Leak in brake fluid reservoir

[Leafsrule531]

Apologies for posting this here but the x5 forums are kind of dead and the concept is the same for this car so just wanted to hear from the experts. (Mods if I am not allowed doing this please delete)

I recently replaced the water pump and thermostat on my 2007 x5 3.0 suv which now has 180k miles. After turning on the car I noticed that the brake is going to the floor. I thought maybe I’ll flush the brake fluid. After putting my pressure bleeder on I notice that there is a leak that’s coming from the master cylinder reservoir. I know there’s no issue with the tool because I bled my brakes yesterday on an e39 m5 and it worked perfectly.

Is my issue with the reservoir or do I need to swap out the full master cylinder as well ? Here is a video of what is noticed:

https://youtube.com/shorts/gbOV97icyZg?feature=share

[Maxima SE]

The issue is with the tool. It is not sealing tightly. Is it a motive bleeder? If so then use the thicker bleeder cap seal. Also check the seal to make sure it is not worn out. I have had the same issue where it perfectly seals my E92 and E46 but not my E86 and I have to swap to a thicker seal for that one.

[Leafsrule531]

Yes it's a motive bleeder. I used it perfectly on my e39 m5 but I guess it's different for an x5 ? Will check again.

Still not sure why the pedals went to the floor.

[Maxima SE]

Yes it's a motive bleeder. I used it perfectly on my e39 m5 but I guess it's different for an x5 ? Will check again.

Still not sure why the pedals went to the floor.

That is not good. If you cant pump up the motive to produce enough pressure then you probably have a major leak somewhere, like a loose bleeder screw or even worse torn brake line hose. Even with a poorly sealed cap, you should be able to pump it up and pressurize the system

[eacmen]

What is the fluid level in the brake fluid reservoir?

Pedal going to the floor indicates the system isn't able to build hydraulic pressure. This indicates one of two things:

1. There is significant air in the system.
2. There is a leak somewhere in the hydraulic system.

What was done to the car since the last time it was on the road?

[bigjae46]

You’d lose fluid if there was a leak somewhere. I did see a case where the reservoir leaked into the brake booster.

But if the pedal is going to the floor then I’d imagine the master cylinder is shot.

[Leafsrule531]

What is the fluid level in the brake fluid reservoir?

Pedal going to the floor indicates the system isn't able to build hydraulic pressure. This indicates one of two things:

1. There is significant air in the system.
2. There is a leak somewhere in the hydraulic system.

What was done to the car since the last time it was on the road?

It's on the max level. I am able to build pressure. It just slowly goes down possibly due to a bad seal at the motive pump.


I thought it was number 1 which is why I tried to bleed the system. But could my brake booster or master cylinder have gone bad ?

Before this, my water pump had gone bad so replaced water pump, thermostat and valve cover gasket. None of those could lead to air in the brakes so not sure. I don't really wanna throw parts at it. Is there a way to diagnose if it's a booster or MC ?