Author Topic: Siren whine- tires, tranny or ?  (Read 1876 times)

Offline arby87

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Siren whine- tires, tranny or ?
« on: September 18, 2017, 09:09:13 AM »
87 V10, 4" lift, new 33" tires, 350, TH400, 10 bolt front, 12 bolt rear, 4.10s, rebuilt drive train (except transfer case), craigslist frankentruck.

Before I did much to this truck, I never heard too much noise out of the tires or the drivetrain- or even when I replaced the tires with a new set. Ever since I had the diffs rebuilt (along with the drive shafts) I now hear a mechanical whine coming from the truck- it sounds just like a police/fire/paramedic siren noise in the distance. I mostly only hear it when coasting, as the engine noise drowns most everything else out when on the gas. It also appears to change in pitch/frequency based on the transmission shifting- as in when downshifting coming to a stop the sound changes based on the gear/rpm.

Should this be normal?

When I am not paying too much attention to it my brain picks it up and I start looking for flashing lights because I think it is a cop or ambulance. Want to make sure I am not missing a sign of possible impending issues with my transmission or rest of the drive train. I am leaking a bit of transmission fluid- seems it is impossible to get that pan to stop leaking. Diff shop tells me the NP208 I have is a bit worn and recommends replacement, but with all the other money I have already sunk into the truck that is going to have to wait.


Offline blazer74

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Re: Siren whine- tires, tranny or ?
« Reply #1 on: September 18, 2017, 03:41:10 PM »
Tires? Aggressive?

Offline arby87

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Re: Siren whine- tires, tranny or ?
« Reply #2 on: September 19, 2017, 10:11:51 AM »
I wouldn't say they are too aggressive- and I don't remember hearing this noise from them before I got the differentials rebuilt, but is possible.

Tires are from Les Schwab- something Rough Country I believe. One of the few models Les Schwab had that would fit my 15" rims. Seems tire choice is limited when looking at 15" these days- need to get bigger rims for next time I get tires. And of course now that I have gotten more used to the truck, I think I want at least 35" tires next time, if not 38". Should be good now that I got the 4.10 gears.....but that is years down the road.

Online bd

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Re: Siren whine- tires, tranny or ?
« Reply #3 on: September 19, 2017, 01:13:44 PM »
...Ever since I had the diffs rebuilt (along with the drive shafts) I now hear a mechanical whine coming from the truck- it sounds just like a police/fire/paramedic siren noise in the distance. I mostly only hear it when coasting....
...I don't remember hearing this noise from them before I got the differentials rebuilt....

Verify that the cold oil level is between 1/4" below to level with the bottom of the differential fill hole.  There may be errors in the gear setup (i.e., insufficient pinion bearing preload, pinion depth incorrect or excessive backlash).  Noise issues should be addressed with the repair shop that performed the gear work ASAP, before accumulating mileage on the gearset.  Noise implies accelerated wear and should be addressed before undesirable wear patterns develop on the gearset.  Once a poor wear pattern develops, eliminating noise often requires gear replacement.


A THM 400 oil pan leak can be effectively corrected by substituting a sand cast aluminum oil pan and decent gasket.  But, unless you have already verified that the pan is the source of the leak, make sure ATF is not seeping past the shift shaft seal, detent pass-through o-ring, or fill tube top hat seal, etc, and running down to mimic pan leakage.
Rich
It's difficult to know just how much you don't know until you know it.
In other words... if people learn by making mistakes, by now I should know just about everything!!!
87 R10 Silverado Fleetside 355 MPFI 700R4 3.42 Locker (aka Rusty, aka Mater)