Brakes Rumble on Rough Road

[JMI]

The E34 brakes work fine when on pavement. However I need to navigate down a small hill on a dirt road that is pretty rough due to rain run off. When using the brakes here I can feel through the brake pedal some sort of rumbling, almost a grinding, from the brakes. Get onto the paved main road and no more rumbles or noise at all.
Will be putting the car up on jack stands for some other unrelated work soon and will pull the wheels to get a better look.
Does the above description give any clue what I should be looking for?
If this was happening on a paved road I'd think the pads are worn and grinding into the rotors but I know that they are not.

TIA

[blackcat1134]

Well, just remember that you're braking on gravel. It'll take you a lot longer to stop and such. I had the same problem, it was just the actual brake pads needed replacement.

[liquidtiger720]

wheel bearings?

[Rustam]

The E34 brakes work fine when on pavement. However I need to navigate down a small hill on a dirt road that is pretty rough due to rain run off. When using the brakes here I can feel through the brake pedal some sort of rumbling, almost a grinding, from the brakes. Get onto the paved main road and no more rumbles or noise at all.
Will be putting the car up on jack stands for some other unrelated work soon and will pull the wheels to get a better look.
Does the above description give any clue what I should be looking for?
If this was happening on a paved road I'd think the pads are worn and grinding into the rotors but I know that they are not.

TIA

The description above suggests to me that you may have the same "problem" as I have - ABS kicking in. Sometimes my brakes feel like they are being grinded when ABS kicks in...
The fact that you may be braking in gravel suggests possiblity of ABS usage...

[Alexlind123]

The description above suggests to me that you may have the same "problem" as I have - ABS kicking in. Sometimes my brakes feel like they are being grinded when ABS kicks in...
The fact that you may be braking in gravel suggests possiblity of ABS usage...

I agree, the ABS feels almost like a grinding/hammering on the pedal.

[MSM]

If you really want to confirm it is the ABS kicking in, you could temporarily disable the ABS system (pulling the pump fuse will usually work on most cars) next time you are driving over that sort of surface.

I tend to disable ABS on any car I am driving through snow or on other loose surfaces. ABS tends to increase braking distances on snow/loose surfaces.

[JMI]

Just to close out the thread:
It was indeed the ABS working. This was confirmed a few weeks ago going down a hill and hitting a patch of black ice. They are very rough sounding and feeling. The incident with the ice ended uneventfully. Whew :p