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Backdoorz
New User
Sep 9, 2014, 8:36 PM
Post #1 of 3
(4177 views)
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No brakes on 280Z
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Car is a 1976 Datsun 280z coupe, 2.8 liter engine, with automatic transmission. I am the original owner. Been having brake issues off and on for about 2 years now. I will not go into all the details, but started out with wheel cylinder problems on the rear drums.
My current problem is no brakes. Pedal goes to the floor. The times that I have tested the car in the neighborhood, the brakes will stop the car, but are bottomed out leaving me no reserve at all.
The following have been replaced or repaired in the past 2 years:
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Both rear wheel cylinders. (These are not leaking.) -
Both front calipers and pads. (These are not leaking and the bleeders are positioned to the top.) -
Master Vac (The check valve is operating correctly and reaction disk is properly installed. The internal adjustable plunger has been adjusted correctly for the master cylinder. It holds a good vacuum.) -
Master Cylinder (I am on the third one. All were properly bench bled. Thought this was the problem, that’s the reason for three.) -
Proportioning valve has been cleaned. -
Brake warning light switch has been cleaned. -
Rear drum brakes are new and have been adjusted correctly. -
Replaced rubber brake lines with stainless steel braided lines. -
Vacuum is ~ 15 inches Hg
I have bled the brakes many, many times using several methods. A vacuum pump, a Motive Products Brake Power Bleeder, and the good ‘ol way, with my wife inside the car working the brake pedal.
There are NO leaks anywhere in the brake system. When I bleed the brakes, I see NO bubbles at all and I bleed almost a pint of brake fluid through to each wheel. No brake lines are crimped.
I took the front and rear brake lines coming from the bottom of the master cylinder out and inserted two plugs. This was to determine if my master cylinder was bad. I had both reservoirs full of brake fluid. I started up the car and pressed on the brake pedal and the pedal moved just about a 1/2 inch. The pedal held firm and did not leak down. I re-installed the brake lines and started the car and the brake pedal went to the floor.
Any suggestions, thoughts, or ideas will be greatly appreciated.
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Hammer Time
Ultimate Carjunky
/ Moderator
Sep 10, 2014, 1:57 AM
Post #2 of 3
(4161 views)
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Re: No brakes on 280Z
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You're probably going to need a professional to examine and troubleshoot this. They have techniques for isolating various areas of the system to find out where the weakness is. You could have incorrect parts, defective parts or other failure yet to be determined.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 10, 2014, 3:01 AM
Post #3 of 3
(4156 views)
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Re: No brakes on 280Z
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I think you've ruled out a series of defective master cylinders but the plug test. The dominant reason for lousy brake feel or excessive travel before they apply is the REAR brakes and all adjustments there. Shoes must be correctly adjusted to the drum THEN the parking brake if drums and shoes are within spec limits can be adjusted otherwise old as it is you should never have to.
Assorted bleeding methods if you don't do it right you can suck air back in if any hydraulic item is open with pedal pressure as in for bleeding and released before a line or bleeder is tightened and sealed just sucks back more air. Even that plug test at master lines were off for a while so air again. For that you either push a caliper piston back to push air from front back to master AND if possible squeeze a wheel cylinder to push fluid back and the bubble for rear circuit. May or may not work and back to getting air out all over again.
Simple but not is rear brakes need the adjustment just right with correct in spec shoes and drums - many not depending on what's new or part worn and machined the shoes will flex and have a soft pedal for ages if they could wear into their own but should never have to.
In short - rear brakes and all adjustments known perfect or all bets off for pedal feel even with air out.
These should plain gravity bleed if all is in excellent shape IMO,
T
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