Loose flex plate bolts

Stopping a common Rattle

One of the common problems with Jeep Cherokees withe AW4 automatic transmission is that the flex plate bolts back out after a while.

The flex plate is bolted to the torque converter with four relatively small bolts.  With age and time they get loose.

The noise is often diagnosed as a rod knock or something more severe and the Jeep gets sold cheap or scrapped.  If all the bolts fall out the Jeep will have no drive in all gears and be misdiagnosed as a transmission failure.

Inspecting the bolts is a relatively easy task.  They are hidden behind a small metal plate at the bottom of the transmission bellhousing.

This little plate is very well secured to the transmission. It had two large bolts with 18mm heads and two smaller bolts with 13mm heads.

Flex plate inspection plate

If your Jeep is like most, this area will be covered in mud and oil from a leaking rear main seal.  So it may take some digging to find the two small bolts.

One big issue with this task is that the bolt on the left side of the transmission will not come out unless you also remove the exhaust pipe.  However for just an inspection and tightening, you can get by without totally removing this bolt.  Just loosen the nut so the bolt can be moved back against the pipe.

Flex plate inspection plate

With the other bolts out you can pull the plate back enough to see the flex plate bolts and get a 15mm box end wrench on them to snug them up as necessary.  If you want to work in a torque wrench or put on some locktight, you will have to remove the exhaust pipe.

Once the bolts are tight, you can turn the transmission with the wrench on the bolt. There is just enough room to bring one bolt to the bottom and be able to access the next one at the top of the opening.  There are four so keep count and you will know when they are all checked.

Inspect the flex plate for damage while you are there. If the bolts have been loose for a while the holse my be elongated or the plate cracked.  If this is the case, you will have to remove the transmission to replace the flex plate.

XJ LED dash light upgrade

XJ cluster LED

Adding LED dash lights to the XJ

I recently swapped in a used cluster to replace mine where the odometer has=d stopped working. The bulbs in it were pretty dim. I decided to try using LED bulbs.

i bought these from Amazon:

The listing gave me a a warning that these would not fit my 1991 Cherokee. But since the measurements were correct I gave it a chance. They turned out to be the right bulbs.

XJ cluster LED

The trouble with the LED bulbs is that they are polarized while the originals don’t care how they are installed. Also, the LED bulbs were not marked for + and – that I saw. So I rigged up a test set up using my 12V jump box and some alligator clips.

XJ cluster LED

Now you can trace each of the copper traces on the board and see what is positive and negative, but I decided to just use trial and error. That technique got me through engineering school it can get me through five LED bulbs.
I hooked up a lead to the ground that is handily marked on the board. I touched the positive lead to the solder joint that powers the lights to test each one. See the photo:

XJ cluster LED

To make sure the bulb lit up, I removed the one next to it and peeked inside:

XJ cluster LED

If it did not light up, I just turned it around. It did not take long to get all five in the right way around.

Once the cluster was back in the Jeep I am happy with the way it looks. I also took some time to clean it all up while it was out.

XJ cluster LED
XJ cluster

RX7 1st gen brake racing brake pads

How to install racing brake pads on a 1st gen RX7.

Easiest brake pad swap ever!

Our race team recently obtained a RX7 track day car. It has a 13B swap and a mostly stripped interior and an Autopower cage. S0me minor work has been done to the suspension.

We fitted a set of Hankooks and took it to Atlanta Motorsports Park for Track Night in America.

The little car is well suited to the tight twisty turn of AMP. However after a couple of brisk laps we had to let the brakes cool for a lap before going all out again. We had thought that since the car had several other mods it would have better brake pads but that seems not to be the case.

So today I swapped in a set of Hawk Blue pads.

Begin by removing the wheel. Thn remove the one bolt holding the caliper in place. Flip it up and let it rest on the rotor center. Pull one of the old pads and use it for a spacer against the piston. Use a C clamp to press the piston all the way in.

SInce the rotors looked nearly new, I did not change them. Since they have the bearings as part of the unit this would have added some time to the procedure.

Drop the new pads in place and slip the caliper back over them. Tighten the one bolt and your done!

Put he wheel back on and do the other side.

The Hawk pads require a specific bedding in process. It is not hard to do on the road in front of my shop. But it is important to follow the instructions from Hawk carefully. You will feel the pads suddenly bite in when they bed in. Be careful as sometimes one side will come in before the other making the car pill to one side while braking for that one or two stops.

Looking forward to see how they do at the track. I will update after the first outing.

How to replace the harmonic damper on a Jeep XJ

How to replace the harmonic damper on a Jeep XJ

Recently I heard a strange sound on my Dad’s XJ Wagoneer. It sounded like something hitting the fan. It took me a couple of days to find it but when I did it was obvious. The harmonic damper had come apart at the rubber joint and was working its way forward off the hub.

I caught it just in time.

I began by removing the bumper. This step is not absolutely necessary but makes the job a lot easier. Be careful with vacuum bottle in the back of the bumper when removing it.

Loosen the serpentine belt. On his Wagoneer the tension is adjusted at the power steering pump. Removing the air box makes it easier to get to the bolts.

Using a puller, remove the old damper pulley. The threaded holes for removal are in the center hub so even if the pulley is coming apart like his was, the puller will still remove it.

It is a good idea to replace the seal while the damper is out. When pressing in the new seal absolutely do not hit the end of the crank with a hammer. If you do, take time to file done the edge you created before attempting to install the new damper.

Inspect the key and make sure it is seated in the crank snout. Make note of its position.

Carefully align the key way in the new pulley with the key and try to slide it on. They pulley should fit very tight but you should be able to get it on enough to make sure the key is lined up. You will feel it if it is aligned correctly. If you can’t get the pulley on far enough to feel the key way, stop. Do not go any further. If you try to install with the key way not aligned, you will push the key out and into the timing chain behind it. You will then have to remove the timing cover and replace the damaged parts. So take your time and get the key lined up properly.

If necessary, you can heat the hub with a hot air gun to expand it enough to make it slide on the crank enough to feel the key way. you can also use sand paper to open up the hole just a bit but don’t go too far as there still needs to be a tight fit on most of the shaft.

Once the key way is lined up, press the pulley onto the shaft using an installation tool. Autozone and Advance have these in their free rental program. However be prepared for the counter guy to argue that the only have the removal tool. You can buy your own from Amazon:

Do not try to press the pulley on using the crank bolt. This will damage the threads in the crank and make an expensive mess.

Once the pulley is pressed into place, remove the tool and install the bolt and torque it to specs. You can use a screwdriver in one of the slots to hold it from turning while using your torque wrench.

Reinstall the belt and tighten. Reinstall the air box and front bumper if removed.

These clips will likely be broken on your bumper bolts:

Renix XJ injector upgrade

How to change injectors in a Renix XJ

4 hole injectors renix

My Dad’s 4.6 stroker is in a 1988 XJ Wagoneer. It has the Renix control system.

It has always run rich as we installed the recommended 24lb Mustang injectors with the build.

I recently upgraded the injectors in my 91 XJ so I decided to try my old injectors in his to see how it would run. The difference was immediate.

No more filling the shop with fumes and no more bog on initial throttle opening.

I decided to swap in a set of 4 hole injectors from K suspension. (By the way don’t buy them from any other Jeep injector site on the internet. Not unless you like filing PayPal claims to get your stuff. Just get them from KS.)

Make sure the engine is cool before you start as you will inevitably spill some fuel on the exhaust manifold. You can also disconnect he battery cable if that makes you feel safer.

Unbolt the bracket that holds the fuel return line in place. It is hidden under a bracket that holds some vacuum lines.

Injector install XJ renix

Unclip the fuel line from the regulator and move it out of the way. Remove the transmission cable from the throttle body if you have an Automatic. Then three torx screws that hold the bracket to the throttle body.

Trans cable mount

Use a pick to remove the spring clips and unplug the injector wires from each injector. Be sure to mark them somehow so they don’t get mixed up going back. Leave the clips that hold the injector to the rail for now.

Fuel injector electrical connection removal

Next, remove the four bolts that hold the fuel rail to the manifold. Now use both hands to pull the rail straight off the engine. It won’t have to move far. Make sure the O rings come out with eh injectors. If not, carefully use a pick to pull them out of the manifold. If one falls in; you are in for more work to retrieve it.

Now unclip the injectors from the rail and remove each one. A large screw driver can be used to pry on them carefully if they are really stuck. Gently twist the screwdriver between the flange of the rail and the electrical connector part of the injector.

Coat the new injector O rings with engine oil. I poured some in the bottle cap and dipped each end of each injector in. Be very careful when installing the injectors into the rail not to nick the O ring. Push in firmly and straight. If the o ring gets crooked, pull it out and start over. Some twisting may help.

Now install the electrical connectors. They are much easier to plug in than to remove. Now install the retainer clips to hold the injectors to the rail.

Now, carefully align all six injector with holes they need to go in. Use both hands to firmly press the whole rail in at once. Wiggle it around until all the injectors are seated in the manifold and the holes will line up to mount the rail back on the manifold.

Bolt the manifold back in place. Put the fuel return line back in. You may want to do a leak test before putting the transmission cable back on. To leak test, hook the battery back up and turn on the key. You should hear the fuel pump run. Cycle the key on and off to help pressurize the rail. Check for leaks. If none start up the Jeep.

It may take a moment to get all the air out for the Jeep to idle correctly. Inspect carefully for any leaks.

If none, shut the engine off and reconnect the transmission cable. If you have leaks, try twisting the injector. If it still leaks you have nicked an O ring and it will have to be replaced. You can swap the top and bottom O rings on the leaking injector to get you by if you don’t have spare O rings. If you are in a real bind, try using one from the old injectors.

The Renix computer adapts quickly to changes in the injectors. If it runs really rich after changing the injectors, check to see if the MAP sensor line was knocked loose while moving the fuel rail around. If there is a large vacuum leak check the crank case vent hose.

Enjoy your new better running engine.