very soft brake pedal

Massey165

Driving my 2002 V70XC 152,000 kms, twice in the last 2 weeks have applied the brakes and it has gone nearly to the floor. A couple of pumps and all is good, checked fluid level all good. drive for a week couple of times and then out of the blue does it again, checked fluid all good. Any ideas on what could be the problem.

ramrod

Evening BF

That sounds like an intermittent failing brake master cylinder

Especially if it happens most when the car and weather is hot

Major Ledfoot

How old is the brake fluid?

Sounds like classic symptoms of fluid boil. Brake fluid absorbs moisture/water, and old fluid soaks up a lot. When the brakes work hard or in very hot conditions, the water in old brake fluid boils and bubbles form in the fluid.... then you have no pedal. This is why you see production-based race cars (especially where rules mandate the standard calipers) flush their brake fluid on a regular basis.

ramrod

Yes indeed

I forgot to suggest, changing the brake fluid and re-test.

If symptoms persist, master cylinder is bypassing fluid

Especially in hotter weather the fluid boils easier as well as whilst driving in mountainous areas

Partially seizing calipers can cause fluid to boil as can driving with both feet pushing the throttle and brake at the same time. I found this out once. Sold a car to an old timer who brought it back complaining about the brakes when I knew they were in perfect order. He refused to go on a test drive with me so I could point out his problem, so I had to buy the car back from him. I wasn’t complaining though because I ended up selling it to someone else for a lot more money 💰

You live and learn every day

Massey165

Thanks Sam, Bob appreciate the information Bob