E46 M3 N/S rear wheel smells hot

[Buzzmeister]

E46 M3 Near Side rear wheel smells hot after spirited driving. Off side wheel doesn't smell at all. What could this be? Not sure if the smell is brakes or rubber. Any thoughts?

[duff]

Seized caliper would be my guess.

[Buzzmeister]

duff said:

Seized caliper would be my guess.

Thanks. I did consider that. However, it just passed MOT on Monday and the wheel is not hot to the touch.

[Gruber]

Which bit is hot then?

[Buzzmeister]

Gruber said:

Which bit is hot then?

good question. the hot smell is eminating from the wheel arch. Could it just be the exhaust as it is closer to the n/s than o/s? Anyone else noticed it?

[blondini]

Gruber said:

Which bit is hot then?

After spirited driving... Tyre tread maybe? Possible alignment issue.

[Salom]

I think you'll find that it's the exhaust, check that you haven't lost a heatshield...

[ryandoc]

My guess would be calipers, it happened to me the dust seal goes and they start sticking.

The smell with that if the caliper is sticking on is quite a sickly smell, you'd also, depending how bad it's sticking, be able to notice either slowing to a stop the car won't glide it'll slow down more abruptly. Likewise it might stick/click when you set off and the pad releases.

Do you get any of those symptoms?

[Buzzmeister]

ryandoc said:

Likewise it might stick/click when you set off and the pad releases.

this sounds quite familiar. Especially if the car hasn't moved for a day or two. I suspected the handbrake but it could be a caliper.
Alignment has been checked and rechecked so shouldn't be a problem.
Rubber is winter tyres but I'd expect both sides to be the same if it was this.
I think if I remove both rear wheels quickly after a good drive and check the caliper temps this should highlight a problem.
Thanks all.

[skeeterm5]

Wheel bearing?

[ryandoc]

Buzzmeister said:

this sounds quite familiar. Especially if the car hasn't moved for a day or two. I suspected the handbrake but it could be a caliper.
Alignment has been checked and rechecked so shouldn't be a problem.
Rubber is winter tyres but I'd expect both sides to be the same if it was this.
I think if I remove both rear wheels quickly after a good drive and check the caliper temps this should highlight a problem.
Thanks all.

What I would say is lots of cars brakes might 'click off' from the Handbrake being on a day or two etc. If the caliper is sticking during driving and heating up the disc you might notice this clicking during normal driving when releasing the brakes. One sure way to tell if it's brakes is after a decent run put your fingers through the spoke towards the disc but whatever you do don't touch it. If the calipers sticking on it'll be red hot and you'll feel the heat coming off it. Do this both sides and compare. If one side is sticking it will definitely be a hell of a lot hotter

It happened to me on my E46 M3 after some spirited driving both calipers failed, dust seals went lol.

The smell itself if it was tyre miss-aligned or brake sticking on the smells are quite different, one rubbery burnt smell the other quite sickly.

[ortontom]

calipers i would say on MOT's they cannot do a rear brake pad check or rear pad check under load due to the LSD....well that was what i was told.....

[tgr]

Unless you've driven over a plastic shopping bag, which has then melted onto the exhaust, then started smelling/burning. But my initial thought was callipers

[blondini]

ortontom said:

calipers i would say on MOT's they cannot do a rear brake pad check or rear pad check under load due to the LSD....well that was what i was told.....

Yeah, they shouldn't test an LSD equipped axle on the brake rollers, but this is often overlooked.

[Buzzmeister]

It's definitely not the caliper. I touched both rear discs after a 100 mile drive and they were very similar temps.
Ref. LSD:-
As the LSD in the E46 M3 is not 'plated' but rather is viscous the brake test on the rollers should not matter.

[ortontom]

well kwik fit said their machine said not to run the rollling brake test because of the LSD........i would trust their machines over a local jobby..


caliper smells hot? does it click when you stop IE as it cools down? could it be leaking diff oil you smell, look under the car that sometimes smells like hot metal.....also wash the car and use it if theres a larger amount of brake dust build up on that wheel compared to the other......

[blondini]

Buzzmeister said:

Ref. LSD:-
As the LSD in the E46 M3 is not 'plated' but rather is viscous the brake test on the rollers should not matter.

Interesting point. Have never really taken in how the M diff works.

[Buzzmeister]

blondini said:

Interesting point. Have never really taken in how the M diff works.

From BMW NA press release:
"Any time a speed difference develops between the two rear (driven) wheels, a shear
pump, driven solely by this difference, develops pressure in the silicon viscous fluid in
which the lock operates. In turn, this pressure is directed to a multi-disc clutch that
transfers driving torque to the wheel with the better road grip ("select high"). The greater
the speed difference between the two wheels, the more positively the clutch engages. As
soon as the difference between the two wheels’ speeds begins to diminish, the clutch
begins to ease off."

[tgr]

Have you sorted this yet Buzzer? If all you have to go on is a smell, no parts that seem abnormally hot, my guess is the plastic bag option I mentioned earlier, or some kind of leak onto the exhaust. I can't really see how it would be the tyres. Can you pay an Indy a few quid to get it up on a ramp and have a look around when the car is fully warmed through?

[Buzzmeister]

tgr said:

Have you sorted this yet Buzzer? If all you have to go on is a smell, no parts that seem abnormally hot, my guess is the plastic bag option I mentioned earlier, or some kind of leak onto the exhaust. I can't really see how it would be the tyres. Can you pay an Indy a few quid to get it up on a ramp and have a look around when the car is fully warmed through?

No, I haven't. I suspect it is the exhaust, definitely not the brakes. Good shout re: inspection. I plan to get it up on axle stands, remove the wheels and have a look when it's warm.
Thanks