to the VSS ground using a voltmeter
a. Turn the key to on, do not crank the engine
b. 5V is violet/orange wire
c. Ground/ sensor return is brown/yellow wire
d. If you are getting 5V then it is a bad VSS or something after that
e. If you are not you have a ground or something is wrong with the PCM(computer)
2. If it does still jump:
a. Test the data wire (orange/ white) with the VSS ground
b. should be getting 5V if VSS is unplugged
c. if not the data has wire has a short or something is wrong with the PCM
d. to isolate the a ground problem cut the data wire close to the PCM
1. Before you cut any wire disconnect battery first
2. This is an orange/ white wire going to PCM white connector, pin B27
3. Be careful to cut the right one.
4. There is also an orange/white going to the PCM grey connection
5. But lucky the white and black PCM connection wires are bundled together, grey connection wiresare bundled separately.
6. Drive around
7. if it stops you have a ground, if not PCM
8. if you have a ground you have 2 choices:
a. find the ground
b. route new wire between PCM and VSS, solder both ends
9. And there you go, one less excuses to tell a cop why you are speeding
