Hydroboost question/problem

[colelkhunter]

Just picked up a 77 k30 4x4 with a hydroboost master cylinder on it. Brakes work ok when the truck is running, but when you shut it off and it sits for just a minute you can mash the pedal to the floor with ease. Is this normal for a hydroboost system? As soon as the truck is started the pedal comes right back up with decent pressure. Wierd

 

[diesel4me]

What your experiencing is the "reserve" power boost in the hydroboost's accumulator being exhausted--it allows a stop or two with power assist with the engine off...
So long as the brakes work normally during regular driving I'd say dont worry about it--I bet if you rolled the truck down a hill with it shut off ,it would still have brakes and stop,though you'd have to stand up hard on the pedal,it might "feel" like its going to the floor but probably isn't..if it flies right to the floor with no resistance something might be amiss with it though..or possibly the rear brakes aren't adjusted close enough to the drums,resulting in excessive pedal travel...my diesel pickup with hydroboost will feel like the pedal sinks towards the floor with the engine off,and will push back against your foot when youy start it up...

 

[BGKYK5]

How long is the accumulator supposed to hold pressure?

 

[colelkhunter]

Drove it around some last night. Brakes seem to be fine, cut it off on a side road while driving and there was plenty of brakes to stop truck. guess it just felt wierd with little resistance while in the driveway.

 

[4xcrazy]

You can sure tell the people who have never driven a vehicle without any power assist braking "you have to stand on the brake pedal to stop"

no ya don't, it's just alittle stiffer, harder pedal to push than with power, the brake still work the same though.

I tow strapped my crewcab dually home when i bought it awhile back, it had no motor, so obviously no power to the brakes. It WAS alittle hard on the brake pedal, but as said, the brakes still work fine, even stopping the CC AND the towing/pulling truck as well.

Yes, the pedal will feel power assisted the first and probably half the next push, but it will get harder to push after that, but like i said, the brakes still work, just not power assisted