Front disc brake conversion

S

Skimoe55

Junior Member
Helping my neighbor with his 56 Montery disc brake Speedway Motors conversion, we have bled brakes multiple times and finally with a pressure bleeder. Pedal almost on floor so drilled a new hole 1 inch lower but the angle of pushrod is too severe, tried tilting booster up in front but can't get a proper angle. All pushrod to master checked and adjusted with proper gauge freeway about 1/4 inch. So has anyone had these problems, starting to think we have to change brake pedal, Thanks for any info.
 
Does full pedal travel bottom the piston in the booster? And did you check the clearance from the booster to the master? I’ve seen more that one “kit” that needed changes. Even on tri 5 Chevy’s where they sold hundreds of them.

Edit: was that an original power brake car with a treadle vac?
 
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I think that's part of the problem, even redrilling pedal to booster mount one inch lower we still are not getting a full stroke on master cylinder. This was a non power drum brake car, booster to master rod is adjusted to .025 . When we have about two inches of solid pedal and then start car power booster takes it to floor, I'm thinking master cylinder is suspect maybe along with geometry of pedal to booster. Before moving mount down one inch we only had 7/8 inch stroke of booster rod to master.
 
Sometimes the calipers are installed on the wrong side. When this happens the bleeder is at the bottom, and air can be trapped in the upper half of the caliper. If this is it, do not be embarrased, I have seen it happen before.
 
Both calipers are on the right sides and bleeder are at the top, we are going to remove master and remeasure total pushrod stroke again with pedal mount drilled lower.
 
This is an odd one, but I had it happen and it drove us crazy.

Finally we happen to start the car with the master off the booster. I was under the hood, and the damn booster moved a 1/4” out. He didn’t touch the pedal. The owner called the guys he bought the kit from and the immediate response was “that’s a partial booster failure, send it back”. That solved it. So have a look while you have the master off.

The other thing I’ve seen is not having the rear drums properly adjusted before doing the bleeding. Gave the low pedal like you described. I don’t know if you’ve got self adjusters on the back (either oem or updated), but that’s worth a look.

Both long shots, but cheap and easy to check.
 
Thanks, we will be pulling master cylinder out and checking rod travel and have good look to make sure booster isn't pushing out.
 
The kit I got for my 57 Ranchero was kicking my butt. Just could not get good brake feel, low pedal, soft stopping feel. Must have blead two quarts through. A friend came over, looked under the dash and asked "why is the brake pedal not all the way against the stop?" Turns out the push rod was 3/4" short. Made the adjustment and all was well.
 
So we have tried everything to fix this problem, replaced rear wheel cly, flexible hose to rearend ,pressure bled the brakes starting at pass rear a dozen times . No air in lines , pedal is near floor but solid, car will stop but at anything over 20 m.p.h a panic stop is out of the question.
When we replaced rear wheel cylinders we measured drums before replacing shoes and found drums way over specs so my question is where does one find replacement drums with the 5x5 wheel bolt pattern, he even looked at rear disc brake conversion kits but are not available for this reared. Starting to think only fix is to upgrade to a more modern rear axle , Thanks
 
Does that have the Dana 44 (or a variant) rear end? FOMOCO used the Dana’s in wagons, police specials, Tbirds, and pickups at least thru 56, and many Mercury’s. The standard rearend was not robust enough. That changed when the 9” came out in 57.

If it’s one of the Dana’s (google Dana 44 there’s pictures of the rear end gasket for id) there may be some alternatives.
 
Let me get this in before I am discovered ...​

miker98038 said:
Edit: was that an original power brake car with a treadle vac?
Click to expand...

!!! GOOD POINT !!!​

If the MERC (or LINC) came through with TREADLE-VAC, the pedal assy has to be changed to a manual brake car take-off pedal assy before it can operate a vacuum booster ...
 
If the MERC (or LINC) came through with TREADLE-VAC, the pedal assy has to be changed to a manual brake car take-off pedal assy before it can operate a vacuum booster ...
Click to expand...

1st ILL - MANUAL BRAKE PEDAL INSTALL

2nd ILL - POWER BRAKE PEDAL - TREADLE-VAC​
 

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  • BRAKE PEDAL ASSY - MANUAL - 1956 MERC.jpg
    BRAKE PEDAL ASSY - MANUAL - 1956 MERC.jpg
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  • BRAKE PEDAL ASSY - TREADLE-VAC _1 - 1956 MERC.jpg
    BRAKE PEDAL ASSY - TREADLE-VAC _1 - 1956 MERC.jpg
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91032000Dual 7 Inch Brake Booster Master Cylinder Combo, 1 Inch
Speedway 11 Inch Disc Brake Conversion Kit, 1954-56. Also looking at your parts diagrams im pretty sure it's the regular non power pedal, we are thinking of getting a pressure reading from the master cly. New flexible hoses all around, pressure bled brakes multiple times and still require two feet on pedal to try and make a panic stop. Even on loose gravel can not lock up any wheels
 
I am going to start posting tech info as I go along -


The 7-inch DUAL DIAPH is not going to produce as much assist as say a 9-inch SINGLE.

He bought the 7-inch dual to clear the FYB exhaust manifold? Did it (MC) actually clear?

Did anyone selling the kit(s) mention needed hydraulic valving?

Can you post photos?
 
2nd Realization ...

Did the SPEEDWAY disc kit include 4-PISTON CALIPERS or GM ONE PISTON CALIPERS?

Give PN if you can.
 
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