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  #1 (permalink)  
Old 12-09-2012, 10:46 AM
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Gotta love a turbo!
 

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Cannot get a pedal...

Frustrating!

I had a brake system in my Maverick for several years that functioned poorly, but had a good hard pedal. This manual brake system consisted of GM Metric front calipers (2.38" bore) on 11" rotors, factory Ford Racing 11" rear drums, and a Granada 15/16" master. I decided to replace the front calipers with Wilwood big-bore (2.75" bore) stock replacements. After bleeding, the pedal would go to the floor, but pumping it a few times it would stay off the floor. I figured the master was running out of fluid with the larger front pistons. Tried a 1" bore Corvette C3 master but it was too wide and hit the valve cover. Now I've got a Ford F-100 master with a 1" bore and still cannot get a pedal. I did notice that the Wilwood calipers do NOT have the bleeder screws at the high point, so I removed them and stuck a 1" hardwood block between the pads so I could bleed them with the bleeder screw straight up.

Things I'm seeing that don't jibe:
  • Seemed to take forever to bench bleed with line loops, finally got it air-free after 50 plus strokes.
  • If I reach through the window and slowly depress the pedal with a broomstick, fluid flows up and out of the forward chamber of the reservoir (rear brakes), the other chamber does not do this.
  • When I pressure bleed, even with 30# on top of the reservoir, I can still rotate the rear wheels by hand as if the rear brakes are not working at all.
  • When I "suck" on a bleeder screw with my My-T-Vac, it looks like bubbles are coming out, but if I use my pressure bleeder (or a foot), solid fluid stream and no bubbles?

I have no idea where to go from here, I plan on calling Wilwood Monday to see what they say. If I could find a helper, I would use dial calipers to check for caliper deflection. Defective master? Wouldn't know where to start as far as pressure gauging parts of the system. Anyone ever done this?

Russ

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Old 12-09-2012, 10:31 PM
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TAKE A KID TO A CAR SHOW
 

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Sounds like the proportioning valve is out of center you need to reset it if it has! That could be part of the problem.

Jester
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Old 12-10-2012, 04:50 AM
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Is it a new master? If used, did U rebuild? Could be problem w/ master or prop. valve.
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Old 12-10-2012, 07:35 AM
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brakes

i'm thinking the bubbles are coming from the threads of the bleeder when loosened.. second i'm going with your m/c is too big (15/16). i have the same fronts as u and a 8" drums in back. my m/c is 3/4 and it'll stop on a dime... another thing is making sure your brake peddle is at least 7" from pivot point to center of pad where your foot goes.
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Old 12-10-2012, 08:57 AM
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Gotta love a turbo!
 

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No prop valve, took that out earlier. Just have banjo bolt fittings to resid valve(s), then direct to brake lines (tee in front system). The master is a "new" Cardone unit as opposed to their rebuilt offering.

According to my Excel brake calculation sheet, the stock 2.38" bore calipers with the 15/16" master at full 1 1/8" stroke, would move the caliper pistons 0.087" per side. Subbing the larger 2.75" bore calipers reduces their piston stroke to 0.065", a 25% reduction in total movement. Hence the pedal hitting the floor, as the master can no longer supply enough fluid at full stroke to sufficiently engage the pads to the rotors.

Now subbing the 1" master into the equation increases the large-bore caliper stroke to 0.074". Not back where it was originally, but now a 15% reduction in movement instead of 25%. Either the master is still unable to supply enough fluid or there is caliper deflection. I'll call Wilwood and get their input later. Hate to say it, but after all this d!cking around will prolly end up back at square one. Nice pedal and poor stopping.

And still no idea why the rear brakes appear to be a total fail... Surely with 30 PSI on the master cylinder reservoir, the rears should be showing some signs of engagement ? ? ?





Russ
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Old 12-10-2012, 10:40 AM
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Gotta love a turbo!
 

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OK, just got off the phone with a Wilwood tech. He said the 15/16" master might have been marginal, but the current 1" bore should be plenty. He's sure there's still air in the system and recommended the 2-person bleed method so I'll have to wait 'til the weekend for my son to return from vacation before trying that.

He was as puzzled as I about the fluid back-flowing up out of the reservoir's base port. His thought was the piston seal is defective, causing the fluid to push past it and bypass back into the chamber. Which would explain the lack of rear braking.

Any volunteers with an older setup (pre step-bore) willing to pull their reservoir cover and observe what their fluid does when the pedal is (lightly!) pushed?

Russ
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Old 12-19-2012, 10:04 AM
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Gotta love a turbo!
 

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I'm through!

What a fiasco, dropped $250 on parts and now they're all back on my shelf collecting dust. After doing a 2-man bleed on the 1" master, still no pedal. I gave up and went back to my original 2.38" calipers, but after swapping the first one, decided to bleed and see what the pedal looked like. With one of each, I now had a solid pedal, but close to the floor. After swapping both, I again have a nice pedal. I haven't driven it yet, but I'm pretty sure the brakes will s&ck even worse than before with the smaller-bore master. I've e-mailed Wilwood and informed them that these calipers will NOT work with a 1" bore master and they should inform customers of this before they drop the cash and go through the trouble.

Hope this saves someone some grief and cash,

Russ
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Old 12-24-2012, 04:37 PM
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Gotta love a turbo!
 

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Fixed!

See here, got 'er up and driving!

Russ
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