I just installed a ford 9" w/disc brakes. I previously had drum in the rear. I switched to an s-10 typoon master cylinder since they had rear discs, and it was a direct bolt in.

The brakes are still soft. Maybe I need to bleed more, but damn I've bled it a lot. Looks like I got it all out?? I still have the old 1/4" line running to the rear where it tee's to 3/16".

could the 1/4" line be too big for running disc brakes?? Is the large dia. soaking up too much pressure?? I have 3/16" for the front discs. Help!!

I would reply, and tell you that you probably will need a inline residual pressure valve to hold the rear lines and calipers full of fluid while the pedal is up, but, If I did, I'm sure it would be just like the last time and there would be a bunch of know it all kids (who wern't even born by the time I stopped wrenching for a living) telling you that you would have dragging brakes and all kinds of other problems....so I won't:D

I had the same prob on my cj, but went with a m/c from a 70's trans am and it cured the prob, but I do have the combination valve in place still so like it was said I do have a residual pressure to the rear but it doesn't really drag and they lock about the same time so I will leave it for now

I drove the truck today, and I guess it's just the power brakes. They still feel a bit soft but the power brakes don't help. I might try to bleed them again sometime just to be sure. I did lock em up today so I guess a proportioning valve would be in order.

Residual pres. check valve???????
In rear discs ????????
This valve became obsolete in the early to mid 70's when drum brakes started using cup seal springs....
NO need on a Disc set-up.

Maybe ya should have kept wrenchin' into the modern age :flipoff2:


Back on topic....
Brake line size will not affect line pressure.... It is equal in all parts of any hydraulic sys. (each part) Will affect flow rates...
Volume issues .

Cory

[QUOTE]Originally posted by Lord Baskerville
[B]Residual pres. check valve???????
In rear discs ????????
This valve became obsolete in the early to mid 70's when drum brakes started using cup seal springs....
NO need on a Disc set-up.

>>> I rest my case...

Thank you, I knew someone would come thru....rotflmao

thanks for all your inputs. I got my prop. valve today in the mail and will be putting it in soon. I of course will have to rebleed my brakes so I'll see what happens then.

You do not need nor want to use a residual pressure valve with your setup.

REsidual pressure valves are used when the master cylinder is lower than the calipers or wheel cylinders like in an under the floor installation in a race car or really low street rod. In this case it would be a 2psi valve.

With drum brakes a 10psi valve is used to maintain slight pressure on the wheel cylinders to keep the piston seals in contact with the cylinder bore when the brakes are off. A disc brake caliper is totally different and doean't need this valve.

Be advised that many stock MCs or combination valves incorporate this valve, as well as proportioning valves and metering valves. that's why it's important to have the corect parts for the setup

In case you think I'm a know it all kid - feel free to read all about disc brake system valving at

www.mpbrakes.com

Thanks for the info billavista...
I'm gonna pull the r/p valves out of my rig tonight, and I'm calling all my buds so they can do the same...
whew ! I'm glad I learned "all about valving" in that 1 minute of reading...

Hey, maybe you could foreward that to CNC so they can learn all about brakes also.


Thud, thud, thud...

Where is my staple gun ? ...my fuggin sides are splitting

While not at all suprised by your stance, I am continually intrigued....like watching a car wreck.

Soooo, would you care to explain exactly what it is you think the r/p valve is doing for you in a 4 wheel disk setup?

Please don't just say:


will need a inline residual pressure valve to hold the rear lines and calipers full of fluid while the pedal is up

Because GRAVITY does that for you when the M/c is higher than the caliper.

Let me ask another way, You said "to hold them full of fluid", so logically, without it, they (the lines / calipers) would NOT be full of fluid....so, ummmmm, exactly what would they be full of if you removed your r/p valve?

Look, I know you hate reading things in books, blah blah blah...but you're going to have to do a lot better if you wish to convince me, or anyone else, that every brake handbook, every race car builders book, is wrong...and you alone are right!!!

Don't know who / what CNC is.

BTW - is it a 2 OR 10 LB you use? (curious, and always willing to learn...ya just haven't convinced me yet)

Some learn by reading, but without actually experimenting for yourself, you will only know as much as the authors.
I like 2 lbs front and rear for a nice firm pedal with manual brakes.

CNC makes some pretty good hardware, I'm running 2 of their 3/4" mcyls. and about a 7" pedal right now, it's working great, but I'd like to try the 7/8" bore sometime to see how it feels.


BTW ...I'm not getting paid for this, and I don't care if I convince anyone else.:flipoff2:

OK Dirtrod...
The 2 PSI valve I can live with.
Is this a trail only/mostly truck and if it is a street driver....
Does the 2PSI cause much wear or overheating of the rotors?
Or, is it so little that it really isn't an issue?

Your original post seamed to suggest a typical valve which would have screwed anyone who tried it :flipoff2:

10Psi and you might as well leave the P-brake on a click.:D

Cory

Some learn by reading, but without actually experimenting for yourself, you will only know as much as the authors.

Yea, agreed, but some of us learn by doing BOTH, that is reading to learn the theory, physics, vast experience of others, and THEN fiddling around with stuff ourselves. Doing one doesn't preclude the other.....I just like to read and understand all I can too.

Heck - think of it like this...if I read your advice and accepted it without question, I'd be doing just what you seem to dislike :flipoff2:

Now - back to the topic.....I didn't realize you were talking about manual brakes, and I don;t know much about manual brakes...but I suspect this makes a difference.

BTW ...I'm not getting paid for this, and I don't care if I convince anyone else.

Yea you do you grumpy old guy....you just want to help, like everyone else....otherwise you wouldn't even be here....you just like being grumpy while you're at it ;) :flipoff2:

If we go back to my original post you will see I said " you Probably will need a r/p valve", The "probably" has to do with the fact that I've seen setups without r/p valves that claim to have good brakes, and I've seen setups with r/p valves that claim to have good brakes, and then I have my own experence, that a r/p valve has helped in my rig.
There can be lots of variables that can stack-up in your favor or against you when you start putting pieces together to create a system, if you know the bore and stroke of each component you can figure it out, but most of us end up using trial by error, and end up with oversize rear calipers that need too much oil to be in balance with the fronts. (jmho)
Then there is the personal prefference aspect, some people will say that their s*it works great, when imho, it don't work at all, that's usually because they have run out of ideas, patience or willpower and find it easier to live without brakes...

With that said..I'd try a 10 lb. valve in the rear line close to the adj. prop. valve if I had a spongy pedal with power brakes (assuming that the lines are bleed and that the hoses are in good shape and the rotors were somewhat true).


As far as helping others... sometimes it's just not worth the effort, and that can make you grumpy.

if you know the bore and stroke of each component you can figure it out, but most of us end up using trial by error,

That's very true...I started trying to do all the math....but tired of it pretty quick!

As far as helping others... sometimes it's just not worth the effort, and that can make you grumpy.

Well, despite the fact that we've made a hobby of rubbing each other the wrong way...I appreciate you taking the time.