Issues putting brake system together

1973 barracuda.

Parts :
Prebent brake like kit from Inline Tube
Using metering block Inline tube recommended for 4wheel disc
Using manual valve inline recommended to set bias to rear
Stock style master cylinder and booster
Front - Stock style calipers with 11 rotors
Rear - aftermarket conversion kit thAt uses gm eldorado style calipers

I have bled the brakes and all wheels have fluid.

Issues :

No braking at the front
Tight drag on the rear.

Questions :
Will the stock style booster/master combo work with 4wheel discs ?
Is there an adjustment on the rear to reduce drag?

Thanks !

I'd start by setting the booster pushrod clearance to the bottom of the MC piston "thimble" at .020" then "bench" bleed the MC for starters.

Booster maybe, MC. not without mods



Yeah, remove the residual pressure valve out of the front port of the master cylinder.


I hope it is nothing but a distribution block, all disc setups do not use metering.



What does that statement mean? Are you talking about a proportioning valve? And it's adjusted how?

Ok I can do that

Yes, it's just a distribution block. What I was told is that there will be no way to create bias in the system so the guy at Inline Tube told me I need this adjustable valve (look in picture at valve with knob) to set bias by adjusting with this valve.

what a mess.

And is there a difference in a manual a power brake pedal?? the car had a manual MC on it when I got it

it looked like this

Try adjusting more bias to the front.

Not an E body guy so I dunno if there is a difference between manual and power pedals. That adjustable valve is called a proportioning valve. Brake bias can be setup without it, but it takes a thorough knowledge of braking and your specific setup as you will be using caliper bore diameter, pad material, rotor diameter, tire sizing, weight distribution and other issues to dial it in.

Since most people aren't detail oriented and no aftermarket company can cost effectively figure that out for you on an individual basis, unless you are rich, they crutch it with an adjustable valve that is "good enough" for most.

I was naive enough to think I could gather some decent parts, and with my reasonable amount of know-how I could get a braking system that works pretty good. But it is way more complicated than that, I have learned. I am not rich but I ain't broke either but I am not making a show car, race car, or track star - just a cruiser. I believe setting the bias with the proportioning valve will suit my needs. I surely don't want to die or cause anyone else to!

Power vs manual brakes there is a difference in the pedal linkage under the dash. I can get you a pic of the power linkage later if you need. Manual just has a rod directly off from the foot pedal arm into the master. Maybe you are missing the power linkage for the pedal?

Concerning rear calipers, Those look huge, like they are front calipers. You will need to adjust the rear line pressure with the adjustable prop valve you have in the rear line.

Parking brakes -- are they in the caliper or under the rotor hat? If in the caliper, you need to hook up the cables and get the parking brakes to work.

Well, then that mystery/problem is solved. I do, in fact, have a manual brake lever so I am missing the power linkage .

Yes, I do believe these were originally used as a front caliper and the e-brake is built into it. I have all of that set and I will hook it up when I get my new e-brake cable

Looking at the 74 parts manual, since I don't have a 73. The only difference in the pedal itself is manual/automatic trans. Power or manual brakes doesn't matter. Linkage has setup that reduces leverage into the booster, so if anything you'd have too much brakes without it.

I would try loosening up one brake line at a time on the master cylinder, if you see air and brake fluid bubble out of it remove that line and the pressed in brass seat so you can remove the residual valve behind it

I suspect the orientation of the pushrod to the mounting point on the pedal arm is different between the two bc the mounting point on my pedal arm doesn’t line up so I had to do some fabricating to get it to even work. It’s not right. It’s like two inches above the hole in the pedal arm and about three inches away from
It. I knew it wasn’t right but until now I didn’t know what was wrong.
I think I can make it work if I can set the plunger right according to the instructions I have been given here.

.


I will try that and hope I don’t make a big ole mess !

What RR mentioned has nothing to do with what we are talking about. See picture for what your linkage from the pedal tot eh booster is supposed to look like.

What RR is talking about adjusting is the pushrod from the booster to the master cylinder.

Parts manuals

http://www.mymopar.com/index.php?pid=107

FSM

http://www.mymopar.com/index.php?pid=109

Get both, use them to assist you

Right, I understand that and maybe I should check that measurement.

I just went out and took these. It seems I am missing some stuff for power brakes

Thank you !

As said a MC used for discs must have no RPV under the brass seat where the brake line screws into the drum half (iirc they went from them to a small round disc in the wheel cyls behind the cups to maintain a slight psi) so the odds are less but with what is going on here I would for sure check. pull (unscrew) the 3/16 line from the drum port & stick a drill bit down in the brass cone & if it has one it is just a piece of neoprene and a spring so you will easily feel it if it has one with the springiness & if by chance it does we will post how to pull it & that is assuming the MC is the correct bore (I ain't sayin it ain't) but there might be a mismatch of parts (I hope not, you have alot invested in this), but just going from the prior posts, I ain't up on this conversion.

Drawing above was pretty clear, but I attached picture of the linkage. Maybe it will help you find it somewhere.

You say you're using a "stock style" master cylinder. Is it a disk/disk master or disk/drum?

I got the MC/booster combo from O'reilly's and I ordered it for disc/drum.

Yep - looks like that's what I am missing !

That's your problem. You will never get the brakes working properly if you're using a master cylinder designed for rear drum brakes when you're actually using rear disks. You NEED a Disk/Disk master cylinder. That will solve your problem.

Nope

The only difference is reservoir capacity, just check it when doing an oil change, top off as needed and the residual pressure valve in the rear brake (front port) outlet, which he's already been told to remove.

Even removing the built in residual valve won't make it safe. There is no way I would use a disk/drum master cylinder on a disk/disk system. As the pads wear the pistons have to make up the difference and need larger amounts of fluid. That's why the reservoirs are larger on the disk side. It is ALWAYS best to use a master cylinder designed for the type system you're using. Jury rigging brakes is never a good idea.

then suggest one that will fit his booster rather than pontificate.

Other than the reservoir capacity and rpv there is no difference and if you can't be bothered to check fluids at each oil change then maybe you should be using Uber.

I agree with supercuda, just top offfluid as needed and ditch the rpv.

You can also use a disc disc master for drum drum car.

This doesn't take into account bore sizes but that's a different discussion.

A quick search turned up disk/disk masters for '73 Barracuda at Summit, and I'm sure a quick trip to Napa or AutoZone would turn up more. My point is.. you can use a disk/drum in this situation but when an engineered disk/disk version is available why jury rig the system. Makes no sense to me but then apparently, I'm no expert since you guys seem to think barbed wire and bubble gum is a better idea.

that would be a hell of a trick since a 73 Barracuda never had 4 wheel discs from the factory. Care to link to it, because whatever you think it is, it's not stock and it's will be a jury rig. Surprised you don't seem to have heartburn with the OP's setup since it is all a jury rig.

The OP didn't choose the best conversion kit for sure and that is the main problem. And Summit's parts aside, there are other Mopar disk/disk master cylinders that will fit and work on his power brake booster. They may not be listed for a Barracuda, but given he's using GM style rear calipers, going with a non Barracuda Mopar master cylinder seems trivial.

Provide a link, the OP has an issue, you say there is a correct fix for it, but will not help out with a link. Why?

So what you are saying is there are no Mopar master cylinders for disk/disk that will bolt up to a Mopar power brake booster? Yea, right.

I'm done arguing with someone who is bound to give redneck advice. Have a nice day.

Several have already suggested to remove the residual valve under the brass seat in the rear brake port of the master cylinder. Here's how to do it.

Using a wood screw, screw into brass seat just a few turns. Then use a claw hammer or wire cutters to grab hold of the screw and leverage the brass seat out of the master.

Remove the residual valve and spring, and reinstall the brass seat.

This should resolve the rear brake drag assuming the brake pedal linkage is properly adjusted.

I used a Strange 15/16" master cylinder with the line for the rears going straight back to the T-fitting and the line for the front brakes going straight to the line lock with no blocks or valves in the system. It stops straight and steady from over 120 with no lock up or pedal issues. I used one of Doctordiff's adapters and pedal pushrod. I am still using the original manual drum brake pedal assy.
I was going to use the Wilwood adjustable block but my car stops great now so why waste my money

Gus

In 74 IIRC the Chrysler imperial used rear disc brakes which should have been a bolt on including the master cylinder.. Probably take someone willing to look through the books rather than the normal parts jockey that needs to know if you have A/C to find you a brake light bulb..

No, I believe I was saying you are FOS as evidenced by your repeated inability to provide the link for the part you say will do the job. That is because it does not exist. The is no "disk/disk" Mopar master cylinder that will just bolt up to his existing booster.

does anyone have a picture of a wagner # F84054 [1 1/16"] master ? that is the number for the 74-75 imperial with the four wheel discs. caliper sizes were 3 3/32 front, and 2 19/32 rear. info from my wagner master catalog printed in november of 95.

I dug thru the 2 FSM on the Imp 4 wheel disc setup and really couldn't find anything specific about the MC, other than it's unobtanium.

But it sure had a lot about the Sure Stop setup (ABS)

I am still working on getting the math right for this brake system. I hope you guys can help me finish figuring this out. I may try to use the OE style stock replacement master disc/drum (and remove the residual valve for the rear) along with the stock style booster and see if I get enough pressure going into the gm style rear calipers. I am not opposed to changing the MC but I may as well try the one I have since I've already bought it.

Since this will be a "driver" I want to stay with power brakes if I can.

Front:
Single piston caliper with 2 3/4" bore on 11" rotor

Rear:
Single piston caliper with 2 1/2" bore on 11" rotor
*have manual valve inline to adjust bias

The best I can calculate, it seems ideally I would need an MC with 7/8" bore. I am not sure what the bore is on the stock style MC.

The calculations show I will need pedal travel with 8:1 ratio.

Any help will be much appreciated!

thanks guys!