Technical Mustang II Brakes will not stop OK keyboard Mechanics your time to shine

A friend has a 53 mercury. The car will slow to a stop will not lock the tires down. It is scary to drive and dangerous He just bought it. The car has a Mustang II front end and the typical brake set up.
GM metric calipers 2 3/8 bore
11 inch rotors
Braided 3/16 flex lines
whole system is 3/16 steel line
Standard GM Combination valve
Rear end and brakes are Ford Ranger drum
Master cylinder Corvette style with 1 1/8 bore
Pedal ratio 5.3 to 1
Vacuum booster 7 inch single diaphragm
Motor pulls 14 inch of vacuum at idle
We haven900 psi line pressure at the front Calipers Using a gauge in the bleeder screw
So far tried and not fixed
Change the vacuum booster to 8 inch duel
diaphragm (helped but no fix)
Installed and then removed a 1 inch bore master cylinder. Made low-speed braking better but high-speed worse. So we removed it and reinstalled the 1 1/8 bore.
Brake are bled with no air each time( power bleder) and pumping by foot and bled. Ran over gallon and half of new dot 3 through the system
Change to pedal ratio to 7:1
We are throwing ourselves on your mercy.Any help will be greatly appreciated

 

What's it doing?
Is the pedal going to the floor or is it hard [but not pulling up?]

 

Someone I know recently had similar braking issues on his freshly built car and everything was new. He did everything to sort it out like you and in the end he was pulling his hair out. In the end it turned out to be the caliper pistons as the car had sat for some time, don't forget brake fluid is hydroscopic Also check the MC piston and bore, it could be similar issue there?

Before


After, problem solved.

 

Goes 3/4 of the way to the floor but on a panic stop will with in an 1/2 of inch of the floor sweep is about 8 inches other than that feels normal

 

Thoughts.........rear brakes working? Proper residual valves installed and plumbed properly?

 

There were some 'through the frame' bulkhead connectors sold for the front brakes for awhile that had a large inside diameter with a small [3/16ths] brake line going to each side of it. Problem was air was trapped in the large diameter connector with no way to bleed it off....spongy pedal. Connectors are now available with small inside diameter.

 

It sounds like it has "Low Drag" GM metric calipers [these are designed to pull back off the disc]
The fix is a "quick take-up" [or stepped bore] M/C

Put a feeler gauge behind the pads and measure how much they retract [normal calipers are about 0.005" each side whereas low drag callipers are 0.030" plus]

People try and fix the low drag caliper problem [not knowing such a thing even exists] by a larger M/C but find they can't get enough clamping pressure.
Another band aid fix is residual pressure valves to stop the calipers retracting.

Swap the calipers or swap the M/C so they're compatible with each other

 

I had a car that did similar...it was bad flex lines. They seemed to flow just fine, but under pressure they would expand.
The brakes worked fine to a point, then any added foot pressure was absorbed by the expanding lines instead of going to the brakes. I used a set of vernier calipers and set them snug over the outside of the flex lines, made note of the reading, then stepped on the brakes. Sure enough, the line expanded and changed the reading.

 

Did you properly set the shoe drag on the rear drums, and are you running a parking brake?

 

yes they are working I can hear and feel the shoes move and they are flowing brake fluid when brakes are bled. I can not take a pressure reading I do not the proper fitting for metric wheel cly.

 

Yes and yes

 

Your thread title is misleading. There are NO 'Mustang II" brakes or brake parts anywhere in your description. Further, Ranger rear brakes can be as small as 9" x 2"ish or the larger 10" x 2 1/4". Though the rear brake's contribution varies with speed, weight transfer and tire diameter, if you have the smaller size, they are probably marginal in this application.

I have never been a fan of the GM metric front calipers either. Nonetheless, I agree the existing system should work better than it does.

Ray

 

The calipers are from some company called Helix. I will have to check on that.

 

I will have to get the size.

 

Helix is one of the brand names used by the infamous Hoffman Group of parts marketers of JUNK......tons of threads about their crappy products. Do a thread search on Hoffman/ Helix.

Ray

 

Wow.

 

I was thinking the same.

 

There is a thread just now, down about 15 or 20 threads, on the Hoffman Group. Several pages long.


Ray

 

Oh no.

Please tell me that there are not any other Helix parts on this car.

 

It looks like the whole front end.

 

That's a bad sign. What is in the rear for suspension?

 

Leaf springs and look to me to be Ford Ranger rear

 

Nothing like that in the system

 

Are you buying Corvette-style aftermarket master cylinders, or real ones?

 

Aftermarket

 

First red flag is only 14" of vacuum. Get a UP28 vacuum booster pump and quit beating your head against the wall.

 

If you have the 9" rear drums, they are too small for your application. I had them on the back of my Falcon, and they were marginal, in that application.

I would get a set of calipers from your local auto parts store. Anything 1978 would be good, like a Camaro. Low-drag calipers came later.

I would strongly caution you to replace every Helix part that moves, and watch the others for cracking.

 

If his pedal ratio is now 7:1, there should be no need for a booster, of any kind. Any booster, at that ratio, is purely for driver comfort.

 

Sorry about the misleading Mustang II stuff but I do not know what call this this mismatch pile of junk parts that seems to be in every aftermarket Mustang II front end kit. S10 metric calipers,Chinese eBay brake booster and Corvette styled master cylinders every shape and form.
The reason I have so many master cylinders and boosters to use on diagnosing this is another friend of mine went through the same thing and he just ended up putting on a Hydro boost and Wilwood hubs rotors and calipers and putting all the parts that were tested on his car on a shelf at his work. My friend with 53 does not want to put a Hydro boost on this car because of all the cost so I thought I could help him sort it out but it has me scratching my head