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Very little rear brake action


jesusno2

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I also am wondering if since the 210 was a power brake car, if that combination valve restricts the pressure to the rear wheels with the drum brakes. They say that its only take something like 400 psi to lock up a drum brake. Where a disc setup you need alot more pressure.

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Power assist is just that, it only makes braking effort easier. Generally about 50% increase in brake line pressure.

 

Proportioning valve? Front engine vehicles have more weight on the front tires and during braking weight shifts to the front also. More weight on the fronts means they have more traction and are much harder to lock up. Rears have less wight on them and even less as weight shifts forward during braking. The proportioning valve is there to provide front/rear bias or balance so that the front and rears brake evenly without one locking before the other. On some cars there isn't a proportioning valve. The rear wheel cylinders are simply designed smaller and and don't brake as hard as the fronts.

 

By removing your brake booster, you are also reducing your pressure available to the rears.

 

 

I wouldn't go by what "they say..." 

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So i pulled apart my nabco 7/8 master cylinder and removed the residule valves. Really makes me wonder how the brakes even work with these plungers in there.

2C8DE31F-61CF-41D9-97C3-BFA4B49CD0C8_zps

 

DC22F2E2-C35E-47E2-9C04-BB8C05B2DD17_zps

 

This particular master you remove the 17mm adapters then i used a small easy-out to pull the tapered seat out and the plungers are behind them and spring loaded so be carefull. Then reinstall the tapered seats and tighten the adapters back up. This will reseat the tapered seats for the brakelines

 

As for my brakes i have't driven it yet cause im having megasquirt issues, BUT.. my brake pedal feels more normal now its not rock hard like it was. You can actually feel the the brakes working through the pedal. I will update this when i drive the car see if i have made any progress

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The residual valves allow pressure out of the master but the spring holds back about 8PSI for drums and maybe 2-4 PSI for disc brakes when you let off the brakes. They have zero effect ON braking. The residual pressure on disc brakes keeps the pads gently against the rotors to keep them clean. It's so slight you can turn your front wheels with your finger.

 

The NP or proportioning valve biases front and rear pressures so that both should lock simultaneously. You have altered your braking system with modifications. It's hardly likely the NP valve will be doing it's job as it is designed for drum brakes. Get a Willwood adjustable proportioning valve and adjust so that on hard stops the rears lock at about the same time as the fronts. Do this on dry pavement.

 

Note. Adjustable proportioning valves are illegal on the street. Mount it in the engine bay so that you will not be tempted to fiddle with your settings.

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A proportioning valve will do me no good i'm trying to get more brake pressure not less. I barley had brakes period locking up was not even a possibility. as far as the RPV's i dunno how they figure one is 10lbs and one is supposed to be 2lbs etc this is a 240z 260z master cylinder (rear drum brakes) those valves look Identical to me i even measured them with calipers to try and understand how they work. unless mine were upside down or something?? strange things have happened.

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It's the spring in the residual valve that decides how much pressure is held in the brake lines, stronger spring, more pressure.

I do believe that residual valves were made for the people that don't keep their drum brakes adjusted like they are supposed to, if drum brakes are out of adjustment, the residual valve holds the shoes against the drums for a while so one doesn't have to pump the brakes to get the pedal to the top like brakes that are properly adjusted would be.

The springs holding the shoes on pull the shoes back to the settled position without a residual valve right away.

You don't have to have a residual valve, my work truck doesn't have one, I took it out when I went to front disc brakes as I kept the stock master, and it would have smoked my front brakes if I could keep the vehicle moving in the first place, I turned the drive line out of the 521 4X4 because the front brakes seized before I got home on the first test drive.

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A proportioning valve will do me no good i'm trying to get more brake pressure not less. I barley had brakes period locking up was not even a possibility. as far as the RPV's i dunno how they figure one is 10lbs and one is supposed to be 2lbs etc this is a 240z 260z master cylinder (rear drum brakes) those valves look Identical to me i even measured them with calipers to try and understand how they work. unless mine were upside down or something?? strange things have happened.

 

The point, is the the one you have, may not be letting enough through.

 

Removing it and letting all the rear pressure through may result in the rears locking before the fronts resulting in the severe oversteer or the rear end coming around on you when hard stopping.

 

An adjustable proportioning valve will let in enough to work the brakes but adjusted so they do not lock up too soon.

 

 

(now all this assumes the master is working properly)

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Yes assuming this setup is working now if not that combination valve whatever its called is restricting pressure. Then at that point a adjustable proportioning valve may be needed. Maybe i had air in the mastercylinder before, I dunno the pedal was like concrete though.

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It will be stiffer with the brake booster removed. My 620 had a vacuum loss to the booster. Pulled out of the driveway and had to push so hardtop get stopped that my ass came up off the seat. One way valve was crap, fixed and braking as usual.

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Yea i inderstand the difference im comparing the pedal to my old 510 with manual brakes i had a 15/16 master on it and the pedal felt fine on it had kinda the opposite calipers then my 210 has. The 510 had wilwood 2 piston calipers on the rear and 280zx calipers in the front. My 210 now has manual brakes 7/8 master 4 piston wilwoods up front and 240 sx calipers in the rear. So im kinda comparing the 2

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