Long Travel Soft Brake Pedal

[340sFastback]

I have around 3 inches of brake pedal movement before I feel pressure then can push another 3 inches before pedal won't go any further. I can fit my toes between pedal and floor when brake pedal held down. Pumping brake pedal does not firm up pedal. Brake pedal feel is consistent. Can pump pedal, no change, let car sit over night, no change. Brake pedal always feels the same.

New 10.7 rear disc. Emergency brake pulled released several times. Verified emergency brake is able to hold and release on each side. Brake pedal feel same whether emergency brake applied or not.

New 11 3/4 in front disc.

15/16 master cylinder around a year old. Leveled master cylinder when pressure bleeding. Manual brakes.

Pushed almost a gallon of brake fluid through system with clear tube on bleeder routed up. No air bubbles after bleeding.

All bleeder screws are facing up.

New braided flex lines front and back.

Zero leaks anywhere.

I believe master cylinder fully returns and no slack in brake rod.

Doctor Diff says if brake pedal is consistent and does not improve by pumping pedal then thats the way it is nothing can be done? So he does not think there is any issue???

I havent driven it yet but my guess is car will struggle to stop given long brake pedal travel and spongy feel once pushed all the way down.

Seen threads all over the place ppl had similar problems with no clear resolution and seemed like a lot of ppl never able to resolve. Then others with similar setups say they have a high hard brake pedal??

I dont think pushing another gallon of break fluid through with pressure bleeder is going to improve it. I can put wheels on see how brakes work but I bet they will be weak and struggle to stop the car is my guess??

Suggestions?

 

[Inertia]

You certainly have read lotsa threads, good job.

Adjust the rear brakes till you can JUST feel them drag .
Set the emergency full on .

How's the pedal?

The first pump usually takes up any unadjusted travel to get the rear shoes out to the drum, once they contact the drum, - the second pump is when you feel pedal/resistance.

Setting the emergency, moves the shoe out mechanically into contact with drum, - then, when you pump the pedal, the hydraulics move the rear cylinders pushrods out to the shoe.

The springs can't pull the shoes back cuz the emergency is set, so all possible fluid movement should cease = hard pedal. If bled properly .

You got this.

 

[340sFastback]

You certainly have read lotsa threads, good job.

Adjust the rear brakes till you can JUST feel them drag .
Set the emergency full on .

How's the pedal?

The first pump usually takes up any unadjusted travel to get the rear shoes out to the drum, once they contact the drum, - the second pump is when you feel pedal/resistance.

You got this.

Its rear disc brakes. With emergency brakes released there is drag on rear brakes. So it appears rear caliper pistons do not have any slack. Brake pedal feel does not change with emergency brakes on or released.

 

[Inertia]

Are these the "cobra" calipers that screw the piston out for adjustments.?

 

[72bluNblu]

With that combination I wouldn’t say you should have a “high and hard” pedal but you should still have a good solid pedal with less travel than what you’re getting. The rear calipers in that set up can be tricky, the way the calipers sit the bleeders can still trap an air bubble sometimes. You might try undoing one of the caliper bolts and tipping the caliper so you can get the bleeder at the actual highest point, you may have to put a block between the pads.

The initial emergency brake setting can also be a little tricky, the procedure to set it is a good start but sometimes it needs some fine tuning.

 

[Inertia]

The pad that faces the piston should have a "pin" that fits into a "slot" in the piston, to stop the piston turning/unadjusting .
The pin missing the slot can cause 2 issues.

If the pin misses the slot, it will interfere with the pad making full contact with the rotor, may cause pad to "absorb/bend" till you get pedal. (Soft pedal/extra travel)

If the pin misses the slot, the piston may turn when you release emergency, allowing the pad to "relax" too far, undoing the adjuster, sorta, causing extra pedal travel.

Good luck

P.S. A pad not properly seated in the caliper can cause soft, extra travel.

 

[340sFastback]

Are these the "cobra" calipers that screw the piston out for adjustments.?

I believe the pistons do screw in/out for emergency brake. But with emergency brake off there is a lot of brake drag and pads seem to be against rotor no slack.

There is also brake drag on front brakes too. So I dont believe excessive travel is due to slack between pads and rotors.

 

[Tanker]

Since brake fluid isn’t compressible and you’ve bled the heck out of these brakes with no improvement, I wonder if your master cylinder is too small. Disc brakes use pistons that require a larger volume of fluid to move than little wheel cylinders do, so by adding disc brakes to the rear in place of drums your master cylinder may be overwhelmed. It’s just a thought.

 

[72bluNblu]

Since brake fluid isn’t compressible and you’ve bled the heck out of these brakes with no improvement, I wonder if your master cylinder is too small. Disc brakes use pistons that require a larger volume of fluid to move than little wheel cylinders do, so by adding disc brakes to the rear in place of drums your master cylinder may be overwhelmed. It’s just a thought.

I’ve run the same combo, the 15/16 master cylinder works fine.

 

[Inertia]

Since brake fluid isn’t compressible and you’ve bled the heck out of these brakes with no improvement, I wonder if your master cylinder is too small. Disc brakes use pistons that require a larger volume of fluid to move than little wheel cylinders do, so by adding disc brakes to the rear in place of drums your master cylinder may be overwhelmed. It’s just a thought.

Once the hydraulic system is bled, - it only takes a few drops of fluid to apply pressure.

If pads didn't wear. You wouldn't need any sort of reservoir.

 

[67Dart273]

With that combination I wouldn’t say you should have a “high and hard” pedal but you should still have a good solid pedal with less travel than what you’re getting. The rear calipers in that set up can be tricky, the way the calipers sit the bleeders can still trap an air bubble sometimes. You might try undoing one of the caliper bolts and tipping the caliper so you can get the bleeder at the actual highest point, you may have to put a block between the pads.

The initial emergency brake setting can also be a little tricky, the procedure to set it is a good start but sometimes it needs some fine tuning.

Bleeders can fool you as well. The bleeder has a drilled passage into the cylinder, and it may be at an angle. This means the bleeder might be further down the caliper and appear "not at the top" when in reality, the passage into the actual cylinder is angled, and IS in fact at the top

 

[340sFastback]

With that combination I wouldn’t say you should have a “high and hard” pedal but you should still have a good solid pedal with less travel than what you’re getting. The rear calipers in that set up can be tricky, the way the calipers sit the bleeders can still trap an air bubble sometimes. You might try undoing one of the caliper bolts and tipping the caliper so you can get the bleeder at the actual highest point, you may have to put a block between the pads.

The initial emergency brake setting can also be a little tricky, the procedure to set it is a good start but sometimes it needs some fine tuning.

The picture with red caliper is '93 mustang my son in law has at my house. Looks like same caliper but caliper is more upright then the way its oriented on my car (black caliper). My wife has all original '86 SVO same thing caliper more upright. I will unbolt rotate up see if I can get any air out with spacer wedged between pads or C clamp to hold piston in ect.

 

[Tanker]

Once the hydraulic system is bled, - it only takes a few drops of fluid to apply pressure.

If pads didn't wear. You wouldn't need any sort of reservoir.

Well that’s the puzzle, isn’t it? If the master cylinder piston is moving as he’s pushing on the brake pedal that fluid is going somewhere, so where is it going?

 

[340sFastback]

Since brake fluid isn’t compressible and you’ve bled the heck out of these brakes with no improvement, I wonder if your master cylinder is too small. Disc brakes use pistons that require a larger volume of fluid to move than little wheel cylinders do, so by adding disc brakes to the rear in place of drums your master cylinder may be overwhelmed. It’s just a thought.

15/16 master cylinder is known to work with the setup I have.

 

[67Dart273]

Just for comparison, I, always low buck, stuck a Versailles rear axle---Ford 9" with factory disk--under my 67, along with the usual 73/74 A body disk setup up front. I just thought I'd try it so I left the original master in place off the 9" factory drums. I ruptured the residual valves with a nail stuck through, and they work great. The pedal DOES have a bit of travel, I'd say about 30-40% of total, but when it hits bottom, it is ROCK HARD

As long as you check the fluid "once a year" there is no need to worry about the size of the reservoirs. The important thing is an optional bore size, and no residual valves.

 

[Inertia]

Fluid return to the Master should give an indication of where the problem is. Front or back .

OR - that air remains in the system .

 

[340sFastback]

Just for comparison, I, always low buck, stuck a Versailles rear axle---Ford 9" with factory disk--under my 67, along with the usual 73/74 A body disk setup up front. I just thought I'd try it so I left the original master in place off the 9" factory drums. I ruptured the residual valves with a nail stuck through, and they work great. The pedal DOES have a bit of travel, I'd say about 30-40% of total, but when it hits bottom, it is ROCK HARD

As long as you check the fluid "once a year" there is no need to worry about the size of the reservoirs. The important thing is an optional bore size, and no residual valves.

I put a finish nail into rear brake line port in master cylinder and no residual valve was in there. My peddle has a mushy feel all the way down like 2/3 travel. But pedal always stops at same place and can't be pushed down further.

What method you use to bleed your brakes? Gravity bleed, pressure bleed, two man pump pump hold open bleeder?

 

[MV8]

Drive it to determine if your definition of a "soft" pedal that doesn't go to the floor is really a bad thing.

 

[340sFastback]

Drive it to determine if your definition of a "soft" pedal that doesn't go to the floor is really a bad thing.

I might have to do that because I am not able to determine cause of low soft pedal

 

[340sFastback]

Bled rear calipers unbolted and hanging by zip ties. C clamp firm on piston but I did not over tighten. Zero air came out. And no change in brake pedal travel afterwards. Calipers were very snug up against pads when I removed them. And pin in brake pad was aligned with grove in caliper piston.

 

[AJ/FormS]

My 2cents.
C-clamp all the pistons into the bottoms of their bores, then pump up the pedal, then let the pedal normalize, for several seconds. If you now have a high and hard pedal, then you do not have a hydraulic problem.
Now you can chase the real problem,
which would then be mechanical; maybe flex, misaligned calipers, twisted brackets, or things bending which shouldn't be.
Attack the rear first.
The way that the M/C is designed, If the rear has excessive travel, then the rearmost Power-Piston in the Master, slides on past the rear port until the front Power-piston reaches hydraulic lock. That's a lotta pedal travel right there.

 

[67Dart273]

I put a finish nail into rear brake line port in master cylinder and no residual valve was in there. My peddle has a mushy feel all the way down like 2/3 travel. But pedal always stops at same place and can't be pushed down further.

What method you use to bleed your brakes? Gravity bleed, pressure bleed, two man pump pump hold open bleeder?

I mostly use pressure. I don't like the idea of vacuum because it can suck air in from cups, etc. Guys seem to have good luck with gravity in some cases.

Another thing you might try--which I've done, is to "rig," let's say the hose and caliper and disconnect the hose at the frame/ tube. Use a clamp an block to reverse bleed the caliper, IE force the hopefully pretty full caliper to eject air and fluid out the hose. Then bleed down to the hose/ tube connection by cracking the fitting there.

The sponge, don't know, may be an issue with the parking brakes. See if you can round up a couple of tube unions, usually 3/16 inverted flare, and a couple of same size plugs. Now you can disconnect the tube at the rear where it connects to the hose, and plug that. If you get a rock hard pedal, I'd investigate further into the rear calipers/ parking brake.

 

[340sFastback]

Another thing I should mention is I first bolted Dana rear in with 10.7 rear disc, retained stock kelsey hayes front disc, pressure bled entire system, and test drove. Thats when I first saw long pedal travel spongy brake feel. So with all the stock known to work front brakes in place, existing 15/16 master cylinder that had been on for a year, that is when I first saw the issue. But wrote it off as maybe didn't bleed enough. Car could not lock up tires and was slow to stop. Most likely if I bolt tires back on car its likely be the same way.

Doctor Diff seemed to suggest today maybe get a rear caliper tool, rotate rear caliper back in, activate release packing brake several times, then rebleed again? I told him I did hook up and apply and release parking brake before bleeding? But maybe not enough and air is stuck in there?

But I might be forced to start blocking/plugging brake lines, clamping caliper pistons ect and narrowing issue down. But air stuck in rear brakes somewhere for some reason is suspect.

 

[340sFastback]

Rented this caliper piston tool to push rear caliper pistons fully in like Doctor Diff said. The caliper pistons spun right in. Reinstalled calipers then attempted to use emergency brake to extended caliper pistons out to remove all slack in rear brakes per Dr Diff recommendation.

 

[340sFastback]

So with both rear caliper pistons fully seated I pulled on emergency brake main cable under car to set and release emergency brake around 30 plus times. ALL the slack was taken out of the driver side rear caliper. But pass side no slack was removed? So then I found pass side caliper brake hose was preventing lever from fully returning. So I loosened hose bolt, moved hose, and emergency brake lever / cable snapped right back to full release position.

After that I went ahead and pulled on main cable under car to engage / release emergency brake. Also adjusted cable. I was able to get ALL slack out of both rear calipers. Emergency brake handle in car pulls around half way out and gets very firm. Handle released emergency brakes release levers on calipers return to full release. Also, the cable equalizer under car, where main cable connects to two axle cables, is even when emergency brake are fully appied.

Without any further bleeding the brake pedal feel significantly improved. I went ahead and bled all 4 corners again, seemed to be a lot of tiny bubbles on driver side front caliper.

Brake pedal travel may have decreased a half inch or so. But pedal no longer has that spongy mushy feel. Travel is still long but the pedal has a nice feel to it now.

I think I failed to use emergency brake to fully seat both rear calipers on installation causing the mushy brake pedal.

I also recall applying 40 PSI to brake hose Tee when Dana rear was on a dolly to test for brake line leakage. Per Dr Diff you are really supposed to use emergency brake to seat rear caliper pistons before applying ANY brake line pressure and before any bleeding is performed.

So I am going to put tires wheels on car take for a test drive tomorrow report back on how well it stops.