Torque Converter Lockup troubleshooting – The Red Jeep Saga

Torque Converter Lockup troubleshooting – The Red Jeep Saga

Scott’s almost has the red Jeep ready for paint. But there has been one nagging problem that he wanted to resolve before he put in the effort to paint the truck – the transmission seemed to refuse overdrive and the torque converter refused to stay locked up.

At first the trouble was intermittent. It was especially frustrating that when I drove the Jeep, it shifted fine but when Scott drove it, it would refuse to stay in forth and the converter would not stay locked.

For those of you new to this story, this is a 1989 Jeep XJ Cherokee. It was bought for parts with a burned up wiring harness. Scott has put it back together and it runs and drives better than any other Jeep in our fleet – except for its weird electrical problems that occur from time to time.

Scott first tried swapping the throttle position sensor. No change. Next he tried swapping the whole transmission computer. No change.

We tested the resistance across all the transmission control solenoids. All were within spec.

Next we decided to use the diagnostic procedure for the later model Jeeps even though this is a Renix Jeep and uses a different transmission computer. It does however have the same model of transmission, the reliable Asin AW4.

We test-drove the Jeep with the transmission computer unplugged. It worked exalt as expected with first gear only in the 1-2 position, 3rd only in 3 position and OD only in D position. Of course no converter lockup is expected with the computer disconnected.

Next, I rigged up a jumper wire to test the converter lockup. I probed the white wire to the solenoid and the yellow power wire to the computer and made a jumper and had Scott drive us down the road. As I connected and disconnected the jumper we watched the rpms jump and we could feel the converter locking up. So it worked mechanically. Just the computer was telling it not to lock.

This test confirmed my earlier suspicions that the Transmission was actually shifting into over drive and the converter was locking for a second and then as if commanded by the computer it was unlocking and sometimes shifting back to third gear.

Next we brainstormed things that would cause the converter to unlock and read more in the manual about how the converter worked. We found that pressing down on the accelerator should unlock the converter as well as stepping on the brake.

As these two circuits are very different we had to resort back to the older manual with its less specific wiring diagram. We saw that a blue and yellow wire was supposed to carry the brake signal trigger. Having already changed the throttle position sensor we decided to work on the brake circuit first. Inspection of the brake light switch showed only pink and black wires. We took another test run and found that if the brake input wire was grounded, the torque converter would indeed lock up. This test confirmed our theory of the brake input being the trouble.

The wiring diagram was less than helpful has it simply showed the bleu/yellow wire going through a switch to ground. It gave no clue as to the physical location of this switch.

Scott crawled under the dash again and searched until he found the blue/ yellow wire. There was a second switch on the brake pedal above the brake light switch.

We probed the switch and found there was no change in it as the brake pedal was depressed. The switch indicated that the pedal was down all the time.

He pulled the switch out and we found that it would work intermittently out of the Jeep. So I took the switch apart and cleaned it with contact cleaner. Once back together, it worked reliably.

Scott reinstalled the switch and adjusted it to properly indicate when the pedal was depressed. We reattached the original transmission computer and buttoned everything back up.

A tryst drive showed that it work just as it was supposed to. So far the transmission continues to operate properly. A simple solution to a problem that had frustrated Scott for a couple of months now.

How to make your Jeep Last while enjoying it off road

How to make your Jeep Last while enjoying it off road

Jeeps are huge fun to play with. And the best place to enjoy a Jeep is in the dirt mud and rocks. However use in these environments can take a toll on the Jeep if it is not properly prepared and maintained.

Proper preparation is essential to making a Jeep last off road. While Trail rated Jeep vehicles like the XJ Cherokee and Wrangler are very capable off roaders in stock form, there are some simple modifications that will help them last even longer.

One of the most important preparations is to have the proper tires for the environment. It you are going to be in mud, rocks or dirt, you need a strong tire with deep tread. Having a tie with high void area like a Mud Terrain tire helps get even more traction in all off road conditions.

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By having good tires, you will be able to approach obstacles with less momentum and reduce stress on the suspension and body work. Having the right tire and not getting stuck go a long way to improving the overall reliability of the Jeep.

Using lower air pressure in the tires when off road will also improve reliability and longevity. Reduced air pressure will allow the tire to conform to the terrain aiding in traction. Lower air pressure will also allow the tire to flex more over obstacles that might otherwise puncture the tire.

The next area to consider is the armor. Rocker rail protection is critical on Jeep Cherokees. The pinch seam on the bottom of the Cherokee is easily susceptible to damage by rocks and other off road obstacles. If the pink seam is damaged, the overall body structure can be weakened. Rocker protection can be simple or elaborate. There are many styles available for sale or they can be easily fabricated with minimal welding skills.

Protecting the under carriage is helpful as well. Factory skid plates were available and provide adequate protection for most off roading. There are also many versions of skid plates available in the aftermarket as well as self fabricated options.

Lifting the vehicle will also allow more clearance between obstacles and the bottom of the Jeep. Lifting also allows larger tires to be fitted so that both traction and clearance are enhanced at the same time. Being able to drive over more obstacles will help your Jeep last longer in off road service.

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Even when your Jeep is properly prepared, proper maintenance is important to its long life. The front suspension and steering joints are fitted with grease points so that dirt and water can be flushed out after off road adventures. Use a standard automotive grease gun to force fresh grease in to the joints and to flush out contaminants that may have collected there after each trip off road.

Also, if there is a chance that water could have contaminated the differential fluid or transmission fluid, change these fluids as well. At minimum, follow the recommended change intervals in the owner’s manual.

Keeping the seals in good shape will help keep vital fluids in and water and dust out. Replace oil and grease seals when there is any evidence of leakage.

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Despite your beset efforts to keep parts lubricated, moving parts such as universal joints and tire rod ends will wear out. Inspect these parts frequently and replace them when they show signs of wear. If these parts fail, they can take out other expensive parts or leave you in a very dangerous position off road. Inspect and maintain these joints before and after each off road trip.

Dirt is very abrasive and will be the most damaging element of off roading. Therefore after each trip off road, thoroughly clean the Jeep including the under carriage. Remove dirt and mud that accumulates on the suspension parts to keep them moving freely. Keeping the parts clean will also aid in inspection so that wear can be noticed more easily.

Driving style is also a factor in how long a Jeep will last off road. Knowing how and when to use momentum to get over obstacles is critical to safe and damage free off road driving. Learning from more experienced drivers and practicing on smaller obstacles will help you gain the skills needed to safely drive your Jeep through any conditions.

Lowering the Transfer Case on a Jeep Cherokee

Lowering the Transfer Case on a Jeep Cherokee

One common method to deal with drive shaft vibrations on a Lifted Jeep Cherokee is to lower the transfer case one inch to reduce the drive line angles. The pinion is rotated up slightly by using longer shackles or axle shims.

While there are various transfer case lowering kits available in the after market and even one from the Jeep dealer, they all serve the same function: they space the cross member down one inch from the unibody frame rail.

The spacers can be made in a variety of ways. On simple way is to take a piece of 1 inch square tubing or bar stock and drill two holes in it. Another method is to use a stack of washers or a piece of pipe cut one inch long and wrapped around each mounting bolt.

The original mounting bolts must be replaced with longer bolts and the two mounting studs must be removed from the frame. Normally these are replaced with bolts as well.

Bolting a dropped cross member into place can be a challenge. As the transmission engine unit drops it tends to move to the right. Without the studs to align the cross member, it is necessary to hold the cross member in place while starting the bolt into the threaded part of the frame. Because the bolt is now one inch longer, it is easy to cross thread it.

Also, since the cross member hangs down further below the Jeep it is easily impacted by rocks and other obstacles. It is possible to bend the nutsert in the frame making it even more difficult to get the bolts started once the cross member is removed for any reason.

One solution to the bolt problem is to make a longer stud instead of using four long bolts. This will help align the cross member when it is being installed and reduce the change of cross threading. If the nutserts are damaged, you may have to cut into the floor and install a bolt form the top of the frame. Alternately you can weld in a stud from below.

Another problem with the lowered cross member is the angle of the exhaust. The down pipe from the manifold is bolted to the cross member. As the cross member drops, the catalytic converter and the muffler will move down as well if nothing is done to compensate in the exhaust system. The pressure put on the hanger behind the muffler will exceed the strength of the rubber hanger. Also the increased pressure will cause the muffler to crack where the tail pipe exits over time unless the exhaust system is modified.

Having the transfer case sit lower also puts an extra strain on the transfer case shift linkage. If the transmission mount is worn the linkage can slip out of the body mount during off road flexing. When this occurs, the transfer case will not shift from 4wd to 2wd until the linkage is replaced in the bracket.

To eliminate the need to drop the transfer case, a Slip Yoke Eliminator kit is available for the transfer case and when used with a double cardon drive shaft, the transfer case can be used in its original position. See How to install a SYE for more information.

UPDATE: I noticed that the transmission mount for the five speed is about an inch thinner than the one for the automatic. I have not tried it yet but it looks like you could use a manual mount on an automatic to achieve a 1″ drop without lowering the cross member.

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How to replace the track bar on a Jeep Cherokee

How to Change the track bar on a Jeep Cherokee

The track bar locates the front axle side to side on a Jeep Cherokee. The stock bar consists of a rubber bushing at the axle end and a tie rod end at the frame joint. The frame end joint generally wears out first.

To determine if the track bar is bad, hold your hand on the frame end joint while an assistant turns the steering wheel back and forth. Any movement here means the bar is bad.

To replace the bar begin with the vehicle weight still on the axle. Locate the steering so that the 15mm head bolt that fastens the track bar to the axle is accessible. Remove the bolt. There is a special nut with a tab on it behind the axle. Pull it out after the bolt is free.

Now lift the vehicle to a comfortable working height. Remove the cotter key from the mounting bolt. Use a ¾ inch box end wrench to loosen the nut. Do not remove it completely at this time. Run it up even with the top of the bolt.

Use a tie rod end removal tool to press the tapered link out of the frame mount. My favorite is the pesto tie rod puller from JC Whitney    ( Since that tool is no longer available try this one from Amazon) that accesses the joint from the side. Hammer the puller between the bar and the mount. This will likely damage the rubber boot. Put a moderate amount of pressure on the puller by tightening the bolt on the puller.

Then use a hammer to hit the frame bracket. Hit it hard. The idea is to temporarily deform the tapered hole enough to loosen its grip on the pin. When the bar pops loose, the puller will likely fall so watch your toes.

Remove the nut the rest of the way and remove the bar. Clean the tapered hole.

On the new bar, note the location of the cotter pin hole. Be sure it is rotated in a way that will allow you to put in a new pin once it is installed in the cavity.

Slip the tapered pin into the hole. Tighten the nut. Align one of the castle nut opening s with the hole in the pin. Insert a new cotter key and bend it back over the top of the pin.

Lower the Jeep to put weight back on the axle. Fit the axle end of the bar in the bracket and align the hole. The easiest way to align the hole is to have an assistant turn the steering wheel while you line up the bolt with the hole. Alternately you can push or pull the Jeep side to side to line up the holes.

Slip the bolt in and hold the special nut up behind it and carefully start the threads. Run the bolt in but do not tighten it fully. Bounce the Jeep a few times to settle the bushing in place. Then tighten the bolt.

Grease the frame end joint if it is fitted with a grease fitting.


Tie rod removal tool

Jeep 4.0 Oil filter adapter leak

Jeep 4.0 Oil filter adapter leak

Jeep Cherokees and other Jeeps that use the 4.0 are subject to a leak on the side of the block where the oil filter adapter attaches. There are three O rings inside that with age will leak.

Often this leak is misdiagnosed as a rear main leak or even a valve cover gasket leak. When the oil filter adapter leaks oil is blown back and collects on the rear of the engine.

The proper O rings are available in a kit from your local Jeep dealer or form a Crown Automotive distributor. Standard O rings do not seem to fit, so you need to get the proper rings from the kit.

There are two different types of oil filter adapters used throughout the run of 4.0 blocks. One has a 5/8 hex on the surface. The later version has a T60 torx in the end.

Removal of the older hex version is pretty straightforward. Just turn the hex with a wrench and remove the adapter.

Removal of the later Torx version is more difficult in that there is not enough room to put a normal torx bit in the opening and still be able to put a racket on it. One method to gain clearance is to remove one of the bolts that hold the engine mount to the body. Getting this bolt head out of he way will give just enough clearance to put a 3/8 ratchet or breaker bar on the torx bit. As the center unscrews, you will run out of room before the part is all the way out.

One way to deal with the lack of clearance is to use a torx bit that can be fit in a box end wrench. Or you can make a special tool for the job by welding the torx bit into a box end wrench.

When the O rings are hardened, it takes a lot of torque to break it loose initially and there is a lot of friction all the way out until it comes loose. If you make a wrench, be sure to make it strong.

Once the adapter is off the block, you will need to remove the old O rings. If it was leaking, then they will likely be hard like bakelite. The big one often sticks to the bock. Scrape it loose or free it from the O ring groove depending on where it ends up.

The two on the center bolt are best removed using a dental pick. Coat the new ones in oil to slip them in place. Make sure they are seated in their grooves and not twisted when in place.

Set the adapter back up on the block. Align the roll pin with the groove in the adapter to ensure the proper clocking of the adapter.

Carefully start the center bolt into the bock and tighten securely. It does not have to be as tight as it was when it came off. It was stuck by the old O rings then.

Check the oil level, as you will likely have lost what was in the filter. Start the engine and check for leaks.

T60 bit can be turned with a wrench