50 Merc Disc Conversion Problem

[Paul Bennett]

My previous thread re: brake problem turned out to be due to front bad wheel cylinders leaking fluid onto the linings. This gave me low brake pedal. But I did have some brake pedal pressure. Car has new master cylinder, linings and brake hoses, car just wouldn't stop because of the front problem so I decided as long as I needed to fix the fronts, to go whole hog with front discs.

New POL front disc conversion install went well until I tried the brakes. I have bled the brakes till the cows came home, guaranteed no bubbles. But I can't get pedal pressure. It is spongy won't really pumps up hard. I've checked for leaks elsewhere but none. I recall something about a 'residual' pressure valve. I also recall hearing this conversion works with existing mc. I will phone POL but it's after hours now.

Do I actually need to go to a dual chamber MC with residual valves and proportion something. Firewall mount masters need mounting kit for my car. Recommendations? Ideas? Hints? I'm in need of experienced input. Thanks

I realizing this is a non-Ford conversion so I am also posting at HAMB but know there are Merc owners in the Barn who have gone through this.

[51 MERC-CT]

Yes you need a disc/drum master cylinder as well as residual valves and a proportioning valve.
ECI brakes used to sell a right angle bracket to mount the dual master in the original position.
(do yourself a favor and install 'SPEED BLEEDERS' )

[weemark]

you only need residual valves if the MC is under the height of the wheel cylinder - they stop bleed back. Have you bled the MC on the bench before you installed it? might just be the MC needs to be bled. If you have went to discs you should have a disk/drum MC installed however you should get one that retrofits your car - no need to move it to the firewall.

[Paul Bennett]

Weemark - I have NOT bench bled the mc. When I installed the mc recently I didn't bleed it then either but did a vacuum bleed on the system and got pedal immediately.

51 - Sure with I knew the $500 initial conversion outlay was only the beginning of a currency drain. POL wants another $200 for dual mc w/prop valve and bracket. But guess I'm in like a chinese finger trap. No backing out now.

Question for 51 - how easy/difficult does filling/checking fluid for the mc. Do you perhaps have a photo of the mc in position?

[supereal]

Bleeding using a vacuum tool when the wheel cylinders are higher than the master cylinder usually results in a "spongy" brake pedal when some air remains in the system, Most, if not all, master cylinders have a residual valve. this allows the brakes to be applied without having to pump them by preventing back flow when the brakes are released. A dual master cylinder is a good investment, particularly when using existing brake lines. It prevents total loss of braking if any part of the system springs a leak.

[rich b]

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If you decide to keep your single under the floor master cylinder; you will need to remove the internal residual check valve and plumb in external residual valves; 2 psi for the front and 10 psi for the rear. Probably should also add a proportional valve in the rear line at this time.

If you do switch to the dual master cylinder kit, be sure to check, during the process of bleeding, that loss of either end does not result in the pedal hitting the floor before the other end is applied.

In other words have someone open a bleeder while you are applying the brakes to see what happens, then do the same for the other end.

Sometimes these kits are not fully engineered and the extra travel required in "failure" mode is not taken into consideration.

I've seen dual master set-ups that were no better than singles for this reason.

[1948F-1Pickup]

Never done that conversion with a floor level master (or with a single chamber master either- dual reservoir is the way to go here) but like was already posted, if the MC level is below the wheel cylinders, you will need a residual check valve plumbed just before the master, as I hear you have rear drum brakes still. You probably also will need a 2# valve in the front disc circuit because although you don't have the "take up" problem of the pads moving away from the rotor, you still have the master cylinder height issue and the
fluid will have the desire to run back into the master after you release the brake pedal.

[Bob T]

I have done this conversion on my 51 Merc. . 'Fatman' sells a bracket that mounts a dual master cylinder in the stock position. No power brakes [don't need].Used 77 Mustang 2 master #Raybestos MC36440.Did not use residual valves or prop. valve. You do need a fitting for a .brake light switch. I use Harley Davidson switch # 72023-51E. Good luck. I hope this helps.

[richard crow]

paul i am going to ask you a dumb question don,t get mad .but i have seen this more then once .did you install the calapers with the bleeder valve on top faceing up.if they are faceing down they are installed wrong & you will never get a pedel

[Paul Bennett]

Richard - calipers have Top and Right and Left cast into them to help prevent faulty installation which you warn can happen. I've also seen illustrations where a caliper on an angle can hold air but am advised is unlikely with the kit I have.


At this point I am hoping someone with a Fatman MC adaptor will show up as they quit making them and the alternative bracket looks odd to me.

[51 MERC-CT]

Originally Posted by Paul Bennett

Richard - calipers have Top and Right and Left cast into them to help prevent faulty installation which you warn can happen. I've also seen illustrations where a caliper on an angle can hold air but am advised is unlikely with the kit I have.


At this point I am hoping someone with a Fatman MC adaptor will show up as they quit making them and the alternative bracket looks odd to me.

Just called ECI ( Engineered components Inc.) where I purchased my bracket years ago.
Although they stopped making them he would be willing to fabricate one as they still have the patterns.
Call them at (1-860-872-7046 )

http://www.ecihotrodbrakes.com/

[Paul Bennett]

I will call ECI Monday. My emergencies all happen on Friday afternoon after quitting time.

I've just come out from under my car and there is definitely no way the commonly sold mc adaptor bracket will work mainly because of interference with the left side exhaust which I will NOT remove to Fatman it is.

I am seriously considering adding residual valves to the factory mc and start a study of brake systems. Meanwhile I will terminate this thread and start asking questions anew.
Firstly, I need volume info on the disc calipers I just installed and compare that to the volume of the factory drum wheel cylinders. I have the will so there's a way. Thanks 51 for your help and encouragement.

[51 MERC-CT]

Originally Posted by Paul Bennett

Note ECI Phone is 1 860-7046 Last nr is six. But I will have to call Monday. My emergencies all happen on Friday afternoon.

Sorry bout dat. That's one of the symptoms of old age.
Incidentally, as I understand it Fatmans bracket was made as a direct copy of ECI's design with their approval.

[Paul Bennett]

Originally Posted by 51 MERC-CT

Incidentally, as I understand it Fatmans bracket was made as a direct copy of ECI's design with their approval.

Think I saw that re ECI in HAMB threads which go back ten years. I understand business decisions to support '60s car items and drop or phase out 50s cars items which are now much lower volume and hard to support investment in inventory.

While 49-51 Mercs will probably always hold the title of 'most customized car' there aren't many new owners like myself who are making fresh mods and like yourself who are maintaining '49-51 Mercs. Rather than waiting, I recently bought a driver's side mirror at high price as several houses who used to carry the mirror are now out of stock and not reordering. I will also buy other such obsolete-trending items. It strikes me quality ignition condensers are also getting hard to find.

[19Fordy]

Paul, it's gotten to the point where ANY 49-51 Merc part is solid gold.