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5t341tH

Brake bleeding help!

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Hello everyone. I am in dire need of advice for my brakes. I have pathfinder 2 piston calipers on my 620 with drums in the back. I have stainless braided brake lines front and rear. I used to have good brakes until I did my engine swap. Now my brakes are like mush and the brake pedal goes straight to the floor. I have bled them many times and there is still tons of air coming out. I used a hand vacuum pump and pneumatic vacuum pump and air is always coming out. I did bleed the NLSV as well and as everywhere else, lots of air comes out. I have gone through 4 large bottles of brake fluid and my pedal still sucks. I have replaced the master cylinder twice and bench bled them properly. I don't see any leaks anywhere in the brake lines. I've been bleeding for days now and I am getting fed up! Please any pointers?

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Well the front is separate from the rears so start there. Is it just the fronts or is it the rears? I can't see it being both.

 

Air is obviously being sucked in. Try bleeding it conventionally by using the pedal. Once the system is close to full you should be able to put pedal pressure into the lines and watch for any leaks.

 

Any chance the L&R front calipers are reversed and the bleeder nipple is not at the top?

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Both pressure and vacuum bleeding can actually introduce air into the system. The only way a pressure bleeder works as it was designed, is to push fluid back through the system, in other words, from a wheel cylinder up towards the master.

 

First and most importantly, make sure the pedal adjustment is correct, the drum brakes are adjusted properly and if you replaced the booster, that the rod inside the booster is adjusted too.

 

There are a few tricks to getting the air out, but start, as Mike suggested, by using the traditional two person bleeding method. It is the best way to bleed brakes.

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1 hour ago, banzai510(hainz) said:

Im just trying to figure out how swapping a engine did this?

@banzai510(hainz) I moved the master cylinder over to a side and removed the booster to get clearance. I just threw it out there in case it could be an issue. 

 

@datzenmike the pedal goes straight to the floor so I assume it’s front and rear. I drove around a bit and it barely stops. yes the calipers are in the correct orientation. My brakes used to work okay but never great. 

My 620 is a 78 model. I saw one of your posts about the bleeding procedure. Is it this?

 

front valve on nlsv

front calipers

rear drums

rear valve on nlsv

middle valve on nlsv

 

@Stoffregen Motorsports I did adjust the rear drums but I might need new ones because the kinda stick at one certain spot. Shoes are new though. I never replaced the booster but I did take it off to clean and paint. 

 

I will try doing the two person bleeding method. Just need to find a friend to come help me do it

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Without the booster you better check that the pedal push rod is actually inside the master and ready to push on it. The pedal should have about 1/16" of play or looseness before you feel it start to push on the piston inside the master.

 

 

The procedure from the '78 FSM is...

 

Master  front

Master rear

 

front valve on NLSV

front calipers

rear drums (left one first)

rear valve on NLSV

middle valve on NLSV

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7 hours ago, datzenmike said:

Without the booster you better check that the pedal push rod is actually inside the master and ready to push on it. The pedal should have about 1/16" of play or looseness before you feel it start to push on the piston inside the master.

 

 

The procedure from the '78 FSM is...

 

Master  front

Master rear

 

front valve on NLSV

front calipers

rear drums (left one first)

rear valve on NLSV

middle valve on NLSV

 

So the rod should be resting up against the master cylinder bore?

 

 

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Inside the master is a strong spring that must be compressed against to push the piston forward. The push rod from the pedal should be against it so that immediately as you step on the pedal the brakes begin to work. It's important that there be just a slight clearance to assure that the master fully returns to it's rest position. Push down on the pedal with your thumb...it should move easily enough for about 1/16" before the resistance of the piston in the master is felt. The push rod can be disconnected from the pedal by pulling the cotter pin out of the clevis pin. Loosen off the lock nut and spin the clevis out or away from the master to lengthen the push rod to reduce the clearance or play. Put the pin back in and check the 1/16" clearance. When done do NOT forget to tighten the lock nut and for goodness sake do NOT forget the cotter pin to lock the clevis pin in place.

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I will check that out as well mike. Thanks. Stepping on the pedal goes straight to the floor. Feels like no resistance 

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The pushrod inside the booster can easily fall out during disassembly, so I might even check to see if it's there at all.

 

Straight to the floor also indicates a master that needs to be bled.

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OK so I was able to do the usual 2 person bleeding and all lines are free of bubbles now. The truck now stops well like it should but the pedal has far too much free play. I have to step on it almost to the floor before any braking actually occurs. After that, the truck stops strong. How many rods are inside the brake booster? The only one I see is attached to the booster, so I don't think it could have fallen out. The bracket that attaches to the brake pedal is maxed out to the limit of the rod. It feels like the master cylinder is too far away from the brake pedal and isn't getting engaged sooner.

The master is a 13/16. I have dual piston calipers up front and drums in back.

 

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Did you adjust the length of the push rod attached to the brake pedal?

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Matching the master cylinder volume with the caliper/wheel cylinder volume can be time consuming. My cheater method is to try to use the master that came with the calipers. It does sound like you need a larger master though. Assuming all other details are worked out.

 

Do you know what size bore the Pathfinder master has?

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2 hours ago, datzenmike said:

Did you adjust the length of the push rod attached to the brake pedal?

yes the rod is maxed out on the brake pedal side. It is at the end of the threads

 

49 minutes ago, Stoffregen Motorsports said:

Matching the master cylinder volume with the caliper/wheel cylinder volume can be time consuming. My cheater method is to try to use the master that came with the calipers. It does sound like you need a larger master though. Assuming all other details are worked out.

 

Do you know what size bore the Pathfinder master has?

I will have to check

looks like its a 1" master

Edited by 5t341tH

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Good luck pumping a 1" master without a booster.

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11 hours ago, datzenmike said:

Good luck pumping a 1" master without a booster.

i am still using my booster

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A booster roughly increases the hydraulic line pressure by twice. Halving the effort on the pedal. This is a significant reduction of driver fatigue in stop and go traffic. What car or truck today doesn't have power brakes and steering??? Driving shouldn't be hard work it should be fun.

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So I’m not getting full braking power. Did some emergency stops and the pedal isn’t getting enough travel before it hits the firewall. It stops eventually but not in the way it should. Any way to test if my master cylinder is getting maximum push from the rod? 

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Sounds like your master bore is too small.

 

I don't think there is any way to measure the throw of the booster with the master attached, and with the master not attached, it may shoot the rod out like a bullet.

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If you pump the pedal does it build any pressure and get stiffer? Easier to feel with the truck off since the booster is out of the equation then.

I've had issues with a bad master before where the lines bleed clean... but it was still pulling air in through the master-- so it would bleed clean and feel good... but then be soft and if I bled the master again I would get more air out of it.

I might be having the same problem in my 620 now... could not get it bleed with the 2 person method... tried speed bleeders, but the ones I got didnt sit well in the caliper/wheel cylinder.... finally got a vacuum bleeder which helped--- allows me to build a solid pedal feel in 1 1/4 pumps on the pedal... but still not right, leading me to believe there is still air in the system. I think it maybe getting in through the bleeders as I bleed the system --- I need to pull the bleeders and tape them then try again.


A note of caution on the 2 person bleed method--- I think it has a tendency to do damage on our old master cyclinders where the seals may not be as soft as they once were... 

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Pumping the brakes with the engine one doesn’t make it any stiffer. It does with the engine off but I believe that is normal. It doesn’t feel squishy anymore. It just feels like it’s not getting enough travel from the pedal

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Wilwood offers a 1" bore master that looks nearly identical to the original Datsun master. It's a bolt in item. Long history as to how that happened, but Tilton, who used to make many performance parts for Datsuns was bought by Wilwood.

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So I still was having this problem and decided to live with it until today. I found out that there’s a tool to measure booster rod length and that my booster rod might not be up to length. I decided to 3D print mine instead since I can and measured it up. Couldn’t believe how far away the master cylinder bore was from the rod. Will take out the datsun tomorrow and test drive it!
lfCPLxS
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Edited by 5t341tH
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it definitely helped with pedal firmness, but even with that the pedal still goes to the floor with not much braking force. I believe I might need the 7/8 Master or even the 1" from wilwood

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