How much pedal play do you all have after Disc Swap?

70mach1 · Jun 29, 2007

Pedal has almost 3inches of play.

About 3 years ago I swapped in 1977 Grenada front discs (p/n 101614 A1-Cardone). Prop valve, rear pressure reducer and master cylinder. All new hardware.

Rears are adjusted tight
MC is 1977 Grenada Disc front drum rear manual brake unit.
Brakes have been bleed several times over the years.
Tried a 1974 Maverick MC, same results (p/n 101588 A1-Cardone
Car stops fine but my other Mustang has a much firmer pedal (maybe 1.5" of play)

Any thougts? This has bugged me for years ! NE1 who can solve my problem and I will send you a Starbucks gift card in the mail ! Sorry, I live in Seatte.....

DJCarbine · Jun 29, 2007

Is the pedal firm when it does begin to brake though? Does it sink all the way down?

Did you check the pushrods on the MC and compare with original? It could be off like an 1/8th of an inch, and translate into a huge amount of play

70mach1 · Jun 29, 2007

no it engages the MC right away, it just doesn't firm up until after 3 inches. I have fairly new brake lines but they are the cheap ones without the plsati reinforcement rings that come factory. I might buy those and try them out. Or stainless lines.

I have no other idea. I mihght block off the MC front and see if it fixes it or rear. This basically isolates which end of the car is causing the pedal mushhh.

Any more thoughts?

180 Out · Jun 29, 2007

I'll just throw this out there: take the lid off the master cylinder and look in the front reservoir for the drilled-out hole in the bottom. Have an assistant apply the brake pedal. It's my understanding that you should be able to see the piston move forward as it covers up that hole. Only at that point does hydraulic pressure begin to happen. Check where the pedal is when that happens. If the pedal does not feel firm at that point, then the most likely problem is air in the lines. If the pedal is firm at that point, and it is 3" into the travel, then you need to shorten the rod somehow so that piston will cover the hole at a higher point in the travel, to pre-load the piston so to speak.

Other thoughts: have you bench bled the MC? I have never understood why the MC needs to be bled first, without any lines attached, but I have heard it many times that an incurably squishy pedal was cured with this technique.

Does the firewall flex when pedal is applied? Watch the MC while the assistant is applying the brakes and see if it's moving.

Are the calipers mounted on the correct sides? The bleeder screws must be at the highest point or the calipers will always have an air pocket in them.

Watch the calipers as the brakes are applied. If they move around then that can take up a lot of pedal travel before the system gets pressurized.

Last and probably least, a bigger bore MC will firm up the pedal.

70mach1 · Jun 29, 2007

180 out, thanks for all those ideas. Let me address them 1 at a time.

#1 I haven't checked MC pre-laod, but if I do this, the brakes engage if only a little.
#2, I did bench blead MC
#3, The peddle is soft for 3 inches, however, it still engages the brakes during this time, just not hard enough to "bottom out" Even after 1 inch, I get the brakes working a little, just not enough to stiffen up the pedal.
#4, Rear brake an dfront caliper play is at a minimum
#5. Firewall has no flex.

My only guess is to maybe change the front lines. But before that, I think I will block the fronts and see what happans. I do have a Summit Racing rear line pressure reducer. Maybe air is stuck in there.

HistoricMustang · Jun 29, 2007

Bleed the brakes several times starting at the passenger side rear wheel, then drivers side rear wheel, then passenger side front wheel then drivers side front wheel.

Do this SEVERAL times and start the entire process with NEW brake pads all the way around.

HistoricMustang
www.historicmustang.com

70mach1 · Jul 3, 2007

I have new info:

Plugged MC = 2.4" of play
Connected Rear, plugged front = 2.6" of play
Plugged rear, connected front = 3.4" play

My rear brakes felt great.
My front brakes feel like sheeeeeeeeeett.

I am ordering custom stainless lines ! I think that is my problem. The lines I have are cheap. They are new, but don't have the extruded ring of extra plastic aorund them like the factory ones. So I figure SS should be even better.

When I get them installed, I will post again.

Thanks all.

Yankee Traveler · Jun 23, 2016

Did you ever figure out the problem with fron brakes, since I have the same problem.

Noobz347 · Jun 23, 2016

Yankee Traveler said:
Did you ever figure out the problem with fron brakes, since I have the same problem.

That dude hasn't been on for 8 years. I'm pretty sure we have folks around that can help you though. Post up your own description of the problems and symptoms you're having.

@horse sence

How much pedal play do you all have after Disc Swap?

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