Spongy brakes

[66200i6]

I have been working at troubleshooting my new brakes which include the Scarebird swap. According to the shop that did the work, this setup has been spongy from the beginning.

The Setup:
Scarebird in front
Stock 8â€￾ diff drums in the back (10â€￾?)
Ford Vacuum Booster
Dodge Daytona Master

At one point even though the pedal is nearly to the floor, I was able to adjust the portioning valve to lock all four corners in a panic stop. That performance slowly degraded to “Dangerousâ€￾. I figured it was the heat cycling of the new fluid so I bleed the system again. That didn’t help.

I am now down to starting over and dismantling the system and to confirming Master and Slave piston sizes ect. I suspect it is a matter of volume from the Master that is the problem.

Unless of course I can get any feedback from the forum.

Thanks, Ric.

[addo]

It may simply be a defective master cylinder. Certainly sounds like fluid is escaping the high pressure side of things.

[66200i6]

Thanks, that is where I plan on starting. I figured I would start at the beginning by checking for the check valve at the rear hyd line port. If this Master doesn't have one, that is part of the problem. I may end up going back to the correct Ford Master.

Secondly I figure I will go through the bench bleeding process with it intalled. We'll see how that helps.

Ric.

[Frankenstang]

Ric,
Assuming that dodge mc is dual chamber, have you checked for bypassing? Work the pedal multiple times then pop the top, if you see bubbles in the fluid, she's bypassing between front and rear chambers...then the mc is bad.

I'm running the scarebird with the wrong type master cylinder (drum only style out of a '73 Mav), and she's not at all spongy compared to four drums. But I don't have power assist so my pedal feel may not be comparable.

Couple other things to consider, what kind of distribution block are you using for splitting front and back? Also, others have found it necessary to have a brake shop power bleed the system after the scarebird conversion.

[fordconvert]

Couple other things to consider, what kind of distribution block are you using for splitting front and back? Also, others have found it necessary to have a brake shop power bleed the system after the scarebird conversion.

My block was an SSBC / Jegs unit. It included a switch for the brake lights. That dang switch was 90% of my problems. Replaced the switch with a bleed valve and all my problems went away. Bleed anything and everything you can unscrew. In my process I bought 3 different kinds of bleeders and paid to have a shop do it. Doing it the good old 2 person way was what found and solved the problem.

The other issue I read about is if the bleed screw is not the high point of the system because of mounting sometimes they can be bled by the line if thats a higher point.



The switch used to be where you see the brass thing sticking up between the top lines above the 'S' and with the brown leaf around it. Its just a 1/8" NPT hole.

[falcon fanatic]

do you have a residual pressure valve (10psi) going to the rear brakes line? That might help.

[66200i6]

I've been doing some studying the last couple of days on the Daytona Master and disk/drums systems in general. It looks like I do need to remove the Master and inspect. From everything I've read, the front disks needs to be plumbed to the large reservoir, mine is not. The outfit that did this work is really lacking in knowledge and experience apparently.

I will be removing the Master to inspect for the RPV at the front reservoir port (this would explain the earlier problem I was having). As it turns out not all of the Daytona Masters were front disk/rear drum units. The ABS option came with disk/disk so I need to confirm I have the correct unit with the RPV valve. While things are apart I will be checking for correct installation of not only the pedal assembly from Mustang Steve but the Booster. It looks as if the reinforcing plate that should be between the Booster and the firewall is missing as well.

When things go back together I will be sure to perform the bench bleed and plumb the Master properly.

The Silver Lining is that I have found at least one obvious thing, (plumbing to wrong ports) which can be corrected.

Thanks for the info guys, Ric.

[addo]

That may be all it is. First check the plumbing, and existence of a rear RPV. Road test again once verified; if it's still poor try re-bleeding at the wheel calipers/cylinders and then cracking the fixings to your master cylinder while pumping so they weep slightly. Nip up once any air is purged there (it won't be much and you'll hear it).

I get so frustrated when people make simplistic, empirical statements like "The front brakes go to the front reservoir". As you've worked out, they go to the one with largest fluid flow ability...

The other possible, is if you've a pressure drop safety switch of the shuttle valve type it may be cutting off one full circuit by gvirtue of having tripped early in the process of setting up. These switches may be fully removed without fluid loss but once understood they're an asset, to be refitted and wired into a buzzer or light.

Disc/disc or disc/drum or drum/drum masters are going to vary in piston size, existence of RPV and reservoir capacities. There is no strict rule and misusing one in another application may well work. The basic requirement is for drum circuits to have an RPV and disc ones not, plus the latter needs good pumping capacity per pedal stroke.

I'm a believer in boosted brakes; it's the closest you get to a free lunch on cars. Plus, it saves stress on the firewall.

[66200i6]

So this is the latest.

I was sure the plumbing was incorrect. Turns out it looks like the plumbing is correct with the front disks routed to the back port under the larger reservoir.

So, I slept on it. Then it dawned on me, when I gravity bled the brakes I was topping off the smaller front reservoir during the disk bleed and the larger rear reservoir for the drums. Why is that?

I’m ready to try the Ford Master at this point.

Ric.

[66200i6]

More clues are surfaceing.

Disk Brakes should have a Residual Pressure of 2 psi.
Drum Brakes should have a Residual Pressure of 10 psi.

External RPV's can be found to plumb into your system if you do not have the correct Master Cylinder.

More later, Ric.

[fordconvert]

What are you using for a distribution / combination / proportioning valve/block? I went through a million hours of research and theories and spent a crap load on tools and 'power bleeding'. I even ran all new lines making sure there were no high spots. In the end it was a tiny pocket of air in the distribution block.

[66200i6]

This too was chosen for me. From what I could find on the web it is a Brake Proportioning Valve by Allstar #48025. It is rated to provide up to 57% reduction.

Since I can't find any identifying numbers on the Master I will be removing to inspect. If it is obvious that there is no RPV at each port I will be installing external valves for both the disk and drum circuits.

Thanks, Ric.

[66200i6]

Well it's been a very long summer for me. Beginning in mid May I have made three trips to Wichita on business. I just returned to work today after a much needed vacation, the first in over 4 years.

Anyhow to the point, I finally dismantled the Master at the Booster and started taking some measurements. It looked to me that the Master should compress the Input Shaft Seal at the Booster to create a good seal. So this was the focus of why I was taking these measurements, to build a part or spacer to make this so. To make a long story short a buddy suggested that a compression fit is not necessary and convinced me to reassemble. While preparing to do so I took additional measurements of the depth at the Master and the depth at the Booster to confirm the proper Input shaft length. Guess what, the shaft is at least a quarter inch too long!

This whole time, with the brake pedal "at rest" the Master was already compressed at least .25". I wasn't getting full use of the Master Cylinder pistons.

I will be trying to locate a new input shaft so I can get this back together. Any suggestions on where to get another Input Shaft would be appreciated.

More later, Ric.

[Frankenstang]

Most the mustang places have an adjustable rod of some sort available (possibly could be fabbed with some welding and a piece of all thread...but they don't get very long, so that might not be practical). Not sure if you could find something like that in the 'help' section at the auto parts store or not...maybe a race shop, summit or jegs. The price does not appear to be the least bit cheap

http://www.cjponyparts.com/adjustable-d ... /A21161DB/

[Ronbo]

Those "usually" are adjustable but I'm guessing yours is already cranked down as far as it will go? The only other way is a boneyard. you'll have to poke around until you find one the right length. That also depends if you have a boneyard that lets you poke around Good luck with it!

Ron

[Ronbo]

Just an afterthought....can you cut it down to length and re-install the adjuster screw?

Ron

[66200i6]

I'll be doing just that. I have a friend that has been very generous with his business and time to make custom parts and modifications. Marc will be drilling the shaft deeper to accept additional tread and I will reuse the treaded end piece.

A few of the parts that Marc has donated in time and material.
Inline Six Boring/Honing Plate
8 Inch Diff End Caps or Bearing Retainer Plates
Offset Carb Adapter for CI Intake
Aluminum Adapter Plate for 2V Intake to DFV Weber
Spun Aluminum Air Cleaner

Thanks for the comments, Ric.

[Ronbo]

Aluminum Adapter Plate for 2V Intake to DFV Weber

Interesting is this something you can buy somewhere? I assume this is for the Oz head? I wanted to try and use a DGES on it but it doesn't look like it'll work.

Ron

[66200i6]

Opps, my memory is failing. Turns out the plate you are asking about was not for the DFV. I designed it for the 2100 footprint.

A link to the pic is below.
https://home.comcast.net/~tuckerjr3/FordSix/2VAdaptor2100.jpg

[66200i6]

So, back to the brakes.

I installed the shortened MC Input Shaft (thanks again to Marc). The first thing I noticed was that the Booster responded as it should when the engine fires up. With your foot resting on the brake pedal, you should feel a slight movement of the pedal once vacuume is created. A good sign.

So, at this point I have the shorted input shaft, Dodge Datona MCylinder, no RPV valves and no Perportioning valve. From what I have read there are differnt schools of thought on the need for both types of valves.

According to some, the only time there is a need for the RPV valves is if the MC is at any time within a few inches height difference of either of the slave cylinders. The need for the RPV is to eliminate bleed back to the MC. I don't know that I agree with this simply because there would then be no need to have different psi ratings for disk compaired to drum (2 and 10 psi respectively). I plan on installing these anyhow.

I am going to be testing, through use, the need for a perportioning valve. There are many that have written that there is no need and many of those I know personally that do not run with them. We will wait and see.

I plan on bleeding the brakes angin myself once I find someone to operate the pedal. I have a feeling that the previous attempts were doomed for failure due to the loss of MC piston travel. Full travel was restricted due to the extended length of the input shaft. This never allowed the MC piston to return to full rest.

We'll see, Ric.

[burnoutstang1]

I'm at the same point you are in the install. I have everything hooked up with the power booster and master cylinder supplied from Scott Drake. I don't have a proportioning valve/block hooked up and the brakes feel really weak when I step on the pedal. I can tell the booster is doing its job, I can feel it. But the pedal goes almost all the way to the floor before the car really brakes. My master cylinder is for disc/disc however. I think that's going to necessitate a distribution block w/ proportioning valve to limit pressure going to the back brakes. Right now it feels like they're the only part of the system actually working despite several attempts at bleeding it.

[66200i6]

I haven't tore into it yet. I have spent the last week moveing my oldest into her new place.

I will be putting the car up on blocks and really inspect what was done. I will be looking for how the installation was done and for places that air could get trapped.

Good luck with your's, Ric.

[63futura289]

I had this problem with my scarebird setup.I kept reading and trying things until i got it fixed.It is my understanding that the calipers from this setup are a Gm Quick take up designed for low drag(better mpg design).If these type of calipers are not used with a corresponding Master cylinder for this the result will be a lower spongier pedal.I fixed my car by using the mustang steve 87-93 4 cyl. booster kit with the 87-93 mustang plastic res. master cylinder and proportioning valve.This master cylinder is a quick take up design.My brakes are now awesome.Hope this helps. Barry

[66200i6]

Great info, thanks. I'll look into it, Ric.

[66200i6]

Berry, I just received conformation that the Master Cylinder from the Dodge Daytona "is not" of the Quick Take-Up or Fast Fill designs. I plan on returning an early Maverick master and exchange for the 87-93 master.

Can you tell me if the bolt pattern to the firewall and booster is that same as the early design?

Thanks for the info. I'm looking forward to driving the car again, Ric.

[66200i6]

So I returned the Maverick Master for the 87-93 Fast Take-up master. The bolt pattern is the same but the boss that retains the piston is slightly larger. There is a risk that it will not fit the booster I have installed. The brake line ports are also on the opisite side of the master. I will have to re-plumb the system but that should be easier that before since their away from the finder wall.

I'll have to get some pics of this, Ric.

[66200i6]

The views below are of the 87-93 Mustang quickfill type Master Cylinder. The outside diameter of the boss at the end, which retains the piston, is 1.572 inches. According to a buddy that has access to the online Mitchell’s Manuals the large bore diameter is 1.25 inches (high flow low pressure). The stock Maverick boss measures to 1.461 and the Dodge Daytona 1.4 inches. I believe that this new Master will probably fit. The Booster opening measures approx 1.63 diameter. I say “probably fit” because I’m using the measurement of the disk that seals around the Input Shaft and the inside surface of the Booster. It will be close.

So from this point I will be tearing the entire assembly apart, from the pedals to the hydraulic tubing to redo.

Having fun, Ric.

[Frankenstang]

Hey Ric, I for one am very interested in your results, as I'd like to make the conversion to power brakes in the future. This is the first I have heard of the 'quick take up' design you and 63futura mention...sounds a little like a residual pressurve valve set up within the m/c...the diagram I found shows that this is controlled at the base of the reservoir ...can't find the diagram now...but will still be very interested in your results.
Also, do those fox m/c's sit flush/level or are they pitched up a bit? Good luck with your conversion!

[66200i6]

This is a graphic view of the QucikFill type Master. The cylinder has a larger diameter bore at the rear of the piston than the forward end. In the cylinder, a fast-fill or quick take-up valve replaces the conventional vent and replenishing ports for the primary piston. When the piston reaches a certain point in the first part of its travel the excess fluid returns to the reservoir, while the remaining fluid builds pressure at the forward business end of the piston.

The large bore at the base of the Cylinder is meant to provide a Low Pressure High Flow fluid supply to all hydraulic lines to move the piston calipers and rear shoes into position. The high pressure finishes the job. Check out the view below.



The Forward and Aft right hand ports go the Proportioning/Metering Valve. This is then split to the Front Right and Rear. There may be a valve that is suppose to be installed in the lower port like the graphic view. I will be checking an exploded view tomorrow at the local Ford dealership.

What I am trying to solve now is the type of fitting that is needed for the ports. If I can’t find the info, I will have to take Barry’s advice and make a trip to the local Salvage Yards.

More later, Ric.

[66200i6]

The view below shows brake line adaptor fittings from Edelmann. Fitting numbers 271300 and 26500 convert the 10mm and 12mm DIN Master Cylinder (MC) ports to standard 3/16” flared seat. I went this route to try and keep this change as simple as possible.




There are also pre-fabricated brake lines available that have the metric bubble on one end and the standard flare on the other. Some hydraulic outfits will also custom make hoses with any ends that are needed.

One thing I don’t understand is why the forward port has a larger diameter and thread. Both ports on the MC have the same size opening to the bore. The flow through both will have the same restriction and flow at equal pressures.

The only thing left is to fix my MC input shaft. Unfortunately I found out about this MC fix after I had already shortened it to work with the Daytona MC. The depth of the new MC is nearly identical to the Maverick. Now I need to find a way to add half an inch to the shaft to get it back to it’s original length.

Ric.

[Frankenstang]

One thing I don’t understand is why the forward port has a larger diameter and thread.

My guess would be to prevent an inadvertant mixup on the lines during m/c replacement.

The depth of the new MC is nearly identical to the Maverick.

Same length as a maverick equal size chamber or the longer big/small version? Or could you post measurement of length?
Rear reservoir is for the front brakes,right?
1/2" longer...I'm stumped. Don't know if you could find a replacement rod in the help section at the autoparts or not. There are generic adjustable ones available out there, but pricey.
Great info Ric especially given that alot of the conversion kits seem to use large volume single piston calipers now, thanks for sharing!

EDIT: oops! yet another question...did you find out what the lower port was for? Thanks again

[66200i6]

I think you're correct about the port diameter and thread. While checking my current setup, I found the hydraulic lines to be the same size but the nuts different. Unfortunatly these adapter fittings convert to the same size flared lines and nuts. I will have to replace the rear line from the MC to the Proportioning Valve and rear brake supply. Not a difficult fix.

The Input Shaft length I was referring to would be from the mounting surface of the MC to the Booster. Measuring from this surface from one MC to another would give you the difference in length needed.

Barry had the right idea when he picked up a set from the Salvage Yard. This not only provided the correct connection at the MC by also provided the hook-up configuration. Unfortunatly there is a new standard here in the Puget Sound area. You are no longer able to "Pick" your own parts. I was not going to pay someone to pull and possable damage the lines I need.

I was unable to locate any schematic for this model that was of any help. According to the Ford schematic the part number is a % sign. This indicates that these lines are hand made for each car. I did confirm the info Barry provided from his installation. The side and lower ports are for the front calipers. The switch I had mentioned is located in the line to the RHand side and is a low pressure indicator.

Now I need to tear things down and get to work, Ric.

[Frankenstang]

Ric, thought it would be better to reply to your thread (at the risk of derailing another Scarebird topic ).
I agree a compilation or survey thread RE: scarebird installs would be helpful for a number of reasons. Seems like each member's experience and end result is a little different. I know when I was doing mine, 'williboy' was doing his at the same time, but our issues mainly involved wheel fitment, and I haven't seen him around lately. Maybe a poll would even be worthwhile, or just a thread asking 'who has done scarebird', and 1)what was the experience, 2)what components did you end up with in the end, and 3)how happy are you with the results...heck it could even cover all disc swaps for that matter...not sure what's best way to approach it, since I think it would be best if it were open for a while to sift as much info as possible.

The main comments I remember (which is not a great source ) were either regarding the lack of reduced pedal effort when converting from manual drum to manual disc (which to me was not surprising since both involve significantly more effort than power assist), or 'spongy' as you're experiencing, which as TJ or someone mentioned in the other thread either seems to do with bleeding issues or like your experience, getting the pedal geometry correct. Heck, I'd probably even suggest a sticky on all disc swaps, but don't know if that's a good idea since I think other members are 'stickied' out...but there really aren't any brake stickies to speak of, and yet the topic comes up alot [shrug].

[Williboy]

I'm alive!!!! Just bought a house and have been very busy with all the fun of home ownership!!!First time back to the forum in a long time.

I'll answer Frankenstangs questions:
1) My experience doing the Scarebird was a headache. My biggest problem was getting 4-lug rims to fit. I previously swapped out the rearend to a 65-66 Mustang ( wider than the Ranchero's) so anything that would fit the front was too wide for the rear. I ended up getting a deal on a set of Maverick rims and a 8" rearend so I swapped it all. Also when I went to install the rotors I found out that I had two different IDs. Of course I had the hubs turned down for the larger of the two so I had to grind the hubs some more.
2) I went with the recommended Scarebird list of parts. No problems there, except for the before mentioned different sized rotors. No proportioning valve, 74 disc/drum manual m/c.
3) How happy am I??? Well I'm happier than the drums that liked to pull when now-and-then. But they do feel spongy ( hence me reading this post) . I bleed the #*%^$ out of them and even made my own pressure bleeder. Been wanting to take them to a brake shop to professionally bleed, but they aren't so bad that I can't drive. And I haven't found a good "old school " mechanic in my new area that I would trust. I just find myself pumping them a couple times as I brake.

[66200i6]

Be Careful! That is how mine started. After a year of driving it continued to get worse.

I apologize, but I was asked to return to my previous position in the Labs and haven’t had a day off since the first of the year. I took today and the weekend off just to spend some time in the garage and to take care of other things that need attention.

Good luck and be safe, Ric.

[66200i6]

Ok, Guy's.

It's back together and I performed some panic braking this morning. It seems that now I need to deal with the suspension before I can get this proportioning valve dialed in. My back end raises up so high when I hit the brakes, it seem like, it wouldn't make any difference how I have the valve set all the weight is removed from the rear wheels and they skid.

I knew I needed to work with the suspension I just didn't think I would need to work it as part of good braking.

Has anyone experienced this?