Snailed Posted May 19, 2013 Share Posted May 19, 2013 You probably need to reset the brake safety switch. If you only have line pressure on the rears, or only on the fronts, then you've probably tripped it and it's locked off one side or the other. My guess is this^ (didn't know Datsuns have these) or the rear shoes could be contaminated with grease, oil or brake fluid. Even if you "clean" them with brake clean they can still be extremely grabby and the self energizing nature of drums makes locking the rears very easy. Try new shoes if they were are any time wet with any fluid. Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 Theres only the issue of the rears working and not the front is one the first pedel press. If I were to basically pump it once and then apply the brakes it will work just fine. Front brakes and all. Its just the first press of the pedel that the front doesn't grab. New MC new New calipers New wheel cylinders About 2 gallons of new DOT 3 fluid has been pushed through. Ive bled the system about 15 times now with the same issues. I dont know what the HELL the problem is. Please help! Quote Link to comment Share on other sites More sharing options...
Domzs Posted May 22, 2013 Share Posted May 22, 2013 (edited) Did you do any adjustment to the shoes ? If so , may be too tight . Post some pic of your brakes . Edited May 22, 2013 by Domzs Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 22, 2013 Share Posted May 22, 2013 The pistons in the calipers are supposed to stay essentially where they end up after the last time the pedal was pushed. The dust seal draws them back a hair so that they don't rub the disc. As I understand things. If I was in your predicamnet I would try to get a good look at the pistons while applying the pedal and see what they do. You might have a retainer or some odd thing acting as a spring and pushing or pulling the pads back, pushing the pistons in to the bore. If there's no air on the inside then the problem must be external. Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 I did adjust the drums a few times now. Made it tight, made it loose. I have it now to where it spins freely without the shoes touching hardly at all with no pedal pressure. I'm about to plug the rear brake lines and see what happens. I'm at a loss. Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 Could it be my booster? There is a hiss sound that I hear near the MC/BOOSTER when I have a friend pump the brakes. Guess I just thought it to be the fluid surging. Quote Link to comment Share on other sites More sharing options...
RebekahsZ Posted May 22, 2013 Share Posted May 22, 2013 I had a brand new tilton that was unreliable. Called tech support and they said to put a plug in it to test it so your idea is a good one. You may actually wind up pluging all four wheels. You might be right about the booster since it takes less power to lock the rear wheels due to weight transfer. Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 Well I'm going to stop at Nissan and see what they have to say. The manager there is a big Z and 510 fan. Quote Link to comment Share on other sites More sharing options...
johnc Posted May 22, 2013 Share Posted May 22, 2013 Sounds like the you have the brake lines reversed on the MC. Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 The got at Nissan said it's the brake proportioning valve. Hes worked there for 35 years and races a 510. Now I know someone mentioned a brake safety switch. How do you reset that? Other options? Quote Link to comment Share on other sites More sharing options...
Leon Posted May 22, 2013 Share Posted May 22, 2013 Sounds like the you have the brake lines reversed on the MC. Seconded for emphasis. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 22, 2013 Share Posted May 22, 2013 Just to add a little more as to "why" that would cause this. Are you guys saying that he's bottoming out the MC piston because the MC cylinder portion designed for the low volume rears is working on the high volume fronts? It would be odd to get the lines switched if he's using a stock MC. 77 isn't in the middle of a design switch period. He could still eye-ball the line from the big reservoir down to the front calipers. Pretty easy to confirm. Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 The issue occurred after I removed the calipers and changed out the wheel cylinders. I never touched the MC. I checked just now to be sure though. They're good. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 22, 2013 Share Posted May 22, 2013 (edited) Maybe you're just ignoring my suggestions (maybe I should use more emoticons), but have you watched the pistons and calipers for "springing"? If the MC pistons are doing their jobs and applying hydraulic pressure through the metal brake lines, and have enough stroke, then the fact that you have to pump the pedal means that something is elastic in the system, resetting the starting point when you release the brake pedal. Basically, every time you use the brakes they are out of adjustment, and you have to refill the lines to get the pads to make contact. If there is no air (which would give a compressible bubble), then it has to be mechanical. I fought my front brakes for quite while until I realized the bleeders were on the bottom. I have a little empathy... Edit - Just remembered also that if the brake warning switch is working correctly, your brake warning light will light up if there's a pressure imbalance front-to-back. That might be the switch that Xnke referred to, although it's only an indicator and should reset automatically when the pressure imbalance is fixed. Unless it's clogged or leaking (it has rubber seals inside and could leak internally I believe). It's the one with the wire coming out of the top, below and forward of the MC, bolted to the frame rail. Edited May 22, 2013 by NewZed Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 Trust me brother I'm not ignoring any suggestions at this point. I will remove the front wheels and check out the actions of the caliper compressing. I understand what your saying and it makes sense. I'll take a video and see about sending it to you or posting it on YouTube for you and others to take a stab at it. Haha. I did just now plug both rear lines. Went on a test drive and still the same issue. Just trying to eliminate piece by piece. Just not understanding how anything changed other than the damn fluid. I appreciate all of guys support. Just trying to update you guys after every step I take. Quote Link to comment Share on other sites More sharing options...
NewZed Posted May 22, 2013 Share Posted May 22, 2013 It could be something as simple as a bent anti-squeal shim, acting as a flat spring, or a pad hanging up on its mounting pin. Maybe even silicone or adhesive between the pad and piston. Still seems like an air bubble is more likely though, due to the volume. Good luck. Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 Will report back soon. Appreciate your help NewZed! Quote Link to comment Share on other sites More sharing options...
Snailed Posted May 22, 2013 Share Posted May 22, 2013 I didn't realize it was only on the fist application... It could be something as simple as a bent anti-squeal shim, acting as a flat spring, or a pad hanging up on its mounting pin. Maybe even silicone or adhesive between the pad and piston. Still seems like an air bubble is more likely though, due to the volume. Good luck. Anything that can push or pull the pistons back in the front calipers is suspect...warped rotors, calipers not square to the rotor, the mentioned shims, dust boots etc. Does anyone know if the OE prop valve has residual valve(s) in it? Generally you wouldn't have a residual valve in the front unless the master was lower than the calipers, but I really don't know any specifics on the 70's datsun stuff (mine has been at the metal recyclers for a while now) Quote Link to comment Share on other sites More sharing options...
Snailed Posted May 22, 2013 Share Posted May 22, 2013 More ideas. If the wheel bearings are too loose the rotor will push the pistons back in when the wheel/rotor rocks. If the seals in the calipers are in backwards I have heard this can let the piston retract, but I don't know this 1st hand. Quote Link to comment Share on other sites More sharing options...
RangerWill Posted May 22, 2013 Author Share Posted May 22, 2013 Got the wheels of and spun the rotors by hand. They were so mid turned they were rocking the pistons back into the caliper. The tech at the auto skills center used a machine that allows you to turn the rotors while they're on the car. The machine was wobbly as hell. I asked him multiple times if it would do a good turn with it wobbling like that and he was so so damn sure it was fine. Well they are fixing the F up now on a actual turning machine. I raised hell about it. Had to go Drill Sergeant mode. Haha. But, left the hat at the house. So hopefully this fixes it. Thanks again NewZed. I'll let yall know the outcome once mounted and a test run. Quote Link to comment Share on other sites More sharing options...
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