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620 brake struggle


ErickwithnoK

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Not to hijack a tread.....Rear seals on both my slave cylinders started leaking which of course toasted the brake pads. Both sides upper springs were broken! (Don't know if I did that removing the drums) Started looking for a new rear spring set...no joy  Finally found a set at NAPA, has to be shipped from CA.

Parts are getting harder and harder to find!

 

Happy New Year everyone!

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Not to hijack a tread.....Rear seals on both my slave cylinders started leaking which of course toasted the brake pads. Both sides upper springs were broken! (Don't know if I did that removing the drums) Started looking for a new rear spring set...no joy  Finally found a set at NAPA, has to be shipped from CA.

Parts are getting harder and harder to find!

 

Happy New Year everyone!

 

Good luck with that, makes me glad my problem was as small as it was. I spent a total of $8 on brake fluid and a clear vinyl bleeder tube...

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Not to hijack a tread.....Rear seals on both my slave cylinders started leaking which of course toasted the brake pads. Both sides upper springs were broken! (Don't know if I did that removing the drums) Started looking for a new rear spring set...no joy  Finally found a set at NAPA, has to be shipped from CA.

Parts are getting harder and harder to find!

 

Happy New Year everyone!

Try installing a 2 lb residual valve. It will help keep the lip seals in place and eliminate the potential for leakage.

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The reason I mention it is because I rebuilt my entire brake system in my 320 and inside 5 years, they started leaking. After I installed a dual circuit master (with built in residual valve) the wheel cylinders stopped leaking. Turns out, it's a common problem with old drum brake systems and guys have been modding them with residual valves for years.

 

Yes, your 40 year old units are probably due for replacement.

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Actually, a residual pressure valve holds fluid in the lines, in the wheel cylinders rather than letting it back into the master.  This would promote more leaking, but less pedal-pumping to get the brake pedal feel "right" instead of sinking to the floor.  Unless your seals have dried out from non-use, I don't see how it would help prevent leaks.  Even then, a Wilwood 2 psi residual pressure valve will bleed down over time - a matter of months (winter storage).  In some trucks (think 2-ton) where you have multiple wheel cylinders at each wheel, the volume of fluid required to activate the brakes is greater than the volume of the master cylinder.  My '55 Chevy 6400 required 5 full pumps of the brake pedal to fill the 8 - 1 1/4" wheel cylinders, so a secondary residual pressure valve was required.  A functioning master cylinder in a Datsun should be fine on its own.  

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Yes, but no. It keeps the lip seals pushed out. The old lip seals on the wheel cylinders had no spring or anything and were just a rubber cup. Applying the brakes doesn't make them leak, it's when they sit without use.

 

Not only am I speaking from personal experience, I also had a lengthy conversation with a known brake specialist about this.

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I get it.  They need the fluid behind them to stay "hydrated."  

 

Friends bled my brakes in the race truck Thursday night, and the pedal feel was terrible.  Yesterday I readjusted the drum brakes and re-bled the rears with a vacuum bleeder and got a HUGE air pocket out of the rear line.  They may actually work now, as the pedal feels great!!!  Without any power booster, it'll be interesting to see how they feel.  

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