Braking problems when hot : Bomb ? / Servo pump ?

[thyrsted2@olsy.dk (Kenn Thyrsted)]

Hi Guys

Got this weird brakeproblem:

When starting in the morning @ approx 7-15C the brake is feeling OK and the
pedal is firm at the upper quarter !

Driving 20-50km on the highway is no (big) problem either pedal may become
"spongy" at first but firm at 'bout 1/3 down.

Driving in the city for more than 15-30 minutes, not abusing the brakes, the
pedal has no resistance on the first 2/3, and then it acts slightly "spongy"
but it can still brake OK.
Once as this happened i stuck a thermometer down the pentosin-reservoir and
i measured 75C.
(Yes, i know; dangerous if the ABS has to kick in)
When this happens i can park the car for maybe 15 minutes, and when i start
the loose feeling is gone...

To complicate matters further compression on Cyl #5 is gone, thus causing
the engine to stall intermittently :(
When RPM drop below 700 the brake pressure warning light comes on yellin'
and screamin'.

The strange thing is that when #5compression and idle were OK, i could enjoy
the yellin' and screamin' from the brake pressure warning light.
This indicates that the "hot"/warm running servo would have problems
building pressure to acceptable level.

If this is the case, could the culprit be the servo pump and not the bomb. ?

How does it feel when the servo-pump is bad ?

Comments, please

TIA

Kenn Thyrsted
'87 200 TQavant , head transplant pending..