Brakes wont build pressure

[75LB620PU]

Hi there my name is Chris. long time lurker first time posting. my rig is a 75 long bed 620. l20b with w53 head. Weber dgv5a carb and 3 speed auto transmission.

So here's my issue. rebuilt all four wheels brakes. brand new wheel cylinders, shoes, hardware, drums and even a new adjuster assembly on the right rear. bench bled the master cylinder and then bled the brakes starting at the furthest point from the MC and moving closer. the pedal pressure wont build. if i pump it up about 10 times it will almost start to build. while driving the brakes barely work. i have to pump em up 4 or 5 times and press all the way to the floor and then some for the brakes to start slowing the truck down. Ive adjusted the shoes 3 or 4 times now and nothing seems to be working. MC is only a few months old so i don't suspect its the culprit. any help would be great its my daily and i drive it as it is right now so its real sketchy.

IMAG0123 by warrenchris90, on Flickr

IMAG0121 by warrenchris90, on Flickr

2012-10-28_13-24-38_547 by warrenchris90, on Flickr

2012-10-28_13-24-23_437 by warrenchris90, on Flickr

 

 

 

[H5WAGON]

Did you Bench Bleed the Master Cylinder...?  Completely...

[75LB620PU]

yeah i took it off the truck put it in the vise. made sure to keep it level. hooked up some spare brake lines for the output holes back into the reservoirs and bled it for almost half an hour. while tapping on the body of the cylinder to release air as well. there was solid stream of pressure no bubbles at all.

[75LB620PU]

my next thought is to maybe rebuild the MC?

[datzenmike]

Lift each wheel and turn adjuster until you feel the brake drag while spinning the wheel by hand.

 

Now bleed them. Keep master full of fluid at all times.

 

Pump pedal several times and hold while loosening the bleeder. Let out air and fluid, close bleeder. Repeat until only clear fluid comes out. Continue to next wheel. 

 

The '75 shouldn't have the NLSV which needs to be bled separately.

[75LB620PU]

i searched along the whole brake line to make sure no NLSV. and i will try that and see if results differ from the first time. after i adjust them out to where they drag. do i press the brake pedal to center the brake shoes and check for drag again? thanks for the input guuys :thumbup:

[datzenmike]

Yes center the pads but if no, or little pressure, they might not move.

[wayno]

I have a question, when you started  the farthest away from the MC, did you stay there till you had good flow coming out, or did you move on before you had good flow?

Please explain exactly how you are bleeding the brakes, who pumps the brake, and who opens the bleeder?

[75LB620PU]

i stay at the farthest until solid good pressure and clean brake fluid are coming out. my fellow ratsuner pumps and holds the pedal whilst i release the bleeder valve. i use a piece of 3/16" clear rubber hose to attatch to the bleeder valve and submerge the other end into a clean bottle of brake fluid. so there is no chance of air getting back into the system

[ggzilla]

Great first post! Pics and good question and symptoms description

 

 

What I do for drum brakes is tighten until the wheels won't turn, pump the brakes, tighten more if they still turn, then finally back off until they turn. Because the drums can have a slight drag even if they are a long way off, until they are centered.

 

The other common cause is pushrod wrong length.

[75LB620PU]

How do I figure out pushrod length and adjustment. I didn't do any of that when I installed the new MC? thanks for the help and replys

[wayno]

You said that the master had been installed a couple months before, so I assumed it worked fine till the latest work on the brakes, that is why I asked about the bleeding procedure.

If it worked fine before, then the rod is not likely the issue.

[75LB620PU]

It didn't necessarily work. I've always had to pump the brakes 3 or 4 times. When I removed the drums to do the work. All 4 wheels were completely rusted and torn apart. Wheel cylinders were blown out all the springs were chopped up. The drums looked like the surface of the moon lol. So they've never really worked properly

[wayno]

Brakes are a pain in the ass sometimes, and new dual masters are a double pain in the ass sometimes, I have found sometimes it's better to just go to the wrecking yard and find a like vehicle with good brakes, buy everything I need and install it on my truck, bleed the brakes and I am good to go.

I have bought 2 rebuilt dual masters from the parts store and had both of them be bad, then I bought a new Centric dual master and had no issue at all, it sounds like you know how to bleed the brakes as long as you did not let the reservoirs get low, so I guess there is a possibility that the rod is the wrong length, it depends on if you went from one type of master to another.

[ggzilla]

To tell if the rod is right length look under the dash where rod meet pedal. The rod should not move until pedal moves a mm or so.

[kgrantkey]

Brakes are a pain in the ass sometimes, and new dual masters are a double pain in the ass sometimes, I have found sometimes it's better to just go to the wrecking yard and find a like vehicle with good brakes, buy everything I need and install it on my truck, bleed the brakes and I am good to go.

I have bought 2 rebuilt dual masters from the parts store and had both of them be bad, then I bought a new Centric dual master and had no issue at all, it sounds like you know how to bleed the brakes as long as you did not let the reservoirs get low, so I guess there is a possibility that the rod is the wrong length, it depends on if you went from one type of master to another.

I have gone thru many remanufactured master cylinders over the years. Swapped boosters before. Yesterday I went to look at a rear end. My brakes have done the same as yours. My truck sat for a long time and each time I drove it I had to pump the brakes more and more until now after bleeding and adjusting EVERYTHING my pedal would go to the floor. I did just what wayno said above. I now have brakes.

 

 

That booster and MC are out of about a 1985 Datsun pickup. It barely fit physically and had to be modified to bolt to the existing firewall bracket and the linkage to the pedal had to be shortened. I bled the MC on my truck, hooked it up and had brakes.

 

Before the pedal went to the floor after hours of adjusting and bleeding and repeating.