Trying to figure out brake problem with rear disc upgrade

[Hydratech®]

If all else fails, you may have to get into port plug diagnostics. Even though this article is written for hydroboost applications, the basics still apply to a manual or vac assist brake package: http://hydratechbraking.com/Hydratech/braketech1.html

For instance, you could plug the ports at the rear axle flex hose, obtain a good pedal, THEN connect one rear caliper at a time, bleed it out and see what you've got. Since this axle was handled / transported, it strikes me that you may even be fighting an ever so slightly tweaked caliper mount bracket (that could've been thumped while wrestling the axle around).

[CreepinDeth]

Well it wasn't the master!!!!

So instead of taking the Repro Vette master off and plugging it and checking to see if it was bled properly,
I decided to just ASSUME it was bad, paint the new Raybestos one, plug it, bleed it, install it.

Then for the hell of it I threw the repro MC on the Vice and plugged it.
Bench bled it , plugged, with the screwdriver and ZERO bubbles came out and it locked up before 1/8".
I tried 15x and it's definitely bled properly. So now I really have no idea WTF it could be if it wasn't the master.

Tobin, you're saying air in the system, but I really bled the crap out of it several times. It's aggravating the ****
out of me. I'm wondering if I really do need a smaller bore MC but then other guys are running rear discs too with
this MC but it's possible the pistons are different. I"ve got power brakes, I thought it would be cake......nope!!!

Originally Posted by Hydratech

Since this axle was handled / transported, it strikes me that you may even be fighting an ever so slightly tweaked caliper mount bracket (that could've been thumped while wrestling the axle around).

IF that was a factor in the hydraulic system, I'd see some fluid leaking somewhere for the mushy pedal though no ??

I don't see any fluid leaking.

[Hydratech®]

Great! Now you can definitely rule out the MC as the culprit, and can continue moving your diagnostics further downstream in the brake system.

FYI - A bent caliper support bracket would be not readily visible to the untrained eye, and could cause the caliper to deflect crooked / cocked ever so slightly off plane in relation to the brake rotor. Then when you try to apply pressure to the caliper, you are "wasting" all of the fluid volume going to the caliper while the caliper straightens itself out by trying to clamp straight on the rotor. Take a close look at the calipers, pads, rotors to see if you spot anything ever so slightly "off" angle. Take a bright light and see if there is any air gap at say the front of the pads, yet no air gap at the rear of the pads (or on any other plane in relation to the rotor).

One glaring question - are the bleeder screws at the tops of the calipers? I just can't tell you how many times I have seen the calipers installed backwards (left caliper swapped with the right caliper, finding bleeder screws at the bottom instead of the top. You could run a tanker truck of fluid through the brake system and never get the air out if this is by chance the case.

Humor me - run up to the auto parts store and get some 3/16 brake line plugs in the brass section, then plug the rear axle flex hose where the steel brake lines go out to the calipers. Fill the MC up with fluid, leave the two ports open on the end of the brake flex hose, then wait for the fluid to start dripping steadily out of the ports on the rear axle brake flex hose (gravity bleeding discussed in our online article that I put a link up to in my previous post). Once the fluid is dripping steadily, then go ahead and pop the brake line port plugs into the flex hose and snug them up. If you then find a solid brake pedal, you have ruled out everything else in the vehicle's brake system except for the rear disc brakes (where this whole problem started). You could then connect one rear caliper at a time to the rear axle flex hose and bleed it out and see what happens. If everything goes bad again with say the driver's caliper hooked up (or vice a versa), then you can focus your attention to the specific area and then likely nail the problem.

Pneumatic testing: While potentially very messy and 'dangerous' to painted surfaces, you could also take a rubber tipped blow gun and actuate the brakes by hitting the brake lines (at the MC) with compressed air (use a large towel to catch any possible brake fluid). I know we are trying to rid the brake system of air, but push come to shove sometimes you do what you gotta do to figure out what in the heck is going on. With the compressed air, you can watch the brakes engage and release when you hit them with pressure, and might just spot something.

[CreepinDeth]

Originally Posted by Hydratech

One glaring question - are the bleeder screws at the tops of the calipers? I just can't tell you how many times I have seen the calipers installed backwards (left caliper swapped with the right caliper, finding bleeder screws at the bottom instead of the top. You could run a tanker truck of fluid through the brake system and never get the air out if this is by chance the case.

Are you serious ??
That's how these are......the bleeder screw is at the BOTTOM of each caliper on both sides.
This is the passenger side caliper, and right is front. The bleeder screw is at the very bottom.
My front stock disc brakes bleeder screws are at the very top.

Another member took this whole rear end off his 70 something Chevelle and it was functional.
So I'm baffled as to why that would all the sudden create problems......but not doubting it.

[CreepinDeth]

YOu know what ??? You're right!!!! EVERY SINGLE PIC I FIND......is the other way around.

http://www.mustangmonthly.com/howto/.../photo_23.html
http://www.mustangmonthly.com/techar.../photo_20.html


I have to go look up install instructions now to see how the hell that happened , and if I can switch them with minimal issues.
THANKS!!!!! I would have thought the Vacula would have sucked out the air though.....but I guess not.....worth a shot I guess.

http://www.buybrakes.com/store/BAER-4302002

[Hydratech®]

I suggest you swap the calipers and live happily ever after with the bleeders up top where they are supposed to be.

What the previous owner may have done to get it to work this way: While absolutely most certainly not the right way to do it, you *could* yank the calipers loose while leaving the brake lines connected, put a some appropriately sized hardwood inside of the pads to take the place of the rotors, orient the bleeder screws up top, and then bleed the air out the brake system. Once bled, you could then re-install the calipers and take the vehicle out for a test drive. If you feel that all is well at that point, then you could swap out the calipers right / left at any point, though I do suggest you get it done right now...

[CreepinDeth]

I got my work cut out for me today. I'm kinda a brake newb still....

I'm swapping them. Thanks again guys!!!! Muchos Grassy Ass