If it were me I might be inclinded to replace all rotors and pads *after* being absolutely sure you don't have air in the system or a leak... The fact that they work fine when DRY sort of tells me that air in the system or leaks are unlikely.

The only problem with pulling the rotors is it looks like the Torx screw that holds your rotor on is pretty rusted; in all likelihood I bet that thing will be frozen in the hub it's seated into. If you do it, make sure to have new Torx screws and anti-sieze lube for the new ones. They can be a bitc* to remove. In my case (on my '05 MCS) three of the four Torx heads sheared right off...

 

Well, this is a puzzle, and I assume your front tyres are in good or better condition. Since you say you haven't changed anything and this only happens in the rain, I wonder if you might have gotten some water based "goop" onto the pads some time in a past rain storm. Now every time the pads and rotors are wet, it reactivates the goop. Pure speculation though. I hope you get this sorted out and let us know what it was that caused this. Cheers!

 

Thanks for everyone's input. Just got my MINI back from INSKIP in Warwick Rhode Island.

Here was my solution:

https://www.northamericanmotoring.co...want-them.html

 

Reading into that post, did you indeed have a frozen caliper piston? I ask because it could well explain your symptoms but also just curiosity

 

Mechanic found no frozen pistons as I thought too.

From what I can see, the pads were badly glazed over apparently from a hard brake I did to avoid a BFT trying to sandwich me into a guard rail about a month ago..... (BFT= Big F%^&* Truck) Once they are glazed over like that, the pads are useless first few pumps until enough heat is generated to dissipate wet weather buildup. As you know, that also takes more than a few pumps of the brakes too...........

 

Glazed pads are usually ineffective regardless of wet or dry... no?

 

When wet they were scary ineffective as they did not heat up enough to dissapate water.

When they were dry, I had no issues probably since a MINI is not a 4,000 lb car................

 

hate to bump an old thread, but did your replacement brakes resolve your hissing problem? did you have to swap the booster? I recently had the ABS engage during hard braking in the rain, and now the pedal hisses when it returns back to its original position.

 

I installed the JCW Sport Brake Kit....a wonderful upgrade for these cars.

Best I can tell, the pads were glazed over from the "panic stop" I had done weeks before.

Hissing like a vac leak ? Check the fluid reservoir, and maybe a good idea to have it checked out.