Brakes Gone!

[Murd]

Just went out for a quick drive, a few hundred feet down from my driveway brakes for a stoplight and pedal went to the floor. While backing out of garage and driveway pedal felt firm, I have a carb that likes a bit of throttle till it warms up so used to pushing the brake and blipping the throttle and it was firm for backing out.
Setup is wilwood pedal box and masters I got from forte. Same setup as FFR but different masters. Front 2 piston PBRs and rear 94 95 cobra brakes.
Got home, can’t find any sign of leaking fluid, pumped a hundred times with no change in feel, fluid resivoirs are all full.
Pulled the acces panel for the pedal box, front master seems to compress completely, rear seems to be working, so I believe it is the front circuit.
Checked again and no sign of leaks. I also checked drivers footbox and frame for signs of fluid, nothing.
Where to start?
My only thought is something has broken inside my master cylinder, not sure that there is anything that could happen to a caliper to allow this without it leaking.

Thoughts?

[NAZ]

Are your M/C reservoirs vented? They have to be vented to work properly. But you need a very flexible elastomer membrane above the fluid to seal it from atmosphere. The membrane allows the fluid to see atmospheric pressure without actually exposing the fluid to air as it will absorb moisture from the air.

[Murd]

Yes they are wilwood reservoirs with the membrane you speak of. Don’t think that would make it go from hard brakes last time I drove to nothing though

[cv2065]

Has it returned to normal or still out? If it was sporadic, could be air pockets in the circuit that maybe were not purged? If its still out, then I would swap out the MC and see if you have any change.

[Railroad]

I think just one master cylinder defect would make the peddle feel like you have no brakes. Any chance a hill or steep incline is involved and the location of your reservoirs related to your master cylinders.
Ford master cylinder pistons used to have a butter fly reed valve on the end of the master cylinder piston.
The smallest piece of trash under this reed valve would result in no brakes. You could stab the peddle and dislodge the trash sometimes. Wilwood or Mike Forte might have some suggestions. Let us know what you find.

[Jeff Kleiner]

Have someone push the pedal down while you crack a front bleeder. This will tell you whether the MC is pushing fluid or not.

Jeff

[Murd]

Thanks guys, just off the phone with my ex formula car racer buddy. He also asked about a hill. I did have it up on jack stands today. Back end was up in the air for a while.
He said the sometimes had this problem when a car was on a steep incline air that was trapped somewhere would appear and cause problems.
Jeff,
That makes sense, will try for sure.
2000km on the road and brakes have always felt solid, it’s weird for such a sudden change.

[Railroad]

You might have to raise the reservoirs. I have the Wilwoods and FFR reservoirs. ,,, not running yet, but looks like the reservoirs will need to be topped off, to keep the fluid level above the master cylinders.

[Murd]

I have the wilwood reservoirs, clear plastic, full to the line. With the back end up on jack stands the masters were likely above the top of the fluid though. Is that enough to let fluid run out and air go in? I have to jack the backe end up first usually, can barely get jack under fuel tank as is. Might have to find a new procedure and do front end first

[Murd]

Spent some time tonight working to find out what’s up with my brakes. Hooked up blended bottle and it’s not bleeding fluid, actually opposite, it’s sucking fluid into the caliper from the bottle.
I don’t have a pressure bleeder, tried a makeshift one using a large syringe. I could get it to seal well enough to flow fluid through the system. A couple times I got a hard pedal, then a few more pumps it would go away.
I tried having my wife pump the brakes while I tried to pressure the fluid in, I was getting pressure back from the master to the reservoir. When the reservoir was low I could actually see a jet of fluid shooting out when she pushed the pedal.
Seems the valve to the reservoir is broken or has something clogging it up and it’s not closing, so the master can’t apply any pressure to the calipers. It worked briefly a couple times then back to not working.

Thoughts and solutions?

Thanks everyone

[Murd]

Also while trying to pressure fluid through the system sometimes it flowed freely, sometimes it didn’t want to flow at all, like the valve was closed

[Clover]

Not sure this is really possible on this car but on an old 944, I replaced the master and did not get it lined up right. Every time the plunger was pushed, it deflected to the side slightly which let in air. In that case, I was never able to get a firm peddle and I went through more brake fluid then I would like to admit before I pulled the master and noticed what was wrong. If you can pump the brakes with the front bleeder open and not get anything out, then I suspect something is wrong with the master calendar and you are not moving any fluid.

[edwardb]

IMO, need to settle down here and approach this one step at a time. For your pedal box installation, is the brake arm stopping before the frame rail? The MC's need to stop against their internal C-clip stops. Not against the frame rail. Some have had a problem with the MC valving not working correctly when the pedal arm was stopped short. Then, for bleeding, pick a method and stay with it. If you're going to do traditional bleeding (open bleeder, press brake pedal, close bleeder, etc.) then do that. If you want to do pressure bleeding (which I personally really like) then I'd recommend getting an actual pressure bleed setup or a pressure cap for your reservoir(s) and use very low pressure compressed air. In the 5-6-7 PSI range. It doesn't take much. I don't think using a syringe is the right approach. Also, for pressure bleeding, never press the brake pedal down while the system is under pressure. Not good for the components and I have no idea how that might affect the process. If you let the fluid in the reservoir(s) go too low and the system pulls air, then you're back to square one and need to start whatever process you're using over again. Having the back end jacked up first shouldn't affect anything if you have the reservoirs at the proper height. It sounds like you might have a defective MC. But you need to get consistent bleed process to make sure all the air is out of the system first in order to confirm.

[Railroad]

I could not follow your explanation of the bleeding and testing you did. Do you have your master cylinder push rods adjusted with some slack in them. They need to let the master cylinder piston back up to full return. If your push rod can be wiggled with no brake application you should be good.
There should be no VALVE from the reservoir to the master cylinder. This should be an open line from the bottom of the reservoir to the top of the master cylinder.
If when your assistant pressed the brake peddle and fluid moved into the reservoir, you have the master cylinder plumbed wrong, (not likely) or the master cylinder is by passing and is bad.

[Murd]

My brake pedal does not hit the crossbar, has some free play, but not sure that the master pushrod might still be a bit tight, was thinking of this in bed last night, I’ll play around with that.
No chance it is plumbed wrong.
This is not a build. This is a car that has been saftied, plated and on the road since May with strong brakes for 2000 km then all of a sudden nothing. The brake system has been filled bled and working for a year and a half.

[Murd]

I am strongly leaning to the MC gone bad diagnosis

[Murd]

IMO, need to settle down here and approach this one step at a time. For your pedal box installation, is the brake arm stopping before the frame rail? The MC's need to stop against their internal C-clip stops. Not against the frame rail. Some have had a problem with the MC valving not working correctly when the pedal arm was stopped short. Then, for bleeding, pick a method and stay with it. If you're going to do traditional bleeding (open bleeder, press brake pedal, close bleeder, etc.) then do that. If you want to do pressure bleeding (which I personally really like) then I'd recommend getting an actual pressure bleed setup or a pressure cap for your reservoir(s) and use very low pressure compressed air. In the 5-6-7 PSI range. It doesn't take much. I don't think using a syringe is the right approach. Also, for pressure bleeding, never press the brake pedal down while the system is under pressure. Not good for the components and I have no idea how that might affect the process. If you let the fluid in the reservoir(s) go too low and the system pulls air, then you're back to square one and need to start whatever process you're using over again. Having the back end jacked up first shouldn't affect anything if you have the reservoirs at the proper height. It sounds like you might have a defective MC. But you need to get consistent bleed process to make sure all the air is out of the system first in order to confirm.

I tried traditional bleeding first, mc would not push fluid, wanted to pressure bleed to make sure there was fluid in the master, didn’t have a pressure bleeding setup so used what I had, it pushed fluid through, enough to flush the system.
MC still not pushing fluid after that, except a couple times the pedal got hard, almost as normal, few more pumps then to the floor again.

[Murd]

Just back out in the garage. Pushrod does have a bit of free play and again pedal does not hit crossbar.
More important there is now brake fluid filling the mc boot, which it wasn’t yesterday when I started working on it, so I imagine that means it is toast?

[Dave Howard]

Hi Andrew,

Sounds like you've done a thorough troubleshoot so far. Regardless of the method used for bleeding, sounds like you have bled the brakes. You can bleed the brakes just as well for 0$ capital outlay with the help of a buddy a 6 beer as opposed to the pressure bleeder. Bleed all 4 corners. If the brakes worked for 2K and now are acting up, something has changed. No visible leaks any where. The master cylinder must be passing. A seal or O-ring might have failed or been damaged. These were new units from Forte?

[initiator]

I think fluid in the MC boot is a clear sign of MC failure. Not aware of any other way the fluid could get in there.

[Jetfuel]

By now you should have the master cyl removed, find out what size cup it uses (7/8?) and bought new ones for almost no $ at all..

[Murd]

I’ve been out on the road away from home for work, going to try and get some time to get it out tonight. I ordered a new one today, should see it next week.
Spoke to wilwood today, he said it’s usually from the pushrod not being centred. I have a bias adjuster and the cable it’s the side of the footbox and pushes the bias bar over a bit, but the pushrod still looks to go in straight.
I’ll pull it apart and see what’s up

[Railroad]

Since you have to pull one of the M C you can check the spacing on the center pivot. I am thinking it is some like .025" You had better verify that before you change or set yours. That could be a reason the rods would be not in line.

[Murd]

Railroad, sorry I’m not following. Do you mean the spacing between the pedal and the clevis? I do remember adjusting that during the build.
Got the MC out, not too bad once I took the steering column out.
Wilwood told me to get it out and bench bleed it to see if it’s working. I set it up in the vice with a spare reservoir and a piece of brake line going to clear tubing going back in the reservoir.
It is pumping fluid, but sucking it all backwards when you let the pushrod out, I pumped it enough like this that I bled all the air out. I recalled it only really pumping one way when I did this during the build. I tried attaching it to my bleeder bottle with fluid in the bottom. It would pump out and suck it all back in. Wouldn’t fill bottle or run down reservoir level.

Took mc apart, don’t see anything wrong. Wilwood tech support said if the pushrod has been not centred it will hit the side of the bore and score it, causing a leak. The bore in mine looks clean. None of the seals look damaged, no holes looked clogged.
Kind of lost.
There is a small hole in the side of the bore near the bottom, below the reservoir return holes. What does this do?

[Murd]

I should add there was a small but not insignificant amount of fluid had leaked out the pushrod end after I had bench bled it.
I cannot see any sign of significant wear or damage that would cause it to not function properly or leak.

[michael everson]

It should suck it backwards. Since you have it out, you might as well replace it. I don't have a solution for you. Strange that the brakes come and go. Hydraulic brakes ae incredibly simple. Not much to go wrong.
Mike

[Murd]

Mike
I believe it should suck some backwards but it should pump most through. Normally if you have a one man bleeder bottle, with the tube going into fluid so it doesn’t suck air back in, when you pump it it empty’s the reservoir and fills the bottle. Mine used to do that, now it sucks back everything it pumped out.
I already ordered a new one, I’m sure it will work, but without knowing what caused this or even what the problem was, and the instant brake failure, I’m nervous as hell to drive it.
Called wilwood again today with the results I found and they had no ideas or advice other than rebuild or replace

[Railroad]

Well my advise was off 1 decimal point. The spacing I was referring to should be between .20 to .250.
Page 4 of this pdf explains it. Does not sound like this was your problem, but still needs to be correct.
https://www.wilwood.com/PDF/DataSheets/ds252.pdf

[Murd]

Just went and jammed a stack of feeler gauges in between the pedal and Clevis washer. Pretty bang on 0.20. I did adjust it to the wilwood instructions before.
The one potential problem area I see is my bias adjustment cable. As anyone who has one will probably tell you, not much room for the cable to curve so it hits the passenger side of the drivers footbox and push’s the balance bar towards the drives side, and maybe lifts it up too. Could cause the pushrod to not travel in perfectly straight but I doubt being off .10 is causing too much trouble. Up and down angle may be a bigger deal?
The bore of the mc isn’t scored so I don’t think that was the problem.

Any more ideas?

[Railroad]

I think with your correct clearance on the bias bar, the mc push rods would stay centered enough to not create a problem. On the adjuster, I bought the Wilwood and saw the same cable issue. I was informed of a Tilton 90* gear box, that attaches to the end of the bias bar and allows the cable to attach at the given 90*. The cable still moves front to rear as the brakes are applied. I am still in the build stage, so no application experience, but the design is better, IMO.

[Murd]

I’m aware of the 90 tilton box, when I was searching others setups lots just curved the cable like I did with no issues so I didn’t worry about it. I’ve been considering it now but don’t think that’s the issue as enough others have that setup with no reports of problems.

[michael everson]

Did the "pedal to the floor" only happen once? if so maybe the front caliper pistons were somehow compressed causing the pedal to have to travel much further.
Mike

[myjones]

The one potential problem area I see is my bias adjustment cable. As anyone who has one will probably tell you, not much room for the cable to curve so it hits the passenger side of the drivers footbox and push’s the balance bar towards the drives side, and maybe lifts it up too. Any more ideas?

Murd;
I put the bias cable on the other end of the shaft and made a lazy loop in the cable back toward the middle of the car so the cable doesn't try to kink/bind.
Not as much for the connector to rub or bind against on the outboard end of the bias shaft so it works out great on my 33.

Dale

[Murd]

Mike
I pumped it 100 times and it went to the floor. Randomly after sitting it would get firmer, a few pumps and it would go back to the floor. When it would go to the floor there was no resistance at all.

Dale
I tried the other side during the build but I have a hydraulic clutch and it seemed to interfere more on that side, I’m assuming you have the cable?

Thanks again all.

[davekp]

Maybe just ditch the adjuster cable. I had a cockpit bias adjuster on a formula ford and never used it once I got the right bias dialed in. Do you really need one?

[Murd]

I have considered ditching the bias adjuster cable, not sure it has anything to do with my problem though as I don’t know what the problem was. I haven’t used the adjuster but would like to when I can find a safe spot and time to dial it in. Brakes worked well but I think I can dial in some more rear.
New MC should arrive Thursday.
I’m away till Monday night, when I have some time I will put the old one back together and see if I can figure out what it’s doing.

[Murd]

Update.
Got new master in last week and back to good solid brakes. Had a really tough time bench bleeding the new master, I think air is getting trapped in my reservoir hoses. I’d think I had it all out and 20 pumps later see a bubble again. After about 3 hrs pumping and alternating between jacking the front and rear up I got it all out.
Brakes bled easily after that and back on the road.

I took the bias adjuster off but don’t think that was related, still don’t know what caused it, after my difficulty bench bleeding I’m wondering if I had a trapped large air bubble in my reservoir line? Seems like it should have made its way out already but who knows?

[GoDadGo]

Murd,

When you have time try gravity bleeding each wheel starting with the longest lines first.
Bleed each wheel separately so that the fluid is flowing from the reservoir through each Master Cylinder and then out of your caliper.

> Do the right front, then the left.
> After that do the right rear, then the left.
> Just make sure that your reservoir(s) don't run low.

Once you gravity bleed, you will need to do a little more pump it, pump it, pump it method to make sure that things properly firm up.
Yes, the rear is a pain in the neck since you may need to jack the front up a bit, but it does work pretty well.
Also, a little Fish Tank or equivalent clear tubing goes a long way to keep things tidy.

Good Luck & Hope This Helps!

Steve