Brake issue

[nkhd1]

New stinless brake lines, new master cylinder, new booster, new wheel cylinders and calipers
new 76 proportioning valve, new everything. frame off build - several years in the making.
I have bled and bled then went and got a vacuum do-hickey and bled again
I can only get a little bit of brakes if i pump it several times.
not bled enough?? master cylinder bypassing?? not enough vacuum (96 exploder with EFI) - still should have some brakes.
can find no leaks.
exasperated. thanks in advance for ideas/opinions/stuff to try......

 

[Wild horse 75]

Did you bench bleed the master before you installed it?

 

[chuckji]

^^^ That, and double check the calipers aren’t on backwards (left on right and vice versa). are The bleed ports at the top?

 

[chuckji]

What disc brake calipers are you using?

 

[nkhd1]

What disc brake calipers are you using?

76 77 calipers may be from 78 cant recall
vents at top
master bled multiple times to be sure

 

[jrussells]

if you’ve got drums still on the rear, make sure they’re adjusted out enough

 

[Torkman66]

Had similar issues a few times. Only way I fixed it was with a two person bleed process. Start at farthest wheel, passenger rear, and open close brake valve with another person pushing on brake. Open valve, push brake down and hold it. Close valve, have them pump and pump and pump. Then open, push down and hold it. Close . they let up and pump. Do that 3 or 4 times at each wheel. Only way to get trapped air at MC out.

 

[nvrstuk]

I'll second the rear brake drums need to be adjusted properly first.

 

[nkhd1]

i think i have found it the rear cylinders may be leaking behind the backing plate. there is fluid between drum and backing plate that i do not think got there when bleeding. once i locate the key for the wheels i can take off and confirm.
I did notice that once i pump up the brakes the pedal will hold until i release then its back to the floor.

 

[nvrstuk]

The key is your last sentence. You probably have a small leak but the brakes aren't adjusted properly from what you are describing. If you had a "good sized leak" your pedal would not hold firmly and it would go to the floor like it does when you have a real leak- like bleeding the brakes leak!

That symptom you described means when it's taking several pumps to move the rear shoes far enough towards the drums and HOLDS firmly - that the air is essentially gone. When you release the pedal all that fluid gets "pushed" back to the mc via the springs retracting the shoes to their "set" position.

You needing to pump the pedal 4,5,6 times (you didn't say) means it takes that much fluid movement to push the shoes against the drum whereas it should take half a pump of the pedal.

Locate & fix the small leak, clean everything well (brakekleen is extremely toxic- it causes Parkinson's and I have two local buddy's that have it and both were big users of Brakekleen), fix it, then adjust the rear shoes properly. That is rarely done properly now because nobody seems to know how to work on drum brake vehicles.

 

[DirtDonk]

You’re getting a lot of good answers on places to look. All are possible culprits.
But one more, and very common issue, is mating up a new master cylinder to a new booster.
The distance between the booster rod and the back of the master cylinder piston is critical. Even a slightly too large of a gap will leave you with a very low pedal.
I’m not sure if pumping the brakes alleviates that at all, and if not, then that’s probably not your issue.
But it’s certainly something to review.
Unfortunately, they don’t always just bolt together correctly.

 

[nkhd1]

i had already readjusted the rear brakes and i had found a previous post of yours on the mating the master and booster and had done that too. i hope i am down to just the leaking rear cylinder.
Thanks for the inputs guys...Much appreciated.

 

[nvrstuk]

Let us know what you come up with. Always hard to diagnose over the keyboard.

If the brake pedal is firm and doesn't depress towards the floor when holding it, then pumping brakes and losing fluid should not get/keep a firm pedal. Got me curious. lol

 

[nkhd1]

got back to it found the plunger tool for the proportioning valve and re bled a couple times set the rear drums where i cannot get them off to take out the slack.
still have no brakes forgot i had the plunger in the proportioning valve and it seemed it had a little more bite.
but not driveable. next step is replace parts can probably get a new master local and swp it out then bypass the prop valve with a different setup.....