Click Here -> Please Consider Making a PayPal Contribution to the FordSix Forum!
2019 Contributors:
NJwpod, 1strodeo, mightynorseman, maxtrux, 6d7coupe, broncr, Phase3, 68Flareside240, bmbm40, mustang6, WorldChampGramp, justintendo, BigBlue94, ags290, motorsickle1130, Rooster, ousooner919, ethanperry, rzcrisis, DoctorC, jamyers, Motorboy, fastpat, Silverback280, chad, drag-200stang, THE FRENCHTOWN FLYER, Jimmys61falcon, rjonah, Sooshi, Robert92867, Invectivus


PLEASE TEST ON http://dev.fordsix.com

<<<***PLEASE READ*** New Site Update >>>

Can't Get ANY Brake Pedal! UPDATED

Moderator: Mod Squad

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Can't Get ANY Brake Pedal! UPDATED

Post #1 by stu in wichita » Mon Jun 06, 2011 1:59 pm

Everytthing is new on my '61 Ranchero:
- Scarebird conversion with the specified Cavalier calipers and Fairmont master
- New 9x2-1/4 rear drums, shoes, wheel cylinders and hardware
- New hoses and hard lines
- Brake pressure distribution block with differential pressure switch from '67 Fairlane

I bench bled the master cyl, then bled the whole system starting at right rear and working to the left front. There's almost no resistance at the pedal. I'm not talking about spongy, the pedal goes clear to the floor if I push it. It must be making a little pressure - the calipers move slightly and the rear brakes creak (they are adjusted properly). There are no fluid leaks.

Here's what I've tried:
- I thought maybe the reman master was bad, so I replaced it with another (Autozone) and bench bled it thoroughly.
- Checked the master cyl pushrod - there is about 1/16" of movement before it contacts the pison inside.
- Re-checked rear brake adjustment. If anything, they're a little on the tight side.
- BLEED-BLEED-BLEED!!! I've bled this system every which way - pressure bleed, reverse pressure bleed, vacuum bleed and the old trusty "pump and hold" method. No signs of air.
- I installed speed bleeders yesterday and ran a quart of brake fluid through each corner with wife at the pedal and me watching for air, but no bubbles.

And still no pedal. Nothing has had ANY noticeable effect. I'm at a total loss. Could I have gotten two bad master cylinders? Maybe try a new one instead of reman.?

Any other ideas? I just got my engine running and would love to take this bird for its first spin in decades. Thanks for any help.
-Stu
Last edited by stu in wichita on Tue Jun 21, 2011 1:57 pm, edited 1 time in total.

User avatar
Frankenstang
Registered User
Posts: 1180
Joined: Tue Mar 25, 2008 7:12 am
Location: Grand Prairie, TX

Re: Can't Get ANY Brake Pedal!

Post #2 by Frankenstang » Mon Jun 06, 2011 4:30 pm

stu in wichita wrote:Could I have gotten two bad master cylinders?


IMO, this is a definite possibility...the rebuilders' quality aren't getting better and the cores aren't either...have had more than one bad rebuilt m/c, starter, water pump, etc. in a row :bang: .

stu in wichita wrote:Maybe try a new one instead of reman.?


That would be my first recommendation. EDIT: My first guess is the rebuilts are bypassing. There are a couple 'new' options out there available from Dorman and Centric IIRC at least in the '74 Mav man/disc version.

I'd also make sure you're not experiencing any fluid loss (assume not or you'd have probably mentioned it), and that you're using the longer original fruit jar m/c pushrod to maintain sufficient m/c piston stroke.

When bleeding the cavalier calipers...I'd recommend removing the caliper from the scarebird brackets and orient them such that the bleeder valve is at the top/apex of the caliper piston chamber (you can shim them up with loose rotors or enough wood/metal blocking)...the large volume calipers can be a bear to get all the air out otherwise...images at the bottom of this page are likely more help than my description...
http://www.performanceonline.com/blog/2 ... -bleeding/
Good luck!
-Robert
Image
66 Mustang 200+30, 67 BH, 89 4cyl T-5, 71 Comet 4 lug 8" 3:1rear, 85 T-Bird v6 DS, 10 Mallory Unilite Hyfire VI-A, 08 Vaporizer 1bbl, 68 Cougar 2" exhuast,65 pipe, 74 Mav man disc m/c & Scarebird(87 Stanza rotors 89 Cavalier calipers), 73 Datsun 240z Appliance Wire Mags, 03 Mustang Leather seats
All in one car! Johnny Cash would be proud...I got it One Piece at a Time

User avatar
bubba22349
Global Moderator
Posts: 9244
Joined: Sun Jan 03, 2010 4:46 pm
Location: Flagstaff, Az. 86005 near the old Route 66

Re: Can't Get ANY Brake Pedal!

Post #3 by bubba22349 » Mon Jun 06, 2011 4:34 pm

Spent Sat. afternoon (two weeks ago) replacing the rebuilt master cylinder on my daughter’s car that I had replaced back on Dec. 31 but it did have a lifetime guarantee. :hmmm: Replacement is a brand new one and also has a lifetime guarantee the difference in price was minor but this new one works like it should. I am done with cheap auto store rebuilds especially if it’s an Aluminum master cylinder I think there is little if any quality control now days. I would still rebuild them myself on the old cast iron type cylinders if they measure in spec.
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Re: Can't Get ANY Brake Pedal!

Post #4 by stu in wichita » Mon Jun 06, 2011 6:00 pm

Frankenstang wrote: My first guess is the rebuilts are bypassing.

That makes sense. It seems that I should be able to get SOME pedal from one side of the dual system, even if there was still problem in the other side.

Frankenstang wrote: There are a couple 'new' options out there available from Dorman and Centric IIRC at least in the '74 Mav man/disc version.

What kind of options? I went with the Fairmont since it is more available, but not sure what the differences are between it and the Maverick version. I think one difference is the ports are on the passenger side of the Fairmont version, so there's more room to plumb it. Either way, I'm willing to change to a completely different M/C and re-do those brake lines.

Also, is there any issue with needing a residual pressure valve, either built-in to the M/C, or do I need to add one? Scarebird doesn't mention it being needed.

Frankenstang wrote:I'd also make sure you're not experiencing any fluid loss (assume not or you'd have probably mentioned it), and that you're using the longer original fruit jar m/c pushrod to maintain sufficient m/c piston stroke.

No leaks anywhere. Like I said, it's building a little pressure and you'd think that any leaks would show up then. I'm using the original fruit jar pushrod. It seems to make full stroke, although the instructions recommend not to completely bottom out the piston in the M/C.

I figured I might have to tip the caliper to get the last bit of air out. Still, it sure seems like I should be getting some hint of firmness in the pedal, even if there is a small Apocket of air.

I really appreciate your input and help. I'll keep posting until I (or I should say "WE") figure it out.
-Stu

User avatar
Frankenstang
Registered User
Posts: 1180
Joined: Tue Mar 25, 2008 7:12 am
Location: Grand Prairie, TX

Re: Can't Get ANY Brake Pedal!

Post #5 by Frankenstang » Mon Jun 06, 2011 6:37 pm

stu in wichita wrote:
Frankenstang wrote:Frankenstang wrote:
My first guess is the rebuilts are bypassing.

That makes sense. It seems that I should be able to get SOME pedal from one side of the dual system, even if there was still problem in the other side.


One sure sign of bypassing is to pump the brakes several times, then pop the lid, if bubbles are present it's definitely bypassing between chambers ie little to no brakes.

stu in wichita wrote:What kind of options? I went with the Fairmont since it is more available, but not sure what the differences are between it and the Maverick version.


Not too familiar with the Fairmont option, and figure SB started recommending it cause it's more likely to be stocked (later model)...but this is the '74 Mav Manual Front Disc Brake/Rear Drum M/C I am using with scarebird...works great :thumbup:
https://www.partshighway.com/product.ph ... RNB-M86133
Rockauto might carry this one and the Centric Brand IIRC

stu in wichita wrote:Also, is there any issue with needing a residual pressure valve, either built-in to the M/C, or do I need to add one? Scarebird doesn't mention it being needed.


Should not need additonal RPV's. The m/c will have some already mfg into it at each fitting and pressure rating of RPV is diff by design...2-3psi for disc...8-9psi for drum IIRC. So just getting the proper manual disc m/c for a front disc/rear drum setup will give you the proper RPV's already in place as well as the proper piston bore for pedal feel...as mentioned the 74 Mav spec'd one works great with my 4-lug scarebird man. disc conversion.

And yeah, don't want to 'completely' bottom out the m/c piston when bleeding, but should not be able to after system is properly bled.

Fordconvert had a good thread going where some folks here had listed their diff disc converion setups and related various component options/selections. For my 4-lug, the new Dorman Calipers and the new Dorman M/C both from the 'Parts Highway' people worked great with a simple two line/chamber distribution block from '67 or later w/o the need for a proportioning valve either (no rear wheel lock up even on the hardest pedal stomp).
Hope that helps some.
-Robert
Image
66 Mustang 200+30, 67 BH, 89 4cyl T-5, 71 Comet 4 lug 8" 3:1rear, 85 T-Bird v6 DS, 10 Mallory Unilite Hyfire VI-A, 08 Vaporizer 1bbl, 68 Cougar 2" exhuast,65 pipe, 74 Mav man disc m/c & Scarebird(87 Stanza rotors 89 Cavalier calipers), 73 Datsun 240z Appliance Wire Mags, 03 Mustang Leather seats
All in one car! Johnny Cash would be proud...I got it One Piece at a Time

mustang6
VIP Member
Posts: 1435
Joined: Thu Oct 23, 2003 11:32 pm
Location: near Tacoma, WA USA

Re: Can't Get ANY Brake Pedal!

Post #6 by mustang6 » Tue Jun 07, 2011 3:13 am

Here's a simple method I've used to troubleshoot spongy (or worse) brake conditions- get a couple of solid plugs and screw them into the master cylinder, fill with fluid, pump the pedal a few times and it should be rock solid. If not, there is a problem in the master cylinder. If it passes that test, pull one of the plugs and reconnect one half of the brakes (I usually do the rears first). Bleed and do whatever is necessary to get a firm pedal back, if you can't then the problem is in that half. Then pull the other plug and do the other half. If necessary you could plug the rears back up before going to the fronts but I haven't really found the need to do that.
Scott

68 Mustang 200 ci, Aussie 250-2V head, Dual Headers, Comp Cams 252H, DSII w/MSD 6AL, T-5, V8 suspension.

65 Ranchero 200 ci, late 170 head, Autolite 1101, 3.03 3 speed, Maverick 8" 4 lug rear with 3.55 gears.

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Re: Can't Get ANY Brake Pedal!

Post #7 by stu in wichita » Tue Jun 07, 2011 11:10 am

Robert, you're a huge help. as usual. I'd didn't think I'd need the RPV, but it's good to hear you verify it.

I'll check the master for bubbles. If that doesn't indicate a problem, I'll plug the outlets like mustang6 suggested and hope for a solid pedal. If the M/C isn't the culprit, at least I can eliminate it and continue to hunt for the problem. Thanks, guys.
-Stu

dagenham
Registered User
Posts: 311
Joined: Tue May 06, 2008 9:59 pm

Re: Can't Get ANY Brake Pedal!

Post #8 by dagenham » Fri Jun 17, 2011 9:53 pm

Could it be the prop valve that you are using.
I would try an aftermarket one that is adjustable.

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Can't Get ANY Brake Pedal! UPDATED

Post #9 by stu in wichita » Tue Jun 21, 2011 1:52 pm

Well, I'm now at my wit's end. Here's what I've tried:

1. Re-plumbed the entire master cylinder. All lines are below level of m/c ports.

2. Removed pressure differential switch completely. Rear port goes straight into front brake "T" and front port goes to rear brakes.

3. Added 10 lb. residual pressure valve in line to rear brakes. It's about 3 feet downstream from the m/c, but I don't think the location makes any difference, does it? Double checked that it is installed in the right direction.

4. New master cylinder - no more reman units.

5. Bled system again and again and again - I'm on my 5th quart of fluid. Removed calipers and rotated them to the optimum position for the bleeding. (Thanks for the link, Frankenstang - I did get a tiny bit of air out of each side).

6. No sign of leaks anywhere. All connections are tight - pretty sure I'm not sucking air back into the system.

After all this, still no pedal firmness at all. I'm running out of ideas.

-Stu

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Re: Can't Get ANY Brake Pedal!

Post #10 by stu in wichita » Tue Jun 21, 2011 1:56 pm

mustang6 wrote:Here's a simple method I've used to troubleshoot spongy (or worse) brake conditions- get a couple of solid plugs and screw them into the master cylinder, fill with fluid, pump the pedal a few times and it should be rock solid. If not, there is a problem in the master cylinder. If it passes that test, pull one of the plugs and reconnect one half of the brakes (I usually do the rears first). Bleed and do whatever is necessary to get a firm pedal back, if you can't then the problem is in that half. Then pull the other plug and do the other half. If necessary you could plug the rears back up before going to the fronts but I haven't really found the need to do that.


I like that idea. I plugged both ports and got a hard pedal, but I'm not sure what happens inside the master cylinder when only one port is plugged. Can I troubleshoot one half the sytem with the other half plugged? Or will the pressure just "dead head" at the plug and keep the master cylinder from going further?

I'm thinking this method will help me isolate the problem.
-Stu

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Re: Can't Get ANY Brake Pedal!

Post #11 by stu in wichita » Tue Jun 21, 2011 2:00 pm

dagenham wrote:Could it be the prop valve that you are using.
I would try an aftermarket one that is adjustable.


No proportioning valve at this point. I may find it necessary after testing the front/rear bias.

User avatar
bubba22349
Global Moderator
Posts: 9244
Joined: Sun Jan 03, 2010 4:46 pm
Location: Flagstaff, Az. 86005 near the old Route 66

Re: Can't Get ANY Brake Pedal! UPDATED

Post #12 by bubba22349 » Tue Jun 21, 2011 3:37 pm

Added 10 lb. residual pressure valve in line to rear brakes. It's about 3 feet downstream from the m/c, but I don't think the location makes any difference, does it? Double checked that it is installed in the right direction.


The master all ready has the right residual valves internally, so you don't need to add or change them.

In changing mine out the front disks had some air was a ½ working system (bad master). After thoroughly bench bleeding the new master (short lines back into the master reservoir so they were below the fluid level no air bubbles. I than installed it leaving the lines about ¼ or so of a turn loose. Had my helper step down on pedal and hold it while I tightened both lines. Than had him pump pedal repeated cracking the lines on master about 3 to 4 times than started to get some pedal bled the front wheels 2 X and had a great pedal. The front disk cal. are the hardest to get all the air out of. You can also run some plastic tubing from the bleeder at wheel down into a can or jar with fluid so it can't get air back into the system. Good Luck
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

User avatar
Frankenstang
Registered User
Posts: 1180
Joined: Tue Mar 25, 2008 7:12 am
Location: Grand Prairie, TX

Re: Can't Get ANY Brake Pedal! UPDATED

Post #13 by Frankenstang » Tue Jun 21, 2011 9:46 pm

bubba22349 wrote:The master all ready has the right residual valves internally, so you don't need to add or change them.


Yep, as mentioned no need for additional RPV's (residual pressure valves). M/C will already have correct ones built in. I'd delete that in line one you added first and see what happens. I could see a significant amount of air getting trapped between two RPV's in the same line :hmmm:

I like bubba's other tips on bleeding as well...I've done the crack the line while someone slowly pushes the pedal down, in order to bleed the two small lines going from the m/c to the distribution block...just be sure the lines are closed before the helper lets the pedal up :nod:

stu in wichita wrote:I plugged both ports and got a hard pedal,


That means the problem is definitely after the m/c.Good luck!

EDIT: PS Stu, I'm assuming you're checking the pedal feel with the calipers loaded and mounted on the rotors along with the drums on and shoes adjusted out...might have someone check the travel of the caliper pistons and pads while you check the pedal feel...after deleting the inline rpv you added and re-bleeding the rear lines of course. Otherwise sounds like there's gotta be a leak somewhere after the m/c.
-Robert
Image
66 Mustang 200+30, 67 BH, 89 4cyl T-5, 71 Comet 4 lug 8" 3:1rear, 85 T-Bird v6 DS, 10 Mallory Unilite Hyfire VI-A, 08 Vaporizer 1bbl, 68 Cougar 2" exhuast,65 pipe, 74 Mav man disc m/c & Scarebird(87 Stanza rotors 89 Cavalier calipers), 73 Datsun 240z Appliance Wire Mags, 03 Mustang Leather seats
All in one car! Johnny Cash would be proud...I got it One Piece at a Time

User avatar
Frankenstang
Registered User
Posts: 1180
Joined: Tue Mar 25, 2008 7:12 am
Location: Grand Prairie, TX

Re: Can't Get ANY Brake Pedal! UPDATED

Post #14 by Frankenstang » Sat Jun 25, 2011 10:45 am

Hey Stu...any luck?
-Robert
Image
66 Mustang 200+30, 67 BH, 89 4cyl T-5, 71 Comet 4 lug 8" 3:1rear, 85 T-Bird v6 DS, 10 Mallory Unilite Hyfire VI-A, 08 Vaporizer 1bbl, 68 Cougar 2" exhuast,65 pipe, 74 Mav man disc m/c & Scarebird(87 Stanza rotors 89 Cavalier calipers), 73 Datsun 240z Appliance Wire Mags, 03 Mustang Leather seats
All in one car! Johnny Cash would be proud...I got it One Piece at a Time

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Re: Can't Get ANY Brake Pedal! UPDATED

Post #15 by stu in wichita » Sun Jun 26, 2011 12:02 pm

Unfortunately, when I putting one of the calipers back on, I noticed some runout in the rotor. Closer investigation found a crack in both the rotor and hub coming out of one of the lug studs. I think this was a result of the two hole patterns being slightly off. I remember one of them seemed like a tighter press fit than the others. Anyway, I have another hub and a new rotor. This week, I'll get the hub turned down and do the conversion again, but more carefully this time. I'll ream the lug holes in both parts together to get a perfect fit. The hub on the other side is okay.

Meanwhile, the brakes will have to wait. A couple of questions:

1. If I use a plug to isolate the front or rear brake circuit, how can the master cylinder provide pressure to the other circuit? In other words, once the m/c hits the plugged circuit, how can the piston continue to travel providing fluid to the other circuit? Maybe I don't understand what happens inside the master cylinder.

2. Since adding the residual pressure valve didn't change anything, I probably didn't need to add it. I'm still not positive that the Fairmont m/c has one, so what if I leave it in, at least for now? Will the additional RPV hurt anything?

A little bit of good news - I managed to get my dash and doors painted so now I can start assembling and wiring the dash. I need some positive progress to keep me enthused.

Thanks for sticking with me through this.

-stu

User avatar
JackFish
VIP Member
Posts: 2798
Joined: Thu May 26, 2005 7:31 pm
Location: Winnipeg Manitoba Canada

Re: Can't Get ANY Brake Pedal!

Post #16 by JackFish » Sun Jun 26, 2011 12:18 pm

stu in wichita wrote:
dagenham wrote:Could it be the prop valve that you are using.
I would try an aftermarket one that is adjustable.


No proportioning valve at this point. I may find it necessary after testing the front/rear bias.

How can you do all this and not have one?
Image
1978 Ford Fairmont station wagon
1978 Ford Fairmont station wagon
Yup, I bought another one.
1996 Chevy Caprice 9C1 (3)
1999 Dodge Ram 2500

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Re: Can't Get ANY Brake Pedal!

Post #17 by stu in wichita » Sun Jun 26, 2011 2:24 pm

JackFish wrote:How can you do all this and not have one?

The component you show does at least two things besides proportioning.

First, it's also distribution block. The same function can be accomplished with T's, crosses, and other fittings, but a distribution block cleans up the plumbing and eliminates a number of potential leaks. It's simply a machined block which controls the direction of flow.

Secondly, that component also incorporates a brake pressure differential switch. Inside the body, a shuttle piston is spring-balanced between the front and rear circuits. If there is low pressure in one system, the piston shifts that direction against the spring. This movement completes a circuit to turn on an indicator light or buzzer via the connector on top. The switch is definitely a worthwhile feature, but absolutely not necessary for brake operation.

The need for a proportioning valve depends upon how much rear-to-front bias is required to prevent lockup in either circuit. Variables are the operating volumes of the master, wheel cylinder and caliper,as well as vehicle weight, even tire size. For better or worse, most of us are building systems with wildly varying component combinations. Until the system is tested, the amount of bias required is unknown.

The proportioning valve shown is fixed, set by Ford for a specific vehicle. In our "mix-and-match" systems, the bias created by a fixed valve is no more likely to be correct than the bias of the system without one. That's why adjustable proportioning valves are popular. Simply put, if i can't be adjusted it's still just a crapshoot - you may get lucky, maybe not.

I hope I don't sound like a know-it-all. Obviously, I'm not - I can't even get my brakes bled :lol: Still, there is so much confusion about brake hydraulics that I wanted to try to clarify part of it. Anyone with better understanding is welcome to chime in and correct me.

-Stu

User avatar
Frankenstang
Registered User
Posts: 1180
Joined: Tue Mar 25, 2008 7:12 am
Location: Grand Prairie, TX

Re: Can't Get ANY Brake Pedal! UPDATED

Post #18 by Frankenstang » Sun Jun 26, 2011 2:28 pm

EDIT: Stu, posted this book :lol: before I saw your last post...so sounds like you got a pretty good handle on it, but I'm still not sure what kind of 'valve' you installed, and where 'inline' you installed it :?:

Okay, fair warning this is long...like really long, but feel the need to clarify some terms and differences in parts and terminology that I believe are adding to the confusion. First thing I would do is forget about RPV(s) (Residual Pressure Valves). You don’t need to add any as I commented back on June 6th…they are already built into the m/c.

Frankenstang wrote:Should not need additonal RPV's. The m/c will have some already mfg into it at each fitting and pressure rating of RPV is diff by design...2-3psi for disc...8-9psi for drum IIRC.


If you added one inline, remove it. Initially I would also not worry about adding a "Proportioning Valve" until you have an issue with 'rear wheel lock-up'...I never did, so I never added one, but that's just my $.02.

Okay, so here goes...
To hopefully clear some of this up I’ll offer the following layman descriptions for the three main components involved, all have a different purpose:

1) Distribution Block – is not much more than a splitter/junction of 1 incoming line going to 3 outgoing lines in the old fruit jar system, or 2 incoming lines going to 3 outgoing lines in the dual chamber system. (the 3 outgoing lines in both setups being the left front, right front and the rear axle line…the rear axle line is not split between the two rear wheels until it actually reaches the axle). So a Distribution block is really nothing more than a splitter or junction block to distribute fluid to all lines further down. No affect on pressure or delivery rate in it's basic form.

Some distribution blocks also serve as proportioning valves like the one Jackfish posted.

[Note: Not important for your purposes, but...Many distribution blocks also contain a “Pressure Differential Switch” (not the same as a Proportioning Valve or Residual Pressure Valve). Instead this mechanical switch that has an electrical component to trigger a ‘brake light warning’ (dummy light) to let you know there is an issue in one part of the system when pressure is out of whack]

2) Proportioning Valve – is essentially a restriction on the delivery of fluid (unlike RPV which governs ‘return’ of fluid). It essentially biases delivery of fluid to one section of the system by limiting or restricting fluid delivery to another section. They are primarily used to restrict/limit delivery of fluid to the rear portion of the brakes system (drums) which creates a bias or greater delivery of fluid to the front section of the brakes (discs) and prevents real wheel lock-up (where the drums fully engage ahead of the discs. You don't want to stomp on the frakes only to have the rear wheels lock up before the discs can properly apply...Dangerous!

Okay, gonna describe an RPV here, but concerned this is some source of confusion. Again you should not concern yourself with these…I.E. don’t add any, don’t remove any…they are built in and pressure rated according to using the proper M/C (e.g. drum/drum, disc/drum, disc/disc). As long as you purchased a correct “Disc/Drum” M/C you do not need to do anything else regarding Residual Pressure Valves…again, don’t add any, don’t delete any….

3) Residual Pressure Valve (RPV) – this valve maintains a certain pressure in the line as the brakes retract (does not affect hydraulic pressure while brakes are applied). The RPV simply prevents the brakes from retracting and hydraulic pressure from back flowing completely unrestricted. One thing the RPV prevents is vacuum from occurring at the wheel cylinder or caliper by affecting the speed at which the brakes retract (hydraulic pressure flows backwards to the m/c). The higher psi rating of RPV’s for drums is because their retraction is mechanically assisted via springs (return springs at the drum assembly pull the shoes off the drums with force). The lower psi rating for RPV’s on the disc half of the system is because there is no mechanical assistance in the retraction of caliper pistons other than friction. The friction of the pads against the rotors applies friction to retract (push back) on the caliper piston. This force is not as significant or direct as the return force of the springs that pull the shoes off the drum part of the system. Hence there is not as significant force pushing back against the pads and caliper piston (so the RPV does not have to be as substantial a restriction against back flow). In addition calipers do not have a base point per say to travel back towards. They will retract only the amount sufficient to no longer apply friction between the pads and rotors. While drum systems will retract the shoes completely (or all the way to their base point which is set by how far out the adjuster/star wheel is set).
-Robert
Image
66 Mustang 200+30, 67 BH, 89 4cyl T-5, 71 Comet 4 lug 8" 3:1rear, 85 T-Bird v6 DS, 10 Mallory Unilite Hyfire VI-A, 08 Vaporizer 1bbl, 68 Cougar 2" exhuast,65 pipe, 74 Mav man disc m/c & Scarebird(87 Stanza rotors 89 Cavalier calipers), 73 Datsun 240z Appliance Wire Mags, 03 Mustang Leather seats
All in one car! Johnny Cash would be proud...I got it One Piece at a Time

User avatar
Frankenstang
Registered User
Posts: 1180
Joined: Tue Mar 25, 2008 7:12 am
Location: Grand Prairie, TX

Re: Can't Get ANY Brake Pedal! UPDATED

Post #19 by Frankenstang » Sun Jun 26, 2011 3:18 pm

Sorry if that last post was TMI :lol:

stu in wichita wrote:1. If I use a plug to isolate the front or rear brake circuit, how can the master cylinder provide pressure to the other circuit? In other words, once the m/c hits the plugged circuit, how can the piston continue to travel providing fluid to the other circuit? Maybe I don't understand what happens inside the master cylinder.


A 'brief' :lol: description would be that the m/c piston chamber that fills full of fluid for delivery to the plugged section will not compress nor deliver fluid when it meets the immediate head pressure of a plugged line...however the unplugged side of the system and it's relevant piston chamber will still compress and deliver fluid. Plugging one half as Scott suggested should result in a stiffer and higher pedal (less travel) but will still deliver enough fluid with enough pedal travel and pressurize the unplugged side sufficiently to identify issues, leaks, etc.

One other suspect for leaking are the banjo bolt fittings on the front calipers...notorious for issues (e.g. copper washers often can't be re-used after one torque sequence..a box full from the help section at the auto parts store is a good thing to have on hand)...also make sure the hose is oriented correctly for proper seating...leaking at the banjo bolt connection can be very light, but nuke the breaking power.
Good luck!
-Robert
Image
66 Mustang 200+30, 67 BH, 89 4cyl T-5, 71 Comet 4 lug 8" 3:1rear, 85 T-Bird v6 DS, 10 Mallory Unilite Hyfire VI-A, 08 Vaporizer 1bbl, 68 Cougar 2" exhuast,65 pipe, 74 Mav man disc m/c & Scarebird(87 Stanza rotors 89 Cavalier calipers), 73 Datsun 240z Appliance Wire Mags, 03 Mustang Leather seats
All in one car! Johnny Cash would be proud...I got it One Piece at a Time

User avatar
stu in wichita
Registered User
Posts: 197
Joined: Mon Mar 09, 2009 3:37 pm

Re: Can't Get ANY Brake Pedal! UPDATED

Post #20 by stu in wichita » Tue Jun 28, 2011 9:56 am

Robert-
Thanks for the explanation - it all makes sense now. I appreciate the details - no such thing as TMI (at least as far as technical info goes).

Before I started, I read about bleeding issues with this disc conversion, but I figured, "not me!" After all, I've been working on cars for 40+ years, so I should know what I'm doing, right? :shock: I guess old age and knowledge don't always come as a bundle.

I hope that over the long weekend I can get this issue behind me. I could actually take the car for a drive down the street once I know it will stop.

Thanks again for all the help.
-Stu

User avatar
Frankenstang
Registered User
Posts: 1180
Joined: Tue Mar 25, 2008 7:12 am
Location: Grand Prairie, TX

Re: Can't Get ANY Brake Pedal! UPDATED

Post #21 by Frankenstang » Wed Jun 29, 2011 8:35 am

Hey Stu,
I hear ya, I'm no spring chicken myself (have owned and worked on my i6 car for 20+ years), and thanks to the collective experiences here at FSP I've picked up quite a few good tid-bits of info and mods for the ol' girl...and now she's better than she's ever been. Glad to share some of my experiences along the way...when I can remember them :lol: (like those copper washers giving me a bit of trouble).
Had some slight problems with getting the right studs mounted and the rotors seated myself too, but I'm pretty sure once you've got her all buttoned up and bled out you're going to be very happy with the results of the scarebird swap...one of my favorites :thumbup: Look forward to hearing your review...good luck!
-Robert
Image
66 Mustang 200+30, 67 BH, 89 4cyl T-5, 71 Comet 4 lug 8" 3:1rear, 85 T-Bird v6 DS, 10 Mallory Unilite Hyfire VI-A, 08 Vaporizer 1bbl, 68 Cougar 2" exhuast,65 pipe, 74 Mav man disc m/c & Scarebird(87 Stanza rotors 89 Cavalier calipers), 73 Datsun 240z Appliance Wire Mags, 03 Mustang Leather seats
All in one car! Johnny Cash would be proud...I got it One Piece at a Time

Who is online

Users browsing this forum: No registered users and 3 guests