Residual Valve redundancy? Scarebird

[Franklyn49]

In reading up on all the many posts here about disc conversions, I see multiple postings that suggest removing the residual valve from the original M/C, AS WELL as adding a 2 lb and 10 lb valve if retaining rear drums.....

My question is, isn't this a redundancy? or an extra step, for at least one of the valves that is being added?

If the residual pressure valve in the MC is 2lbs....   why not then just leave it in, and then go ahead and add ONLY a roughly 8lb-10lb valve to the rear? 

The maths line up.... therefore, I am either missing something or understanding these valves incorrectly.  someone straighten me out? 

Edited November 21, 2018 by Franklyn49

[vintage6t]

I guess you could leave the built in 2lb valve to the front disks. For the rear drums though I don't think you'll get additive pressure if you use two valves in line.  You will have 2lbs pressure on the input side of the external 10lbs valve instead of 0lbs without the built in valve.  I'm not positive but it seems to me this will subtract from the 10lb output rating of the external valve making it effectively 8lbs or less. In other words, the 2lb valve up stream from the 10lb valve may try to hold the 10lb valve partially "open".

 

This of course assuredly MC has built in valves in the first place and that they are both 2lbs meaning the original MC application is for a 4 wheel disk system.

 

Edited November 21, 2018 by vintage6t

[Adam H P15 D30]

The valve built into the original master cylinder is more like a 10lb residual valve. My disc brakes were dragging with it in there. I removed it and added no external valves and it’s been working fine for some time now. Even after sitting for weeks I never have a low pedal. 

 

Adam 

[48ply1stcar]

On 11/21/2018 at 6:43 AM, Adam H P15 D30 said:

The valve built into the original master cylinder is more like a 10lb residual valve. My disc brakes were dragging with it in there. I removed it and added no external valves and it’s been working fine for some time now. Even after sitting for weeks I never have a low pedal. 

 

Adam 

Are you still running the original MC as stated,  I have been thinking of the valve and using 2 and 10 PSI valves.

[Adam H P15 D30]

Yes, at the time I was thinking about adding the residual pressure valves but I tried it without them.  That was ~5 years ago and thousand of miles ago.

[48ply1stcar]

16 minutes ago, Adam H P15 D30 said:

Yes, at the time I was thinking about adding the residual pressure valves but I tried it without them.  That was ~5 years ago and thousand of miles ago.

Originally, I was thinking the ECI master cylinder, $425 convinced me otherwise.  Then I thinking a GM style master cylinder mounted behind the original MC, then I remembered some had were still using Original MC.  Alittle warmer and I'll be ready for my Scarebird Disc conversion to match up with my 2000 Cherokee rear axle.

 

Thanks for the response so now I have a couple of questions:

After looking at the manual after removing the valve, did you use somthing else for the sping to ride on?

I don't know if this is relevent or not, are you using this setup on the car with hemi or a car with l6?

[Adam H P15 D30]

I took the rubber out of the valve and reinstalled the metal part.

Is you rear axle disc or drum brakes?

I am using this on the 49 with the flathead.  The HEMI car has 4 wheel power disc brakes.  Nothing stock except the body and the middle 6 feet of frame.

 

Edited March 25, 2020 by Adam H P15 D30

[48ply1stcar]

3 hours ago, Adam H P15 D30 said:

I took the rubber out of the valve and reinstalled the metal part.

Is you rear axle disc or drum brakes?

I am using this on the 49 with the flathead.  The HEMI car has 4 wheel power disc brakes.  Nothing stock except the body and the middle 6 feet of frame.

 

Cherokee drum brakes and thank you for the information Adam H.

Edited March 25, 2020 by 48ply1stcar

[Sniper]

Residual valves were phased out at some point when they started making rear wheel cylinders with internal expanders.

 

The original purpose of the residual valve was to keep a bit of pressure on the wheel cylinder cups to prevent them from leaking and draining out your M/C over time.

 

Some use the 2lb residual valve as a band aid to prevent spongy brakes on a disc equipped car when the M/C is below the floor.

 

If your M/C is above the calipers you don't need them, if it's below you might.

 

If your wheel cylinder's cups are all rubber you need the 10lb valve in the rear line.  If the cups have a metal expansion ring molded in you probably don't, but having the valve won't hurt.

[Edward Garcia]

I am building the 99 Explorer disc brake conversion. My Stock Master cylinder is under the disc brake calibers. So i am adding the 2lb. value to prevent the spongy feel others say you might have. do you think i need to add the rear?

Also i am not changing the stock master or do i need to re valve  it?   

[Sniper]

I think your single port master cylinder already has a residual pressure valve in it, did you remove it? 

 

Residual pressure valves used in a drum setup (like your stock master has) tend to cause discs to drag due to too much residual pressure being held in the line. 

 

I would not run any extra residual pressure valve at first.  See if the discs drag too much, there will always be some drag due to the design.  If it passes that I would see if the brakes are spongy first thing in the morning after letting it set all night.  If either happens you can address it.  If neither happens then you don't have to worry about it.

[Adam H P15 D30]

The factory valve will be too much for disc brakes, been there - done that.  Remove it and try without any valve, you may be pleasantly surprised as I was years ago.

[Edward Garcia]

thank you both  what does the value look like?

[48ply1stcar]

2 hours ago, Edward Garcia said:

thank you both  what does the value look like?

The residual valvu is the first thing inside the back of the master cylinder.

[Sam Buchanan]

Does a spacer or sumthin' need to be used in place of the valve?

[Edward Garcia]

perfect   thanks. 

47 minutes ago, 48ply1stcar said:

The residual valvu is the first thing inside the back of the master cylinder.

 

15 minutes ago, Sam Buchanan said:

Does a spacer or sumthin' need to be used in place of the valve?

 thanks  thats what i thought.

 

[48ply1stcar]

18 minutes ago, Sam Buchanan said:

Does a spacer or sumthin' need to be used in place of the valve?

In #7, Adam says to remove the rubber and re-install,

[Sniper]

No spacer needed, it's just a piece of rubber.

[Edward Garcia]

thanks again. i have been posting the progress on the P15-D24 TO 95-2001 EXPLORER DISK CONVERSION forum  need to combine ALL of them  its really hard to narrow this stuff down,

[40desoto]

4 hours ago, Edward Garcia said:

thanks again. i have been posting the progress on the P15-D24 TO 95-2001 EXPLORER DISK CONVERSION forum  need to combine ALL of them  its really hard to narrow this stuff down,

Hey Edward, what caliper mounting plate are you using on your front disk conversion?  Are you also going with disk in the rear?  

[Edward Garcia]

i designed a new bracket. here are pictures  as soon as i figure out how i will upload the template on PDF

Edited April 6, 2020 by Edward Garcia
upload image

[Edward Garcia]

On 4/1/2020 at 11:13 PM, 40desoto said:

Hey Edward, what caliper mounting plate are you using on your front disk conversion?  Are you also going with disk in the rear?  

here is the link

https://www.jalopyjournal.com/forum/threads/p15-d24-to-95-2001-explorer-disk-conversion.702258/page-4

Edited April 6, 2020 by Edward Garcia

[48ply1stcar]

I have finished the brake converion.  Then I removed the rubber washer around the residual valve, that was fun.  Tried to bleed the brakes.  I had my nieghbor pump the pedal while I opened and closed the bleeder valve.  I done this many times before, but this time I cound't get any resistance at all and then I had some and then none again. 

I started with the front brakes because they had little or no fluid in the lines.  Next I'm going to try a vacuum pump, starting at the back passenger rear and try to evacuate the old fluid.

[48ply1stcar]

On 11/21/2018 at 6:43 AM, Adam H P15 D30 said:

The valve built into the original master cylinder is more like a 10lb residual valve. My disc brakes were dragging with it in there. I removed it and added no external valves and it’s been working fine for some time now. Even after sitting for weeks I never have a low pedal. 

 

Adam 

Adam did you have any problems with bleeding the brakes?  See above.

[Adam H P15 D30]

No problem bleeding the brakes....  Try removing the lines at the master cylinder and use your fingers to seal the holes while you have someone in the car slowly cycling the brake pedal, kind of like an on car bench bleed.  Is there pressure?  Check the holes at the bottom of the reservoir for obstructions, use a wire to clean them out.  Was there any crud in the bore of the master cylinder when you took the rear cap off to remove the valve?  I sprayed some crap out of mine while I was there. 

Edited April 6, 2020 by Adam H P15 D30