Please help diagnose whining noise (manual tranny)

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Hi,

I own a 1997 Volvo S40 with a manual transmission (FWD, gearbox is french made by Renault...). The car has 330'000km (200K miles).

I seem to get a slight whining noise, especially in 4th and 5th gear that appears related to vehicle speed. The noise is very similar to electric interferences heard through the radio on badly earthed cars but in my case it is definitely a mechanical whine.

When parked, in neutral and revving the engine, I don't get any noise so I guess the primary shaft bearings in the box are not at fault. The noise appears at around 70kph in 4th/5th gear and the pitch increases with speed but is quickly. However the noise is very faint and I wonder whether I'm not too picky about it or not. I have no issue selecting and changing gears, clutch operation is smooth (clutch/release beraing have been renewed 70K km ago).

The left driveshaft is mounted inside the transmission differential with a tripod and needle bearings. Since the whining appears related to vehicle speed, I have to distinguish between the usual suspects:

- secondary (layshaft?) bearings
- differential bearings
- wheel bearings
- left driveshaft inner tripod (needle bearings)
- final drive (gear whine)

I suspect the noise is gearbox related. Do you have any basic DIY procedures to identify the origin of the noise, especially to distinguish between a secondary shaft bearing and a differential bearing? Can the inner tripod (needle bearings) make a whining noise too?

Grabing the front wheels at 12-6 o'clock and attempting to rock doesn't show any play. Rotation doesn't appear rough although I get some brake rubbing. But what can I do to make sure it's not a wheel bearing?

Thanks
 
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My best would be the syncros are wearing. My 2004 GMC has slight noise @ 119k and my 1996 @ 250k I noticed it making slight noise too.

As long as they are working well, I'd not worry about the noise.

Doubt it is a bearing.

FWIW...

Bill
 
Thanks for the input.

Why would syncros make noise (whinning) with the gearbox in gear? I guess they'd make noise (if any) when engaging a gear but not when the car's in gear no?

Also what would be a typical gearbox engine noise? Would this be a loud whinning noise or only faint?
 
The way I understand it is everything is spinning and the syncros are the first thing to make noise.

Most truck transmissions make a slight whining noise I've found and most car transmissions are pretty quiet. MY 1986 Jetta with 380k (and had its ONLY transmission fluid change @ 292k miles) is as silent as my 2005 Corolla with 150k.

Loud or noise that is different from "mnormal" would be a concern in my book. Faint noises are normal.

Take care, Bill
 
Quote:
he noise appears at around 70kph in 4th/5th gear and the pitch increases with speed


Have you tried speeds in excess of 70kph and coasting through the speeds in neutral?
 
Originally Posted By: Gary Allan

Have you tried speeds in excess of 70kph and coasting through the speeds in neutral?


Yes and I still get the noise. This is why I suspect either the secondary shaft bearings, differential bearings or a wheel bearing. But I have no evidence it could be a wheel bearing because I can't feel any play in it and the noise doesn't change when turning. My guess now is between the secondary shaft bearings or the differential bearings..although it may well be anything else too
 
I just had a similar problem with my Toyota truck, it was driving me crazy, changed transmission fluid, inspected UJ's and drive shaft center bearing, but it turned out to be a wheel bearing.
Strangely the bearing looks OK and only feels slightly rough.
 
It isn't the synchros. They are not dong anything when engaged.
Could be main carrier bearings , gear whine from teeth meshing, or maybe even wheel bearings.
What to do? I'd get new lube in there. A slightly thicker version would be my choice, of a premiium dedicated gearbox oil.
Red Line or Amsoil are the best, IMO.
 
Aren't failing wheel bearings more of a growl than a whine? Or does it start as a whine? Seems you might have ruled this out anyway, if the noise doesn't change as you load and unload it during a steady turn?

I'd say change the transmission fluid (to a synthetic) if it's old, and stay tuned in.
 
I didn't hear the noise, but added [last] that wheel bearings may even be a problem. Depending on whats wrong, they can make all sorts of noises.
Ruumph ruumph is a common noise from puked wheel bearings.
 
The fluid has been drained at 50K km intervals recently, with full synthetic fluid. The last change was about 20K km ago. I'm running a MoS2 gearoil additive made by LM in this oil for the past 70K km.

The fluid level was perfect when checked last week. Since the oil is black due to the MoS2, it's easier to see shining metallic particles. I didn't drain the fluid but just got some out of the filling hole and I've seen very few metal particles in it, most probably from brass syncros rings because they seemed non magnetic. I guess normal operation does produce some tiny bits of metallic particles, especially with syncros so I don't think that's an issue. The gearshifts have not changed, no grinding etc.

I will monitor the noise and make a more thorough check by removing the front brake caliper as the front left one seem to bite a bit more and the wheel was turning slower than the right wheel when the front was jacked. Running the car in 4th gear at idle and listening for noise from the box or from the wheel bearing should be easier then. Will let you know. Thanks!
 
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