Break problems

[Chuckdiesel]

Ok well usually breaks are real simple and most problems are easy to find, however I dont know whats up. First off, the previous owner replaced the break booster and master cyilnder. the problem is that when I push on the petal while driving, the first time is weak, lots of petal travel, but if i press it again its hard like it should be. Also, I have noticed that if I hit the breaks at the same time i push in the clutch, like at a light, its fine but if i slow down or coast and then hit the breaks its soft,so the secoend time its hard.----When the truck is off the petal is hard, but when I press the petal air bubbles up in the master cylinder,plus theres a thunk that i believe comes from the rod thats attached to the petal that goes in to the booster, and in that spot thats when air bubbles out. Remember that the master cylinder and booster were replaced by a not so very qualified guy. So im lost any ideas. oh yea and the booster moves like a 1/8-1/4 inch or so when i push the breaks with the truck off. oh and i have a new vaccum pump

 

[dsblack]

The booster should not move.
Air bubbling up is a sign of air in the system. The pedal is hard when the truck is off due to no vacuum at the booster.
I would tighten the booster so it does not move, and get some heavy duty bleeding and leak checking done on the system.

 

[Mr_Roboto]

There's your problem. If the booster moves, either the nuts are loose or else the firewall is broken around the bolt holes. There are 4 nuts up under the dash.

And when you press the brakes, the master cylinder is moving rather than applying the brakes.

And when you press the brakes the second time, the booster / master is already "out".

After everything is tightened down, I'd suggest gravity bleeding the brake system. Just open up one bleed screw at a time, and let it drip for about 10 minutes each. Make sure you keep the master cylinder topped off.

 

[Chuckdiesel]

There's your problem. If the booster moves, either the nuts are loose or else the firewall is broken around the bolt holes. There are 4 nuts up under the dash.

Ok well that makes sense. i'll give it a shot.

is it normal when the truck is off that theres a clunk when the petal is depressed only slightly with even hand pressure at about 1' of petal travel

 

[Mr_Roboto]

I've never had clunking brakes!!

The sound is probably the booster moving (and stopping).

 

[oldmisterbill]

Proper adjustment of the brake actuater rods-both between the master cyl & the booster-as well as the pedal to the booster??????

 

[Chuckdiesel]

yea most likely. the breaks dont clunk the rod on the petal that goes in the booster does after an inch of travel only with truck off. also a side note is it normal for oil pressure to drop at idle to the N in normal then to straight up after a min or so of driving

 

[jauguston]

Chuck,

Trucks the age of ours with the 6.9 had a known gauge problem. There is a fix that will let the gauge show a higher reading. It consists of a different oil pressure sending unit and a plug in inline resistor type thing that together make the reading higher. You will need to talk to a good parts man at a dealer. Some of the dummies don't know about it because they weren't born when our trucks were built (-: I did it to mine. Take a look at the wire that is attached to your oil pressure sending unit and see if there is a short wire plugged into it and the stock wire attached to the short wire. If it is there the fix has all ready been done.

Jim