Brake pedal drops to the floor - Team Camaro Tech
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post #1 of 26 (permalink) Old Nov 18th, 17, 12:36 PM Thread Starter
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Brake pedal drops to the floor

OK, all new brake system, front and rear discs. Just got a new master cylinder and the brake pedal just drops to the floor and no stopping. I can pump them up but the pedal just sinks...
Bad Master cylinder?

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post #2 of 26 (permalink) Old Nov 18th, 17, 04:41 PM
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Did you do the basics?
Bench bleed mc
Bled system starting at furthest wheel from mc to the closest?
Mc rod too short/long?
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post #3 of 26 (permalink) Old Nov 19th, 17, 06:09 AM
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Re: Brake pedal drops to the floor

X2 Yes we need to really know the prep cycle of the master you followed, and all the changes you made to the existing rod and peddle combination.
Could be air, could be a bad master, missing or too short master cylinder push rod. Fill us in.


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post #4 of 26 (permalink) Old Nov 19th, 17, 07:51 AM
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Re: Brake pedal drops to the floor

Quote:
Originally Posted by bondora68 View Post
Just got a new master cylinder, I can pump them up but the pedal just sinks...
Bad Master cylinder?
When the suggestions given are done, this symptom is saying bad master cylinder.
Once pedal is depressed, once or several times, pedal should be rock solid.
Unless a leak has occurred elsewhere.

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post #5 of 26 (permalink) Old Nov 19th, 17, 08:03 AM
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There was a time when i redid my whole brake system with new lines original mc and booster. Driving down the road my pedal would go to the floor and you could hear the brakes grinding. Turned out that the booster went bad
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post #6 of 26 (permalink) Old Nov 19th, 17, 06:04 PM Thread Starter
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Re: Brake pedal drops to the floor

Thanks to all of you for the advice, I may have it sorted out.. My new master cylinder came with a little insert that is shaped like a bullet and goes into the end where the rod inserts. I removed that insert and then rebled the MC. I then rebled the system and got a pedal. Not a really tall pedal mind you but brakes seem to be working. Tomorrow I will take a test drive around the block to check it out.

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post #7 of 26 (permalink) Old Nov 20th, 17, 11:09 AM
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Re: Brake pedal drops to the floor

Quote:
Originally Posted by bondora68 View Post
Thanks to all of you for the advice, I may have it sorted out.. My new master cylinder came with a little insert that is shaped like a bullet and goes into the end where the rod inserts. I removed that insert and then rebled the MC. I then rebled the system and got a pedal. Not a really tall pedal mind you but brakes seem to be working. Tomorrow I will take a test drive around the block to check it out.
It's been too long but I do remember the bullet is used with a booster and not used if manual brakes. There is also 2 positions for the clevis rod to connect to the pedal. also there should be threaded adjustment between the clevis & rod and the rod may need to be cut and hopefully not already cut too short. when I did my 4 wheel manual disc's the issue I ran into was the pedal was too high off the floor.

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post #8 of 26 (permalink) Old Nov 20th, 17, 06:25 PM
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Re: Brake pedal drops to the floor

Two pushrod lengths

Two MC hole depths:

The difference is 1.350"

Generally the deep hole master was used on manual brake systems, so the pushrod would not fall out if the pedal was pulled back quickly by the return spring. The short depth masters are for power brakes, but GM did use a cup adapter to use them on manual brake equipped second gens.

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post #9 of 26 (permalink) Old Nov 21st, 17, 05:08 PM Thread Starter
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Re: Brake pedal drops to the floor

After a really short test drive, the pedal still sinks to the floor....I can pump it up but it does not hold. I unscrewed the rod out as far as it would go...

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post #10 of 26 (permalink) Old Nov 21st, 17, 05:23 PM Thread Starter
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Re: Brake pedal drops to the floor

According to the above information, my new master cylinder is for a manual brake set up! Maybe that's the problem..?

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post #11 of 26 (permalink) Old Nov 21st, 17, 06:47 PM Thread Starter
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Re: Brake pedal drops to the floor

Could it be the booster?

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post #12 of 26 (permalink) Old Nov 22nd, 17, 10:22 AM
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Re: Brake pedal drops to the floor

Quote:
Originally Posted by bondora68 View Post
According to the above information, my new master cylinder is for a manual brake set up! Maybe that's the problem..?
You can still use a manual brake MC with a booster, but as discussed, you need to have the correct rod from MC to booster for sure. Measure your old MC and rod and make sure the new MC rod or rod with extension is the same exact length as your original setup relative to the booster. If the rod is too long, it won't let the the MC piston retract fully.

You should be able to plug both ports on the new MC and get a firm pedal, then the MC is good. These things are tested before sales, even the rebuilt ones, so it should be ok, but I've heard sometimes they aren't.

These pedal collapsing to the floor problems are almost always an issue with air in the system somewhere. Unless I missed it, not sure you mentioned if you bled the MC properly prior to installation.

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post #13 of 26 (permalink) Old Nov 22nd, 17, 01:05 PM Thread Starter
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Re: Brake pedal drops to the floor

Quote:
Originally Posted by ctcz28 View Post
You can still use a manual brake MC with a booster, but as discussed, you need to have the correct rod from MC to booster for sure. Measure your old MC and rod and make sure the new MC rod or rod with extension is the same exact length as your original setup relative to the booster. If the rod is too long, it won't let the the MC piston retract fully.

You should be able to plug both ports on the new MC and get a firm pedal, then the MC is good. These things are tested before sales, even the rebuilt ones, so it should be ok, but I've heard sometimes they aren't.

These pedal collapsing to the floor problems are almost always an issue with air in the system somewhere. Unless I missed it, not sure you mentioned if you bled the MC properly prior to installation.
I tried my best to bench bleed the MC. What is the best method to do this?

Tony
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post #14 of 26 (permalink) Old Nov 22nd, 17, 01:33 PM
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Re: Brake pedal drops to the floor

get one of these
https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds

install the fittings run the tubes into the mc bowls filled with brake fluid

push the plunger in and out until you see no air bubbles exiting the tubes

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post #15 of 26 (permalink) Old Nov 22nd, 17, 02:16 PM
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Re: Brake pedal drops to the floor

You can bench bleed without the tubes. I do it this way with no issues. https://www.cardone.com/tech-help/br...ding-procedure

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