Grinding humming noise from front end on Braking and Reverse

welcome to priuschat! how many miles on her? how long have you owned her?

 

It is normal for the inverter to make humming sounds when the car is decelerating.

Perhaps the friction brakes are making the grinding noise? The regen braking stops at around 7-8 mph and all braking at lower speeds is done by the friction brakes.

If you want to try cleaning the friction brakes, find an area with no traffic, speed up to around 50 mph, then shift to N and slow down gradually. This will force the friction brakes to provide all braking effort. Repeat a few times and see if that helps the grinding noise.

 

Howdy,

When I first read your title, I thought Electric motor bearings...

But if the humming is more like a buzzing, Patrick is probably quite right. Brake Pad tell tale sound. And the grinding is probably metal to metal contact. Get your brake pads checked / replaced ASAP!

Otherwise, you'll be up for new disks/ rotors as well.

Cheers,
Al

 

I'd suggest doing a transaxle (ATF) drain and fill as soon as possible, and take a good look at the condition of the existing fluid. This is a very easy job, similar to a regular oil change, and there are several posts outlining how to do it if you search these forums.

 

Further to uart's suggestion:

If it's genuine 50k miles, hopefully, the seller dropped if because his brake pads are worn out and the noise freaked him out. Chances are, you've got a good one. No need to panic about the ATF fluid change yet. Get your grinding noise sorted first. 50K is a good time to change it, but it's not gonna matter if it's 55K mi.

If you want to know more about what you bought, before you drain and replace the Transaxle ATF, (or at the same time), take a clean, dirt free ATF sample and send it to a good Oil Analysis Lab. (First, clean all around the ATF drain hole, which is the 10mm Allen-keyed plug, or the level plug on the front side of the trans casing if just taking a sample.) That will give you a better idea of what state the major component is in. And just ignore Lab comments about sand and dirt in your oil. They still don't seem to understand that the Prius Transaxle is a semi-sealed unit that only vents outwards. High silicon levels can be sand, but in the Prius, seems to come from the sealants used in assembly. I've got microscope photos (not yet posted) of loads of chewed up pieces of silicon sealant in my ATF sample.

There's a lot of chat here about oil sampling and changing your ATF, but don't waste your time wondering about what ATF to use. Just use the genuine Toyota ATF WS. (It comes in a special steel tin for a reason - they don't want moisture getting in.) Everything else currently fails into the uncertain / experimental category.

 

An audio/video clip might help.

 

In the US, Toyota ATF WS is sold in black plastic US quart bottles.

Here is an example of what the bottle looks like, and the fluid is manufactured in the US:

 

How about that? I guess we have to import ours from Japan. Maybe yours are made locally, so hopefully are fresher. I'll post my pics when I find the camera... But I figure that Toyota is a bit paranoid about condensation and water absorption by the oil, hence the one-way breather on the Transaxle. Makes perfect sense, given the high voltages present. Even then, I wonder if the seemingly high aluminium levels seen in UOAs isn't potentially due to electrostatic corrosion and/or EDM. But maybe we're running a bit OT...

 

Grey plastic 1litre bottles here in Europe

 

Not my image, but mine looked just like this. A 4 litre tin.



With a tear off seal on the pressed steel cap. "Special" Not to mention expensive. About NZ$150.

Actually, if your best price in the US is USD33 per quart, the NZ price ain't too bad. But I'm sure I've seen people talking US$6 or 7 per quart here somewhere?

 

USD33 for four US quarts. Local dealer price ~USD9 per US quart.

NZD150 for four litres: the container should be silver-plated.

 

Solid, I'd say.

 

Every time I despair at the high price (relative to the US) we pay for stuff for here in Australia, along comes someone from New Zealand to make me feel like we're not getting such a bad deal.

BTW Al, that 4L metal container is how the WS is sold here too. I think the last one I bought was about $65 (au), which puts it a about double what they're paying in the US. But wow $150 in NZ, you really have cause to feel ripped off!

Each time I pick up one of these I joke with the guy at the parts counter that "last time I accidentally cooked my chips in it" (referring to the metal container making it look a bit like cooking oil).

Here's a picture of one (empty) I had laying around. This old one has been sitting around for a few years so it's a bit rusty. Seeing as I like to make the joke, here it is next to the oil that I do actually cook my chips in.