Troubleshooting my FJC...

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Mtbcoach

Mtbcoach

10 Year 15 Year
Joined
Jun 29, 2006
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Location
Carolina Beach NC
I'm looking for some help, guidance, advise on my FJC.

This past weekend, during the Spring Tide Ride, leaving the OBX on Sunday, I heard a new but not good sound. Regina and I tried to diagnose it from the seat as we came into Nags Head. Due to my previous experience ignoring sounds (Harlan 2 yrs ago), I hope I've learned to not ignore such things.

Checking wheels, lug nuts first, then a firm shake on each wheel, I discovered some movement on the passenger trailer wheel. I pulled the cap and adjusted the axle nut to take out the play. Got back on the road, still hear the sound. Pulled over again, do the same to the driver's side wheel. Sound still there.

Pull the trailer off to see if I could isolate the sound between the FJC and the trailer. No trailer = sound still there = FJC holds the problem, it begins at slow speeds and increases in frequency with speed. When I let off the gas, sound goes away. This eliminates wheel bearings for me. It sounds like its coming from the rear end/drivetrain.

No clunking or chunking, FJC ran well throughout the weekend other than the sound. I'm planning on putting the rear end on stands and spin the wheels to see if I can hear anything then. If not, I'll start it and put it in gear to see if I can isolate the sound. I plan on draining the rear diff fluid to see what it looks like (I did submerge it) in case it looks compromised and examine for metal shavings/debris.

I'm open to suggestions for troubleshooting this for me, thanks...
 
Sounds like the right approach to me Jerry. Will be interesting to see first if the diff oil is milky, but if the sound goes away when off the throttle, that makes me think otherwise. Keep us updated as you go along and hopefully someone will know more about this than I can offer.

:beer: R
 
Just spitballing here............ You say it sounds like it is coming from the rear and from your description sounds like only under load. Think you may have some movement in your pinion for and aft? That would make noise under load but most likely not when off the throttle. Could also be a piece of the ring gear broken off as well doing similar.

Your course of action sounds like a good one.
 
If I had to guess i'd say there is some movement in the pinion under load. I don't think anything is chipped because you should hear it at all time not just under load.
 
If there is anyone that could figure it out would be Rick C. BMThiker. Pretty sure he has had just about every noise in his drivetrain there is. And replaced just about everything. Shoot him a pm.
 
Thanks for all the feedback, keep the spit-balling. Good idea Marshal to check with Rick.

A bit more info...I took it for another drive to see if it would offer anything new. Noise is what seems like "wheel speed". In other words, as wheel rpm's increase, so does the sound. Definitely noisy under load, not heavy load, any load. I accelerated and popped it in neutral, noise went away. No noise coasting at any speed. Turning left (pressure on right), hear the noise under load (at slow speed). Drained the diff fluid (Royal Purple), still looks purple but dirty (pics tonight), nothing milky or dirty with water contamination.

Diff plug magnet had some significant "paste" on it, interspersed with metal flakes (like fine gold flakes) imbedded in the paste. Scraped it off and spread it on a paper towel to look for shaving and such. Nothing obvious, just the thick paste, pics later.

This wouldn't concern me if I had 65k on the fluid but its been changed at 4 times since I've owned it, last time being this past summer, Royal Purple since 15k. I'll have to check my records to see the exact miles but it couldn't be 7k miles since the change. I changed it then because it seemed to be noisy and I wanted to check the level as well as the debris then. Similar results as this fluid check.

I'll check the pinion more clearly tomorrow. Yet, my "gut" feeling is that a bad set up may be causing bad/uneven/premature wear when I had the 4.88's installed at 32k miles. I've not had any type of catastrophic event or even thought anything has been damaged wheeling. Not saying I don't stress my rig out, just that no event would make me think I've chipped/broken off a tooth.

I'll post pics of the fluid and diff plug tonight...
 
I'd check your u-joints. They will produce noise under load and then go silent under freewheel too. cheap fix and good start point...tends to match "wheel speed" if noise not related to hub.
 
If you were closer i would say bring it by. Sounds to me like either a pinion bearing / gear itself or hopefully u joints. Wife had the same thing in her truck while i was deployed one trip and she just turned the radio up. The pinion bearings were completly shot.
 
I second Rick's comment on the u-joints. I would set the parking brake, chock the wheels and place the transmission in neutral. Then, check for play in the u-joints. You might even get a better check by putting the rear axle on jack stands.
 
Another +1 for ujoints, but in my experience you have to drop the driveshaft to really check them well. Jerry if you need a hand any evening or this weekend, let me know.

Sent from my Droid using IH8MUD
 
The newb I am, I'd say the same. I've been meaning to do the ones in the 40 because it sounds the same way. Just under power, and I get some vibration. Not like the last STR, but just a little! :D
 
Agree with others that u-joints may (hopefully) be the culprit.
 
little_joe said:
Another +1 for ujoints, but in my experience you have to drop the driveshaft to really check them well.
Click to expand...

This has been my experience too. Just shaking/twisting the driveshaft didn't pan out. Also, if it's not the u-joints, it's easier to isolate "other things" while the DS is off the vehicle.
 
Here are the pics I promised, nothing really of note on the drain plug...

FJCreardiffplug-2.jpg

FJCreardiffplug-1.jpg

FJCreardiffplug-3.jpg


Yet, with a bit of common sense, I wouldn't have wasted anyone's time speculation. Its amazing what you might find if one just gets under their rig and uses their eyes...

Oily diff, where is the oil coming from...
FJCoilleak-2.jpg


Put this exhaust on last fall, why so oily up here...
FJCoilleak-3.jpg


Following the trail, nice bit of residue and drips on the rear of the skid plate...
FJCoilleak-6.jpg


And, we have some clear spraying of oil near the output of the Inchworm...
FJCoilleak-4.jpg


Now, I'm no genius but, if I had started here, I might have figured it out. The powers of casual observation win. I'll be ordering a new seal and bearing at the least, probably smart to still replace the u-joints while I'm there.

Yes, I am a dumbass...
 
You're not a dumbass, just looking for information from those that may have similar experience.
 
NCFJ said:
You're not a dumbass, just looking for information from those that may have similar experience.
Click to expand...

that part is debatable Stan, but not because of this scenario ;)

Glad you got it figured out Jerry. Hopefully this can be serviced w/o dropping the tcase?

:beer: R
 
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