brake problems

[malte_berlin]

hi there, i have a hj75 troopy and since one week i have a problem with my brakes: when engine isn't running, the brake pedal feels very good and hard. but as soon as the engine is running, the brake pedal slowly falls to the ground when pushed. i can still brake, but i have to renew the pressure on the pedal when braking slowly like when rolling onto a red traffic light etc.

i checked the brake fluid lines and couldn't find a leak, also the fluid level in the reservoir stays where it is, so i don't think there is a leak. the brake fluid was renewd just 2 months ago, so there should be no air or water in it as it was working fine the last two months.
my suggestions would be some leak in the vacuum lines for the brake booster or maybe something damaged in the master cylinder (but then shouldn't the same problem occur with the engine off???).

has anyone had a similar or the same problem? other suggestions what could be the problem or what checks i can make to figure out where exactly the problem is?

any help is much appreciated, thanks!

[DUDELUX]

Give the system a good bleed, just to rule out air in the system.
Then, start looking at vacumn/booster.

Does your car have a LSPV like the Hiluxs do?? If so, make sure you bleed that too.

[malte_berlin]

yeah, i tink i will try that...what is a lspv?

[DUDELUX]

LSPV.
Load Sensing Proportioning Valve.

My Lux has one. It basically takes braking power from the rear and sends it to the front, to prevent the rears from locking up under heavy braking.

They are usually mounted, one end to the chassis rail and the other to the rear axle housing.
I think the bleeding sytems say to bleed the LSPV last.

[dogbreath_48]

I have a similar problem except that i seem to lose assistance; the pedal remains hard but has less effect (after repetitive light braking inputs). I assume its a vacuum problem - can anybody tell me where to start looking for problems? How can i differentiate between a line leak/restriction, a booster problem or vac pump problem? The alternator is new and was supplied with a healthy vacuum readout.