Riddle me this. . .

[Mudstud]

Got a 76 K5 1 ton with 4 wheel disc. factory booster but with the 1 ton MC. Direct lines to front calipers and Wildwood Adj Prop Valve on the rears. Have SS lines all round. I have great brakes except, it seems, when I flex pretty good. The peddle with get soft and I pump it once or twice and it firms back up nicely. I have power bleed the system twice. What could be causing this problem? I was thinking perhaps the vacuum line outta the booster is being pulled slightly during flex allowing a temporary vacuum leak, then when it's back on relatively flat ground it reseals and builds back up. Any thoughts on this problem would be greatly appreciated.

 

[cbbr]

if you mean power bleed with a mity vac, just bleed it the old fashioned way. Mine mity vac just would not get all of the air out. About a gallon of fluid and regular bleeding did the trick.

 

[YZEATER]

you could flex it out, and then check for tight hoses lines. maybe it's just more air working it's way out due to the angles.

 

[Mudstud]

No I used an electric bleeder- twice now. Once after the first trip out and the problem developed and again after it. This is the first time it's been out wheelin since the second power bleed.

Power bleeder.

 

[Mudstud]

More air breaking loose was my thought too- thus the second round of power bleeding. Here is another question in all of this. I was bleeding FOREVER manually after replacing the MC and never could get brakes when the truck turned on. I unscrewed the brake rod under the dash a few turns and then the brakes were awesome. Then a friend (Boz42) told me according to a brake book he has, the correct way to adjust that brake rod is to slowly push the brakes- with the cap off- until you see the fluid displace (current in the reservoir). This should happen about 1/4" into the brake peddle. Well it turns out that mine started this emmediately even when I screwed brake rod all the way in (stock location) but this time I still had good brakes.

Couple folks have suggested ramping the truck to try and recreate the problem. Once I have no brakes try rolling off the ramp without hitting anything and bleed them on the spot.

 

[Mudstud]

TTT anyone have any thought on what to do/replace?