More brake troubles...

[grayw0lf]

Continuing the saga of disc brakes up front... I think the brakes are bled thoroughly. In fact, they won't release. What is wrong!?.

When I bleed the brakes at the MC, they get harder. When I bleed them at the wheels, they get all soft like there is lots of air in the lines. Either way, they don't stop the truck worth $%#t. I can't possibly lock up a single wheel, even though the pedal is hard. I even unhooked the brake booster b/c of how slow they are to come back up.

They won't stop grabbing the wheel, yet they won't stop it either. I'm to the point of fixing my brakes with my SKS.

[69_hafton]

Are the rubber lines new? If they're old, they can deteriorate to the point of acting like a one way valve and lock the brakes.

[grayw0lf]

The front is all new 6 lug conversion, new rubber lines. I also bent new 3/16" lines from the MC to PV & the 3 way T up front, leaving 1/4" in the back.

The back lines were never a problem before. I'm at my wit's end here.

[grayw0lf]

Here's a pic to go along... tell me if you see anything

.

[70c10]

I recently did the disc conversion also and that prop valve in your pic looks like a 3/4 ton (not positive but it's different than mine) and the MC you have looks like a drum version but not 100% sure. Mine looks different in shape and mine has 2 clips to hold the cap on. I used a 71' prop valve off a 1/2 ton truck and a 71' MC. This is what mine look like.

[BurnoutNova]

on my truck the lines are reversed from your pic, the front MChole goes to the rear PV hole, and the rear MC hole to the front PV hole

not sure if it matters, and im having brake probs of my own but maybe that will help

[Sport/Truck]

Originally Posted by BurnoutNova

on my truck the lines are reversed from your pic, the front MChole goes to the rear PV hole, and the rear MC hole to the front PV hole

not sure if it matters, and im having brake probs of my own but maybe that will help

I think the front MC line goes to the front P valve….Like the one in the top picture. Try switching them and see if it fixes your problem.
s/t

[cdowns]

i'd think its a bit difficult to switch those 2lines since they're different sizes

[BurnoutNova]

Originally Posted by cdowns

i'd think its a bit difficult to switch those 2lines since they're different sizes

i'll take a pic of mine... there definately reversed from the above picture. not to say mine are right but the lines apear to be factory

[grayw0lf]

Here's the setup. The PV is apparently a 3/4 ton & came attached to a 3/4 ton MC. On the 3/4 ton MC, the lines were crossed back to front as the rear chamber was the larger for discs.

It is a 71 1/2 ton MC (large front chamber) & going front to front, back to back. Do I need to get a 1/2 PV?

The output lines from the PV are front to front, back to back.

[grayw0lf]

A little update. I think I resolved the brakes locking problem. The pushrod in the booster was adjusted too far out.

I'm still stuck wondering why my pedal is hard & I have no stopping power.

[ERASER5]

Here's a "This happened to me" story. Short version.

Pulled engine -- rebuilt -- reinstalled. Maybe two months during the summer.

After rebuild-- VERY hard brakes.

After much fighting, bleeding, replacing M/C, PV, Vac Booster, Still Hard peddel.

Started to pull the Vac Booster again, yanked out the check valve thingy and saw the problem.

MUD DOBBER NEST IN MY CHECK VALVE!

It's the little things that get ya.

[70c10]

Originally Posted by grayw0lf

A little update. I think I resolved the brakes locking problem. The pushrod in the booster was adjusted too far out.

I'm still stuck wondering why my pedal is hard & I have no stopping power.

Just curious, where is the adjustment to the pushrod made?

[grayw0lf]

There are 2 places, at the back of the pedal, which seems fine. The second, which I just changed is on the rod coming out of the power booster, going into the receiving end of the MC.

[hvychve]

not sure if you mentioned you had changed master, but I remember that if you stay with the same master you need to pull the residual check valve out of the port just under the tapered fitting under the line (I screwed a metal screw into it and pulled out with vise grips and wulla , pull out and discard the valve) I have done conversions on rear discs on other vehicles and using the same master was ok, but had to remove this check valve. I may have missed in your postings, that you already changed master to proper disc/drum combo, if so , sorry and disregard my post, good luck

[69_hafton]

My "rebuilt" vacuum booster was bad and I had to stand on the brakes as hard as I could to brake and could not lock up the brakes for anything. Much worse than having drum brakes without vacuum assist. Well, I put a hand vacuum pump on the booster to check it and could not pull a vacuum. Tried another rebuild and it was a night and day difference.

Also look at anything that might obstruct the engine from pulling vacuum on the booster - hose, check valve or the engine condition. I checked the vacuum the engine was producing with the hand pump and showed 18-19 inches of mercury at idle.