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!
This didn’t happen to me, but a friend of mine. He parked his wrangler at work, and went inside to do his business. It popped out of gear and rolled backwards a bit, the security guard on duty saw it, jumped in and “yanked on everything” to engage the parking brake so it would hold. Friend gets in the jeep, starts it, slips it into gear, let’s off the clutch and…..nothing. won’t move at all. Forwards or backwards, it’s just NOT moving at all! So he had it towed to a transmission shop. Where they called him about two minutes into looking at it…the security guard, in his zeal, pulled it out of 2hi and into neutral, so there was no drive. I’m not sure if they charged him or not, but he was facepalming pretty hard.
A few years ago at work we had to have one of our trucks towed under warranty. On the phone the GM people instructed me to put the transfer case into neutral. Couple of hours later get a call from the dealer panicking about why the truck won’t move. So even dealers can mess this one up.
If you had just kept driving, eventually the nub or something would wear down enough that the noise would stop, and all would be well…Old Jeeps are self healing!
It was definitely the best idea to call the tow truck, and I’m glad it was that easy to fix once you were in a good position (home, rested, hydrated) to diagnose and fix the problem.
Seriously underrated tool for troubleshooting and repair: the right state of mind. The best way to break something is by trying to execute a hasty execute due to impatience, hunger, fatigue, or pure hatred for that stupid POS car-shaped junk that was supposed to be fixed by last week why does this stupid thing keep breaking!
She has a name
It’s either Griffin or Elise? Unless Griffin is the name of the Jeep?
One day I headed off for an autocross in my GT6. I’m about to get on the highway when I noticed I couldn’t rev above 3000 rpm. So I turned around and went home. I went looking for help on all the forums and had the local Triumph club over to my house to help diagnose. Everyone expected the fuel pump to be the problem. The two that the club brought over turned out to be faulty. Yup. Both of them. So I bought a new “high quality” one for over a hundred bucks. That one worked great but it didn’t fix the problem. So I took the air filters off the carbs to put the air box back on. Upon reassembly, it occured to me that maybe, just maybe….
Yup. After all that, it turned out I had at least one of the air filters on upsidedown, blocking a port on the carburetor. It took three weeks to figure that out.
I once had a 1992 Civic (red hatchback, of course) towed when I suddenly lost the ability to get it to move. I’d put it in gear and let the clutch pedal out, then nothing. I thought I’d lost the trans completely. It turned out one of the inner CVs had worked its way out of the transaxle. You know how they’re held in by a C-clip on the splined shaft, well somehow mine got free and decided to exit the output of the transaxle far enough that it wasn’t engaged at all any more. I could have fixed it just by pushing it back in really hard.
Conversely, in that same car, I DIDN’T call a tow truck when one of the wheels fell off while driving on the highway (because I forgot to tighten the lug nuts after doing a brake job). Instead, for some reason I can’t explain, I took one lugnut off each of the remaining wheels to bolt the spare onto the missing one (so now each wheel had 3 lugnuts holding it on) only to discover my spare was flat. So walked like 2 miles to use a gas station payphone (cell phones weren’t commonplace yet) to call a friend to bring me a pump. Also, while walking to the gas station I looked for the missing wheel that took off at like 100mph when it freed itself from my car. Never did find it. Imagine going to Big-O and telling them you need one wheel and tire. Also #2, the car sliding to a stop on the highway ground down the threaded/nutted part of the lower ball joint but I still chose to drive it home. Not sure what I was thinking.
I wouldn’t have towed it either, that seems like a totally reasonable way to fix the problem
Agreed, but only if you’re 25 or under. Any older and you should know better.
The quality of a solution is relative to the cost and what is affordable.
There was a time when a DIY solution like this would have been far more reasonable than spending money I couldn’t afford on a tow truck.
Thank goodness that’s passed.
What should I know better than? Driving with three lug nuts, driving with a ground down ball joint, walking to a payphone, or asking a friend for help? Because I really don’t see *major* issues with any of those.
If one of your wheels falls off while driving on the highway, you don’t think it might be prudent to have that vehicle towed so that you can thoroughly assess the damage?
Especially when the alternative is to cannibalize lug nuts from your other wheels, slap on a spare, and continue to drive on the highway?
C’mon man.
This sort of thing happens!
Ages ago I bought a new 4dr Chevy Tracker, and soon noticed that it had a substantial clunk coming from the front end. Sometimes it happened on bumps, sometimes it didn’t – just generally inconsistent. Took it back to the dealership N times to get them to fix it and they were flummoxed, but it seemed to be operating normally otherwise.
Then one day I was on the interstate with a strong crosswind… and noticed the hood was vibrating up and down. (Woohoo, shaker hood!) It turns out that the hood latch was not installed/adjusted properly and had a noticeable amount of play in it, allowing the hood shake. No one had spotted the issue earlier because the first thing the mechanics did when I brought the car in was pop the hood. 🙂
This sounds a lot like my average diagnosis experience. Replace $3,000 in parts only to finally figure out it was just a loose connector.
I had my MR2 Spyder towed 80 miles home from San Francisco(also requires a flatbed) because I was convinced the parking brakes were seized in the braking position. When I got home the car rolled freely and there was no noticeable problem. I still don’t know if I overreacted or the bumpy tow truck ride caused them to release, but I sure felt foolish.
Sounds like aging drum brakes to me. I’ve had parking brakes sieze in the winter. Toss the car in reverse, roughly engage the clutch, and it’ll usually pop loose. I’d believe that a bumpy tow truck ride could pop them loose.
MR2 Spyders use a second small caliper on the disk which is mechanically actuated by the ratchet in the lever, a lot like bicycle brakes but with a ratchet. The cables end up sticking in their sheaths and not releasing. But the same point still works, if they aren’t stuck too badly and jostled that could cause them to release.
Huh cool, TIL.
My car has rear drums. 90’s Camry’s had rear discs with a miniature drum in the center of the rotor. It’s cool to learn of another approach – thanks!
I had a Chrysler 300 that had a similar setup, and those miniature drum brakes were prone to corrosion and were a real pain to replace. Especially if you were doing a rear brake job but hadn’t bought the parking brake parts, since you couldn’t tell there was an issue until you pulled the discs off.
Actually I was wrong about the Spyder, I forgot that it is actually the twist type, where the parking brake cable mechanically actuates the main caliper an hold it into place. But the corrosion and sticking issue I mentioned is still the problem. Part of the reason why many cars have switched to electronic parking brakes that eliminate the cable.
I’m sorry, but you’ll need to change your girlfriend’s name. My dog is Elise and I couldn’t get that out of my brain.
Ha, not to mention that the name is similar to Elsie, those of a certain age will know: https://daily.jstor.org/wp-content/uploads/2019/12/who_was_elsie_besides_the_worlds_most_famous_cow_1050x700.jpg
My dog’s name is Elsie, so now you have to change the cow’s name.
Counterpoint: no. Because me like Beethoven.
MacGyver never had this problem with his YJ.
This is because I love YJs. He’s trying to torment me.
I’m sure he does worse things to torment you on a daily basis
I try to torment you with periodic mentions of The Beatles. Every little bit helps.
Thats a speed sensor? For the speedometer?
I would have thought the YJ used a speedo gear in the NP231 like an XJ.
I’m perplexed as well. Googling “speed sensor” and “YJ” I see the typical speedo gear sensor shown. Maybe it’s ABS related? I didn’t think YJs had ABS either, but I’m hardly an expert on the platform.
It’s not the Speedo sensor since that’s in the T-case. I think it may be the aftermarket cruise control?
Its a small electromagnet that adds about 1 ft-lb of torque to your drive shaft. It must have already been out of alignment and that’s why you couldn’t get up the hill.
Gotta be aftermarket. I can’t imagine a janky bracket like that came out of the factory. Even a Chrysler factory.
Have you seen David’s exterior tire carried for his Grand Cherokee? It very well could have come direct from Chrysler.
Yeah, there’s no way that sensor is a factory installed part. Such a thing was common with aftermarket speed control installations back in ye olden days.
Yep, it’s for aftermarket cruise control. Have something similar on my 76 CJ-7.
Incidentally, I have a tilt steering column from a SJ, it had a cruise control stalk and I was able to wire it up to the aftermarket cruise module so my cruise appears to be stock.
What a strange way to do it.
California David is getting soft
He never would have noticed the clunking before he moved, because every car in Michigan sounds like that going over our cratered roads.
I was driving my HMV Freeway on the freeway (I mean, it’s right there in the name) when I started smelling overheated rubber, then heard and felt the characteristic symptoms of a disintegrating drive belt. I coasted to a stop at, happily, the side of the road at the end of a convenient offramp.
Replacing the belt means removing the drive chain from the rear wheel and jackshaft, unbolting the jackshaft, freeing the shreds of the old belt, installing the new belt, then putting everything back together. Fortunately I had prepared for just such an eventuality. There’s not a lot of room for carrying tools and spares in a Freeway but I had managed to make sure I had everything I’d need, just in case.
Except the spare belt, which I had inadvertently left at home.
https://live.staticflickr.com/3680/9525901728_0f26be8698_c.jpg
adorable lol
Oh yeah, before each and every road trip in my VW bus I would always double-check that I had spare fan belts on hand; people would make fun of me for that but your experience is simply testimony to the importance of being prepared (though “inadvertently” is indeed just part of the nature of old car ownership, what with Murphy’s Law and all, so no need to feel bad or anything, it happens to the best of us.)
Speaking of belts and VW buses… A college housemate was an avid rock climber who had a friend that was a fellow rock climber with a VW bus (split-screen, this was some 35 years ago when such buses were still relatively affordable) which they would take to the mountains. One time they were returning home but still in the mountains when the fan belt broke but they didn’t have a spare fan belt. However, they did have a roll of duct tape so they fabricated a fan belt out of duct tape which actually held until they made it to the nearest gas station and repair shop which was fairly distant. When the mechanics installed the new fan belt they asked if they could keep the duct tape belt and put it on display. Some time later the rock climbers stopped by that gas station and saw their duct tape fan belt still on display 🙂
I don’t suppose those crafty dirtbags would have been living around Spokane at the time, were they?
Ha. Nope, this was East Tennessee/western North Carolina, home to the Great Smoky Mountains National Park 🙂
Ah, I figured it was unlikely, but I had a few friends over there back then who were avid climbers, and one owned a ‘66 (non-Westy) camper they often took to the trailheads.
Regrettably a Freeway’s drive belt pretty much has to be a drive belt:
https://www.youtube.com/watch?v=bH7qhmsB4fg
Dang. Pretty cool! Good to see that video. Oh, yeah, duct tape ain’t gonna cut it for such an application, regardless of what Red Green or MacGyver might have to say… Now I’m wondering if DAF’s Variomatic system would actually still work if one of the two drive belts were to break.
Speaking from experience, yes, it will. On my Volvo 66 GL (a rebadged DAF 66) both belts drive the same differential, which in turn drives the rear wheels, so losing a belt just means more stress on the remaining belt. On the DAF 55 and earlier, each belt drives one rear wheel, so losing a belt means the car has one-wheel-drive. Note this doesn’t apply to the DAF 46, however, which only has one belt driving its 66-style differential in the first place.
Then there’s the DAF 500 YM Pony which is four-wheel-drive but with only one belt, transversely-mounted:
http://www.bravocie.nl/collectie/historie/YM500_Pony/historie/Pony-bouwtek-640.jpg
Only reason I’ve called a tow was because my tire blew out on the Interstate and my dumbass forgot to put the lug wrench back in the car.
These days it doesn’t matter if you have a lug wrench, most cars don’t have a spare to swap. If the damage is catastrophic you’re dead in the water.
Thankfully the Fiesta ST came with a full size spare!
Better than the time I got stranded on Zzyzx Rd off I-15 (Google it, anyone who has driven from L.A. to Vegas will recognize this) with a flat tire because the car I was in had aftermarket wheels and the factory lug wrench would not fit in the lug holes. Had to get towed back to Baker, California, which was its own adventure.
I once called AAA to borrow a jack when I came out to a flat after going out for breakfast with a couple of friends. It was only 10 miles or so each way for him and he was happy to wait at the edge of that quiet parking lot while I used my own lug wrench and spare, but I still felt like a bit of a goose.
Something vaguely similar happened to me. I was heading to a trailhead in my Jeep. Locked the hubs and turned onto the track. Instantly came to a halt in the sand. Rear tires were digging but the front weren’t. Made sure it was in low range 4x. Nothing. Aired down to single digits and managed to dune-buggy out of the sand to harder ground. Started looking at u-joints and pondering ring and pinions when I glanced down to find one front hub unlocked. Rewind to the day before when some kids were playing around by the Jeep and ran off laughing. I figure one had locked a hub and figured it was funny. I had simply unlocked it and locked the other.
Haha, I have a similar story. Back in the mid 90’s, teenage dirtbag me was out messing around one night in a muddy dirt lot in my squarebody Chevy. Got bogged down and locked the hubs, but nothing, no 4wd. Had to call for a tow, luckily I knew the tow guy and he didn’t charge me, just a lot of ball busting.
I thought I blew a u-joint or something in the t-case but turns out I had assembled the locking hubs backwards when working on the front end a few weeks prior. The felt like they were working as they twisted just fine, but they weren’t engaging anything behind them.
Damn, I think my rocket bike is better hacked together than the speed sensor setup and this is on an offroad vehicle, one where a sensor hanging off the undercarriage from what looks like plumber’s hanger strap might get hit.
When I can’t readily ID something like that, I always look for marks like the wear on the driveshaft or anything that could have clearance issues under use even if it looks like it clears when static. Of course, that’s also a lesson I learned through aggravation rather than genius inspiration. Haven’t forgotten, though, and it’s come in handy! Then you look like a genius when you get to teach someone else who hasn’t learned that lesson yet. Mine was with something simpler, though—metal-on-metal squealing when cornering at speed in one direction. Turned out to be a brake backing plate that would contact the rotor. Looked far enough away that I ignored it as a cause—even though the sound seemed about right—but not when things flexed under cornering.
At least it was a free and easy fix!
Is that some sort of aftermarket add on? I’ve never seen anything like that before.
Been there. I had a steering clunk/pop that seemed to move about the steering rack, confusing me if it was an inner or outer tie rod end. I kept checking the steering and nothing looked bad, and finally I decided to check the upper and lower A-arm bushings, which is when I found the culprit: a paper folder caught in the suspension at just the right angle that when viewed from the front the dark grey folder blended in with the inner fenderwell, but was clearly visible when viewed from behind. The folder had wear marks from rubbing the tire and suspension, and as soon as I removed it the noise was gone. It is still beyond me how to flew up there and wedged itself like that…
Its okay, I had a tensioner fail such that my engine was knocking and I thought it was internals going bad. Had a shop look and said the belt tensioner was whacking things as it flung around more than it should when the spring broke.
Didnt chuck the belt off either, just made a ding/clunk that perfectly matched engine rpm.
Felt like a doofus.
Once when I did a timing job (suck it David, it’s not that bad), I got the car back together and started the engine and it knocked. Sounded like valve knock. After freaking out for a few minutes, I eventually tracked the noise to the plastic timing cover. It wasn’t seated right and was vibrating.
why is the sensor out in the open like that? Seems like it is ripe for ice/snow/mud/ anything to hit it.
Seems like you would integrate something like that into the end of the transfer case housing or rear end so that it was all enclosed. Like a wheel speed sensor in a hub assembly.
*Troy McClure voice* “We’ll call her Elise. You may remember her from such articles as…”
Simplify and add lightness.
As a long-time reader, and 5-time jeep owner whose girlfriend and now wife (31 years together) once let me buy a 70 commando that needed towed to a mechanic to be my daily driver. If this “Elise” loves you enough to stay with you and get back into an old jeep with you, she LOVES you and is a keeper.