[Hybrid]

I love trying to describe sounds on forums but here goes. My older 89 sierra has started making a whine/whooping noise only on decel. While accelerating it's fine. The reason I say whooping is it's not a consistent frequency it cycles whoop whoop whoop like a bad tyre does only definitely gear/bearing whine. I'm guessing rear diff but is there a way I can isolate the transfer to rule that out? I tried dropping it from 4H into neutral on the transfer but the sound persisted so all I've really ruled out by that is that it's from the output rotating side of the transfer back. Any suggestions or similar experience?

Finally if it is the diff whats the general consensus these days, rebuild or replace with 2nd hand? I've rebuilt two transfers and two transmissions without a drama so I've got the gear but how hard is the job replacing the bearings without stuffing up the setting of the R&P?

Cheers,

John

[watermouse]

Remember the drive shaft and transfer output gears are going about 4-5 times the revs than the wheels. If you think the "whoop" is per tyre revolution it is almost certainly ring teeth damage.

However, I've said this elsewhere, wheel bearings can make similar noises to diffs including different sounds under acel and decel. I know, I have had issues with both in the past with almost identical sounds. That is until the diff went bang, bearings just got noisier.

If you have diff damage just replace the entire third member with a good second hand one, but don't try to adjust it. Replacing ring and pinion gears is difficult and/or expensive.

[Hybrid]

Thanks for the suggestions watermouse. It was the diff but not what I expected. There seemed like barely any movement in the pinion until I removed the drive shaft. Once that was off I could shift the whole flange forward 15mm. The pinion nut had come loose. When accelerating the thrust force pulled the r&p into each other and no noise. On decel the thrust was the opposite way trying to push the pinion out causing all sorts of racket. I can't see any damage to the gears yet the pinion has cut consistent gouges in the carrier. All bearings seem great too. It's a weird one as I've never had the third member out in all the time having it yet it decides to undo in the last 10km. I'm going to post up in the wanted section looking for a replacements.

[jdk81]

Ouch

That ring and pinion and bearings are all toast

Perhaps someone rebuilt it and/or replaced a seal etc and didnt use a new crush tube, or crushed it incorrectly.

[watermouse]

I would say that is right. I think it is fairly common for people to try and undo the pinion nut thinking it is part of the third member removal.
It would have to be the tightest nut on the car by a mile. Unlikely it would eventually undo itself. Plus is should be caulked into the groove in the pinion thread.

[Hybrid]

Yep, my first thought was the crush tube but then I thought that should have just messed up the preload. Regardless of preload how could that nut come loose if it was pinned into the pinion. I'd put money on the previous owner owner doing a pinion seal swap and not pinning the nut back in. It's all just guessing now though. On the bright side I think the diffs are the last thing on that zook that I have to worry about as otherwise I've done the full driveline from the radiator fan to the wheel bearings. Guess I better check the front pinion now.