I just installed H&R cup kit this weekend and all went well, and been driving it for the last few days and no issues. All the sudden when I was driving, the brake pedal was very hard to press down and the car wouldn't stop. Then it started to work, then stopped working again. Is it the brake master cylinder or some brake line I damaged? Anyone ever had this problem?

 

Normally if your pedal is sinking, it's a brake master cylinder or slave.

sometimes it's your brake booster but the way to test that in most cars is have the car off. depress the brake pedal and buildup pressure, when you turn on the car, it should feel like normal.

have you checked your fluid level? leaks?

 

Lack of brake boost would come from a vacuum leak. Make sure the line from the vacuum pump (metal round thing on the front right side of the valve cover) to the brake booster is not leaking.

 

The vacuum pump is number 1 in this picture.

And it is the gold looking thing closest to the camera in this picture.



The brake booster is hiding in a normal spot for a brake booster, attached to the firewall on the driver's side. Looks like two dinner plates attached to each other.

 

The fact that it went away, came back and went away again seems to indicate that you have a slow vacuum leak somewhere. Look for a disconnected vacuum hose somewhere.... or one that has touched something hot and melted.

Aside: Do they still have diagrams of the vacuum system under the hood of all cars? I don't remember seeing one in the MINI but I admit I haven't looked. Used to be standard fare in US cars.

 

Guys, I fixed it. It happened to be the hose that DDM supplied to me was too weak and collapsed under vacuum pressure. I highly, may I repeat, HIGHLY, suggest that you go down to your local store and get a fuel hose or a hose that is braided to support brake booster vacuum. Lesson learned

 

Glad to hear you got it sorted! Thanks for posting back with the solution.

 

My car does this sometimes and my brakes are stock...

 

I hope you let DDM know about this. This is a huge issue for them if someone has a crash because their choice of hose being incorrect for the intended use.