Toney Posted January 4, 2015 Report Share Posted January 4, 2015 Hey guys so long story short I've been having issues with the brakes locking up. I pulled the proportioning valve off and it was all gunked up and the piston inside is seized. Ive been soaking it in penetrating oil for a couple days now and still no movement. So I am looking for another one in working condition. Let me know if any of you have an extra one laying around! Thank you. Quote Link to comment
thisismatt Posted January 4, 2015 Report Share Posted January 4, 2015 The piece with the single wire off of it? That's not a proportioning valve, just a brake circuit failure sender. Which brakes are locking up? Fronts? If so, could be too little play in the brake master push rod, not allowing the piston to fully return, building up pressure. Quote Link to comment
yellowdatsun Posted January 5, 2015 Report Share Posted January 5, 2015 The 510 didn't come with a proportioning valve. On top of that, most brake setups don't need one. I'd bet that 3/4's of the guys out there that have one installed, don't need it. Good for the track when you're constantly driving at the limit, but that's about it. So if your car does have one that someone installed, there's a good chance you don't even need it. I pulled mine out after realizing it wasn't necessary, and I have a highly modified brake setup. 1 Quote Link to comment
datzenmike Posted January 5, 2015 Report Share Posted January 5, 2015 To bias the difference between front and rear braking, the engineers simply made the rear wheel cylinders larger or smaller to reduce rear lock up. Your car likely is lowered with firmer springs and struts on the front which would reduce weight shift when braking, plus gripper rear tires. Most 510s are this way now and could actually add some brake effort to the rears. Quote Link to comment
Toney Posted January 5, 2015 Author Report Share Posted January 5, 2015 Awesome that is good news! I've been really stumped over that I even called nissan and the guy had no idea what I was talking about. So with all that said how would I go about that considering that the piece had 2 inlet and 3 outlet. A T-adapter for the front and coupler for the rear? Thank you for the info Quote Link to comment
Toney Posted January 5, 2015 Author Report Share Posted January 5, 2015 Thanks! I will also mess with the pushrod Quote Link to comment
thisismatt Posted January 5, 2015 Report Share Posted January 5, 2015 Just get one that works. Easiest thing to do with that part. Quote Link to comment
datzenmike Posted January 5, 2015 Report Share Posted January 5, 2015 Thanks! I will also mess with the pushrod No need to mess with it. Push down on the brake pedal with your thumb. It should have a little play in it. About 1/16" of easy movement before the push rod meets any firm resistance in the master cylinder. If no play, then, you can then pull the cotter clip and the clevis pin and after loosening the lock nut turn the adjustment in to get the required play. Quote Link to comment
69datsun510 Posted January 10, 2015 Report Share Posted January 10, 2015 I heard of this problem happening if using the larger master cylinder for a 4 wheel disc set up, on the 280ZX front disc and drum rears. The larger master had some preload pressure to keep the disc pads in contact with the rotors. I'm sure its been talked about several times on the forum. The search function will get you lots of useful information when used. Quote Link to comment
datzenmike Posted January 10, 2015 Report Share Posted January 10, 2015 A residual valve. All Datsun masters have these. Drums (rear or front) use about a 7-12 pound residual valve to counteract the heavy return springs on the shoes. This reduces the travel and keeps the shoes closer to the drums. Disc brakes need only a couple of pounds to keep the pads lightly against the rotor to keep them clean. A drum residual valve on a disc brake will only heat them up and wear them out faster. A disc residual valve on a drum brake will be spongy. I have a 15/16" zx master on my 710. I fit the stock 710 rear drum residual valve in it because the zx was rear disc. Have a care to not mix them up. I could not see any difference between disc and drum proportioning springs. Don't mix them up. None of the above affects the brake pedal push rod adjustment. 1 Quote Link to comment
Toney Posted January 10, 2015 Author Report Share Posted January 10, 2015 Great info however I am still stumped on this problem. The only part I haven't replace on my 510 is the brake valve. I would like to replace it with another one. I found an aftermarket one at a local auto parts the outlets are different positions which is ok because i plan to replace the hardlines anyway while i am at it. And with the fact it is two inlets three outlets its not just a matter of using a flare nut coupler and getting rid of the whole thing. Also eventually upgrading to all wheel disc when i do the coilover upgrade Quote Link to comment
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