Learning how to build Lotus Seven replicas...together!
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PostPosted: Fri Aug 22, 2014 5:39 pm 

Joined: Tue Feb 12, 2008 2:08 am
Posts: 252
Location: Olympia WA
I have a completely stock me on a break system, with the addition of half pound residual valves for the both front and rear brake lines. At this point, The reservoir is below the calipers. (I have had remote reservoirs, yet they seemed to leak a lot. ) My challenge is, both front and rear pads hang up a bit at the end of an autocross run.

If I take the residual valves out, how long will it take for the brake fluid to bleed back? I am thinking that I'll just get in the car pump the brakes once or twice the pressure would be back in little be just like normal.

Do you run residual valves in your car?
Thanks for your time _ JEB

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PostPosted: Fri Aug 22, 2014 6:49 pm 
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Joined: Thu Jan 10, 2008 4:47 pm
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Location: Massachusetts
I don't think you need those valves. The fluid won't bleed back unless you have leaks in your calipers.

Atmospheric pressure should keep the fluid up for at least 30 feet. I don't know how good the seals are supposed to be though.

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PostPosted: Fri Aug 22, 2014 9:46 pm 
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Joined: Mon Apr 12, 2010 5:40 pm
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Location: san francisco bay area
First off, I'm a lot more forgiving of residual pressure valves than I used to be.
That 37 Olds I worked on with a manual single master driving a boosted single master driving 4w drum brakes did it to me. :ack: :BH:
Effectively the only thing that a residual pressure valve does in a disc system is eliminate any "take up" before the brakes begin to function but you know that, siphon drawdown is one problem but you know all about that too based on your post. ..
If you have a slightly out of true rotor (very common, especially on vehicles driven "spiritedly") and no valve it will knock each side back separately resulting in a wider gap, with a valve in place it will push fluid back and forth between the pistons (or back and forth on the sliders for a single piston) only releasing the pressure above 1/2 psi back to the master.
Hot or cold it shouldn't make a difference on pressure settings.
I'm having a hard time blaming the residual valve for dragging when the brakes are heated unless it's in a location that gets the valve itself hot. .. I suppose it could be because of the friction material itself getting more ornery when it's hot?
Still, 1/2 psi ain't very much applied pressure. ..
I'm interested in how much free play you have in the pedal when the system is heated up compared to when it's cold.

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