Ford Muscle Cars Tech Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
196 Posts
Discussion Starter #1
heres my issue ,when i restored my mustang i used a donor 68 cougar for the power brake booster, master cylinder and proportionong valve,while i used a granada front disc brakes and spindles,to convert my manual drum car to power discs.the booster and master were rebuilt by a reputible shop,and installed.the problem is the brake pedal is rock hard and only seems to get worse as you drive it.i checked the vaccumm and it seems great coming out of the intake ,and the check valve at the booster seem to be fine too.i added a vaccumm canister to see if that helps and it made no diffrence at all.not sure what else too do! need advice. thanks
 

·
Premium Member
Joined
·
1,330 Posts
Manual brake and power brake pedal is different. Does brake pedal move at all?
 

·
Registered
Joined
·
196 Posts
Discussion Starter #3
yeah brake pedals off the cougar also.it moves but not much.it gets very hard to push after you stop at a light after a few seconds
 

·
Registered
Joined
·
196 Posts
Discussion Starter #6
tried the brake pedal at start up. dosent move at all.checked vaccumm got lots.valve only blows through one way.all the pedals and brackets look right. what gives?
 

·
Premium Member
Joined
·
1,330 Posts
Do the brakes stop the car easily? It could be a bad booster or incorrect pedal rod adjustment. If you open a bleeder does the pedal go to the floor when pressed?
 

·
Registered
Joined
·
196 Posts
Discussion Starter #8
yeah it bleeds just fine.it stops but the pedal is rock hard.how do you adjust the pedal,i see no adjustment
 

·
Premium Member
Joined
·
1,330 Posts
Sounds like a bad booster.
 

·
Registered
Joined
·
196 Posts
Discussion Starter #12
Just ran thecar for a couple min,shut it off and pulled the booster check valve out.lots of suction.booster seems ok.what about seized sliders on the calipers? Could this be keeping the brakes tight to the rotors,without locki.g up the brakes.not givinge any pedal travel?. Just drawing straws now.
 

·
Premium Member
Joined
·
34,853 Posts
Lift all 4 wheels and block car. Start car, engage in drive hit brakes. If you cannot stop the wheels you have issues.

For the front wheels have someone roll them and hit the skids to see if they stop with the engine off, then again with the engine on.

If all else fails take it to a rolling dyno and see how well the front brakes stop. That's how they test brakes in the UK and Europe to see if they meet M.O.T standards.

Or you can remove a caliper and push the pedal and see if the piston moves on either side. And make changes from there.

If your brake pedal arm is off a non power car and you go to a power setup the braking force is multiplied, not reduced. the non power setup have slightly different angles in some cases to assist in brake pressure.
 

·
Registered
Joined
·
10,315 Posts
If you have:

  • a properly bled system
  • properly adjusted booster push rod
  • working check valve
  • vacuum in the booster housing
but you don't have power brakes, your booster is bad. Pulling the check valve and hearing air rush in only means the check valve is good. The booster has seals, a diaphragm, springs and two more valves inside, and if any of those aren't working right it's bad - even if (or especially if) it's getting vacuum. Some can be cheaply rebuilt, and others not.

David
 

·
Registered
Joined
·
10,315 Posts
FYI - there are two booster types for the '68 Cougar - Bendix and Midland. The Bendix has no clamp band around the middle, and is $70-90 with exchange:

The Midland booster has a clamp band and runs about $130-150 with exchange:

These examples are from Rockauto.com, and remanufactured by A1Cardone. Right now, RockAuto has a better price for one with a fresh master cylinder on it than just the booster alone. There are other sources like Booster Dewey that provide the service on your original if that's imortant to you.

David
 

·
Registered
Joined
·
196 Posts
Discussion Starter #16
well i rebuilt the booster replaced the master and still had the same issue.well it turns out when the disc brake conversion was done someone,possibly and likely me,didnt grind the hole in the firewall bigger for the rod and it was binding on the firewall when i applied the brakes.i new it had to be something simple.thanks for your input,they proably need ed to be replaced anyway.now everything is fresh. although i still have a problem of a rock hard pedal at a stop light.when driving the brakes work great.i did a vaccum check and it turns out at idle i only have 12lbs of vaccum.i dont think thats enough to work my power brakes,when i hit the gas and rev the engine i get 22lbs of vaccum in a instant.i guess that monster cam in my engine is to blame. i tryed adding a vaccum cannister can,and it seemed to help slightly but not enough.looks like i may need a electric vaccum pump! anyone use one of these,know a good one,or can give me some advice on this it would be appreciated,cause i know nothing about these. thanks
 
1 - 16 of 16 Posts
Top