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Discussion Starter · #1 · (Edited)
Okay...
Put power disc brakes on all four corners of my "61 Impala. (still working out bugs, car has less than 100 miles on it so far).
booster to MC spacing is correct. Pedal adjustments made.
MC was thoroughly bench bled. All lines bled.
All appears great. Drive car brakes drag..
Adjust pedal rod to booster all is great...but once the engine is ran for a while..
the brake pedal appears to fade away...also it seams it does not return
to correct stopping point .

With this said..again, I adjust all and its great until the car runs for a few miles...then seams to go to hell.
engine is pulling 20inch# of vacuum and the brake booster is the only item
connected to vac. on the motor.

Any suggestions would be great.

I know the description of the issue is probably lacking...but it is a weird issue.
Hammerit-
 

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I would power bleed the entire system. It is difficult to get all of the air out of the system pumping the pedal. A hand powered vacuum fluid pump also works it just takes longer than opening the tap on a twenty gallon jug of brake fluid and letting compressed air pump fluid through the system until it runs clear.

Big Dave
 

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If the Eldo rear calipers are like the RWD calipers from the 70s, they have a turning piston that is ratcheted when the parking brake is applied. It is essential that that the parking brake be set every time you use the car. This causes the rear pads to stay close to the rotor and will prevent you from having to pump up the brakes to get pressure. This is actually the reason that GM stopped using rear discs on the RWD cars like the Fleetwood Brougham: Cadillac customers didn't use the parking brake (even though GM provided a vacuum feature that releases the brake when the car is put in gear).
 

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Discussion Starter · #6 ·
Okay,
I plan to re-bleed the system (actually it will be about the 20th time).
Also, get into the habit of using the parking brake.

I was not sure if I was pulling too much vacuum on the booster or what...
Thank you,
Hammerit-
 

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Make sure you have the calipers on the correct side (bleed screws to the top), and tap them with a mallet as you bleed to release air bubbles that can stick to the casting.
 

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Tapping the caliper with a mallet (I assume we are talking about a plastic a dead blow hammer and not a seven pound sledge) is a new one on me. How hard do you smack them?

Big Dave
 

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Yep, plastic or rubber. Not hard. Think like the same force as knocking on a door. Can't promise it will help, but it is worth a try. I really think the problem is the parking brake issue. I did a ton of research into Cadillac rear calipers. I have two sets.
 

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Okay...
Put power disc brakes on all four corners of my "61 Impala. (still working out bugs, car has less than 100 miles on it so far).
booster to MC spacing is correct. Pedal adjustments made.
MC was thoroughly bench bled. All lines bled.
All appears great. Drive car brakes drag..
Adjust pedal rod to booster all is great...but once the engine is ran for a while..
the brake pedal appears to fade away...also it seams it does not return
to correct stopping point .

With this said..again, I adjust all and its great until the car runs for a few miles...then seams to go to hell.
engine is pulling 20inch# of vacuum and the brake booster is the only item
connected to vac. on the motor.

Any suggestions would be great.

I know the description of the issue is probably lacking...but it is a weird issue.
Hammerit-
Did you change front brake lines to 3/16" line. Using a fixed 60/40 proportioning valve? Change out all flex hoses, include rear one? If brake pedal fades to floor, the MC is leaking or lines to it. Unless your running big power, rear disc brakes waste of time and money; Front brakes do 60 % of the braking which is adequate for stock.
 
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