Brake Problem

[BobsMK4]

I have a MK4 complete kit with manual Mustang GT disc brakes. It has the Wilwood pedal assembly with separate brake reservoirs for the front and rear brakes. I have bled the system several times without much luck to get a hard pedal. I first used a vacuum pump to suck out the air. Then I got my wife to push down and hold the pedal while I opened the bleed screw and drained some fluid into a jar of brake fluid. I got a small amount of air out the First time and then all fluid. We did this several times. We had a hard pedal for a little while. When I went for a test drive I would periodically have a hard pedal then The next time the pedal would go to the floor. This was my 3rd go around at trying to bleed the brakes. When I installed the Wilwood pedal assembly with dual master cylinders, I did not bench bleed the cylinders. I was unaware that I needed to do that step. Today I went to 2 different auto repair shops to see if they could pressure bleed the system. Since the brakes were soft intermittently, they thought that the problem could be one of the master cylinders are bad. They said if I still had air in the lines the brake pedal would be soft all the time. I'm at a loss as to what to do next. I would hate to buy a master cylinder if that's not the problem. How to do you test for a bad master cylinder and how do you determine if it's the front or back one?

[edwardb]

I'm assuming you've carefully checked everywhere and you don't have any leaking lines, right? The shop might be right about a bad MC, but since you didn't bench bleed the masters, you may still have some pockets of air floating around in the system. Personally I would start there before throwing parts at it. Bench bleeding on the car is an easy step. You will need to make up a short piece of brake line to reach from the MC to the reservoir. One at a time, remove the brake line at the MC, attach the short piece and put the other end in the appropriate reservoir. Now pump the brake pedal repeatedly until you have a solid stream of fluid with no air. Repeat for the other MC. If you note either MC doesn't work exactly right, e.g. not good flow, somehow intermittent, whatever, this might be a clue to an MC problem. But assuming they both bench bleed OK, now do the 4-wheel bleed again. Start with the farthest rear, then the other rear, farthest front, other front. If you're doing the traditional method, open bleeder, pedal down and hold, close bleeder, release pedal. Speed bleeders make this a little easier if you're interested. I'm personally a big fan of pressure bleeding using a pressure cap with the CNC reservoirs. A few pounds of air pressure in the cap, then just open the bleeder until it runs all fluid. No pedal pumping. Good luck.

[Gordon Levy]

Please make sure your calipers are on the correct sides. Ford bleeder point backwards and not up.

[BobsMK4]

I'm assuming you've carefully checked everywhere and you don't have any leaking lines, right? The shop might be right about a bad MC, but since you didn't bench bleed the masters, you may still have some pockets of air floating around in the system. Personally I would start there before throwing parts at it. Bench bleeding on the car is an easy step. You will need to make up a short piece of brake line to reach from the MC to the reservoir. One at a time, remove the brake line at the MC, attach the short piece and put the other end in the appropriate reservoir. Now pump the brake pedal repeatedly until you have a solid stream of fluid with no air. Repeat for the other MC. If you note either MC doesn't work exactly right, e.g. not good flow, somehow intermittent, whatever, this might be a clue to an MC problem. But assuming they both bench bleed OK, now do the 4-wheel bleed again. Start with the farthest rear, then the other rear, farthest front, other front. If you're doing the traditional method, open bleeder, pedal down and hold, close bleeder, release pedal. Speed bleeders make this a little easier if you're interested. I'm personally a big fan of pressure bleeding using a pressure cap with the CNC reservoirs. A few pounds of air pressure in the cap, then just open the bleeder until it runs all fluid. No pedal pumping. Good luck.

I have checked many times for possible leaks and there are none. I will try to bleed master cylinders tomorrow. In order to pressure bleed, is there a special cap for the CNC reservoir? Do you have to install a fitting into the cap? If you reverse bleed the system, do you still need to bleed the master cylinders?

[skullandbones]

Hi Bob,

I have the Wilwood pedals and 2000 Mustang GT brakes. I have had similar problems but not in the beginning. I won't go through everything I did but I will tell you what the Wilwood technicians told me after many attempts to get my problem fixed. They told me to balance my balance bar and not use it to bias the MC as I had thought they were designed to do. So basically, I evened the bar so each MC got the same pressure from the pedal. I have a proportioning valve attached to the rear line so I knew I could use that if needed. Long story short, it worked. I did not need to pressure bleed and didn't in the initial install either. I did have a bad MC but it was due to the misalignment that occurred due to my using the balance bar to induce a lot of bias on the MCs. I had mistreated my brake system on the track so I guess that was the reason for the leaky cylinder. Maybe that was the straw that broke the camel's back so to speak. Anyway, if you don't have that bar balanced it could cause a MC failure. It may not be obvious but it still can be sucking air (very difficult problem to diagnose, at least for me).

Good luck,

WEK.

[ram_g]

Please make sure your calipers are on the correct sides. Ford bleeder point backwards and not up.

Umm...no? Maybe the orientation of the caliper is different on the actual Mustangs but in my complete kit with the same brakes the bleeders definitely point up.

[edwardb]

I have checked many times for possible leaks and there are none. I will try to bleed master cylinders tomorrow. In order to pressure bleed, is there a special cap for the CNC reservoir? Do you have to install a fitting into the cap? If you reverse bleed the system, do you still need to bleed the master cylinders?

The CNC pressure cap is their part number CNC1459A. It's a regular style round cap with a Schrader type valve installed. I always do the MC bench bleed, and then use the cap to bleed each wheel. Maybe the MC bench bleed isn't necessary with this method, but I've never tried without it. Other than a problem I had on my last build with the wrong length pushrod between the MC and hydroboost, I've had perfect brakes every time the first time.

[michael everson]

Seems weird that the problem would come and go. If it was trapped air, you would always have a soft pedal. A defective master would leak if it was letting in air. If you continuously press the brake pedal with out moving, does it do the same thing? I am wondering if something in the brake system is causing the pistons to retract too far causing the pedal to the floor.
Mike

[smithbks]

I had almost this same problem and after many headaches it was...not bench bleeding the MC before installing! Do as Edwardb suggests above. That is exactly how I bled the MC in the car as well. It completely solved the problem and I have been happy ever since! And I learned to bench bleed the MC before installing from now on!!! haha

[Jim Schenck]

With the balance bar it may take one additional person to do the bleeding until the system is completely free of any air bubbles. What you need to do is have one person on a front wheel and one on a rear and have them both crack the bleeder on the same pedal stroke each time. Because the two pushrods are connected by the balance bar it can prevent one of the masters from getting completely through their stroke and that leaves a tiny spot for the air to sit and not be forced into the lines. You have to watch the reservoir pretty closely because your fluid will drain out twice as fast this way.

[oldguy668]

Umm...no? Maybe the orientation of the caliper is different on the actual Mustangs but in my complete kit with the same brakes the bleeders definitely point up.

Gordon is right, ram_g is wrong:



I've done 6 cars with Ford brakes and Wilwood master cylinders and I have NEVER bench bled the masters. I use a vacuum bleeder kit and have had 100% success, except for the time I installed the fronts with the bleeders facing up.

[Jim Schenck]

Joe,

That isn't the complete kit caliper, the bleeder should face upward on the two piston PBRs that come with the kits:

frontcaliper.jpg

[2bking]

I. When I went for a test drive I would periodically have a hard pedal then The next time the pedal would go to the floor. Since the brakes were soft intermittently, they thought that the problem could be one of the master cylinders are bad. They said if I still had air in the lines the brake pedal would be soft all the time. How to do you test for a bad master cylinder and how do you determine if it's the front or back one?

The problem as stated is not air in the system so bleeding will not solve it if the pedal is hard again after being soft. The auto repair shop was most likely correct saying it's a master cylinder problem. I would inspect the balance bar operation while pressing the brake pedal and observe the travel provided to each master. If one is soft the bar will pivot and depress that master while the other is still. Doing this several times may show which cylinder(s) is causing the problem or if there is a different problem.

[skullandbones]

With the balance bar it may take one additional person to do the bleeding until the system is completely free of any air bubbles. What you need to do is have one person on a front wheel and one on a rear and have them both crack the bleeder on the same pedal stroke each time. Because the two pushrods are connected by the balance bar it can prevent one of the masters from getting completely through their stroke and that leaves a tiny spot for the air to sit and not be forced into the lines. You have to watch the reservoir pretty closely because your fluid will drain out twice as fast this way.

X2 on that. It's a balancing act. Pun intended. It is a three person effort. We didn't vacuum bleed but did have tubes and bottles of fluid attached to the valves to avoid any air bleeding back into the system. I have the smallish reservoirs so it keeps you busy refilling. If you have the none see thru then you will have to be doubly careful.

Good luck,

WEK.

[BEAR-AvHistory]

Took a few shots pressure bleeding. Depending on which reservoir you have (internal Threads) you may need a custom cap made up. You also want to bleed PS both calipers together first then the DS both calipers. You can get bleeding bottles for the calipers from Amazon that will let you do it without any help.

Finally to get the thing to actually stop its a good plan to lose the FFR pads & get a set from HAWK. I have HPS in front & the + versions in back. My manual brakes will stop in about 100ft from 60mph. Used "about" because the 100 feet is marked on the street so there might be a small variance in hitting the brakes consistently at the start line.

That said I went from very unhappy to very pleased with a bit of trial & error with help from some of the guys here & BBQLover who let me drive his car for a camparo in braking.

I had a contemporaneous thread of the adventure is posted here last year.

[Norm B]

I agree with 2bking that, if the problem is as described, then it is very unlikely to be due to air in the system. You should not have a hard pedal at any time if there is air in the lines. You either have a bad master cylinder or something is causing the brake pads to be pushed back too far. Look for leaks at the masters and check all rotors for side to side play. Check your front spindle nuts.

Good Luck
Norm

[Jim Schenck]

We have seen an inconsistent pedal with air stuck in the master cylinder, doesn't mean it isn't a bad master but I would definitely try the alternate bleeding before starting to replace parts.

Also the newer MKIV kits come with Stoptech pads which are a more aggressive compound, if your kit came with them I would try those before throwing in a set of Hawks even though I agree they are great pads as well.

[BEAR-AvHistory]

STOPTECH are good pads too. Anything but what ever they used too have seems good to go err Stop.

[oldguy668]

Joe,

That isn't the complete kit caliper, the bleeder should face upward on the two piston PBRs that come with the kits:

frontcaliper.jpg

My mistake. I grabbed the wrong photo.

[ram_g]

My mistake. I grabbed the wrong photo.

Thank you.

Hey it's intimidating enough to try to correct an icon of the FFR world Mr. Levy himself, to then have the Super Moderator Big Kahuna Top Dog tell you you're wrong...you begin to wonder if the brakes you're so familiar with are really something else and you're living in a parallel universe...

Kidding aside, I think it's an issue of earlier or later Mustang brakes. The later twin piston ones are the ones that are supplied with the Complete Kit while I suspect what you and Gordon were referring to were the earlier single piston Mustang calipers that a lot of the MkIII and earlier builds used.

[BobsMK4]

Hi Bob,

I have the Wilwood pedals and 2000 Mustang GT brakes. I have had similar problems but not in the beginning. I won't go through everything I did but I will tell you what the Wilwood technicians told me after many attempts to get my problem fixed. They told me to balance my balance bar and not use it to bias the MC as I had thought they were designed to do. So basically, I evened the bar so each MC got the same pressure from the pedal. I have a proportioning valve attached to the rear line so I knew I could use that if needed. Long story short, it worked. I did not need to pressure bleed and didn't in the initial install either. I did have a bad MC but it was due to the misalignment that occurred due to my using the balance bar to induce a lot of bias on the MCs. I had mistreated my brake system on the track so I guess that was the reason for the leaky cylinder. Maybe that was the straw that broke the camel's back so to speak. Anyway, if you don't have that bar balanced it could cause a MC failure. It may not be obvious but it still can be sucking air (very difficult problem to diagnose, at least for me).

Good luck,

WEK.

I haven't touched the balance bar. The bar is even. Today I bled both MCs and started to bleed the rear brakes using a vacuum pump. I ran out of time. Tomorrow I will get my wife to hold and release the pedal while I bleed the rear brakes hopefully for the last time. I hope bleeding the MCs will solve the intermittent soft pedal.

[BobsMK4]

Seems weird that the problem would come and go. If it was trapped air, you would always have a soft pedal. A defective master would leak if it was letting in air. If you continuously press the brake pedal with out moving, does it do the same thing? I am wondering if something in the brake system is causing the pistons to retract too far causing the pedal to the floor.
Mike

When I first bled the brakes and drove around the neighborhood in go-cart form the brakes worked fine with a hard pedal. A couple of months went by and the next time I drove the car the pedal would go soft every 2 or 3 times that I applied the brakes. From then on, I have had this problem. I have bled the brakes several times and each time I got some air out of the system. Each time the brakes would stay hard when the car was in the garage. As soon as I would go out for a test drive, it would periodically go to the floor and 1 pump it would be hard again. Very strange!

[Jim Schenck]

If you are bleeding with just one assistant you can still do two calipers at a time but they both need to be open together, so crack one and with the pedal still being held down move to the other end of the car and crack another, then tighten both before lifting the pedal. I know some people are disagreeing with this but we have had the exact same symptoms in a couple of cars and this was the fix, adjusting the balance bar to center wasn't enough to get the travel needed. The other thing besides a bad master (which is still very possible) that can cause an unpredictable pedal when the car is moving is pad knockback. You usually don't see it with sliding calipers but it can happen, particularly if one of the sliders is sticking or there is an abnormal amount of rotor movement. Most likely this would be in the rear brakes if there is a lot of c-clip play but it could be in the front if the wheel bearing didn't get tightened down or is faulty. If you can feel a decent amount of slop by pulling the rear wheels in and out then I would check the calipers to make sure they are able to slide freely, otherwise as the axle is moving it can force the pistons back off the brakes and give a similar feeling to having air in the system.

[Gordon Levy]

Listening to your description it sounds like you may have a crack in a flare. Not really enough to cause a wet spot on the floor but enough to draw air back in. Go through and check every joint and flare.

[smithbks]

I recall having very, very similar symptoms as BobMK4. I would bleed the brakes and everything would be hard pedal. Then after a while (days) I'd come back and it was soft. I would pump them up and they would be fine again and the cycle would start over. For me, bench bleeding the MC - actually doing it in the car like Edwardb describes - is what solved the problem for good. I'm not a brake expert so I don't know why - it just did

[BobsMK4]

Today I finished bleeding the rear brakes and then moved to the fronts. Before lunch, I bled the front brakes and then checked the pedal. I pumped it a few times and had a hard pedal. I waited a few minutes and tried it again. The pedal went soft on the first push. The second push it was hard. I kept pressure on it for 5 minutes with the pedal staying hard. I waited a few more minutes and on the first push the pedal was soft again. If one of the master cylinders are bad, how do you determine which one? I rechecked for leaks and found non. I'm at a loss as what to do next?

[BEAR-AvHistory]

If the masters were bled you most likely still have air in the lines. With the twin masters you want to bleed the PS first doing both calipers at the same time. Then do the DS both at the same time.

If you did not bench bleed the masters it can take a number of attempts to get the air out. If they need to be bled open the brake line where it enters the master cylinders. Attach a hose to the masters & run the hose into the reservoir. Pump the brakes till no bubbles are showing in the reservoir.

Reattach the brake lines & do a normal (pressure) bleed

[BobsMK4]

Today I pressure bled the brakes. I did the rear brakes first and then the fronts. I got a little air out, but it wasn't much. I had a hard pedal for a while. I waited a while and tested again. The pedal went soft. I pumped it up and it was hard again for a while. I decided to put the wheels back on and take it for a test drive. Every 2nd or 3rd time, the pedal would go soft and 1 pump it would be hard again. There was no change from my previous brake bleeding using a vacuum system. I checked again for any leaks and could not find any. The MCs are not leaking. There just can't be any air still in the lines. I did try moving the balance bar a few turns in each direction. I couldn't tell any change in the pedal. I guess I need to determine if one of the MCs are bad. How exactly do you check for a bad MC?

[michael everson]

When you get the soft pedal, does it travel all the way to the floor? Also as you are pushing the pedal watch both master cylinders. The one that travels the furthest would be the likely culprit. I bet one barely moves and the other is collapsing. Hydraulic brakes are very simple. Theres got to be something we are all missing. Try holding the pedal down with some type of pole or something and leave pressure on it over night. There should still be pressure on it in the morning. If not start looking for a leak. If the master cylinder is bad, it will eventually start leaking through the boot.
Mike

[CraigS]

Another item to check would be to make sure the sliding pieces of all 4 calipers are free and slide easily.

[Norm B]

I agree with Mike. We must be missing something simple.
Have you adjusted the rear calipers since installation? If you haven't, I believe the procedure is to depress the brake pedal (once you have a firm pedal) and pull on the park brake.

HTH
Norm

[BobsMK4]

When you get the soft pedal, does it travel all the way to the floor? Also as you are pushing the pedal watch both master cylinders. The one that travels the furthest would be the likely culprit. I bet one barely moves and the other is collapsing. Hydraulic brakes are very simple. Theres got to be something we are all missing. Try holding the pedal down with some type of pole or something and leave pressure on it over night. There should still be pressure on it in the morning. If not start looking for a leak. If the master cylinder is bad, it will eventually start leaking through the boot.
Mike

When I get a soft pedal sometimes it goes all the way to the floor, but not always. This morning I put a 2x4 to hold the pedal and keep pressure on it. After 4 hours, it is still holding pressure. I don't see any leaks around the MCs.

[BobsMK4]

I agree with Mike. We must be missing something simple.
Have you adjusted the rear calipers since installation? If you haven't, I believe the procedure is to depress the brake pedal (once you have a firm pedal) and pull on the park brake.

HTH
Norm

I have not tried adjusting the rear calipers since install. Since I have pressure on the pedal with a 2x4, I will set the emergency brake. Do I do this just once or repeat? When I tested the brakes several times, the car stops straight and in a short distance. I've looked at all 4 calipers and I can't see anything out of the ordinary. I only have 150 miles on the car.

[Norm B]

I believe you pull the brake on and release it multiple times until it stops getting tighter. I lent my Mustang maintenance manual to a friend for his roadster build. Maybe someone can chime in with the exact procedure or Google might work.

[BobsMK4]

When I get a soft pedal sometimes it goes all the way to the floor, but not always. This morning I put a 2x4 to hold the pedal and keep pressure on it. After 4 hours, it is still holding pressure. I don't see any leaks around the MCs.

It has been over 16 hours and the pedal is still holding pressure. It hasn't budged. The problem has to be one of the MCs. There is still no leaks around the MCs. When I get a chance later today or tomorrow I will try to check the MCs.

[BEAR-AvHistory]

Just a thought. Is the pedal coming all the way back to the stop when you release it? I put a light return spring on mine.

[6t8dart]

Have you tried replacing the master cylinder yet? They are not that expensive and after all the hours you have troubleshooting, it would be where where I would start. I know a stock mc is about $75, not sure what the wilwood runs.

I had a diminishing pressure leak issue with my Dart, it turned out that corrosion in the mc bore allowed fluid to leak at certain points in the bore travel.

[BobsMK4]

Just a thought. Is the pedal coming all the way back to the stop when you release it? I put a light return spring on mine.

Yes, the pedal is returning back to the stop.

[BobsMK4]

Have you tried replacing the master cylinder yet? They are not that expensive and after all the hours you have troubleshooting, it would be where where I would start. I know a stock mc is about $75, not sure what the wilwood runs.

I had a diminishing pressure leak issue with my Dart, it turned out that corrosion in the mc bore allowed fluid to leak at certain points in the bore travel.

As soon as I can determine which MC is bad, I will replace it.

[BobsMK4]

With a friends help, we determined that the front brake MC is bad. We eliminated any of the calipers from being the problem. There were no leaks from the brake lines or the MCs. Always the first push of the pedal it would go to the floor. The next push the pedal was hard. With the balance bar centered, I pushed the pedal and the front brake pedal push rod would completely collapse. The rear push Rod would move a normal small amount. To recheck, I rotated the brake bias adjuster to the front MC and the push Rod collapsed and the rear moved slightly. I then rotated the brake bias adjuster to the rear MC and I got the same result. Although there is no visible MC leak, there must be an internal issue with the front MC. After all the bleeding and caliper checking, I am finally relieved to find the problem. The front MC will be way easier to remove than the rear. I contacted Factory Five with the hopes that they will cover the MC replacement.