Rear disk bleed fail - proportion valve removal

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Re: Rear disk bleed fail - proportion valve removal

Postby 3X00-Modified » Thu Jan 10, 2013 10:11 am

Burning_Beard wrote:
yellow3800 wrote: Aside from my original LEFT REAR failing to bleed, which is still unsolved


I have the same problem with my left rear, but I'm completely stock. I went through 4 bottles before I rage quit. I just figured there's air in my master. I haven't decided whether to do a bench bleed or get a new master for the hell of it.


New cylinder? The bleeder screw could be all corroded inside and blocking fluid flow.



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Re: Rear disk bleed fail - proportion valve removal

Postby yellow3800 » Thu Jan 10, 2013 10:37 am

not sure what to tell you on your left rear not pushing fluid. I think its inherent design. I have 3 master cyliders, original used, and 2 new ones. All do the same thing as you just said. Read below. For arguments sake, new calipers.

My problem is resolved! Guess what? There is a 30 degree rotation in my proportion valve near the max restriction [wilwood 85% block ability, single in single out] where fluid is allowed to move through the valve, get this, through the entire range. yep, thats right, put the valve inline with the left rear, open it up for 15% blockage rate, and NOTHING comes out. Now the interesting this is, the right rear works great. okay, swap em. ...same thing. I bought another valve and swapped left to right, and right to left, ....same thing. 3 valves, same thing.

Drilling the output holes larger in the master cylinder for the left rear and fronts fixed my problem. I now set the left rear proportion valve in its sweet spot to block 85%, or close to it, and it matches the rear pretty closely. The rear is full 85% blocked. The next time I have to mstr cyl bleed, I'll enlargen the front output holes a little more to increase bias up there, that'll be probably 5 or so machine drill bit sizes larger than the near 1/8" stock size.

Maybe because my car is so heavy in the front, 85% block to the rear is not enough. While my brakes are the best they've ever been since the drilling of the master cyl, rears still lockup on wet pavement, and this means i expect it to on hardest possible dry pavement braking.

The real way I believe, is to copy curtis walker/ turboz24 last design, use a camaro mstr cyl w/ 2 ouputs. then use 2 wilwood proportion valves [one in, two out]. one for front, one for rear. that way, the outlet hole in the master cyl is set for rear disk already, and the valves just hone it in a little better.

I'm happy enough with mine not to change it. ...for now.



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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Thu Jan 10, 2013 11:10 am

So I'm assuming this would be a 90-ish Camaro master cyl with factory rear disc? And it bolts directly to our booster?


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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Thu Jan 10, 2013 11:23 am

Just did a little digging on Napa and it appears a 91 Lumina master cyl may work. It has a slightly bigger piston and the OEM application is rear disc and FWD. The 4 ports are the same thread as well. Might have decent proportioning on its own.
http://www.napaonline.com/Catalog/Catal ... 0358744600

I'm still curious if the older RWD style masters fit our booster. I have a currently unused 1" bore rear disc master cyl from my Camaro I could test for free. Would just need to tee the 2 outputs to the Beretta lines.


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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Thu Jan 10, 2013 11:47 am

Bias should be very close from the Lumina master to a Beretta stock front caliper Neon rear caliper scenario. The Lumina has 1.652 dual front pistons and 1.376 rear single pistons. Beretta is 2.241 single front and Neon 1.338 single rear. That means the Lumina rear caliper has 34.5% of the piston area of the front. The Neon rear has 35.5% of the piston area of the Beretta front. That's just about perfect.

Edit: found specs on the F-body/C5 calipers (1.75 dual pistons) and it comes out to more front bias obviously: 27.8% with Neon rears...so front is doing 72.2% of the braking. So the Lumina master may still lock up the fronts first and leave a little on the table with rears during a hard stop. I gotta think it would still be better than a Beretta disc/drum master though.


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Re: Rear disk bleed fail - proportion valve removal

Postby yellow3800 » Fri Jan 11, 2013 10:46 am

yep, the camaro mstr bolts to our booster. I just don't know what year. I'd start at 94 and work my way older if it didn't mate up. Curtis said he liked it because the piston was larger and the car brakes have the feel of a corvette.



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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Fri Jan 11, 2013 4:22 pm

According to Napa the 94 Camaro master is 1" (25.4mm). The 91 Camaro master is 24mm, same as the Lumina FWD disc/disc master. It looks like both Camaro masters would fit, but they both have the brakes pointing toward the engine, which might be pretty tight on a FWD.


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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Sat Apr 20, 2013 8:57 pm

Here's an update to this thread. I finally got my rear discs installed and measured brake pressure front & rear with the stock master. Up front I got 1400psi and out back was 500psi. So I bought the 91 Lumina master and I'm installing it now. I swapped the Beretta reservoir on it because it looks like the Lumina one wouldn't clear the hood. I will report back when I get psi numbers out back with the new master.

Has anyone bench bled one of these FWD masters? I've done plenty of RWD ones with two ports, but the FWD ones with four ports all have different/odd threads that I can't find adapters for to bend some lines back to the reservoir to bleed.

Here's a pic I found online of how I always do it. Is there a kit available for the FWD stuff?

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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Wed May 01, 2013 12:55 pm

Got the Lumina master done and the rear pressure is at 950 max now. Almost double what it was with the drum master, but still less than the front. There must be some proportioning built in.

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Re: Rear disk bleed fail - proportion valve removal

Postby 3X00-Modified » Wed May 01, 2013 1:05 pm

There will always be some proportioning built in... Those masters will never be a 50/50 pressure split.



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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Wed May 01, 2013 2:02 pm

I was kind of surprised the pressure was not higher. Less pressure is also couple with less piston area in rear than I back, so it reduces the clamping force in a couple ways. The 3.94 area of the 2.241 diameter front caliper piston at 1000psi creates 3940psi of pressure, while the rear 1.335 piston creates 1390psi on the pad. That's a big difference. And at max braking in this application (1400/950) it ends up being 5516psi front / 1320psi rear. That's just under 20% rear braking.

I may even check this to see if it is equal to certain point and then splits...or if it is a fraction of the front all the way through the pedal travel. It seems to me like it should be the same under light braking and the rear should stop increasing as the front continues to increase to make up for the weight transfer under hard braking.


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Re: Rear disk bleed fail - proportion valve removal

Postby MY91GT(Z) » Wed May 01, 2013 9:17 pm

so it def soundsblike.its a decent updrade that ill be doing also i wonder.if the boosters would.also.change the pressure also ???



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Re: Rear disk bleed fail - proportion valve removal

Postby yellow3800 » Thu Sep 12, 2013 10:41 am

I've been told that the larger dia. piston in the master cylinder gives the braking authority like a corvette. If you haven't hit the brakes in a vette, just know its MUCH more powerful and less pedal pressure required. Having said that, I doubt a booster will do anything. well, that is worth changing out for anyway. I have to believe it would damp out the feedback too - like power steering in the cars from the 60's or 70s. It was so good, it provided no feedback and made it harder to drive.

I'm still using my stock brake booster and pontiac 6000 master cyl and beretta reservoir. It can still use some improving only because my car is so much heavier up front [4spd auto trans too] and THAT fact alone skews the proportioning required. if 85/15 pressure split doesn't take care of me, then 90/10 may not either. It would be close at 90/10 and I'd gladly take it.

I wouldn't change the booster even in all the hybrid parts of my setup.



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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Thu Sep 12, 2013 11:53 am

Corvettes actually run a smaller piston than comparable cars...and that is what I put in my Camaro. Stock the Camaro was a 1.125" bore and the Corvette one is 1". That smaller piston gives you more line pressure for a given input force than a bigger piston. This is at the cost of pedal travel though. If you get a smaller piston to increase line pressure by 20%, it will also increase your pedal travel by 20%.

I can say after driving the car with the new (bigger bore) master there is definitely less pedal travel, but I also went from drum to disc and rubber to braided hose...two other factors that also reduce pedal travel.


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Re: Rear disk bleed fail - proportion valve removal

Postby yellow3800 » Thu Sep 12, 2013 12:01 pm

Good! finally someone has concrete numbers!




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