Found a bug Semi power brakes

[sandrow]

Checked vacuum lines they are new, checked the vacuum pump behind the master cylinder steady suction very strong and even. I'm stumped whats next? what else could it be symptom is intermittent power brakes

 

[bghnkinf350]

Have you used a gauge or just your thumb over the hose?

 

[OLDBULL8]

Get a vacuum gage. You should maintain about 22 inches of vacuum. The most vacuum you can pull is 29 inches.

 

[Compu Doc]

Maybe a bad diaphragm in the booster itself.

 

[sandrow]

Don't have a vac gauge I have kids. Last I saw of the vac gauge my son borrowed it

 

[freebird01]

so beat his ass and take it back... lol

 

[subway]

yea you need a gage to really see what is doing, it could "feel" ok but i might be low and not pulling a vacuum consistantly

 

[RLDSL]

You could be pulling a vac, but if you have a pinhole in your reservoir ( and it's nothing more than a dang coffee can with fittings, they rust through REAL easily ) or some such thing, you won't build enough vac to do much but want to stop

 

[RLDSL]

The low vac switch is a common leak spot.
Also, don't be shocked if you never find a problem. I went through mine and blocked out all the findable leaks, low vac switch and cruise, nothing else was leaking, everything else would hold a hard vacuum, and a new pump would build plenty, but going down the road the brake would go in the toilet, and I never did figure out what the heck was causing that. It made zero sense, I drove myself insane over that vacuum system ( and I'm used to tracing Mercedes vacuum systems ). But it made for a great excuse to put a hydroboost setup in there... best mod yet

 

[bobracing]

Might look at the Master cylinder. Had a friend that couldn't get the "soft" fading brake out of a F250. After bypassing the ABS and trying a few other things, he ended up putting the F450 master on (~$150). A little oblonging the holes and it fits.
This cured all problems with the brakes.
This or a Hydroboost is probably a not far future mod for me.

 

['94IDITurbo7.3]

if you do some searching you can probly find all my thread about my brake issues from this past spring. it is still not quit right. I hav noticed lately though, especially this morning on my way to school, that the pedal feel is getting much better. i have done nothing with the brakes since all my troubles last spring. it seems to be magically fixing itself. when i am sitting still idleing the pedal is soft, but once i get driving around the pedal comes up and gets a real nice feel to it with plenty of power. I ain't complaining.

I replaced every single thing in the brake system except the booster and nothing changed.

get a vac gauge to put on there. i got one from car quest for ~$15. i diagnosed a bad vac pump with it. if you have any questions about how to test the system with the vac gauge let me know and i along with others on here can walk you threw it.


H-boost is on my want to do list.

 

[sandrow]

it was 20 lbs the first check shut it down restarted and it was 10 checked again and it was 20. the mechanic suggested replacing the vac pump. sound right????????

 

[phazertwo]

Sounds right to me.

PZ

 

[h2odrx]

it was 20 lbs the first check shut it down restarted and it was 10 checked again and it was 20. the mechanic suggested replacing the vac pump. sound right????????

will make world of differance

 

[flareside_thun]

x2 on the hydroboost. I've got the unit and lines here...but it's a chevy unit and I don't own any stepped drillbits.