Rear disk bleed fail - proportion valve removal

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yellow3800
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Rear disk bleed fail - proportion valve removal

Postby yellow3800 » Thu Jan 26, 2012 10:04 pm

Scenario: proportion valves removed from stock beretta/pontiac 6000 master cylinder [new]. after using stock proportion system for the last 15k miles, its determined that more front bias is desired.

When the in-master-cylinder proportion valves are removed from the master cylinder, the left front and right rear are great. I have my own in line rear proportion valve and couldn't be happier! despite the small beretta master cyl piston [pontiac 6000 same size], I am happy with it.

now the right front brake works fine and equals the front left in brake action. the left rear outputs <100psi and does not deliver pressure or fluid to the left rear caliper just like your failsafe piston block in the event of having a cut line. There is not a blockage - just low pressure.

WHY?

could this be because the left rear output of the master cylinder is in front of the master cylinder and delivers pressure after the main pushrod delivers pressure to front left and right rear before losing force in the in-line spring inside the master cyl before hitting the front chamber piston?

It does not make sense to me that the other diagonal chamber is okay if this one isn't. All parts are individually tested and work fine.

Other memebers have used camaro 2 line output master cylinders then went to a distribution block and then further to rear separate proportion valves. I want to use my beretta/6000 master cyl full open, with my own separate proportion valves for each rear caliper.

One thing I noticed- before removing the stock valves, this left rear was really weak evidenced by no/little pad wear on the left rear caliper. I didn't check it out thoroughly because I was about to install my own rear valves and remove the ones in the master cylinder. removing the valves was easy, and not disorienting. I did not tamper with the main piston shaft that runs along/through the base of the master cylinder. If its assumed to be a faulty master cylinder, I remind you that i have two of them and they both do it, so I doubt it.

no, my rear valves are not used with the stock proportion valves. this is a no no on any setup.

What do you other rear disk guys use for master cylinders?

Anyone using the beretta master cylinder w/out the stock internal proportion valves?

Andy
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Re: Rear disk bleed fail - proportion valve removal

Postby 3X00-Modified » Fri Jan 27, 2012 6:39 am

I have a completely stock brake system with N-body front calipers and Neon rear calipers... never had a problem with it yet that's made me feel like I need to change the Bias.



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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Fri Jan 27, 2012 10:16 am

I wondered this as well, because why I swapped rear disc on my Camaro with the stock disc/drum master you could turn the rear wheels by hand with pressure on the brake. Swapping to a Vette disc/disc master fixed my problem.

Jon, how is the pad/rotor wear on your rears?


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Re: Rear disk bleed fail - proportion valve removal

Postby 3X00-Modified » Fri Jan 27, 2012 10:51 am

I don't know, haven't checked... I know with the pedal pressed though you can't rotate the tires that's for sure.

Also no one even knows what an acceptable wear is on rear pads, on factory vehicles they don't wear much. I also do not put that many miles on this car so its hard to see.



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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Fri Jan 27, 2012 4:04 pm

True, and with rotor swaps up front you can't really judge front vs back either.

I know Tiff's Subaru has plenty or rear bias...the rears are always shot well before the fronts!


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Re: Rear disk bleed fail - proportion valve removal

Postby yellow3800 » Sat Jan 28, 2012 6:28 pm

To anyone reading this thread who notices rear bias... I noticed mine when coming to a stop on a down-sloping road to a stop sign in the rain. not just wet, rain. The rears locked up, and I slid through the stop sign. good thing I was slow enough to turn anyway and there was no traffic. If there was, I may have nailed the front to get more power up there, downshifted, etc. That was years ago, and I was just mindful of it. I knew I had a problem for like 100', so ample time was there.

test your car to be sure you wont get in trouble if you have rear disks and unknown bias.

anyway, as far as my problem goes, I suspect that since the left rear line is low on pressure, that my master cylinder proportion valve removal has differed between chambers. the left rear is actually the closer chamber to the master cylinder input [rear of the car] and the front left/right rear is driven by the front chamber of the master cylinder so my theory of internal master cyl pushrod spring tension failure is out the window.

I'm putting this off for a few weeks to see what this thread collects, then I'll take off that reservoir and spill fluid all over the place in hopes to solve it.



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Re: Rear disk bleed fail - proportion valve removal

Postby Barry » Sat Jan 28, 2012 8:27 pm

I know this bothers Jon, but my rear pads still looked new after 2 sets of front pads. Hardly any rear clamping power.

It just ain't right



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Re: Rear disk bleed fail - proportion valve removal

Postby scd88ga » Sun Jan 29, 2012 1:27 am

Barry wrote:I know this bothers Jon, but my rear pads still looked new after 2 sets of front pads. Hardly any rear clamping power.

It just ain't right



I was just discussing this with Robert89gt a couple days ago. I think the rear disc swap is completely pointless without changing the proportioning % F&R. I'd rather have drums that clamped good then disc brakes that don't do jack! :fool:
Last edited by scd88ga on Sun Jan 29, 2012 12:16 pm, edited 1 time in total.


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Re: Rear disk bleed fail - proportion valve removal

Postby GTZfan » Sun Jan 29, 2012 4:30 am

No brake dust at the wheels => Rear drums FTW


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Re: Rear disk bleed fail - proportion valve removal

Postby berettaboi » Sun Jan 29, 2012 11:36 am

to the original poster: if your rear drums are clamping too much, start with readjusting them. back them off just a touch and test if a safe area. a few vehicles i have had that issue on. also when i first got this beretta, the back drums were very prone to locking up. i started by pulling them apart and cleaning everything. still locked up. then i heard something about swapping the shoes around front to back can help sometimes, that solved it.

could also be really cheap pads, could also be out of pad material, or separation of the wear material from the shoe backing, and therefore binding in the drum... easy to figure that stuff out though... just open it up and look. pretty rare that part of the brake hydraulic system fails, mainly the brake lines due to rust, calipers that start sticking and leaking rear cylinders.


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Re: Rear disk bleed fail - proportion valve removal

Postby 3X00-Modified » Sun Jan 29, 2012 7:01 pm

So we have one guy saying its too much and locked up on him when every else argues with me that it's not enough, and sorry Barry comparing your 10 pad wear up front against the rear swap is not equal since those tiny undersized brakes cook pads like nothing already especially with the way you beat on that car.

You can do what you wish I'm happy with my setup just the way it is.



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Re: Rear disk bleed fail - proportion valve removal

Postby woody90gtz » Mon Jan 30, 2012 10:43 am

I guess I will see when I finally throw on my discs. What Camaro master is it that fits our booster? Is it disc/disc spec?


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Re: Rear disk bleed fail - proportion valve removal

Postby 3X00-Modified » Mon Jan 30, 2012 10:54 am

I haven't heard of any master that fits ours that's disc disc specific... The only option that I can think of would be a Lumina 3.8L or something... but no one has tried anything different.

BUT when you look that up, the masters avilable for that setup do not differ for rear disc or rear drum setups.

two examples

CENTRIC Part # 13062090 Centric Premium
Rear Disc Brakes
Rear Drum brakes; 4-Wheel ABS

ACDELCO Part # 174739 {#18029914}
CYLINDER,BRK MAS w/FRT & RR DISC ANTILOCK BRK(JL9) or ANTILOCK DISC/DRUM BRK(JM4) or SEO POLICE CAR,LIMITED CONTENT(9C3) or SEO TAXI CAB(9C6)

I'll inspect/measure my pads soon, I need to put the car on stands and I'll have the tires off shortly.

HAWK HP neon pads are 0.615 thick new from what I can find
HAWK HP Grand Am pads are 0.661 thick new.



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Re: Rear disk bleed fail - proportion valve removal

Postby Robert 89gt » Mon Jan 30, 2012 5:53 pm

Since i need new rotors soon anyways.Im just going to swap to 92+ up front.I had brett pick me up knuckles so im going to use them.Then get a new pair of shoes for the rear and hardware.I haven't changed them in maybe 8 years or so.And i noticed they didn't look great last year so.



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Re: Rear disk bleed fail - proportion valve removal

Postby weba » Tue Jan 31, 2012 7:41 am

My 4-wheel disc swap gets brake dynoed at every, yearly inspection.

The braking power of the rear wheel has been about half of the front. Granted that there would have to same brakes on both ends to direct comparison, but the rears could use a more line pressure i think.




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