Folks, it’s time that I own up to an embarrassing misdiagnosis — one that led me to call a tow truck to have my 1991 Jeep Wrangler towed all the way home as my girlfriend (whom we’ll call Elise) and I rode in the truck’s cab. Yesterday, after months assuming the problem was a blow front U-joint, I asked Elise to jump behind the wheel of the broken Jeep and gently roll the vehicle backwards as I looked underneath trying to determine what was making that loud “clunk.” I then saw the issue, and boy did I feel dumb.
You’d think someone who has owned over a dozen old Jeeps, who helped engineer the current-generation Jeep Wrangler, and who has spent the last 15 years rebuilding engines, transmissions, transfer cases, driveshafts, and just generally wrenching like crazy would be able to figure out the cause of a banging noise under an old YJ. But nope, I screwed this one up.
It all happened back in January, when I took my 1991 Jeep Wrangler YJ off-roading with a friend, who brought along his lifted TJ. I was feeling fairly confident that day, so I took the Jeep up an absurdly steep grade that, from the bottom, looked impossible.
I would have pulled it off, too, were it not for the loose sand towards the top of the grade, which my Jeep sunk down into. I tried over and over, turning the front wheels back and forth to get grip on some new ground, backing up to gain momentum, applying more throttle, etc. — but every time, I just sank and spun up those 235 75R15 all-terrain Walmart tires. Here’s one short clip, which doesn’t do the grade justice, because it was gnarly:
I spent about 10 minutes on that grade, but I just ran out of grip, causing the Jeep to sink, at which point I ran out of ground clearance. After hammering on this Jeep trying to get it up the grade, I drove back onto the main trail and began hearing a clunking noise under the Jeep. I took a quick peak, but ignored it; I’d solve that later, I figured.
Fast forward a few hours, and after an incredible off-road trip, Griffin, owner of the TJ, and I hit the road and headed back home. I still heard the clunk, but it seemed mostly fine. Then, while on the highway going 60, things escalated. “CLUNK CLUNK CLUNK CLUNK CLUNK!!”
Loud and in rapid succession, these clunks were alarming and impossible to ignore. I pulled over onto the shoulder and looked under the Jeep; I didn’t see anything obvious.
I continued driving, cringing as whatever storm was brewing below my butt, thundered loudly into the cabin. I took the next exit, and came to a stop in a Costco parking lot. It was clutch, really, because Elise and I were hungry. We wolfed down a hotdog and slice of pizza, and then I returned to the Jeep and lifted the rear axle using the underhood factory floor jack:
To me, the noise sounded like it was coming from the drivetrain, and given that, in two-wheel drive, the front driveshaft doesn’t spin due to the YJ’s vacuum-powered front axle disconnect, I figured I’d turn the rear wheels and listen. I didn’t really hear much, but I did notice lots of end-play in those rear axle shafts. Hmm.
I jacked the front wheels, and I heard only a slight noise from the front left wheel — that’s gotta be it! A closer inspection showed that, indeed, my driver’s front axle u-joint was indeed toast, and was banging around a bit:
The weird thing, I thought, was that I’d driven a $600 Jeep XJ for an entire winter with a much worse front U-joint, and though it banged around, it wasn’t nearly as violent as the noise I had just heard under my YJ. I hopped back into the Jeep and drove a bit more — the noise sounded like it was coming from under my seat or towards the rear! Plus, it seemed to change based on the ride height, getting worse when hitting bumps.
“This has to be a sprung part of the vehicle,” I thought to myself. The front axle U-joint wasn’t sprung, so when the suspension went into jounce/rebound, it didn’t actually change the position of that component. Why would the sound change?
I checked the front driveshaft; it seemed fine. I checked the rear driveshaft — nothing looked or felt out of the ordinary. Damn.
I convinced myself that the rear Dana 35 was the issue, though not only is it unsprung, but normally an axle shaft failure would result in the shafts actually pulling out of the housing, taking the drums and wheels with them. This wasn’t happening with my YJ.
Anyway, I wasn’t sure, and the noise while driving was extremely disconcerting, so I called up AAA, and had the YJ towed about 45 minute to Van Nuys, with Elise and I hanging out with the jolly tow truck driver. It was a fun experience for Elise and me, actually; the cab was huge and comfortable, and it was nice talking with the gentleman about his job and his life in LA.
Anyway, fast forward to yesterday when I heard the noise quite prominently as I backed out of Elise’s driveway. I called her and asked if she’d come outside and hop behind the wheel as I looked underneath. She did, and that’s when I noticed this:
I saw the driveshaft close against the driveshaft speed sensor, and when the “nub” on the driveshaft spun around, it rammed right into the sensor and made a loud “bang!” that reverberated through the Jeep’s frame.
I simply grabbed the bracket upon which the sensor is mounted and bent it back. The problem was now solved.
How the heck had I missed this? Well, I think that, when I looked under the Jeep in the Costco parking lot, the sensor wasn’t actually touching the driveshaft, so I ignored it. Only when the nub spun around did that nub hit, and only when I hit a bump did the sensor make contact with the body of the driveshaft, leaving rub marks as shown above.
It was the simplest, easiest-to-fix problem ever. I had my Jeep towed for no reason. D’oh! I guess we all screw up every now and then!
When I read the headline, I thought you meant “Some idiot had my Jeep towed for no reason”
Seriously? That’s how jeep did a speed sensor? Not integrated with the t-case?
I guess it’s not the worst solution, but even for the early 1990s… that’s dumb.
That absolutely doesn’t look original to me, so now I’m even more confused!
Honey, Im going to lay under the Jeep and have you back it up okay ? that is some trust in that relationship
At least it only cost on e AAA tow (no real money) and gave you a story!
What good is paying for AAA if you don’t use it every now and then?
that is what I told my BIL when we blew up the rad on his e38 while sitting in the car, waiting for the CAA (Canada, eh?) and NOT making it to camping….
it was me who blew the rad by the way…. but at least it was also my CAA LMAO
Do they have a joint Autopian corporate membership? Can you imagine how that call went?
“Hi, we’d like to start a company policy”
“Sure! And how many vehicles would this cover?”
“About one hundred, to start with”
“And how many full time employees?”
“Um, about five”
I’ve had my car towed from a gas station. I was out of gas, but I had improperly diagnosed my problem. We all do dumb things sometimes when we are distracted by other parts of our lives (girlfriends, work, etc…).
Better question… this is how your vehicle monitors speed?????
That is my question, too. There’s going to be a vehicle speed sensor in the transfercase tailshaft, so what it that thing? Maybe an aftermarket cruise control speed sensor? Does not look OEM.
It has always been my observation that obstacles never look nearly as difficult later in pictures or videos as they did when you were actually encountering them on the trail.
Commonly known as “The GoPro Effect”.
Eh, I had to have my vehicle removed from my home garage with a flatbed because I got cocky using a key reprogrammer. Shit happens!
I assume the code name “Elise” is because she’s English and doesn’t come with much baggage.
And maybe her real name is ‘Evora’ or ‘Elan’. Or maybe ‘Seven’.
You two have been together long enough that you shouldn’t need to impress her with a fancy meal like that anymore.
Right? What decadent person needs a hot dog AND a slice of pizza at Costco’s generous serving sizes? The very literal definition of conspicuous consumption.
Have a similar story with my Land Rover Disco 2. Started hearing that clonking as I drove by a workshop. The guy in the workshop listened as i rolled slowly and said the driveshaft is broken. So, drove extremely slowly home, spent the night on the internet browsing for any used driveshafts and found one.
Got under the car a couple of days later to start the work and as I was about to begin wrenching, saw that some sort of heat plate or similar, located above the driveshaft had fallen off and was caught next to the driveshaft, making that noice with every turn.
So, two metal screws later problem was solved and driveshaft sent off to some other miserable Disco owner trying to keep their vehicle on the road.
Actually this one was a little sneaky.I’m not sure i would have caught it either!
Poor tow drivers.They must get the exact same conversation from every customer haha.I did it too
Haha, the first and only time I had my car towed (because it was sitting for 4 years and was afraid to start it), i had a nice ride with the driver and talked about the same thing. I also discovered we were just about the same age ~40 and he just had his first child! He seemed really down to earth and all around a nice guy.
What are the vehicles most likely to be on the flat bed of a big, big, tow truck??? Jeep, Jaguar, Jeep, Mercedes, Jeep, Aston, Jeep, Jaguar, Jeep, BMW, Jeep, Jaguar, Jeep, Rolls, Jeep, Porcha, Jeep, VW, Jeep, Alpha Romeo, Jeep, Mercedes, Jeep, Fiat, Jeep, Ram, Jeep, Maserati, Jeep, Chrysler, Jeep, Ford, Jeep, you get the idea………………
One, you live in California now, they hate all things ICE, and if they want to tow your damn jeeps for no reason they can. Two, your girlfriends name is Rusticia Jones Rustybottom. Three, the cats you saved are working against you. They hate BMW’s. Doubt me on this? When did one of your stray cats ever sleep in anything that wasn’t Jeep or Mopar? They are as sick of hearing about your fricken I3 as I am. Caught a kitty snoozing in your BMW lately? No? I rest my case. The cats are coming for you David….They want shower tuna…. meet there demands, or….
My RDX started making a clanky rattle on the passenger side after I drove over a slice of someone’s tire tread at highway speed. I have checked the underside and wheel wells, nothing. All I can see is a dent in the muffler, which may predate the tire incident. I’m at my wits’ end trying to debug this.
Going to sound nuts, but check your lug nuts and make sure they are tight
This is good advice. My dad once spent weeks driving about with a gradually increasing rattle, eventually took it to a garage (he is no wrencher, he’s an art teacher), and the back left wheel was a few turns of the lugs from falling off…
I can’t imagine the ambivalence that accompanies a noise like this. On the one hand, “another PITA I’ve gotta fix,” but in the other hand “content for my next column!”
I applaud the return to the use of the word “gnarly”. That said,
Just Expect Eventual Problems
Janky engineering elicits pain
Here we the Jeep in its natural habitat perched upon a rollback bed
In the early 90’s, I had a friend who had a fairly ne Accord. The only problem was it would make a banging sound, but only when it rained.
She took it to her mechanic, and he could never duplicate the problem. She even took it to him when it was raining, and it refused to make the noise.
As she drove away from his shop in the rain, the banging started back up! She immediately turned around and had him get in the car with her! She drove onto the street, an lo and behold! The banging noise manifested!
He had her pull over, he got out, went around to her door, opened it, tucked the belt from her raincoat into the car, closed her door got back in, told her to drive, and – viola!! – no more banging sound.
She felt kinda stupid, but he just laughed and said “It happens.”
Your friend is a violist?
She worked for a bank. Not sure exactly what she did.
NO WAY! haha That one needs to become an urban legend
Customer says….