Hi Everyone, I just bought a 2012 G37X and new to this site. I sometimes feel a grinding sensation in the brake pedal. It's not there each time I apply the brakes which has me worried it has something to do with the AWD. I've never owned an awd car, but can't imagine this is normal. The car has 203K miles and has never had any of the differential fluids or transfer case fluid changed. The previous owner states that he changed the trans fluid once at 135k. So I had the front diff fluid changed, which was pretty clean (due to the mostly highway miles I suppose) and that didn't help. Could this grinding be coming from the transfer case and could that explain why its intermittent.....I'm guessing the transfer case has clutch packs that could be worn due to never having the fluid changed? I'm thinking of having the rear diff fluid and/or the transfer case fluid changed next.

I've had the brake pads looked at by a mechanic and he claimed I had plenty of pad thickness left. I'd really appreciate any help I can get as I'm wondering if I should keep this car or trade it in and take my losses.

 

Aside from checking the thickness did they check to see if there's any debris between the pads and rotors? The rotors look good? Wouldn't be a bad idea to remove the pads and inspect along with inspecting and re-greasing the caliper pins. They say if you're only feeling it in the brake pedal and not the steering wheel then it's the rear brakes (assuming it's actually brake related).

 

Fluids are good up to 100k I'd change trans,diff,rad,ps fluid which is atf fluid to start

 

Stick to the brake issue, please.

 

Worn fluid can cause this kind of feedback he is getting

 

You threw every fluid into that list. Keep to brakes. Thanks.

 

Well if high mileage close to 100k just wanted to list off others to change at same time

 

Thanks for the feedback. We've all driven cars with grinding brakes and know that sensation. This feels a little different (not as course) and is not always there. I've tried putting the car in neutral (to try to rule out the transmission) when I get the grinding sensation to see if it goes away and it doesn't. But, if I'm correct, the transfer case is always engaged even when the car is in nuetral so perhaps I should change that fluid next.

 

Do you see any scoring on the rotors if so piston could be bound

 

The outsides of all the rotors look smooth. When the mechanic at Jiffy Lube looked at the brakes he said they all looked ok, although I thought I saw some minor scoring on the inside of 1 rear rotor. Here's my question.....can I jack up 1 rear wheel of the car and spin the wheel to see if it rotates freely or will it not tell me anything since it's attached to the driveline (unlike a fwd car)? I can put the car in nuetral, but not sure if that allows the wheel to spin the way it does on a fwd car.

 

You can also check the dust shield or even between that and the rotor. You may have to bend it back if it's hitting the rotor but I'd imagine that would be a more consistent noise/feel. I'm trying to recall the last time I worked on my brakes but I think they will turn independently. Only one way to find out for sure!

 

Try this go to car wash and pressure wash between pads and rotors see if it dislodges anything

 

So I took it to a shop yesterday to have the transfer case fluid changed......the fluid was pretty dark so it definitely needed it. I bought 2 quarts of matic J but it really only took 1 quart. I asked him to check out the brakes and he felt that one of the rear brakes was dragging. He removed the wheel and showed me that the dust boots were not ompletely covering the slide pins and the pins had a lot of rust. So clearly my caliper slides couldn't be working properly. The grinding sensation is still there after changing the transfer case fluid, so I'm now pretty confident it's the rear brakes and even thinking of doing it myself (haven't worked on my own car in forever). Planning to change the pads, slide pins, and hardware.

 

What does the pad contact area of the rotors look like? Are they smooth or rusted too?

 

Ok, so I attempted to change the rear brake pads myself, but couldn't loosen the slide pins so I was forced to take it to a mechanic and the only one around on a Sunday evening are the mobile ones you can find online. So I took it to this mechanic's backyard garage and he proceeded to heat the slide pin before placing a wrench on it and banging it with a hammer. He wound up breaking the slide pin, so we had to get a new caliper and replaced one caliper along with the brake pads. The grinding sensation is still there. I have already replaced the transfer case fluid (with matic J), front diff fluid, and rear diff fluid (both with regular Valvoline 80W-90 oil) and the grinding sensation is still there. I also had the tires rotated and still there. So the only thing I can think of is it's the transmission or possibly could it be brake fluid? I haven't done the trans fluid because I feel like I have to take it to the dealer (at least a Nissan dealer) since it seems a bit involved. Any suggestions on a good brake fluid I could use?