Buick Disc Brake Conversion

[r***@rammbackhoe.com]

I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
out why it won't work. Here is a summary of what we did:

Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.

Here is what she is doing:
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.

Any suggestions on what to do?

[Bob Johnstone]

Post by r***@rammbackhoe.com
I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.
Any suggestions on what to do?

I can't comment on the hard pedal at rest vs the no pedal under
power....... it sounds like you touched all the bases, but did the
master you installed, have the fluid capacity to actuate the calipers,
vs the drum wheel cylinders. Disks require a lot more fluid,
especially if you installed them on all 4 wheels and the master has a
much larger bore. There is also the issue (on some cars) of the
actuator rod from the pedal into the master being adjusted correctly.

[Eugene Blanchard]

Just by chance. Did you hook up the front and rear brakes correctly to the
master cylinder? The big reservoir which is typically closest to the
firewall is for the front disk brakes. The small reservoir which is at the
front of the master cylinder is for the rear drum brakes.

Post by Bob Johnstone

Post by r***@rammbackhoe.com
I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.
Any suggestions on what to do?

I can't comment on the hard pedal at rest vs the no pedal under
power....... it sounds like you touched all the bases, but did the
master you installed, have the fluid capacity to actuate the calipers,
vs the drum wheel cylinders. Disks require a lot more fluid,
especially if you installed them on all 4 wheels and the master has a
much larger bore. There is also the issue (on some cars) of the
actuator rod from the pedal into the master being adjusted correctly.

[.boB]

Post by r***@rammbackhoe.com
I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.
Any suggestions on what to do?

If the brakes work and you have a good pedal when the
engine is off, and then the brake pedal sinks to the
floor with the engine on, the problem is the booster.

"The booster is an empty shell that is divided into two
chambers by a rubber diaphragm. There is a valve in the
diaphragm that remains open while your foot is off the
brake pedal so that vacuum is allowed to fill both
chambers. When you step on the brake pedal, the valve
in the diaphragm closes, separating the two chambers
and another valve opens to allow air in the chamber on
the brake pedal side. This is what provides the power
assist."
http://www.familycar.com/brakes.htm

Essentially, you're getting too much vacuum assist.

[Kevin Bottorff]

Post by .boB

Post by r***@rammbackhoe.com
I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.
Any suggestions on what to do?

If the brakes work and you have a good pedal when the
engine is off, and then the brake pedal sinks to the
floor with the engine on, the problem is the booster.
"The booster is an empty shell that is divided into two
chambers by a rubber diaphragm. There is a valve in the
diaphragm that remains open while your foot is off the
brake pedal so that vacuum is allowed to fill both
chambers. When you step on the brake pedal, the valve
in the diaphragm closes, separating the two chambers
and another valve opens to allow air in the chamber on
the brake pedal side. This is what provides the power
assist."
http://www.familycar.com/brakes.htm
Essentially, you're getting too much vacuum assist.

no it would not go to the floor with too much assist. It would stay hard
anyway. KB

[Eugene Blanchard]

***@rammbackhoe.com - once you figure out what the problem is, make sure
you post the solution. It's always interesting to see what happened.

[v8z]

Post by r***@rammbackhoe.com
I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.
Any suggestions on what to do?

My guess is that the problem has to do with an incorrect or incomplete
proportioning valve and/or hold-off valve setup.
Take a look at the info on http://www.inlinetube.com/pro_valves.htm
Lots of pics and descriptions of the various setups used over those years.
They might be able to help you sort it out if you take photos and email
them.

[*]

I would bet that you have the calipers on the wrong sides.

Post by r***@rammbackhoe.com
I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.
Any suggestions on what to do?

[NoTop442]

Post by r***@rammbackhoe.com
I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.
Any suggestions on what to do?

All the posted suggestions you should look into. I have a 1972 Buick
GS I did a conversion on. By the way a Stage 1 would be a 455 engine.
You can email me direct if you need assembly diagrams or info from the
factory service manuals which I have.

visit us at www.cyrusnet.com/~notop442

[SSIII]

Post by r***@rammbackhoe.com
I just purchased and put on a disc brake conversion for a 1968-1972 GM
A body car. My car is an 1971 Buick GS with the 350 Stage 1. I
purchase the kit off of ebay from waterloo tire company out of Iowa.
Of course it came with no instructions. I put on the parts myself and
could not get it to work. I took to local mechanic and he can't fiqure
Installed new bearings, spindle and rotors. New SS braided hose. New
chrome power booster, master cylinder, proportioning valve and lines
from mastercylinder to proportioning valve. Had to get new lines to
rear becuase could not get fittings to match. Had new rubber brake
hose made from front to rear.
When car is turned off I have hard pedal. When cranked there is no
pedal. I have bench bleed master several times and power bleed it. I
can't get any pedal when it is cranked. No stopping except a if not
going fast rear brakes will lock up and gradually stop the car. I
plugged the master cylinder and it has hard pedal.
Any suggestions on what to do?

maybe call the company and ask for instructions?