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620 brake struggle


ErickwithnoK

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I've been at this a few days now, and have done a lot of reading but haven't been able to figure out my brakes on my 76 620. I can stop, but the pedal travels 3/4 of the way down before getting any stopping power. At full pedal, the brakes aren't as tight as I'd like them to be, particularly in reverse where they can hardly keep my truck from rolling backwards down a hill.

 

The PO made the following modifications:

 

     New drums, shoes and cylinders in the front, and a new master.

 

This is what I've done so far: 

 

     PO gave me a set for the rear, so I put in drums, shoes and cylinders in the back. After replacing the rears, it still sucked at stopping. I put the car back on jacks, and pulled all the drums. Removed and cleaned all of the adjusters and cleaned them so they slide nicely and made sure the shoes were all facing the correct direction (PO put the fronts on wrong and now the leading shoe is facing the right way). After everything was back together, I adjusted all of the shoes until the wheel locked up, then backed it out 12 clicks as per my manual's instructions. The drag was awkward and uneven, so I went around the truck and re adjusted until they barely rubbed. Then i got in the truck and stepped on the brakes hard to center them, and re adjusted. I took it for a little drive and it was a little better but still bad. Then I bled each wheel and re adjusted and it still sucks. 

 

Also, in the rear: The adjusters slap around in their slot every time I brake while rolling forwards or backwards. For instance, backing up in the driveway and stopping to check for traffic causes the adjusters to slide to the back of the slot and make a "clank" noise when they hit. Then when I start driving forward again, the first time I stop causes them to slide the other way and smack the other end of the slot. I can't understand how this could happen if the shoes are adjusted out far enough...which I think they are. Hopefully someone can tell me I've done something stupid!

 

Any insight would be much appreciated, this is the first time I've worked on brakes and I don't know if I can find anything else out without some expert opinions.

 

I'll supply pics if someone has an idea, but if I can avoid removing the drums again that would be great, since I've had them off four times so far.

 

Thanks Ratsun

 

Eric

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I would start with adjusting them. The farther they have to move out to contact the drum the farther your pedal goes down to the floor.

 

If this doesn't work they need bleeding. Air is compressible, hydraulic fluid is not. Get all the air out first. Was the master 'bench bled'? before installing?

 

This should all have been the first things mentioned in your reading.

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Thanks for the quick replies  :thumbup:

 

Sounds like you need to adjust the brakes and bleed the lines

 

I did, possibly wrong....but I did.

 

 

 

I did read about the master cylinder but I didn't see anyone bleeding the master when bleeding the brake lines. It sounded like a procedure that you do when you install the new cylinder, not when bleeding lines for new drums/shoes/wheel cylinders? 

 

I bled each wheel until the fluid ran clear and no air came through the tube. My bleeder line was submerged in clean brake fluid and I pumped the brake with the valve open, then had the brake pedal down as I closed the valve. 

 

The brakes are adjusted until they drag a little. Do I need to adjust them until they drag more than just a little?

 

I've learned a lot but I'm probably overlooking something here...

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Do you need to pump to get a hard pedal or do you get a hard pedal on the first push-it just has too much travel?

 

 

Pump? You have a leak.

Solid pedal on one pump; adjust.

 

I get a better pedal when I pump, I'll have to poke around to look for leaks! Hopefully no leaks on the hard lines...no idea how I would fix that  :crying:

 

Good idea, thanks.

 

This may be a stupid question but like I said I don't have a great understanding of brake systems: How important is the seal on the master cylinder reservoir caps? One of my caps is really hard to put on, and the other one doesn't seem tight at all. Could this be a "leak" in pressure on my brake system?

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If the adjusters slide, you probably have too much clearance between the shoes and drum.  Did you have the drums turned?  if the drums were turned, the inside diameter of the drum may not match the outside diameter of the shoes, when the shoes are pressed against the drums.   Does the contact scraping noise seem pretty even as the adjuster is tightened, or does it scrape on only one part of the rotation of the tire and wheel?

 

Datsun brake slave cylinders do not have two ports in them, only one port.  If there is air in the slave cylinder, and you do not let the brake shoe springs collapse the slave cylinder, any air in the slave cylinder cannot be pushed back out the bleeder valve.  You cannot use a pressure bleeder on a Datsun.  you have to put pressure on the brake system, open a bleeder valve, and do not close it until fluid stops coming out.  Then close it, and let the pedal up, and reapply pressure.  Do not let the master cylinder go empty.

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Ill-adjusted pushrod on the master cylinder could also create odd feeling issues.

 

Try adjusting it in and out to see if it starts to feel better.

 

I will most definitely do some research and try this tomorrow, thanks for the info!

 

 

If the adjusters slide, you probably have too much clearance between the shoes and drum.  Did you have the drums turned?  if the drums were turned, the inside diameter of the drum may not match the outside diameter of the shoes, when the shoes are pressed against the drums.   Does the contact scraping noise seem pretty even as the adjuster is tightened, or does it scrape on only one part of the rotation of the tire and wheel?

 

Datsun brake slave cylinders do not have two ports in them, only one port.  If there is air in the slave cylinder, and you do not let the brake shoe springs collapse the slave cylinder, any air in the slave cylinder cannot be pushed back out the bleeder valve.  You cannot use a pressure bleeder on a Datsun.  you have to put pressure on the brake system, open a bleeder valve, and do not close it until fluid stops coming out.  Then close it, and let the pedal up, and reapply pressure.  Do not let the master cylinder go empty.

 

The drums are new and I did not have them turned. I pressed the shoes against the inside diameter of the drum and it felt and looked like a good fit, but the tolerance you're talking about might be smaller than my sight and feel can find.

 

In terms of the sound of each wheels "contact scraping noise", each one has varying degrees of consistency as it turns. None of them are a constant sound as they turn. The fronts make a sound for about 25% of each turn. The rears make more noise, but I think that's probably the driveline/dif making noise as I turn the driven wheels. 

 

My brake bleeding method included releasing the pedal several dozen times for each wheel, but my bleeder tube was submerged in fluid the whole time. Could that keep air from getting out of the slave cylinders and out the bleeder, trapping it in the cylinder as you suggested? If that's a possibility I'll bleed all the wheels again with the brake down, open valve, let it flow, close valve, pedal up, method. 

 

Thanks again guys.

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You said:

"If that's a possibility I'll bleed all the wheels again with the brake down, open valve, let it flow, close valve, pedal up, method."

 

If that's a possibility I'll bleed all the wheels again with the brake down, open valve, let it flow until it stops, close valve, pedal up, method.

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You said:

"If that's a possibility I'll bleed all the wheels again with the brake down, open valve, let it flow, close valve, pedal up, method."

 

If that's a possibility I'll bleed all the wheels again with the brake down, open valve, let it flow until it stops, close valve, pedal up, method.

 

Got it. Thanks for being specific with me, I am a newbie after all... :blush:

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Another thing you can try, connect clear tube from your bleeder valve to the reservoir. It's dirt cheap. Then you can just pump and pump and pump until no air comes out. No need to close the valve.. just pump away.. When you are comfortable with it. Close the valve and move to the next one.

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Another thing you can try, connect clear tube from your bleeder valve to the reservoir. It's dirt cheap. Then you can just pump and pump and pump until no air comes out. No need to close the valve.. just pump away.. When you are comfortable with it. Close the valve and move to the next one.

 

If DanielC is right, this method can cause some air to be left inside the slave cylinder after bleeding. It makes sense to me to do it the way you suggest, but my brakes don't work so what do I know... :confused:

 

If I'm thinking about that wrong, feel free to let me know

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It looks like you have 2 problems.  

1.  Having to pump the pedal to get a better pedal feel and higher pedal position means air is trapped in the system.  

2.  A long pedal travel means the shoes are out of adjustment.  

 

Put the whole truck up on 4 jack stands.  Adjust all brakes until the drag moderately, while you have 2 lug nuts holding the drums securely in place.  Pump the brake pedal, then check and readjust at least twice.  Now have a friend hold the brake pedal down 1", 2", 3", etc... checking if each wheel rotates at that position.  My guess is that you have 1-2 wheels adjusted significantly tighter than the rest. Ditch the "12-click" method.  You can go tighter than that.  

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Lots of good replies here, but I am firmly in the two person method of bleeding brakes. Doing the open-bleeder thing is fine to get things going, but you've always got to finish them off with someone pumping and the other cracking the bleeder. Be sure the person pumping is pushing the pedal all the way and that they are not going too fast as this can actually cause air bubbles to form. Always start the bleeding procedure with the cylinder furthest from the master, then finish with the one closest. You may need a couple rounds to get it right.

 

Before trying to bleed again, there are a couple things I would check:

  • Daniel mentioned diameter of drums, check that if you can. If you can't measure it, then move on.
  • Check to see that the parking brake mechanism is installed properly in the rear.
  • Make sure the pedal is adjusted with 1/16" free play. No more, no less. (Has someone messed with the upper pedal stop/brake light switch?)
  • Make sure the wheel cylinders are mounted with the bleeders on top. Some vehicles allow you to mount them in the down position, trapping air in the top.

If you do all this and still nothing, then pull the lines at the wheel cylinders and check for flow. Maybe a plugged hard line or a swollen hose?

 

I like to use a power bleeder to get things going (but still finish with two person method), but if you don't have access to a power bleeder, just crack all the bleeders open and walk away. Let them drip for a few minutes (20 minutes), but keep adding fluid to the reservoir so it doesn't run out.

 

If none of this works, then it's back to square one, with a new master or at least bench bleeding the master.

 

Good luck.

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Thank you all for the advice, I'm going to adjust them all down further and see if that helps with my pedal travel, and then do the two person bleed method that a lot of you have suggested. My dad and I tried this method the first time around. I think it's possible we did a few things wrong, like pumping the pedal too quickly, and not leaving the valves open long enough before closing them again. We'll be careful this time and I'll post how it goes, not sure if I can get to it today or tomorrow, but I greatly appreciate all the help! 

 

 

 

 

Lots of good replies here, but I am firmly in the two person method of bleeding brakes. Doing the open-bleeder thing is fine to get things going, but you've always got to finish them off with someone pumping and the other cracking the bleeder. Be sure the person pumping is pushing the pedal all the way and that they are not going too fast as this can actually cause air bubbles to form. Always start the bleeding procedure with the cylinder furthest from the master, then finish with the one closest. You may need a couple rounds to get it right.

 

Before trying to bleed again, there are a couple things I would check:

  • Daniel mentioned diameter of drums, check that if you can. If you can't measure it, then move on.
  • Check to see that the parking brake mechanism is installed properly in the rear.
  • Make sure the pedal is adjusted with 1/16" free play. No more, no less. (Has someone messed with the upper pedal stop/brake light switch?)
  • Make sure the wheel cylinders are mounted with the bleeders on top. Some vehicles allow you to mount them in the down position, trapping air in the top.

If you do all this and still nothing, then pull the lines at the wheel cylinders and check for flow. Maybe a plugged hard line or a swollen hose?

 

I like to use a power bleeder to get things going (but still finish with two person method), but if you don't have access to a power bleeder, just crack all the bleeders open and walk away. Let them drip for a few minutes (20 minutes), but keep adding fluid to the reservoir so it doesn't run out.

 

If none of this works, then it's back to square one, with a new master or at least bench bleeding the master.

 

Good luck.

 

 

Unfortunately, I don't have access to calipers to measure the drum, but since the drag is uneven when adjusting, I may take them to be turned and see if that helps. When it comes time to bleed, I'll do these steps exactly.

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It looks like you have 2 problems.  

1.  Having to pump the pedal to get a better pedal feel and higher pedal position means air is trapped in the system.  

2.  A long pedal travel means the shoes are out of adjustment.  

 

Put the whole truck up on 4 jack stands.  Adjust all brakes until the drag moderately, while you have 2 lug nuts holding the drums securely in place.  Pump the brake pedal, then check and readjust at least twice.  Now have a friend hold the brake pedal down 1", 2", 3", etc... checking if each wheel rotates at that position.  My guess is that you have 1-2 wheels adjusted significantly tighter than the rest. Ditch the "12-click" method.  You can go tighter than that.  

 

I have a good Nissan manual to help me with the pedal adjustments, I should probably do that first. I was hoping I could go tighter on the adjustment but the amount of drag seems to be a matter of feel and not exactness, so I thought 12 clicks would be a good baseline. I'll go tighter and see if it helps!

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Tighten the shoe adjusters as tight as you can get them, and then bleed the brakes. Then back the adjusters off.

 

The pedal adjustment is crucial. If it's too tight, the brakes will lock up and stay that way. If it's too loose, then you will have trouble getting the brakes to work at all. The 1/16" adjustment isn't the pedal to rod adjustment (there is no adjustment there), the rod itself should have 1/16" of play between it and the master cylinder.

 

Confused?

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The adjusters shouldn't slid back and forth. If adjusted anywhere near properly they won't, or barely move at all. Loosen off the emergency brake cables so the shoes are fully returned to rest position. Make sure e-brake cables are not seized and holding the rear shoes. Now adjust the adjusters, spin the wheel until there is noticeable drag. Step on the brakes several times to center the adjuster and check the wheel by spinning. Often it is loose now because only one shoe was pushed out to the drum. Adjust as needed and step on the brake to center the adjuster ans re-check. Repeat as necessary.

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The rod to master cylinder needs to have 1/16th play before engaging the cylinder, and the pedal assembly needs to be adjusted to the specs in my manual? That's my understanding! The nut on the interior end of the push rod that goes into the master cylinder is almost loosened off the end (towards the rear of the vehicle). This is the rod into cylinder adjustment, correct?

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The adjusters shouldn't slid back and forth. If adjusted anywhere near properly they won't, or barely move at all. Loosen off the emergency brake cables so the shoes are fully returned to rest position. Make sure e-brake cables are not seized and holding the rear shoes. Now adjust the adjusters, spin the wheel until there is noticeable drag. Step on the brakes several times to center the adjuster and check the wheel by spinning. Often it is loose now because only one shoe was pushed out to the drum. Adjust as needed and step on the brake to center the adjuster ans re-check. Repeat as necessary.

 

I thought the same thing. How could the adjuster be sliding if the shoes are pressing against the drum? It sounds as though the emergency brake may be a problem, as pulling the brake in the cab is very difficult. I'll adjust the parking brake and the adjusters in the drum and be right back with an update. Thanks Mike.

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The rod to master cylinder needs to have 1/16th play before engaging the cylinder, and the pedal assembly needs to be adjusted to the specs in my manual? That's my understanding! The nut on the interior end of the push rod that goes into the master cylinder is almost loosened off the end (towards the rear of the vehicle). This is the rod into cylinder adjustment, correct?

Yes. The only other adjustment on the pedal is the upper stop. It could have a brake light switch or a bolt and nut.

 

The only reason I ever adjust the upper stop is to try and get the clutch and brake pedal level with each other. But if someone has adjusted this way out of whack, it may add to the confusion.

 

So focus on the master adjustment and then adjust the pedal upper stop, if necessary, later.

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Update: My brakes feel great! Thanks for all the help.

 

This is what I did to solve several issues

 

I wanted to start by adjusting the pedal a bit further into the master, but there weren't any threads left to adjust it further into the cylinder. Great suggestion, though!

 

Then I checked to see how the parking brake was adjusted, since it felt so tight. It was adjusted all the way tight. I loosened it over half way out, and it felt much better in the cab. After adjusting the parking brake the rear wheels felt totally loose and weren't dragging at all. I adjusted them down, mashed the pedal and they loosened up again. This solved the sliding adjuster problem.

 

I continued to loosen the parking brake, crank down the adjusters, and mash the pedal until I got the brakes adjusted to where I wanted them. I also adjusted the fronts a little tighter with the same adjust, mash the pedal, and readjust method. I got those where I liked them too :thumbup:

 

Then my dad and I (thanks dad) bled the brakes for the fourth time, using the method you guys suggested, and we got a few bubbles out.

 

I dropped it off the jacks and took it for a drive. MUCH better.

 

So my understanding of the problems is this: The PO cranked down the parking brake adjustment to compensate for the bad shoes he left on it, then when I put new shoes on it the parking brake wasn't able to disengage, making it impossible to adjust any of the brakes properly. He also botched up the front brake install on both sides. He did both sides differently and didn't get the shoe position right either time, or grease/clean anything. 

 

Thanks again for all the help, I plan to drive it around for awhile and check the brakes after a week or so to see if they need any fine tuning on the adjustment. 

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