Front brakes locking up
 

Just purchased a 67 barracuda fastback. The car is 98% complete with with 100% brand new/reconditioned parts. built from the ground up.
We fired it up for the first time, drove it down the road and back..front brakes locked up..opened bleeder valve on front cylinder and it freed them up.
This has been going on for weeks now. Every time i release one bleeder on front, it frees up both front wheels.. We have already replaced master cylinder and dont want to keep throwing parts at it. entire system should be new or at least remans. Disc front, drum rear.
Ive checked rod from booster to MC.
Replace master cylinder and no matter what ..once we start car and move it 30ft the front lock up...open one bleeder valve to relieve pressure and both are free again for another 30ft.
any ideas would be much appreciated

What brake system did you install in the car?
I'm guessing it has the wrong Pressure Residual Valve installed....

Just my 2 cents
:)

The only thing that makes sense to me is that the master is configured wrongly or wrong master. That is, the push rod is not allowing the piston to fully return. You can easily check this by loosening the mounting bolts with and see if the brakes release.

It "might" be that the distribution block / warning switch is badly gummed up.

Another thing you can try is use a pan/ rag to catch fluid and crack line fitting at the master, see if that relieves pressure.

Please clarify something. You wrote that you only have to drive 30 feet and the brake locks-up. Do they lock up even if you do not apply them? Just want to make sure I am reading it right.

I can not find any pressure residual valve anywhere on the car.
I have tried removing mounting bolts on MC and removing MC from booster..does not free them up.
Nothing should be gummed up. Everything is new.
And yes Fivepoint, My mistake, I can pretty much press the brake anytime.. running or not and the fronts both lock up
Attachment 10203
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Attachment 10205

Can't really tell from photo, but rearmost mc outlet should go to front brakes. MC may have built in residual valve for drum rear brakes.

Yes, Rear port is to front brakes.

Is it a disc - drum master cylinder? You could try temporarily switching lines front to back and see if brakes still lock up.

Yes it is.

Do you still have the old portioning valve? Reinstall it just for testing. Careful the brake will be very touchy.... I think you might have a bad spool valve in the portioning valve?


:)

Also so make sure you have the correct Master Cylinder... Some fit 10" and others fit 11" Disc.
Possible to have just the wrong combo Master... ??? You know
10" Front 9" rear Or 11" front 12" rear.... Different Masters...
If you get what I mean....


:)

?:uzi:

I would suspect they are selling you a master for Drum/Drum brakes.. You need one for Disk/drum system

In the reservoir, can you see the piston returning past the fill port, and fluid returning to the reservoir when you release the pedal?

Residual valves WILL NOT cause this

If you have not.........try releasing pressure RIGHT AT the master

If that does not do it there is only two things left........

problems in the metering/ proportional valve or brake warning switch, depending on what components are installed. "They" may be one piece

or "some" people claim they have witnessed brake hoses swelling up, but frankly I would not have that "high" on my list. In this case both hoses would have to be doing this, and I'm not even sure it could.

I would concentrate on the warning switch / prop valve, IF releasing pressure at the master does not free the brakes

I repeat .........RESIDUAL VALVES will NOT cause this problem.

(On my own car I have 4X disk, 73 Duster on front, and Lincoln Versailles 9" axle in rear). When I first put it together, I simply tried the original 67 drum master. Worked FINE. I did in the next couple of days, puncture the residual valves, which on it are in the master tube fittings