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seattle620

brakes don't stop well when rolling backwards

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Hi,

 

New to the Ratsun board!

 

I have a 1973 Datsun 620 pickup. I had the brakes done about 6 years ago, but drive the truck under 500 miles a year. The brakes work well except the when i am on an upward incline, when it rolls backwards, it hard to stop. I have to pump the brakes and keep the pedal down to the floor in order to keep rolling backwards. Going forward and stopping has never been a issue, it's just when it's rolling backwards. Any suggestions on what may be the issue?

 

thanks!

 

Jay

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Hi Jay, welcome to Ratsun.

 

 

Well it's normal for the brakes to work better when moving forward than backwards. This is from the special placement of the leading and trailing brake shoe linings in relation to the wheel cylinder. 

 

About all I can recommend is adjusting all four corners of your brakes to remove any excess play from normal wear. Adjust and spin the wheel by hand till there is drag from the shoes rubbing the drum. Pump the brakes several times to center the wheel cylinder and check again. Be sure to loosen the E brake first before adjusting and then don't forget the re-adjust the E brake last thing when done.

 

 

Have a care. I find that brakes very slowly loose they ability to stop as the linings wear and you can get very used to pushing harder to stop. When done, you may be pleasantly surprised that the brakes work much better with less effort than before.

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For peak braking action very much so yes!

 

The '78 620 was the first year front disc brakes were used, eliminating any need for adjustment.

Self adjusting rear brakes were introduced in Dec. '81 or about half way through the '82 model year.

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If you have to pump to get a solid pedal, you are out of adjustment.

 

 

I'm with everyone above, brakes work better moving forward. Rolling backwards does not initially engage the leading brake shoes. And you have 4 wheel drums...nothing is engaging as you start to roll backwards.

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Back brakes work great when rolling backward, so if I were you, I'd focus my attention there.  Adjust, pump the pedal, adjust, pump the pedal, repeat until they're as tight as you dare drive on.  Also bleed the fluid until you get fresh coming out the rear ports.  The pedal will feel spongy if there's a lot of water and rust in the fluid.  

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They should work best moving the most common direction.... forward. If they work better moving backwards you have the leading and trailing shoes swapped.

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What new cars.... or '73 620??? 620 and all Datsuns have to be on correctly facing..

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What he means is the lining on the shoes is the same on both sides now, there is no shorter side, I have also noticed this.

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 Picked up some shoes at Canby on the cheap late Sunday when no one wanted to load and take them home. Put them on 2 years ago. They were the old stye. Not likely to need new ones for a while. The linings are both the same length, just 'clocked' differently on the shoe. They had LEADING SHOE on two of them

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Mike, its not that way anymore.  I just installed 2 different brand sets on  2 620s over the last few months.  

Rear brakes generally work better when backing up.  Its a quick trick I've used over the years to diagnose an issue with dragging rear brakes (rusted E-brake cable).  You feel it more in reverse.  

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They should work best moving the most common direction.... forward.

 

Every car I've ever owned, the brakes were like this.

Sometimes I forget to release the parking brake, and could back out of my driveway just fine, but when trying to move forward, arg !

Look, see that I was being a retard, release the parking brake, and be on my merry way.

 

Something to check, the adjuster assembly has to free float for everything to work.

I'm thinking the adjusters are frozen up due to little use. Might be something to look at.

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Maybe the stuck cable is why I find it that way?  Already binding so they grab first?  

 

I'm glad I'm not the only one who found the same length pad material applied to all 620 brake shoes.  Odd for sure.  And yes, I understand the concept of a "leading shoe" but is there ever a leading shoe?  The drum spins in a circle.  How does it know which shoe leads when hydraulic pressure moves both equally?   :angel:

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I think the 'leading shoe' is the one that the wheel cylinder pushes on first, then it pushes o the floating adjuster, that in turn pushes on the 'trailing shoe'

 

It's all BS though, drums just are a carry over from 18th century wagon brakes.

Even at their height of development, Nascar, with segmented shoes, and fins, and big cooling ducts, they were still only good for a couple of laps.

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Mike, its not that way anymore.  I just installed 2 different brand sets on  2 620s over the last few months.  

Rear brakes generally work better when backing up.  Its a quick trick I've used over the years to diagnose an issue with dragging rear brakes (rusted E-brake cable).  You feel it more in reverse.

 

No argument here, I just don't see why this has changed. Historically there is free servo action in the forward direction. When set right, the dominant (forward) direction gets an added boost in braking action over reverse. Simply put the shoe that applies braking in the same direction as the motion of the drum is the leading shoe. The shoe that operates towards the moving drum is the trailing shoe. The lining on the leading shoe should be farthest from the wheel cylinder and closest to the pivot point at the bottom. This point has the maximum leverage and servo action. 

 

OLD SHOES (front to right)

HwPtdex.jpg

 

NEW SHOES (front to right)

vIlVHvJ.jpg

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I guess I have been taking about rear brakes, I thought we all were talking about rear drum brakes, I don't have any front drum brakes on anything anymore.

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The pre '78s were all drum brake but the leading and trailing shoes still apply for rear only vehicles. It's like free assist when stopping. 

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Hydraulic pressure is equally applied to both shoes.  However, forward rotation wedges the shoes tighter to the drum.  When going backwards, the rotation tends to push the shoes away from the drum.  This effect is used on boat trailers with surge (drum) brakes that have a trailer brake master cylinder in the trailer coupler, so you can back the trailer even though reverse motion is applying the trailer brakes.  If a boat trailer has disk brakes, there has to be a solenoid to release hydraulic pressure back into the trailer master cylinder to back a disk brake boat trailer.

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I store boats.  I cannot back up a boat/trailer with my tractor's 3-point using surge trailer brakes.  Period.  Unless I lock them out by preventing the tongue from applying them. 

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