Short Finder tool

They say if you don;t use something in year you should get rid of it.  Well I don’t take that advice on tools. I can;t remember how many years its been since I last used this tool but today it was really handy to have.

When I was trying to figure out the trouble with my Porsche tail lights I found the at the previous wonder had modified the wiring for the left side tail light.  Also, the front corner markers have never worked since I have had the car.

Tracing the circuit, I found a dead short int he left side wiring that would blow the fuse. I assume this is the reason why they have jumpered the tail light wires and disabled the front markers.

Using the above tool, I was able to trace the short to somewhere in the front fender area. Without it I would have just been guessing.

I made a jumper to use the tool to put power to the load side of the fuse and took power straight off the battery. Since there was a dead short I did not want to stress the light switch while searching for the short.

I was able to use the little meter to follow the wire through the car and down into the fender. I then put the car on the lift and removed the belly pan to get access to the wire. Since there was just a short section of wire to inspect I decided to do a visual inspection instead of continuing with the tool.

It took some searching, but I finally found the problem.  The wires inside the left side marker were twisted together and the ground was touching the power lead inside the rubber cover.

I hooked them back up correctly and the short went away.  I then redid the wiring at the tail lights to put it back like the factory intended. now there is a fuse for the left and a fuse for the right. And a another fuse for the tag lights.  Germans like fuses I guess.

Thanks goodness I had this handy Short Circuit finder tool.

G80 time bomb differnetial

The exploding GM limited slip differential

While towing to Track Night at Atlanta Motorsports Park I noticed a strange noise. I kept thinking it was from the trailer or the weight distributing chains.  I stopped several times to inspect the trailer and hitch but kept finding nothing wrong.

I noticed the noise was mostly after left-hand turns and was getting worse.  As I crossed the railroad track 9 miles from my destination there was a very loud pop.   That was when I realized the noise was coming from the rear differential of the Suburban, not the trailer.

I drove as gently as possible on the curvy road to the race track.  But when I started up the steep entrance to the guard shack, I began to wonder if I would make it.  The noise and shudder were horrible.

I made it to my paddock spot and got the race car ready and got registered. Then I set about deciding how to get home.    My co-driver for the event had driven his 2500 pickup so we decided to load the Suburban on the race car trailer and let him tow it home. That put me driving the Porsche  home.  It is tagged and insured so that was legal.  Just not very comfortable.

 Suburban on trailer

Once everything was home and unloaded I put the Suburban on the lift and popped the cover to see what broke.  As I suspected, it was a spider gear.

Broken Spider Gear

What I did not know before removing the cover was that I had a G80 limited slip differential.  That explains how I have been able to pull a loaded trailer to the campsite in Harlan and even make it to the top of the mountain to recover broken Jeeps.

The G80 does work well at low speeds.  However, it is a very strange design.  One website described the internals as looking like a clock.  East Cost Gears has this to say:

The Gov Lock is a ticking time bomb and needs to be replaced with either an open carrier or a quality positraction*

The gearbox works by having a governor that detects a difference in speed between the two axles.   Once the little governor goes balls to the wall, it presses a wedge into the spider gears to lock them together.   Very effective, but very hard on the spider gears.  After 250,000 miles of abuse, my had had enough.

I have found that replacement spider gears are simply not available.  So I will either replace the unit with a normal positraction or maybe search for a used G80 to keep the truck as equipped.

Update:  I found a nice G80 on eBay!  It arrived nicely packed;)

G80 with peanuts

After removing the cover and draining the fluid, I removed the retaining bolt for the cross pin.  This bolt normally has locktight on it. So be sure to use a six point wrench to get it out. Heat may help but mine came out with just some muscle.

With the cross pin out, I removed the wheels and brake drums.  I them pushed in each axle to free its C clip. It took some maneuvering to get the C clip aligned with the narrow slot it can come out through. I used a magnet to fish them out.

With the axles out of the way, I loosened the carrier cap bolts and removed the G80 from the axle. I made sure to note the orientation of the carrier bearing caps and the shims packs on each side.

G80 with shims

Next I used some brake cleaner to clean all the metal particles from the differential housing.  There were lots of broken teeth and other mystery chunks in the bottom.

I had to swap over my ring gear to the replacement carrier.  Note that these bolts are left hand threads so set the impact to tighten to loosen them. I carefully tapped the ring gear into place and used the ring gear bolts to pull it down carefully.  I probably could have heated it up to make it easier but it went on fine like this.

I could not fit the carrier in my vise so I reinstalled the whole carrier and held the driveshaft to torque the ring gear bolts to 65 ft lbs. I discovered one of my torque wrenches will not click in reverse but the other one would.

I then tightened the carrier bearing cap bolts to 60 ft lbs. I used the same shims as came out in the same positions.  I did not do a complete check of the gear sweep or pinion preload.  I just checked by hand that everything felt fine and I decided to just run with it.

G80 installed

After installing the axle shafts, I then replaced the cover with new gasket and filled the housing with fresh grease.  The fill hole is on the right side of the axle housing not in the cover like on Jeeps.

After buttoning it all back up, I took it for a test drive to see how it sounded.  No more clunking was good. And there was no whine at speed so the shim choice must have been close enough also.

944 Tail lights don’t work

Repairing my 944 tail lights – Tail light fuse late 944

944 tail light

After my last trip to AMP for track night, I ended up having to drive my race car home due to a tow vehicle failure.  Halfway home, I stopped to eat and noticed the tail lights were not working.  However, I had two very nice tag lights so I elected to make it home anyway.

Last night I decided to dig into why the tail lights were not working. I expected to find a loose wire or failed bulb.  Neither of these was the case.

I then decide to check the fuses and after searching the inside of the fuse box and several internet searches, I could not find a listing for the tail light fuse.   I read through a couple of forums and still no mention of a tail light fuse.

So next I printed out the wiring diagrams.  These are hard for me to follow but even more so in that, the individual bulb functions are not listed on the diagram.  It shows all the bulbs in the tail light housing but not what each one does.

So I pulled the tail lamp assemblies apart and traced the wires from the non-functioning bulbs to the connector and determined the wire color on the harness side fo the connector.  That is when I noticed that a previous owner had redone the wiring so that the left side tail light was jumpered to the right side taillight. I found that odd but continued.

I finally figured out that the tail light bulbs also power the side markers. I don’t have side markers on the race car but I do still have the plugs dangling from the tail light housings.  I remembered seeing a side marker fuse listed when I was researching.

So fuse 40 and 41 are listed for the side markers.  Sure enough, both these fuses were blown. I tried replacing fuse 40 and it would instantly pop indicating a dead short.  Fuse 41 seem loose.

After tracing the wiring diagram again, I figured out why the previous owner had jumpered the two tail lights together.  The left side marker circuit has a dead short.  So he powered the left side off the right side.

I then replaced the fuse for the right side marker circuit and wiggled it around to get it to seat properly.  After some wiggling of connectors in the rear of the car again had tail lights on both sides.

I will later go back and see if I can locate the short in the left side circuit. I expect this is why my left front marker has never worked.

Loose flex plate bolts Jeep Cherokee XJ

Stopping a common Rattle XJ

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.

Georgia Traverse Trail

Running a portion of the Georgia Traverse

Tom and I decided to try out the Georgia Traverse Trail that runs across the northern part of Georgia. It is documented on the web site

For our first excursion, we chose the section that is between our homes.  There are two alternate paths around the Cohutta Wilderness area – since the road through was closed years ago.  We decided to run both and make a loop.

We met in Eton and began the adventure in Crandle.  I had taken a few minutes to study the map at home and had planned to use my phone to navigate. However, I found it very hard to view the maps on mobile.

So we promptly got lost on the first turn.  After ending up at the Cohutta Spring resort, We made a second go and found 630 to Conasauga lake.

We made our way up the mountain and took the north fork toward Murry Lake.  We never did see the lake however.  Not sure where we missed it.

We took a right on old Hwy 2 and up into Tennessee at the Jacks River Bridge.  This was familiar territory to us form having worked and raced in the Cherokee Trails Rally. 

We paused at the little waterfall alongside the road that is an old railroad grade.

We then made the sharp right up Big Frog loop.  We followed the loop all the way to Peavine road.

Then we took Peavive across the ridge following the south side of the Ocoee River.  We debated returning to pavement at Ocoee#3 powerhouse but decided to continue and make the gravel loop.

Just past Tumbling Creek Campground we turned right to head south. This was new territory for me.  The area by the creek was very popular with every pull off occupied by people playing in the water.

Just after got back to the wilderness area, we encountered our first and only obstacle of the day. A tree across the road.

After some debate, I decided to hop across with Tom spotting.  I made it fine. So I watch and took some pictures as Tom came across in his Amigo.

After we were across we made it easily down to the other side of Hwy 2.  We continued south on  and west. We had to share the road with a large group of horses at one point. At least we came up on them in a place with good visibility and a wide shoulder for them to gather and let us by.

We ended up deviating from the route slightly at the southernmost point.  We followed a sign to 411 that put us on CCC camp road rather than following Cow Pen rd.  

That worked out fine however since we got to see Bryce Falls.

We posed the Trucks for some photos before heading our separate ways.