Pedel goes to floor

[91Sasquatch]

Yes my brake pedel goes 1/2 way to the floor no pedel. Replaced master cylinder, front brake hoses, and front calipers. Ive bleed the system as there is no dirty brake fluid coming out it is clear gone through 1 and 1/2 qrt of brake fluid still cant figure out the reason why no pedel. Any tips would be great. The glove box says its a JB5 brake system

 

[Charlie]

 

[Goldie Driver]

Checked the rear wheel cylinders?
Maybe one is blown.
Or, a bad new MC- I assume it was new, and not a reman.

Just throwing some ideas out there.

 

[PrairieDrifter]

Did you bench bleed the master? I would dare say that you should have had to use more brake fluid then that. I’d say bleed it some more, unless the master is faulty but that’s not that likely

 

[91Sasquatch]

Yes bench bleed the master before install. Yes brand new not remain will not get a remain. Havent checked rear wheel cylinders. But i will this weekend or tomorrow if it ever stops raining.

 

[1987 GMC Jimmy]

Someone correct me if I’m wrong (it’s pouring and not about to lay under the Jimmy and drown), but there’s a center rear brake hose also. Normally I wouldn’t give it a whole lot of thought since it’s not subject to the stress of the front ones, but you’re pretty well lifted so there you go. Other than that, the only thing I can think of is a bad wheel cylinder which was already mentioned. No leaks? I remember when I did my calipers the biggest issue I had was leaks at the crush washers. Had to get more than they gave me to fix it properly.

 

[Charlie]

What was your process of bleeding after MC install? Was it with help depressing pedal while opening bleeder? Sometimes, gravity bleed can be very effective when necessary.

 

[bucket]

It could be as simple as the rear brakes are way out of adjustment.

 

[91Sasquatch]

91 Suburban sorry didnt see a posting for suburban just the Jimmy area. Gravity bleed system then had my son bleed it with me. Up closed bleeder down opened bleeder. Did that about 5-8 time each side Even back as well farthest to closest to MC. Havent checked back for leaks or out of adjustment will do this when it stops raining. Yes it high enough to get under but if rears are leaking would be easy to removed tires and drum to check.

 

[smoothandlow84]

Check valve on booster? Or leaking vac line.

 

[75gmck25]

I've only bled the brakes once on my GMC, but I remember one of the steps was to ensure the proportioning valve was centered so that you got pressure to both front and rear.

IIRC, when there is a broken brake line (no pressure) on either front or back, the valve toggles so that you still hold pressure on the other half. When you replace lines it will act like a broken line until the new lines are filled and will hold pressure.

This is one discussion thread I ran across on another site. https://www.chevytalk.org/fusionbb/showtopic.php?tid/21686/

Bruce

 

[91Sasquatch]

I've only bled the brakes once on my GMC, but I remember one of the steps was to ensure the proportioning valve was centered so that you got pressure to both front and rear.

IIRC, when there is a broken brake line (no pressure) on either front or back, the valve toggles so that you still hold pressure on the other half. When you replace lines it will act like a broken line until the new lines are filled and will hold pressure.

This is one discussion thread I ran across on another site. https://www.chevytalk.org/fusionbb/showtopic.php?tid/21686/

Bruce

I was thinking about the proportioning valve as well but cant seem to find anyone that sell them.

Plus was told my MC was new and found it was a rebuilt so switchibg that out tomorrow with a new one plus the new MC is cheaper but $10.

 

[chengny]

I was thinking about the proportioning valve as well but cant seem to find anyone that sell them.

Plus was told my MC was new and found it was a rebuilt so switchibg that out tomorrow with a new one plus the new MC is cheaper but $10.

Looking closely at your bleeding procedure. That could be the problem - unless I'm not reading this right:

Up closed bleeder down opened bleeder.

You don't want to allow the pedal to return to the top with the bleeder open.

As the brake pedal rises, the piston in the MC retracts. This creates a negative pressure in the system and induces a backflow of brake fluid in the lines.

When the bleeder is opened and the brakes are fully applied, air is purged (along with some amount of brake fluid).

But if the pedal is released with the bleeder still open, any air that was successfully bled out will be drawn back in - plus some more air equal to the amount of brake fluid that came out with it.

Be sure that the bleeder is closed before allowing the pedal to rise. Here is GM's bleeding procedure:

1. Bleed right rear brake as follows:

• 1. Depress brake pedal slowly one time and hold.
  2. Loosen bleeder valve to purge air from brake, then tighten bleeder valve and slowly release pedal.
  3. Wait 15 seconds, then repeat sequence, including 15 second wait, until all air is purged.

1. Bleed left rear, right front, and left front brakes, in that order, using same method as for right rear brake.
2. Check brake operation and ensure pedal is firm. Also check master cylinder fluid level and add fluid as necessary.

 

[91Sasquatch]

Well found the problem brand new MC and found out it was bad. Replaced it again and now works great. Now i need to find a speedo for my truck 1991 suburban yes has electric not cable.

 

[WHEELMAN]

Bleed the brakes..first right rear.then left rear..then right front..then left front..

All so has your front rubber brake lines been changed.change them..

All so you can get a bad new brake master cylinder.