Best way to bleed brakes - Page 4 - Chevelle Tech
Brakes, Suspension & Steering Conversion questions & more.

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post #46 of 76 (permalink) Old Apr 28th, 19, 1:12 PM
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post #47 of 76 (permalink) Old May 22nd, 19, 10:27 AM Thread Starter
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Re: Best way to bleed brakes

Update...
I got a new master cylinder from Wilwood. The one I had was recalled.
I bench bled the new master cylinder and installed it in the car. Bled the brakes using ANOTHER large can of dot 4 fluid and I知 not getting any air. And no leaks.
I now have brakes but almost at the floor. Not safe. And the front brakes are dragging like crazy. I let off the gas and the car almost stops.
My question now is how far can I back the clevis off to drive the rod into the master cylinder? I don稚 want to start with the plunger so far in that I知 covering a port inside.
Again this is a full Wilwood system, 6 piston front, 4 piston rear, no booster, knob style bias valve. I do not have any residual valves anywhere at this time.
I知 also going to reach out to Wilwood tech.
Anyone?

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post #48 of 76 (permalink) Old May 22nd, 19, 10:50 AM
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Re: Best way to bleed brakes

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Originally Posted by 67_LS1 View Post
Update...
I got a new master cylinder from Wilwood. The one I had was recalled.
I bench bled the new master cylinder and installed it in the car. Bled the brakes using ANOTHER large can of dot 4 fluid and I知 not getting any air. And no leaks.
I now have brakes but almost at the floor. Not safe. And the front brakes are dragging like crazy. I let off the gas and the car almost stops.
My question now is how far can I back the clevis off to drive the rod into the master cylinder? I don稚 want to start with the plunger so far in that I知 covering a port inside.
Again this is a full Wilwood system, 6 piston front, 4 piston rear, no booster, knob style bias valve. I do not have any residual valves anywhere at this time.
I知 also going to reach out to Wilwood tech.
Anyone?
I'm going through this exact thing.

6 piston fronts, 4 piston rears.

Wilwood originally told me to use their 1" master cylinder. The pedal moves through like 80% of it's arc from rest to the floor then it "catches" and I have brakes. They said to go to their 1-1/8" master, I did with hardly any improvement. Expensive parts changing!

I love when product manufacturers tell me "nobody else has this problem".

I'm trying a 1-5/16" master cylinder from a 5.3 Express/Savana van. I don't have it yet and while I found metric to standard port adapters, I'm not yet sure about the mount to the booster. I'm sure I'll get it working.

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post #49 of 76 (permalink) Old May 22nd, 19, 11:13 AM Thread Starter
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Re: Best way to bleed brakes

I知 using the 7/8 bore because I am not using a booster, but it痴 interesting that your experiencing the same thing.
Maybe I知 missing something but I don't see how a larger bore would raise the pedal engagement point.

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post #50 of 76 (permalink) Old May 22nd, 19, 11:23 AM
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Re: Best way to bleed brakes

are you guys still using rubber brake lines to the calipers? If so maybe the rubber ones are expanding rather than moving the caliper pistons.

pedal "engagement" will be affected, but it's more because a smaller bore will take a longer stroke to reach the same brake pressure as a larger bore.

If you pump the brake pedal, do you get engagement higher in the stroke?

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post #51 of 76 (permalink) Old May 22nd, 19, 11:37 AM
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Re: Best way to bleed brakes

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Originally Posted by 67_LS1 View Post
I知 using the 7/8 bore because I am not using a booster, but it痴 interesting that your experiencing the same thing.
Maybe I知 missing something but I don't see how a larger bore would raise the pedal engagement point.
I believe it takes a lot of volume to get 20 pistons moving. A larger bore master moves more fluid with less stroke. I think every 1/8" in bore increase is about 20% more fluid displacement.

However, larger master cylinder bores require higher effort. You may need to add a brake booster. I'm using an electric vacuum pump and I have 25 inches of vacuum.

Quote:
Originally Posted by -SS454- View Post
are you guys still using rubber brake lines to the calipers? If so maybe the rubber ones are expanding rather than moving the caliper pistons.

pedal "engagement" will be affected, but it's more because a smaller bore will take a longer stroke to reach the same brake pressure as a larger bore.


If you pump the brake pedal, do you get engagement higher in the stroke?
When using Wilwood calipers, you pretty much have to use stainless braided brake hoses. I'm using hoses from Wilwood, their kits come with the needed fittings.

If you need to pump the pedal to get a higher or firmer pedal, there's probably air in the lines.

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post #52 of 76 (permalink) Old May 22nd, 19, 12:30 PM Thread Starter
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I am running the Wilwood stainless lines from the frame to each wheel, the only rubber line is from the frame to the rear axle.
Good question about pumping the brakes. I tried it and while they do come up a little it’s very little.

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post #53 of 76 (permalink) Old May 22nd, 19, 1:34 PM Thread Starter
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Re: Best way to bleed brakes

Paul Bell, are you running manual brakes? I was told by Wilwood to use the 7/8 bore for manual brakes because you get higher pressure faster. But the trade off is lower volume. Since we池e both running 6 pistons front/4 pistons rear (20 pistons total) I知 wondering if it痴 a volume thing. I do NOT want to add power brakes so I致e got to figure this out with what I致e got somehow.

Another thought is after I bench bled the master cylinder, I lost a lot of fluid from it during install. Because the pre-formed Lin痴 front eh master to the proportioning valve are so hard to install without losing fluid.

Does anyone know if I can used the unused and currently plugged ports on the opposite side of the master to re-bleed the master while it痴 still in the car? In other words bleed it with the lines still connected on the other side. I could just disconnect the clevis and punch the plunger in all the way by hand.

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post #54 of 76 (permalink) Old May 22nd, 19, 2:09 PM
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Re: Best way to bleed brakes

I would think number of pistons would not matter. The entire system should be 100% brake fluid, so the only thing that moves is the volume of fluid in the master cylinder. Big bore has more fluid to move, small bore has less. As soon as you put pressure on the brake pedal, the caliper pistons should be moving. How much is dependent on the MC bore.

Manual brakes should give you the most positive brake feel too.

Maybe get a second set of eyes to watch the calipers (with the wheels off) and see when they start to move in relation to how much the pedal is pushed down.

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post #55 of 76 (permalink) Old May 22nd, 19, 2:09 PM Thread Starter
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Re: Best way to bleed brakes

So just got off the phone with Wilwood. Here are a few things he told me to check:

-The brake hard lines on the car need to be 3/16, not 1/4. My 7/8 bore won稚 move enough fluid for 1/4 lines.
-Make sure there are no residual or proportioning valves left 塗idden in the system. My car has a single reservoir brake system so I had to change the tee on the frame. The new one is empty, ie, a 90 to head to the rear brakes and a tee for the two front brakes.
-I can re-bleed the master cylinder with the lines connected to the proportioning valve by using the two unused ports on the other side of the MC. He said just make sure I get 100% stroke.
-It doesn稚 matter what position the proportioning valve is during bleeding, ie, wide open to the rear or something less. He suggested starting at 50%.
-He told me that the pushrod going into the master should be slightly loose when adjusted properly. If it痴 adjusted to tight, the brakes may not release all the way when you lift your foot because the ports to return the fluid could still be covered.

Lastly, he stated that the 7/8 bore for manual brakes will by its very nature be a lower pedal engagement point. But not as low as I described.
I値l check the diameter of my brake lines when I get back to my shop and let everyone know.

66 Chevelle hardtop - LFX 3.6 liter V6/6L50 6 speed auto trans, 3.07 10 bolt, full Hotchkis suspension, Wilwood 4 wheel discs, white with red interior, cowl hood.

Last edited by 67_LS1; May 22nd, 19 at 2:11 PM. Reason: Spelling
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post #56 of 76 (permalink) Old May 22nd, 19, 2:19 PM
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Re: Best way to bleed brakes

The idea of 1/4" hard lines being too small would then mean your pedal should be harder to push. At least in theory since you are trying to move X volume through a smaller orifice, thus increasing pressure.

They told me the same thing about ports being uncovered with my clutch MC. Upon disassembly of the MC, you would need a lot of static pressure on the MC to keep the piston pushed in so far to keep the port uncovered.

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post #57 of 76 (permalink) Old May 22nd, 19, 3:19 PM Thread Starter
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SS454, the 1/4” lines are to BIG, not to small. And I just checked, I have 3/16” from the MC to the distribution block and across the car to both front brakes,
I have1:4” line from the distribution block to the rear above the axle then 3/16 across the axle to the rear brakes.

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post #58 of 76 (permalink) Old May 22nd, 19, 4:13 PM
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Re: Best way to bleed brakes

I wouldn't think line size would make any difference, once the line is full of fluid it will displace the same amount.... unless you have air in the line.

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post #59 of 76 (permalink) Old May 22nd, 19, 6:42 PM
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Re: Best way to bleed brakes

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Originally Posted by 67_LS1 View Post
SS454, the 1/4 lines are to BIG, not to small. And I just checked, I have 3/16 from the MC to the distribution block and across the car to both front brakes,
I have1:4 line from the distribution block to the rear above the axle then 3/16 across the axle to the rear brakes.
I think I get dumber with age

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post #60 of 76 (permalink) Old May 22nd, 19, 7:09 PM
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Re: Best way to bleed brakes

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I wouldn't think line size would make any difference, once the line is full of fluid it will displace the same amount.... unless you have air in the line.

This is correct.

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