4wheel disk brake conversion/front calipers don't release

[GRAMSCAR]

Need the experts to weigh in on this one. I Have a 65 coronet 500, did a 4 wheel disk conversion and now the front calipers lock up and won't release. I replaced the master cylinder and booster with the correct ones for disk\disk. History note, they also locked up before I replaced the master and booster to the disk\disk.
Has anyone had this problem and what was the correction??
Thanks, GRAMSCAR

 

[steve340]

It could be the adjustment on either the master cylinder to booster pushrod or the pedal to booster pushrod. They both need a little free play so they fully return back.

 

[GRAMSCAR]

I will take a look at those. I'm trying to remember from installing them, been a long project, if they are adjustable?
Thanks steve340, I will post what I find.

 

[themechanic]

Get one of these and check your booster push rod length.


Sunyat Power Brake Booster... https://www.amazon.com/dp/B07ZFDT3BK?ref=ppx_pop_mob_ap_share

 

[steve340]

One quick way you can check - when the brakes lock open a bleed nipple quickly and release any pressure. If the hydraulics are causing the problem the brakes will release.

 

[themechanic]

One quick way you can check - when the brakes lock open a bleed nipple quickly and release any pressure. If the hydraulics are causing the problem the brakes will release.

Yes. If the bleeder doesn't relieve pressure go up the line and crack open the brake hose to caliper connection. Keep working up the line until you find the problem.

 

[GRAMSCAR]

As soon as I crack the front bleeder, they release. Push rod to long?

 

[themechanic]

You don't have to disconnect the hard lines on the MC to unbolt it from the booster to check the push rod length.

 

[themechanic]

 

[steve340]

Yes pushrod to long best guess or a faulty hose is a longer shot. Somehow the system is not releasing the hydraulic pressure. Faulty master cylinder?
Start with suggested clearances check - do the easy stuff first.
The following is not your issue if you let the pressure go and all comes good.
Another thing I came across once.
The disc pads were so tight in the calliper they were jamming - the hydraulics could clamp them on no problem but they were not loose enough to release properly.
The owner had kind of pounded them in with a hammer. They were a **** to get back out but a couple of minutes with a file and they worked fine.

 

[GRAMSCAR]

Thank you Oklahoma! I will check that tomorrow

 

[themechanic]

 

[steve340]

The video themechanic posted is great info but so I get a higher pedal I try and set the clearance to 10 thousands of an inch.

 

[themechanic]

Yes pushrod to long best guess or a faulty hose is a longer shot. Somehow the system is not releasing the hydraulic pressure. Faulty master cylinder?
Start with suggested clearances check - do the easy stuff first.
The following is not your issue if you let the pressure go and all comes good.
Another thing I came across once.
The disc pads were so tight in the calliper they were jamming - the hydraulics could clamp them on no problem but they were not loose enough to release properly.
The owner had kind of pounded them in with a hammer. They were a **** to get back out but a couple of minutes with a file and they worked fine.

FYI, those sliding calipers require bending the tabs on the outer pad to keep it from rattling.

 

[themechanic]

The video themechanic posted is great info but so I get a higher pedal I try and set the clearance to 10 thousands of an inch.

Baer brake video recommended 0-5 thousandths.

 

[GRAMSCAR]

Lots of great help from guys. I suppose my first step is ordering a push rod tool so I can eliminate that issue.

 

[themechanic]

Lots of great help from guys. I suppose my first step is ordering a push rod tool so I can eliminate that issue.

If you are in a hurry and don't want to buy another tool you can use clay or Play Dough, like was mentioned in the speedway video. Might be hard to clean up, though.

 

[steve340]

True go with the Baer setting it is spot on.
I have the tool and it takes all the guess work out of a tricky adjustment.
I bought mine from Corvette Brakes for $25 US on EBAY
First make sure you can be confident the pedal side of the booster is coming right back before doing the booster adjustment.

 

[MIKESPOLARA]

Lots of great help from guys. I suppose my first step is ordering a push rod tool so I can eliminate that issue.

Easy test for front pin, with calipers locked, unbolt master and pull it slightly forward. If it's the pin length the calipers will release.
However if this works it could also be the rear pedal rod is adjusted too long and that is pushing on the master, either one will do that.
Are you certain your master is disc/disc and not a drum/drum master with residual pressure valves inside master? Post a picture of your new master, I can tell

 

[GRAMSCAR]