[1969XR7Vert]

So as I prepare to do a late model Cobra 4 wheel disk conversion, I am wondering what are people using for 4 wheel disk conversion Master Cylinder?

Hoping to do better than this:

http://streetortrack.com/Master-Cylinder-for-4-wheel-disc-1964-73-Mustangs-pr-23771.html

Or Mustang Steve's plastic reservoir piece for $120 and metric fittings on the wrong side.

By finding out "the skinny" on an OEM part that I can just order from Advance or something like that.

I did read online that at least one person has used a stock disc/drum master without issue, but a later model unit with a shared reservoir would be important since the caliper pistons use up reservoir capacity as the pads wear (unlike self-adjusting drums). However (and to the contrary) I read about 10 lb residual valves used with at least some drum or disc/drum masters.

Also, I think I read somewhere that a (70's?) corvette disc/disc master would bolt up/fit.

Lastly, would getting an adjustable prop valve be important or can the stock valve from the disc/drum do the job on a disc/disc setup?

Learn an ECI, will 'ya?

Thanks,

Bob

 

[1969XR7Vert]

Think I am seeing there is no magic bullet for the master, except that Scott Drake (apparently one of the solutions that Street or Track sells) has a drop-in:

http://www.drakeautomotivegroup.com/Store/Product/C7ZZ-2140-4WDB.aspx?wid=141

Or a newer aluminum/plastic unit with metric fittings on the wrong side.

And looks like the adjustable prop valve is a must as well from what I am reading (not unexpected).

 

[xr7g428]

Search is your friend............. LOL! I just had to say that!

What are you doing for a parking brake solution? With a 4 speed that seems important as well.

 

[ahunt191]

The 75-81 Monarch/Granada/Versailles MC will bolt up and work and the fittings are on the correct side. However, the push rod is not the correct length. You will need to re-use your push rod provided you aren't switching between power and manual brakes.

 

[ken68cat]

I installed the 4WDB one above and used my original push rod. Seems to fit fine, although I haven't completed the disc conversion yet.

 

[1969XR7Vert]

Search is your friend............. LOL! I just had to say that!

What are you doing for a parking brake solution? With a 4 speed that seems important as well.

I did use the search, more than one way, but not much of use came back.

On the E-brake, I have to see what the situation with the Cobra rear calipers ends up being. U-bolting cable pieces together as Mustang Steve suggests is not going to fly with me. I think I can crimp new ends onto whatever I end up using for cables with a tool for sailboat stay crimps. Will let you know what I come up with.

So far, looks like I can sneak into this upgrade for about $1300, right around what a one axle upgrade kit costs for the big brakes.

Regards,

Bob

 

[1969XR7Vert]

The 75-81 Monarch/Granada/Versailles MC will bolt up and work and the fittings are on the correct side. However, the push rod is not the correct length. You will need to re-use your push rod provided you aren't switching between power and manual brakes.

I came up with a cylinder with fittings on the wrong side using 81 Granada, and a cylinder with a weird mounting flange (for hydro-boost) for a 77 Versailles (but fittings on the right side - big in back, small in front - backwards from my '69). Any info to point me to on this?

Looking at the SD unit and seeing the front reservoir is still small, I am wondering if this is just a disc/drum unit with the residual valve removed. I could do that to a stock master by popping out the flare seat on the drum side and removing it (something I remember having to do to certain replacement MC's back in the day when I was working as a mechanic).

If I don't get much further with the search (it's starting to look that way), I will likely just buy the SD unit, seems the path of least resistance. The newer cylinders require a fair amount of work to fit and spoil the vintage look in the engine bay.

Regards,

Bob

 

[ahunt191]

The master cylinder I'm using is for a '75 Granada with manual disc/drum brakes. The large reservoir is in the back and small one is in the front. My '67 came with manual drum brakes, so I had to double check the shop manual. It shows the '67 disc/drum MC with the large reservoir in the back also. The '67 Cougar and the '75 Granada master cylinders have the fittings on the drivers side.

Yes, you can pull out the residual pressure valve. You will just need to use an external 2PSI valve.

 

[1970fastcat]

Here's a non adjustable valve for you. They also have lots of other goodies you might need. http://www.mpbrakes.com/products/product-detail.cfm?product_id=613

 

[1969XR7Vert]

The master cylinder I'm using is for a '75 Granada with manual disc/drum brakes. The large reservoir is in the back and small one is in the front. My '67 came with manual drum brakes, so I had to double check the shop manual. It shows the '67 disc/drum MC with the large reservoir in the back also. The '67 Cougar and the '75 Granada master cylinders have the fittings on the drivers side.

Yes, you can pull out the residual pressure valve. You will just need to use an external 2PSI valve.

And these have been used for Disc/Disc conversions?

 

[coolgar]

Bob take a look at this I enlongated my own holes and shortened the stock pushrod on my 67 but they have lots of different bore and fitting sizes to choose from http://www.classicperform.com/Store/StreetRods/MC116L.htm

 

[1969XR7Vert]

...Yes, you can pull out the residual pressure valve. You will just need to use an external 2PSI valve.

Why would I want a RPV with disc/disc?

I have nothing to prove this, but I am thinking maybe the SD MC is just the stock disc/drum type (sure looks to be in a picture) with the RPV removed from the rear circuit. Could be quite a coup to prove that one correct, and I might just take apart one of my "extra" masters to see what the RPV valve consists of. If memory serves or hunches correct, it will be a check valve sort of thing which resides behind the rear circuit flare seat of the MC.

Edit: You gotta love the internet! (And the company name for that matter!!) :buck:

http://ecihotrodbrakes.com/brake_facts.html

The 2 PSI RPV's are only needed if the MC is below the calipers. The prop valves is stated as optional depending on the combination of parts used. Probably a good idea to have one (roll the dice and try the stock one with a stock MC with RPV removed first? Must follow the ECI creed)

 

[1969XR7Vert]

Bob take a look at this I enlongated my own holes and shortened the stock pushrod on my 67 but they have lots of different bore and fitting sizes to choose from http://www.classicperform.com/Store/StreetRods/MC116L.htm

Thanks for that Coolgar, a Corvette style cylinder with ports on both sides, the means to be used with power brakes and cheap. Looks like the 116 (1 1/16" bore) is no longer available, but the 118 (1 1/8" bore) unit is. I guess the only negative (in my mind) would be the GM style housing/top. Otherwise it sounds perfect.

 

[doctordesoto]

for e brake custom e-brake cables try control cables inc---they know their stuff and fast and reasonabley priced
as far as the mith that you must use 2psi rpv when the mc is below the wheel cyl is just that---a mith---if everything is right you will need a 10psi for drum rear to keep the w/c "charged"--my 47 sedan has disc/drum setup .---a 10psi in the rear line , no rpv in the front and no prop valve either--the m/c is 8" off the ground and the calipers are about 19" off the ground--it was explained to me that its kinda like putting a straw in a glass off water and putting your thumb over the end of the straw---you can lift the straw out of the water and none of the water will run out of the straw until you lft yor thumb
most prop valves are just a time delay valve (an oriface)if you put 300psi on any size hole , sooner or later there will be 300 psi on the opposite side of the oriface---you can do the same thing by changing wheel cyl dias and pad/shoe hardness
the explorer rear disc setup is a pretty good disc/e-brake setup for the cost--most of the kits are for big brg 9" rears but i think a guy could addapt the stuff to an 8" or just use the 8.8 out of the exploder--3:73 gear(perfect for an o/d) a rebuildable posi and one could shorten the long side to except the short axle if you want the tubed look
doctordesoto

 

[1969XR7Vert]

Thanks Doc regarding the E-brake cable source and the 2 psi RPV myth (at the very least it seems to not apply to my situation, myth or not).

Just found an older reference to removing the RPV, doesn't take much more than this for me (the ECI) to give it a try - and I'll leave the stock prop valve in place and see how it works. If no good, I can always change master, gut prop valve, install adjustable valve, etc.

http://forums.vintage-mustang.com/2698632-post7.html

 

[1969XR7Vert]

More research:

http://members.boardhost.com/MustangSteve/msg/archive/1273626210.html

The new ones I sell... Do not have residual pressure valves in them. Original 67-70 master cylinders DID have a RP valve in the outlet to the rear drums. Since they no longer put them in new ones, they work fine. Either way, they have a 1.0" bore piston, so that is not an issue. As stated above, as the pads wear, the fluid level will drop, so keep an eye on the fluid and you will be fine. (end)

(ECI Bob speaking) This tells me two things:

1. Probably don't have to do anything with the (new) original replacement master (but will look to see what is behind the rear circuit flare seat anyway) and

2. I would not be the least bit surprised if this no RPV in new replacement masters 'thang has something (or everything!) to do with the difficulties I had getting decent brakes initially with a stock disc/drum setup. (you reading this Mike?)

 

[ahunt191]

for e brake custom e-brake cables try control cables inc---they know their stuff and fast and reasonabley priced
as far as the mith that you must use 2psi rpv when the mc is below the wheel cyl is just that---a mith---if everything is right you will need a 10psi for drum rear to keep the w/c "charged"--my 47 sedan has disc/drum setup .---a 10psi in the rear line , no rpv in the front and no prop valve either--the m/c is 8" off the ground and the calipers are about 19" off the ground--it was explained to me that its kinda like putting a straw in a glass off water and putting your thumb over the end of the straw---you can lift the straw out of the water and none of the water will run out of the straw until you lft yor thumb
most prop valves are just a time delay valve (an oriface)if you put 300psi on any size hole , sooner or later there will be 300 psi on the opposite side of the oriface---you can do the same thing by changing wheel cyl dias and pad/shoe hardness
the explorer rear disc setup is a pretty good disc/e-brake setup for the cost--most of the kits are for big brg 9" rears but i think a guy could addapt the stuff to an 8" or just use the 8.8 out of the exploder--3:73 gear(perfect for an o/d) a rebuildable posi and one could shorten the long side to except the short axle if you want the tubed look
doctordesoto

If you work it out (density * gravitational acceleration * (MC height - caliper height) = residual pressure due to gravity), you will see there is already a couple PSI at the caliper. In this case, a 2PSI RPV does nothing. I was mistaken; it doesn't apply to you Bob.

I understand the straw analogy, but what happens when you bleed your brakes? When you have the bleed screw open and the pedal is not depressed yet, the brake fluid will want to flow back to the master cylinder if your master cylinder is below your calipers. I guess you have to do it with a vacuum pump. Still, this would make me a little nervous. How do you know air isn't getting into your system? With a 2PSI RPV, you keep very small leaks from resulting in squishy brakes.

"Exploder", lol. After the Explorer/Firestone fiasco, that's the only thing my Dad would call them.

 

[1969XR7Vert]

Check out the big brain on Adam, LOL! Seriously though, thanks. Wondering what you are doing your Ph.D dissertation on?

 

[doctordesoto]

i've never had an issue bleeding the brakes , if any thing its easier with a lower m/c because the air in the system rises---this old cus taught me a trick to bleed brakes-------put a rubber hos on the bleeder screw and have it go up 6" or so over the bleeder screw---open the bleeder screw---pump the m/c slowly 4 or 5 times---don't let the m/c run dry ---if you've got fluid out of the hose , shut it off and repete at all 4 cylinders---your done---if you have an issue with a dual m/c , try bleeding one front and one rear at the same time----the thery is that the hose going up acts like a sink trap and doesn't allow air back in the wheel cyl when letting the m/c back out
doctordesoto

 

[1969XR7Vert]

Thinking about the disc/drum master used in a disc/disc application (and the small reservoir for the rear), what about drilling a hole in the wall between the two halves about 1/3 to 1/2 (probably closer to 1/3) way down the wall so the small could share some of the big (as modern plastic reservoir units do)??