loud enough the jeep rolling down the highway behind me heard it
Edit: Driveline origin, not a basic backfire
90 YJ, i6, 5sp Man (AX15???), NP231, manual lockouts, ARB's front & rear, 35" tires
It's working fine but I'm curious as to what might have made the noise.
I was offroad in 4-high (neither ARB engaged) and came onto a highway and parked alongside the clear/dry asphalt roadway to disengage the lockouts. Another Jeep and I decided to visit another local trail up the road about three miles so I re-engaged the front lockouts and pulled onto the highway.
Rolling a mile to the first stop sign I noticed more wheel vibration than typical and remembered I was in 4-high. I pulled to the roadside, came to a complete stop, and selected 2-high. Back onto the highway, up to perhaps 30-40MPH, clear-dry asphalt, I heard a LOUD "BANG... BANG" and pulled over right quick.
No fluids on the ground. No parts hanging or laying on the ground. All looks as it should be. I disengaged the front lockouts and continued on my/our way. All else worked as normal for the rest of the day (trail, 4-low, dual ARB's engaged with four wheels spinning in deep snow, 4-high, all's good). Back on the road, disengage lockouts, 2-high, highway home. No issues.
What could have caused the noise? 2wd/4wd engage/disengage connection popping out (finally disengaging after I started moving) - but why two bangs vs. just one? xFer case chain hopping a tooth (or two)? Other? Impending doom or just "one of those quite rare day things"?
I didn't notice the gearshifts bouncing when it happened, fwiw.
Update: I kept thinking it was the xfer case chain popping a tooth, but no. The front diff... ARB, ring gear and likely pinion gear went to lunch on themselves.
Would be my guess. Few things will make that loud of a pop without massive destruction. If it was 1 pop, I would say t-case slipping into 2 hi, but more than one coupled with driveline vibration.... Check the front pinion bearing, bet its a little worn and you slipped a tooth or two. Accelerating or decelerating?
91 YJ, 350/700R4/231, 8.8/HPD30 with 3.73s, 6" SOA with 38" TSLs. If I ever see the previous owner again, I am going to curb stomp that meth-head brain dead crackpot.
Yes, expensive lesson - though I suspect the bolts were likely loose or mostly out when I purchased the Jeep a year earlier. When I purchased it, I knew the rear locker was toast (an expense known of right out of the box).
The PO said all fluids were just changed by a mechanic - so I figured no need to open the front diff to change fluid or inspect. Had I opened and inspected I suspect I might have found loose bolts holding the ARB together (and I might have been able to tighten and not be in this situation).
I'm not sure being in 4-hi on asphalt (re - drivetrain loading due to differences between front and rear wheel rotations) was the cause but I suspect having the front diff "spinning" faster than normal (trail speed is sub 15MPH) may have resulted in one of the "floating around" bolts being caught up in the flow of thick diff fluid (winter snow run) moving at a faster than typical speed (I have lockouts on the front hubs so the front diff doesn't typically rotate at all when I'm on road). I suspect one of the bolts was slung up and caught either between the pinion and ARB case (note the bolt threads impressed into the case near "pin 4") or between pinion and ring gear. That is likely when "the big bang(s)" first came about. From then it went downhill. I kept using it as it would only happen occasionally and I kept thinking xfer case chain, which I'd open/repair/replace over the winter.