88witha96

My 1988 xj with a 1996 inline 6, 4.0 is shifting rather hard into 4th gear (feels like a jerk). It happens mostly when accelerating uphill (not so much coasting downhill). Everything else seems okay...never misses or slips out of gear. I have found quite a few threads on the internet where people have this same problem but no answers.
The jeep came with a spare transmission. Is mine even bad and how do I know if the spare is any good or better?
Any info on this would be a great help I am trying to learn all that I can.

VTJeep

hmm.. Maybe a bit more info on what the shift feels like? is it a clunk? Or does it just have a significant rpm drop and sorta slug into 4th.

there are a few things to check over before swapping the tranny out.. unless thats your preference, i mean, you do have a spare. maybe the kick down cable needs an adjustment?

tjwalker

1. Fluid. Should be at the CORRECT level on the dipstick. Should be RED in color. Should NOT smell burnt.

2. Throttle position sensor always on the suspect list for shifting issues. More on that below.

3. TV cable adjust as already mentioned.
------------------------------------

RENIX TPS ADJUSTMENT

Before attempting to adjust your TPS be sure the throttle body has been recently cleaned.
It's especially important that the edges of the throttle butterfly are free of any carbon build-up.

IMPORTANT NOTE: Using the positive (red) lead of your ohmmeter, probe the B terminal of the flat 3 wire connectorof the TPS . The letters are embossed on the connector itself.
Touch the black lead of your meter to the negative battery post. Wiggle the wiring harness where it runs parallel to the valve cover and also near the MAP sensor mounted on the firewall.
If you see more than 1 ohm of resistance, and/or fluctuating resistance, some modifications to the sensor ground harness will be necessary. The harness repair must be performed before proceeding
MANUAL TRANSMISSION:
RENIX manual transmission equipped XJs have a three-wire TPS mounted on the throttle body.
This manual transmission vehicle TPS provides data input to the ECU. The manual transmission
TPS has three wires in the connector and they're clearly embossed with the letters A,B, and C.
Wire "A" is positive.
Wire "B" is ground.
Key ON, measure voltage from "A" positive to "B" ground by back-probing the connectors..
Note the voltage reading--this is your REFERENCE voltage.
Key ON, back-probe the connector at wires "B" and "C". Measure the voltage. This is your
OUTPUT voltage.
Your OUTPUT voltage needs to be seventeen percent of your REFERENCE voltage. For
example: 4.82 volts X .17=.82 volts. Adjust the TPS until you have achieved this percentage. If
you can't achieve the correct output voltage replace the TPS and start over.

AUTOMATIC TRANSMISSION:
RENIX automatic transmission equipped XJs have a TPS with two connectors. There is a flat three-
wire connector, same as the manual transmission vehicles have, and it is tested the same as the
manual transmission equipped vehicles--FOR ENGINE MANAGEMENT RELATED ISSUES.

However, the automatic TPS also has a square four-wire connector clearly embossed with the letters
A,B,C, and D. It only uses three wires and provides information to the Transmission Control Module.

Key ON, measure voltage between "A" positive and "D" ground. Note the voltage. This is your
REFERENCE voltage.

Back-probe the connector at wires "B" and "D". Measure the voltage. This is your OUTPUT
voltage. Your OUTPUT voltage needs to be eighty-three percent of your REFERENCE voltage.
For example 4.8 volts X .83=3.98 volts. Adjust the TPS until you have achieved this percentage.
If you can't, replace the TPS and start over.

So, if you have an automatic equipped XJ your TPS has two sides--one side feeds the ECU, and
the other side feeds the TCU. If you have TRANSMISSION issues check the four-wire
connector side of the TPS. If you have ENGINE issues check the three-wire connector side of the TPS.

For those with a MANUAL TRANSMISSION--the TPS for the manual transmission XJs is
stupid expensive. You can substitute the automatic transmission TPS which is reasonably priced.

88witha96

VTJeep:
The best way I can describe the shifting problem is... It feels like someone kicking the jeep from behind (enough to move you forward a bit). Its a faint clunk sound. I don't notice a significant rpm drop or a slug into 4th.

When I bought the Jeep about a month ago the transmission fluid was low. I topped it off. Since then the fluid has maintained at the correct level, is red in color and does not smell burnt.
I should also mention that it is an automatic, 4x4.

tjwalker:
thanks for the suggestions! I will check all that you mentioned and report back asap.

88witha96

I finally figured it out! I never would have guessed it but it turned out to be the u joints in the rear drive shaft. Strange how it only gave me trouble at 4th gear speeds.