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Very little rear brake action


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Ok so i kinda know the answer to my question but just looking for confirmation.


So i have KA24de-t 210 with 240 sx rear brakes. My rear brakes hardly work master is a 240 260 maybe 280 not sure, It isa 7/8 bore with no booster I know im not getting enough line pressure at the rear. Is there a 10lb residule valve in the 7/8 master cylinders and does it actually restrict pressure or does it just hold 10ish pounds on the rear drums?

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Maybe for Willwoods, but for stock system....


Just get the 2-3 pound residual valve from any Datsun front disc brake car and put into the rear system of the master. The 2 pound residual valves keep the disc pads gently against the rotor surface to keep them clean. Ten pound is way too much and may heat them up or cause too much drag.




The residual valve has no effect on brake application. So how do you know the rear brakes are not working very well? What are you going by?

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Going by feel with the car in gear up on jackstand's i can stand on the brakes and it will barley lug the engine down. Now i drove this car with the A motor and the 4 piston wilwoods up front and drums in the rear, and the car had exellent brakes. so this lead's me to believe there is a restricton either in the master or in the combinaton valve on the firewall. Which im not sure if there is any kinda valving in that or if it is just a splitter for the front and rear

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I am assuming like everyone else here that you now have rear disc brakes as I personally don't know what 240SX rear brakes are(disc or drum), but lets just say they are disc brakes, when you bled the master did you bleed the rear brakes/circuit or front brakes/circuit first?

I have always been told to bleed from the farthest away from the master to the closest(bleed rear circuit first). so if you bled the fronts first, it almost makes it impossible on some vehicles to bleed the rear brakes/circuit.

You may have never touched the front circuit, so the fronts have worked the whole time, and this may be the problem, are you positive the air is out of the rear brake lines?

What I would do is go get a clear piece of small tubing/line that fits over the front bleeder valve on either side, put brake fluid in a cup, put the line coming from the front bleeder valve in the cup of brake fluid and open the bleeder, now while keeping an eye on both master brake reservoirs to make sure neither get empty, bleed the rear brakes again, you will have to keep putting the brake fluid in the cup back into the front circuit making sure that clear line never gets air in it, once all the air is out of the rear circuit, close the front bleeder and you should be good to go as long as no air got in the front circuit, if air did get in the front circuit, then you will need to bleed the front brakes.


I hope this makes sense.

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Going by feel with the car in gear up on jackstand's i can stand on the brakes and it will barley lug the engine down. Now i drove this car with the A motor and the 4 piston wilwoods up front and drums in the rear, and the car had exellent brakes. so this lead's me to believe there is a restricton either in the master or in the combinaton valve on the firewall. Which im not sure if there is any kinda valving in that or if it is just a splitter for the front and rear


Was the booster installed????


The booster can increase the line pressure up to 50% with the same foot pressure. Years ago I put a Z24 in my 620 and I guess a spider spent the winter in the one way valve on the vacuum line. I thought the rotors were rusty or something. I had to step on the ROCK HARD pedal so hard my ass came off the seat. Put a new one in and back to normal. Boosters make a remarkable difference is braking effort.

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The calipers work on pressure. A larger master will move more fluid but will be harder to push down on, so you end up maxed out on effort (pedal is rock hard and your leg is trembling with the effort) before you get enough pressure built up. A smaller master will be easier to push down on but will travel farther to move enough fluid and feel mushy.   

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It is a one way valve for the most part, but they do leak down when not used for a while.

If you have a drum brake residual valve on your rear disc brake vehicle, and the rear brakes are not working very good, then the brake master you have is not set up for rear disc brakes, and the front circuit is doing all the work.

The brake master has 2 circuits, the front moves a certain amount of fluid when the brake pedal is moved, the rear circuit moves a certain amount of fluid also, well it sounds like your rear circuit doesn't move enough fluid compared to the front circuit, and there is nothing you can do to fix it unless you either buy a disc/disc brake master(240SX?), or maybe a purportioning valve will fix it, but when I thing of a purportioning valve I think that the rear brakes are always skidding(working too good), and less fluid needs to be going to the rear, so I don't know if one of them will work in your situation.

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If you are sure the rear discs are ok and positive the master and the lines have no air in them.....


Your master needs a booster, if you go to a larger 240sx master you will need a booster even more. You need a booster. I see that you can't.... so the only way to increase line pressure with the same foot effort is to go with a smaller diameter master like a 3/4 or 11/16.


IF you have a proportioning valve in your B-210 that sets the front /rear bias you can remove it. This will send full available brake pressure to the rears but, like wayno says, you may have early rear lock up on sudden stops. The cure is to add a Willwood adjustable proportioning valve. With this you can decrease the pressure to the rears to match the front braking action. I did this on my 620 with 16" of lift. there was too much weight transfer to the front when braking, lifting the weight off the rears and allowing them to lock up.

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So can you remove a residule valve from the master cylinder? Im asking because i dont want to ruin a perfectly good mastercylinder i do have a stock 13/16 master i could possibly pull apart. But it worked perfectley good also lol


You can remove the residual valve, but I don't see that making a difference, all it does is keep the springs from pulling the rear shoes back to the seated position right away, that keeps the pedal up at the top so one doesn't have to pump the brakes if the rear shoes are out of adjustment.

I had to pull the residual valve out of my stock 521 brake master when I converted over to front disc brakes, as the 10lb residual valve was too much for the front disc's, they would get hot and could have possibly started a fire if my engine had enough power to keep the vehicle moving, my 521 diesel kingcab sheared the driveline bolts, as it had the power to do so, the truck came to a skidding stop when the drive line let loose, I removed the residual valve and all was good, but my brakes were locking up because of the residual valve.

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I dunno why that double posted. This master is the same one troy ermish uses in his kits 7/8 shouldnt need a booster to have brakes i had a 15/16 master in my old 510 it wasnt hard to push either really. Im gonna tear apart the 210 master and look at the residule valving in it

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In the past I have thought about this issue you are having, as I am having the same issue with my work truck, but my 521 work truck has a stock single circuit brake master system, the rear drum brakes barely work, but I can get the truck to stop fine, so I have not tried converting over to a dual circuit brake system.

But I always wondered if I could use a purportioning valve on the front brake lines to divert more braking power towards the rear brakes, but I have never tried it so far.

The other thing I always wondered about was if one reversed the lines, meaning if the rear brakes don't work good, but the fronts do work good, could one use the rear circuit for the front, and the front circuit for the rear to make the rear brakes work better on a dual circuit brake system, now I am not saying this is how one fixes anything, but I always wondered if it would make the rear brakes work better without making the front brakes fail to work properly.

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  • 2 weeks later...

If you have a 1 square inch surface and apply 100 pounds you will have 100 PSI. If the surface is increased to 2 square inches and 100 pounds applied the result is 50 PSI. Same effort in, but only 1/2 the pressure out. If the surface is reduced to 1/2 square inch and 100 pounds applied you get 200 PSI out.


You can't get something for nothing. Conservation of energy. A larger master will move more fluid but it isn't free. You have to increase your input pressure.

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