[Yake]

Hey guys just wondering if anyone had any experience with this, I have a 1991 sj70 Sierra and it makes a very loud whine when under acceleration. It starts faintly at around 50-60 k's and gets progressively worse accelerating to 100 k's and as soon as I take my foot off the accelerator it stops haha. I changed both diff oils (which were low) and checked the gearbox and transfer case oil's and they were full/new oil any help would be much appreciated, Thanks!

[shiv]

Check all your unis and slips?

[fordem]

Can you tell where (approximately) the noise is from - perhaps the rear of the car? That sounds like a diff whine to me - the gears may be damaged due to prolonged use with insufficient lubrication. What's the backlash like?

[Yake]

shiv wrote:

Check all your unis and slips?

Nar I haven't I might check them out today, cheers

fordem wrote:

Can you tell where (approximately) the noise is from - perhaps the rear of the car? That sounds like a diff whine to me - the gears may be damaged due to prolonged use with insufficient lubrication. What's the backlash like?

It's hard to say cause everything is so close haha but it sounds like it's coming from the transfer case/gearbox, and yeah I was thinking that as well , the backlash feels normal to me but I haven't driven any other sierras before so not 100% sure :/

[Gwagensteve]

Most likely rear diff.

[Yake]

Is there a way to test it to find out without pulling it apart? haha

[Gwagensteve]

Not really, no.

[frak]

Put it in N and roll down a hill?

[frak]

Is the wind the same when you change gears ie same speed different gear?

[Yake]

Gwagensteve wrote:

Not really, no.

Haha damn.

frak wrote:

Is the wind the same when you change gears ie same speed different gear?

Yeah changing gears doesn't affect it, only when I accelerate.

[rustyzook]

Mine was doing something similar, a new ground on the coil pack fixed it for a few months but it's coming back. Although mine was threw the speakers and I run a g16b it had me stumped for a while but it would only do it under acceleration. It did sound like it was coming from the Center but that's because 4 speakers where making the noise.

I might suggest checking you input and output shafts and diff pinions to make sure they are not loose.

[fordem]

It's always a good idea to shut the radio off when trying to listen to a noise, and you might also want to shut off the a/c ...

My 98GV has what sounds like a very faint gear whine - reproducible only if the a/c compressor is running and the car is moving - shut off the a/c, and the noise goes away, stop the car and the noise goes away - the only way to hear it with the car stationary is to turn the a/c on, put the transfer case in neutral, the transmission in gear, and bring the engine rpms up to simulate 80~100km/h approx. road speed.

It's caused by some sort of harmonic resonance/interference - I quit worrying about it years ago.

[Yake]

Haha well I currently don't have any speakers in at the moment so I don't think that will be a problem and I don't have A/C either

rustyzook wrote:

I might suggest checking you input and output shafts and diff pinions to make sure they are not loose.

Cheers will give it a look at, I've seemed to be under the sierra more then in it lately

If worse comes to worse I might take her in at least they'll hopefully know what the issue is exactly. Did anyone know of a good mechanic on the sunny coast?

[rustyzook]

At least yours is drivable

Try what fordem mentioned, put TC in N and reve threw the gears, see if it's clutch or gearbox related.

[Yake]

I tried it out and it doesn't whine when going through the gears with TC in N :/

[Grags]

The noise you describe sounds like it's only relative to road speed so..
1 - it's in the final drive - that is g'box output shaft, maybe the transfer case, diff pinion bearings or carrier bearings
2 - It's load related, sensitive to power on/power off so very likely the case hardening on the thrust side of a bearing cup somewhere has let go

Break it down a bit further
a- Gearbox Output shaft - you will definitely hear it right next to your leg maybe even feel it with your hand on the gearstick knob as you drive, and seeing as you tried it with the TC in N we can eliminate the gearbox for now.
b- transfer case - maybe, again the sound will feel like it's right next to you, you could try putting it in 4wd and drive down the road, see if that changes the noise at all- TC's are generally pretty good, . which leads us to the most likely suspect, the diff centre.
c - Pinion bearings - high pitched - the noise should feel like it's more behind you or around you. Usually if you grab the flange at the front of the diff it might have a bit of up/down play (there should be no up/down play)- but the bearing that usually goes is the one closest to the pinion gear and don't be surprised of you do not feel anything
d- Diff centre carrier bearings - not as high pitched due to the different rotational speed (about 5 times less than the pinion) it will have a bit more of a rumbly sound to it and given that you don't hear anything till 50-60kph this might be a possibility, if they are badly worn and there's slop in the carrier then yes it'll also mess up the contact patch of the gear teeth on the crown wheel and pinion, and sound even worse.
e- diff gears - maybe but if the teeth of the crown wheel and pinion are shot the noise is usually an uneven pitch again relative to road speed as the things rotate against each other but seeing as you're not describing that then not likely
f - don't be surprised of all the bearings and the gears are shot - the not having enough oil in them will do that!

[Yake]

Yeah its really hard to pin point if you don't know your specific whines haha! I'll keep at it and see how I go, thanks for all the help so far

[Zukeeper]

Mine is doin the same thing atm. My TC bearings are buggered. The faster you go the louder it gets. Ioverhauled my gearbox not to long ago so i know its not that.

[Ookiethezuke]

Yake wrote:

Yeah its really hard to pin point if you don't know your specific whines haha! I'll keep at it and see how I go, thanks for all the help so far

Did You ever find the source. Mine is making a similar whine under similar conditions. i am thinking it is the transfer case.

[Gwagensteve]

Yake last visited the board 6 years ago, so I'm not sure you're going to get much resolution from them.

If you read back through the comments, you'll get a fairly good idea of how to isolate the noise.

If it's connected to road speed not gearbox ratio (i.e it's the same in 4th and 5th) it's unlikely to be the gearbox.

If it's still there in low range it's the gearbox or transfer

Transfers can get noisy but they sound right up near the gear lever.

If your rear diff oil was low that's an indication the car hasn't been well serviced so that could be a solid clue.

Wheel bearing noise will be constant with speed. Diff noise will come and go with power and coast.