Technical 1957 Cadillac disc brake swap with Hydro Vac

Swapped the front drums to disc brakes this weekend. Kit was from POL. After getting it done we tried to start bleeding brakes. Started with the bleed screw on the hydro vac furthest from the firewall and then moved to the screw closest to the firewall. The bleed screw closest to firewall will not budge! I put some penetrating oil on it over night so I will check again today.
Then we bled the two fronts and got a very hard pedal. Big problem is the calipers are not releasing completely on the front.
Does the hydro vac have a built in residual valve for the front drums that is now affecting the calipers?
Or is this going to force me to change out the master and booster to the CaddyDaddy kit?
thanks for your help

 

The master cylinder is above your bleeders on the calipers so no residual value required on the disk brakes. I have one installed and it looks factory on my 57 Coupe De Ville though. It is grimy enough to have been there from the beginning. Drum brakes still. For sure there should be one going to the back as well if I remember correctly.

First things first check that there is proper vacuum on the booster. That the booster is releasing completely.

The valve if installed can stop a disk brake setup from releasing in most cases. Or a set of stuck floating pins which is what caused all the issue with my 65 Mustang.

I would imagine that you will absolutely have issues with the master cylinder and booster without a proportion valve or some ilk. Some kits are custom made to use the exact pressure and fluid volume of the factory unit but nothing for the Cadillac's of that era that I have ever seen have been that way.

This is the shop way of doing a Cadillac of that era, stolen from another site.

1) Remove filler plug from the brake master cylinder.

2) Attach a bleeder drain hose to the bleeder valve screw on the control valve
housing of the Hdrovac unit. Keep the end of the hose below the liquid level in
the jar. Loosen valve 1/2 to 3/4 of a turn. Depress brake petal slowly by hand
to expel air. When the pedal reaches the floor, close the valve before releasing
the petal. Repeat this until no bubbles appear in the drain tube and the stream
is solid liquid. Be sure to keep the master cylinder filled with brake fluid while
performing this step. Tighten the bleeder valve and remove the hose.

3) Now, repeat this same operation at the bleeder valve at the end of the
of the Hydrovac unit. This valve is at the outlet to the wheel cylinders.

4) Now, proceed to bleed all the brake cylinders in turn same as with a
standard (non Hydovac) car -- then you're done.

 

Thanks for the reply. Last night I finally got the bleeder screw open close to the firewall and bled it.
Pedal is great now and slight drag on front disc's. Weather would not allow test drive but will do tomorrow.
Master is on the frame which is lower than calipers. But the remote fill is higher than calipers. Does this make a difference on the residual valve?
I am also trying to determine the right amount of drag that would be natural for the new disc conversion.

 

Figures that there was a bubble there. For disks I would say no valve is required regardless of where the fluid or the master cylinder is located. So you should be good to go.

If this works for you without changing the master cylinder I am going to call POL and order a set up for mine.