Slow return of brake pedal?

[427Swede]

Hi,

Got my 427 -69 back on the wheels yesterday and drove my first 100 feet on the road. Had to stop and go back, it was too much dust on the road after the winter, and then I noticed that my brake pedal was a bit slow to return after beeing depressed. I could feel the hesitation of the brakes for 1 second before they let go of the discs.
I have a totally rock hard pedal, and it is like slamming in to a brick wall when i apply the brake pedal.

The master cylinder and brake booster is brand new, from a well known supplier, and the quality seemed greate. The master cyl. was licensed under GM according to the box, if that is a quality sign theese days...

What can be wrong? The pedal takes just over 1 second to return from fully depressed with the engine running.
Is the internal proportioning valve inside the booster (do not know the exact name of it) out of order or can the booster be a bit slow after being stored in the box for a year and a half before assembly?
Can I hope for this to get better if I drive a bit more?

Regards, Daniel

 

[mrvette]

There is a pretty tuff pedal return spring on the pedal arm itself, connected to a spot toward the rear of the car, on the main brake support, that spring is about 3-4" long and about 1/2" diameter, made of pretty tuff wire.....

 

[427Swede]

I could not find such a spring on my pedal set up. There is a spring acting on the brake pedal but that is positioned right on the brake and clutch pedal bearing shaft.
I tried to pull the pedal back up manually but the pedal pretty much ignored my efforts and continued in it´s own phase...
Maybe later models were equipped with the spring you are talking about?

 

[Twin_Turbo]

Did you properly adjust the booster pin into the MC or did you use too long a pin so that the compensation hole is not open?

 

[mrvette]

Did you properly adjust the booster pin into the MC or did you use too long a pin so that the compensation hole is not open?

Umm....Early/late shark booster/master cyl mix up?? one takes a long dick from the booster into the master cyl.....the other is more typical of most GM products, and just a little/ 1/4 inch? divot....

mix them two up and who knows???


:hissyfit:

 

[427Swede]

Did you properly adjust the booster pin into the MC or did you use too long a pin so that the compensation hole is not open?

Hmmm, now I get a bit uncertain... I used the pin delivered with the booster and I checked that it did not push on the mc piston before the pedal is depressed.
Can you explain what the compensation hole is?
The MC and the booster is correct for my car.

 

[Twin_Turbo]

Been thinking, it can't be the mc, it has to be the booster since the 2 are not solidly together. Even with a hanging mc. Sounds like the floating valve is shot and not opening the vac side to atmospheric quick enough. Is the litlle foam dampener hung up or maybe packing peanuts on there?

 

[010752]

Compensation port is the tiny hole in the bottom of the master just ahead of the seals, that when exposed at rest, releases the brake fluid pressure to atmosphere pressure. It also allows for a slight new charge of fluid if necessary.

You may have your master/booster rod a hair too long, not long enough to keep pressure on the system, but enough to push the reaction disk in the booster.
Loosen the master mounts on the booster a bit and retest. If good, shorten the rod a hair.

The new and older master/booster combos are different enough, with a mismatch, you would have drastic failure.

 

[427Swede]

Been thinking, it can't be the mc, it has to be the booster since the 2 are not solidly together. Even with a hanging mc. Sounds like the floating valve is shot and not opening the vac side to atmospheric quick enough. Is the litlle foam dampener hung up or maybe packing peanuts on there?

Compensation port is the tiny hole in the bottom of the master just ahead of the seals, that when exposed at rest, releases the brake fluid pressure to atmosphere pressure. It also allows for a slight new charge of fluid if necessary.

You may have your master/booster rod a hair too long, not long enough to keep pressure on the system, but enough to push the reaction disk in the booster.
Loosen the master mounts on the booster a bit and retest. If good, shorten the rod a hair.

The new and older master/booster combos are different enough, with a mismatch, you would have drastic failure.

Thank's!! I will loosen the mc a bit and make a new test. I hope I will not have to get a new booster... A nightmare to remove and the cost for a new unit will be around 460$ here in Sweden. I will get back with an update on the test.
Again, thank's!

 

[427Swede]

Update: checked the function with the mc moved away a bit. Same result. Checked the pedal free play in relation to booster and it was a clear play there.
Took it out for a new test drive and to my surprise the phenomena got less and less with each break! When I got back home it was basically ok. Iwill leave it for now.

A real joy to finally drive my car after two years of rebuilding!
Now it is time to change oil in the gearbox and fix a minor water leak.
Thank's for your input!

Regards, Daniel

 

[Stroker-427]

Maybe some grease in the compensation hole of your new booster?

In a very small hole even the pressure will act a very small force..... 1mm hole will result in some 0.8 grams of force @ 1 bar of pressure...... even a drop of grease can substain that force.