The Stovebolt Site Forums The Shop Area Driveline How do your booster brakes feel?

Hi guys

I have an underfloor booster discs front drums back 2lb residual front 10lb back. Stock brake pedal.


I have bled the heck out of it and I don’t think I have any air

Brakes certainly work but the pedal feels weird to me.

I’m curious how others brake feel and if it’s normal given the pedal geometry etc

When I step on the brake the first half inch takes up the slack. Then I get some resistance which is mild at first increasing as the pedal drops six inches or so before it stops under hard foot pressure. It stops about three inches from the floor and it’s not a dead stop it’s kinda spongy. It gives the feeling that I could push harder and it could drop more. But that could just be a feeling

The pushrod moves just shy of one inch from rest to foot hard down (3” above floor)

Does the above description sound like yours?

Or is your feel different


(No change if parking brake applied, shoes adjusted)
(pushrod length adjusted)
(Booster rod adjusted)


Thanks

How do the brakes feel without the engine running ? ( engine off or no vacuum assist)
With out power assist it’s easier to determine if there is still air in the system.
With out power assist the pedal will be rock hard and it will take a huge pedal effort to stop but the pedal will be firm.
The disk upgrade will not feel like modern brakes ..........the pedel feel and travel is different.


As for the manual transmission conflict ........think some of that is for modern drive train upgrades. The shifter linkage and rear trans cross member can be an issue.

Did you bench bleed the master cylinder before installing in the truck?

thanks


The above description is with engine off.

Certainly not hard or needing much effort in fact I can use my hand almost...

Not much different with engine running at all



I’ve power bled a lot...can it still be air? Are they that hard to bleed? Pumping the pedal doesn’t harden it up...so figured not air....could it be an internal leak in the master cylinder? ....

Hi

Yes I bench bled before installing

The geometry of your pedal linkage is wrong, and/or the master cylinder piston diameter is too small. Do a little math calculation, comparing cylinder diameters and displaced volume, and how much pedal stroke will be required- - - - -BEFORE you invest in a bunch of mismatched parts. At this point, the most likely fix will be to install a master cylinder with a bigger bore diameter.
Jerry

What rear end do you have? You can have issues like you describe if the rear drums are not adjusted correctly. If the rear shoes are too far from the drums, you will be using all of your brake fluid for taking up this mechanical slack between the shoe and the drum. This will cause all of the brakes to be weak.

Thanks guys I have a chevelle rear end, new shoes and slave cylinders adjusted so shoes are rubbing about right I think . Pedal feels same with or without parking brake on which I assumed means it’s not rear adjuster issue?

The master came with the underfloor booster kit (for 47- Chevy truck from performance products discs front drums rear) so I assume it’s the right size


Tricky problem to track down !

Drmike,

Just installed a similar front disc brake system on my 58 3100 with the main difference being that I'm not using a booster. I'm running the original rear and drums. Very happy with the result as its a huge improvement over the front drums and old master cylinder.

Pedal operation is about the same as you described except it's hard 4" from the floor.

Sounds like you may still have some air trapped somewhere.

Are you sure you have the residual valves installed in the proper direction?

Do you have a proportioning valve installed?

Setting the parking brake does not affect the slave cylinders, thus won't solve a loose brake adjustment.
You need to make sure that you remove all tension from the parking brake cables before adjusting rear brakes.
Just for giggles, after removing all tension from parking brake cables, adjust the rear brakes so tight that you can't rotate the wheels, then see how the pedal feels. Obviously you won't be able to drive it, but you will be able to tell if the problem is out-of-adjustment related.
If your pedal feels better after this test, back off the brake adjustment as per the specifications for whatever year Chevelle rear end you have.
Carl