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Yeah, but that is two complete bleeding sessions. Even with the Motive bleeder, that's a pain. I dunno.... If I mod a spare cap it'll be easy. Let me see what I see when I dig in
With an MC bench bled, I've replace many without having to bleed the system. The two disconnected lines at the MC really don't have a place to lose fluid. It stays right to the ends unless you force them downwards to drain. And the MC will keep dribbling out fluid as you reattach them so no place for air to get introduced. So you should be able to bleed once after the valve swap, then just swap MCs.
 

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91ss Thank you for post #13 with actual part information and math.

Navy Lifer says that he's running the exact same system as mine and his brakes are acceptable.
Post#15

In post #5 when I suggested a smaller bore MC I referred to this thread:


In post #10 Navy Lifer says this:
My own SS, with the same front & rear calipers, uses a 1" MC which was supplied by Baer WAY back when I bought the original Baer GT system in 1999>2000 time frame (their version of the C5 front caliper setup as offered by KORE3). If I had held off on changing the MC during the original brake install, I think I would be happier, but my current combination still works pretty good.
I think I have been through this tread several times and still do not know which MC you are using. Which one is in the car now?

Then in post #10 Navy Lifer says this:
Bottom line, if you have a 1-1/8" MC, you might consider going to a 1-1/4" MC--the pedal will be firmer
So he specifically states a larger bore stiffens the system. Just as several other people have said.
 

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Navy Lifer says that he's running the exact same system as mine and his brakes are acceptable.
Post#15
Again please clarify with a quote from him or refer to a PM where he says his system is the same as yours. You saying yours is the same as his is different.

Looking at the parts book:

18029976 Brake Booster JM4 front disk, rear drum Wagon and sedan 9" or 11" drum

18029981 Brake Booster JL9 front disk, rear disk police and Impala

Navy Lifer is referring to a Impala with a factory four disk brake booster and you are referring to a wagon which came with a factory front disk rear drum booster.

The brake boost force may be why he thought 1.125 MC was OK.
 

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Couple things Navy Lifer didn't have quite right in the post back in 2013 and may have since clarified. I'm sure he's got it all right and just some times hard to translate into words what you're thinking. I'm guilty of that many times too.
One regarding MC bore size and confusion. There are 2 sizes 1.125 and 1.25. The ones that mention a 40mm bore are the 1.125. The 40mm piston is at the very back and is part of the design they called 'quick take up' It's sole purpose was to push a lot of fluid to start moving calipers and more so the shoes to contact point, then the 1.125 bore takes over. My 91 FSM has good description and cross section diagram of how that MC works. The 1.25 does not have (or need) that piston since it's already displacing more volume. The other thing was his stating you need more volume as pads where down.

"Fluid volume requirements are largely based on pad volume--the total fluid displacement change from 100% new pads and rotors compared to pads and rotors at minimum thickness. The example to present here is the difference in 94-96 Impala SS (RPO JB9) and 9C1 (RPO JA9)--the thicker front pads on the JA9 system were considered to be enough of a volume requirement change to use the 1.25" bore MC to provide desired pedal travel. From the brake engineer's standpoint, using the 1.125" MC would have resulted in greater pedal travel that came too close to the MC piston travel limits at max wear conditions."

That's not quite correct either. Or phrased incorrectly as the next paragraph has it right. The first sentence is right in regards to MC reservoir fluid. The MC bores/piston only have to move the pistons from their resting place. That will be the same whether new or old pads. What is need with worn pads is more starting volume in the calipers. That's taken care of by MC reservoir not bore size. It's the 'auto adjustment' for volume. If he meant 'Fluid requirements..." as in reservoir. then correct. It can be true that one can not have enough volume in the MC bore to apply full pressure to the caliper if it's too small for a given large caliper. But in our caprices, with it's large calipers, both MC's have enough volume. Going to a smaller vette caliper would require even less volume.

Another thing is the operation of the proportioning valve. Took me a while to get it straight too :) It does not delay pressure build up. The meter function delays and only affects the front brakes. A proportioning valve reduces pressure. The pressure reduction is controlled by the spring inside pushing a piston against the inlet orifice. The math works out roughtly to: Pressure in = spring pressure + pressure out. The piston shape at the orifice can affect the net force i suppose. The IN pressure has to overcome the spring first and the remaining pressure is what goes to the OUT. So the stiffer the spring, the less pressure out. Hence why removing it in the stealth mod gives you all the pressure to the out. The adjustable ones like Wildwood just use a screw to vary the preload on the spring.
 

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Discussion Starter · #26 ·
@Z09B4U and @91ss - its cool. We're all friends here. Seems like feathers are getting ruffled. If I misread the original thread, no offense meant so...yeah. I have the .125, but I have the 'vette MC coming so my guess is that this is the issue. I have contacted Tobin at Kore3 and he advises against going to the vette mc due to the "21% increase in pedal travel" due to the way the MC takes-up. He seems to think the issue is within the block, but once I get all the parts and start installing them - we will know for sure.
 

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Discussion Starter · #27 ·
And for the record, I'll do the MC first and then test. I will install the block last.
 

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Didn't see any ruffling. Just sharing our knowledge. Keep on going!
91ss +2
I would like to thank 91ss for another well written post.

Still frustrated with not knowing what is being used on the back brakes.

Atlantadan there should be a lot of acknowledgment for you fighting for your car after a accident, and your problems with the body shop. You have a vision for what you want. Many people do not know the time involved.

In post#5 I thought if all parts were listed someone would spot the problem quick and easy.

Before you try the new MC you might want to quantify where the brake system is now. The FSM lists this for a STOCK system. It would be great to know how your current system compares.

With ignition off and vacuum depleted: Brake pedal travel is 2.25 inches with 100Lb force. The force is hard to measure but if you have a lack of travel the smaller MC bore may work for you.
My B4U should be very close to a stock wagon(same front and back brakes). I can not test mine now but with boost the 2.25" seems correct. For me the Caprice is the most "hair trigger" brake system I have. My newest is 1996 so I have no current comparison.

I have contacted Tobin at Kore3 and he advises against going to the vette mc due to the "21% increase in pedal travel" due to the way the MC takes-up.
You might ask him about brake boosters. I have had cars that passed testing but did not have the feel of an identical car or a new booster.
 

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There are also under dash ratio differences in the cars.
95wagon
https://www.impalassforum.com/threads/master-cyl-upgrades-brake-line-questions.318666/#post-3185322

10205029 Brake pedal with bracket JM4 front disk, rear drum Wagon and sedan 9" or 11" drum

10205031 Brake pedal with bracket JL9 front disk, rear disk police and Impala

18029976 Brake Booster JM4 front disk, rear drum Wagon and sedan 9" or 11" drum

18029981 Brake Booster JL9 front disk, rear disk police and Impala

So you may be running a different booster with a different pedal geometry.

When the parts are all correct the system should work. I had to drive a 1981 dodge van with manual steering, four on the floor, and manual brakes. Even it could do a emergency stop in traffic. Any semi tractor I have driven was easier to steer and clutch than that van and it did require more pedal force than anything I have ever driven,
 

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I will have to crawl under my dash to check which lever I have ,
Pretty sure is the lower mounting and non offset pushrod (this equates to less travel, more effort)
I have the original 1.125 quick take up
44mm-36mm front calipers
This equates to 3.9 square inch roughly.
Rears are 30-28 = 2.86
I will say with a gutted combination valve ( only bias warning light) I never have any complaints about hard pedal and tough to stop.
All the following pads, the braking has been fine.
Textar
Pagid
Hawk Ceramic

The production combo valve does control the maximum rear pressure, even as the pressure before it rises above that threshold
 

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Discussion Starter · #34 · (Edited)
Installed the Corvette MC. Edit: The pedal travel has increased a pretty good amount, but so has the non-panic braking power. I took it for a drive and just cruising around, the brakes are much improved. It stops how I thought it always should have, given the brake setup. However, in a panic stop situation - its like pushing against a brick wall. Very, very stiff pedal and low braking power.

Looking at the Wildwood proportioning block, the threads on the inlets/outlets are different from the OEM stuff. OEM has one fine thread, and one coarse. The Widlwood block is all fine. So it may be a minute before I install that due to having to get new raw hard-line and fittings and making up my own lines.
 

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Dan....while I know its double bleeding, you won't know if it was the proportioning valve or MC that is your issue if you swap both at same time....But with that said if it fixes it than all is good but you won't know what part did fix it

Have not seen Bill Harper jump in or if he even visits the forum anymore but a email to him may bring his comments to your problem
 

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crap my post was after yours Dan about you just installing MC first. Hope the PV does the trick

...and with this "new" forum format I am not seeing how to edit or like posts...hopefully that is still on Admins "to do" list...
 

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crap my post was after yours Dan about you just installing MC first. Hope the PV does the trick

...and with this "new" forum format I am not seeing how to edit or like posts...hopefully that is still on Admins "to do" list...
BALLSS, If you click on the thumbs up, below, it will enter the "Like". I think that's it.

Mark: Snowman-33
 
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crap my post was after yours Dan about you just installing MC first. Hope the PV does the trick

...and with this "new" forum format I am not seeing how to edit or like posts...hopefully that is still on Admins "to do" list...
Mark answered your 'Like' part, but start at Post #221 here for the 'edit' part:

CLIFFS: Edit went from lower right to upper left portion of any post in question. Based on timing of my two nearby replies (one saying, '1 Day Ago' where there is no longer an Edit button, and the other saying '22 hours ago' (well, at least said that when I posted this), where the Edit button is still there) I'm figuring you got exactly 24 hours to make an edit to a post.
 

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Discussion Starter · #40 ·
So after driving it around a bit, I have decided that the long throw on the pedal is not something I want to live with. It almost goes to the floor. The cop MC is back in. I also have abandoned the Wildwood p/v because to install it properly would require re-doing most of the lines under the hood and that's not a job I want to take on right now. The fittings are all different sizes and they're all double flare while the car has bubble flare stuff. I may get another OEM PV and just rebuild it with the available kits that are out there and see what I see.

To be clear, in normal driving, the cop MC is decent and it'll stop the car well. In a panic stop situation the pedal will practically lock up and the car will not stop in anything remotely close to "a hurry". To me, that's a PV issue. Especially since literally everything else has been changed out.
 
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