Transmission Whine

[Devastate]

Is a small amount of transmission whine normal?

I've noticed at lower RPM mainly around 2-3rd gear I get a transmission whine sound. It doesn't sound unhealthy but like the car has a racing transmission in it actually. That is nothing to be concerned of right? It's not obnoxious but it is audible.

2019 ford fiesta S Manual

 

[scotman]

I would check the level of gear oil. Or you could go under and inspect the drive axles where they go into the case. Is the bottom of the case wet or looking oily? Look at the seals in the case where the axles go through the case. Are they wet or look like they were wet in the recent past? The seals are the most common leak area in the IB5 gearbox. The seals are not expensive. But the cv shafts must be removed first to gain access.

 

[Handy Andy]

I've had that ever since I've owned manuals, there are moments where the "drag" on the vehicle is low enough that the tranny "sings". Sounds a lot like the older tires on Dad's car would do when he hits 60MPH and keeps it steady - it "sings".

Manuals do this quite often - from Toyotas to Suzuki's to even wife's Nissan - Shes got a CVT but the gearbox ahead of it is a 3-speed auto tranny that if you let off the throttle just right on a smooth road - it'll howl - but only when it's allowed to nearly coast - so the gears churn out this note only when you don't push the throttle too hard, else when you do, that whine disappears - and when you decelerate too - goes away. takes off the slack in the gears so the oil doesn't churn.

It is my thoughts that why I hear this noise, is due to the gearbox/differential and the engine mounts are set up in a way that you can hear their higher frequency noises better than the lower rumble that road noise is - that the shocks and struts try to take away - so you hear the higher pitched gear churn better than the low-frequency rumble of rolling bearings and tires.

So when you hear the whine, the gears are in a moment where they develop their own resonance in the meshing of the gears teeth to each other - oil gets trapped in the pockets and even air can get squeezed into the oil - a process of foaming - that although doesn't hurt the gearbox as much because it's not pressurized, a pressurized system like automatics and the engines' oil pump - can suffer from friction damages by the surface tension lost from the air in the oil reducing the pressure and volume of oil to keep the metal-to-metal clash it's supposed to do, from ever occurring.

It sounds like you have the right amounts of fluid in there - as you wear down the gears so they have fewer sharper edges and teeth mesh is a little more broad, that churn sound will dissappear and eventually you won't notice it.

The Fluid itself having a viscosity, can also bring this noise too, because cold weather makes the fluid thicker, so it clings to the gear - climbs out of the oil pan and sticks to the gears making the whine more noticeable - not from the loss of fluid, just more of the gear mesh interacting with it. As the car warms up this mesh noise moment will be touchier to obtain because the fluid isn't clinging as much to it.

 

[Handy Andy]

@scotman brings up a good point about this.

Is the bottom of the case wet or looking oily? Look at the seals in the case where the axles go through the case. Are they wet or look like they were wet in the recent past? The seals are the most common leak area in the IB5 gearbox.

In any gearbox, there is a small port that lets' air move into and out of the box to keep seals from "blowing out" - this may sound funny, but it's actually serious.

For example, ever travel thru the mountains? As you drive - you change elevation - and to you drive, the changes are small a subtle in air pressure and even temperature - but for the car, there are several areas that need attention.

Atmospheric pressures affect the Fuel / Air ratios - you know that...

Batteries can "boil" due to the hot weather and heat from the engine - making the electrolyte hotter - and in some instances, can make it burst from the boiling gases caused by higher elevation lowering the battery acids boiling point to a level that it can erupt or pop off the covers doing just that.

​

But what about sealed systems? Designed so they don't leak?

Like Differentials and transmissions - they need to vent else the changes in air pressure can damage their seals too.

Look up this thread,
https://www.fordfiesta.org/threads/random-dangling-hose.8225/post-20330

This might help you in also seeing how siphoning off oil from a gear box that has too much oil can also drain off enough oil to make the level too low and damage the box - because if oil leaks out due to the volume of foaming in the oil from too much gear churn - the oil can then get sucked out thru the siphon - using that hose to drain it out.

So, a simple expansion port hose not seated properly can turn into a trip to the service station and even an expensive repair bill.

 

[Devastate]

I would check the level of gear oil. Or you could go under and inspect the drive axles where they go into the case. Is the bottom of the case wet or looking oily? Look at the seals in the case where the axles go through the case. Are they wet or look like they were wet in the recent past? The seals are the most common leak area in the IB5 gearbox. The seals are not expensive. But the cv shafts must be removed first to gain access.

So I had the car looked at, and one of the guys mentioned that one of the seals was leaking. Perhaps that is what is causing it? I should probably take it in.

 

[Devastate]

I've had that ever since I've owned manuals, there are moments where the "drag" on the vehicle is low enough that the tranny "sings". Sounds a lot like the older tires on Dad's car would do when he hits 60MPH and keeps it steady - it "sings".

Manuals do this quite often - from Toyotas to Suzuki's to even wife's Nissan - Shes got a CVT but the gearbox ahead of it is a 3-speed auto tranny that if you let off the throttle just right on a smooth road - it'll howl - but only when it's allowed to nearly coast - so the gears churn out this note only when you don't push the throttle too hard, else when you do, that whine disappears - and when you decelerate too - goes away. takes off the slack in the gears so the oil doesn't churn.

It is my thoughts that why I hear this noise, is due to the gearbox/differential and the engine mounts are set up in a way that you can hear their higher frequency noises better than the lower rumble that road noise is - that the shocks and struts try to take away - so you hear the higher pitched gear churn better than the low-frequency rumble of rolling bearings and tires.

So when you hear the whine, the gears are in a moment where they develop their own resonance in the meshing of the gears teeth to each other - oil gets trapped in the pockets and even air can get squeezed into the oil - a process of foaming - that although doesn't hurt the gearbox as much because it's not pressurized, a pressurized system like automatics and the engines' oil pump - can suffer from friction damages by the surface tension lost from the air in the oil reducing the pressure and volume of oil to keep the metal-to-metal clash it's supposed to do, from ever occurring.

It sounds like you have the right amounts of fluid in there - as you wear down the gears so they have fewer sharper edges and teeth mesh is a little more broad, that churn sound will dissappear and eventually you won't notice it.

The Fluid itself having a viscosity, can also bring this noise too, because cold weather makes the fluid thicker, so it clings to the gear - climbs out of the oil pan and sticks to the gears making the whine more noticeable - not from the loss of fluid, just more of the gear mesh interacting with it. As the car warms up this mesh noise moment will be touchier to obtain because the fluid isn't clinging as much to it.

this is it, It's only at low RPM in low gears with minimal throttle. Reading your description as to why this happens is super interesting, I had no idea and figured it had something to do with the gears meshing together but was not sure. I think I'm going to take it back and get a second look at that axel seal to be sure there is no leak. But the vehicle shows no obvious signs of being damaged. I've had manual cars before with similar transmission whine and it does sound "cool" just wanted to know if it's cause for concern I suppose.

 

[scotman]

It’s not an uncommon situation with all manual transmission vehicles. The drive axles are not just turning, they also move with the gearbox as we shift gears. The case seals have a tough life between the shaft rotation, temperature variation and exposure to everything that splashes or sprays from the wheels.
I can get you the gear oil part number if you don’t have a owner’s manual.

 

[Handy Andy]

If you ever owned a 4-wheel drive - you wish for the days of 2 wheel for the constant meshing and drivetrain "drag" - can make a simple commute a bit of a workout from the noise levels and constant shifting.

Not that its bad, just a workout.

One of many solutions to this was to place manual lockouts on the front hubs to save even more in fuel costs.

PITA on some winter days but overall - it's not bad.

Glad to know you're ok, and car might have a small leak - get it looked at for CV axles themselves can generate a "thump thump thump" of an out of round condition that makes one wheel seem to be out of balance all the time - or a flat spot on one of the tires.

Boots usually hide this until you spin or lift up the car and chock some rear wheels and engage a gear in the gearbox to make the front tires turn (be safe not stupid about this) - the axle with the issue shows up because you can then see the CV joint bounce the axle - and gently turn the wheel to notice any shimmy while that front end in up in the air - might help answer your question.