500psi T-Bird Calipers

[Broncobowsher]

The caliper needs to be able to move far enough that the pads can be completely worn out, metal to metal with the rotor, and still have some clearance before it can come into contact with the knuckle or anything else. If you want a number for "some clearance" I'd want .06", but I could live with .03"

Lack of travel would clearly effect how the brakes perform, but this won't affect how much line pressure can be generated by the system.

How easily the caliper moves in it's bracket will affect pad wear and brake performance, but not maximum line pressure. One problem at a time.

How are you measuring the line pressure?

But if the caliper is grounding out on the knuckle, the outer pad won't have contact with the rotor. As pressure builds the piston will press the inner pad to the rotor and the rotor can flex. This will be a point where there is expansion (fluid flowing with minimal pressure increase). That is why I was suggesting checking caliper clearance.

 

[chuzie]

Did some more tests and came back inside to thaw out.

With rear brakes plugged off...
- Front driver caliper = 500psi (no change)
- Pedal resting height from floor = 5.75"
- Pedal min height from floor
-- Engine ON = 2.75"
-- Engine OFF = 1.5"
- 1.5 oz of fluid after 5 pumps from caliper bleeder
- 1.5 oz of fluid after 5 pumps directly from MC port
- 1500 psi direct from MC to caliper using a 15 foot coiled steel line

With rear brakes unplugged...
- Pedal resting height from floor = 5.75" (no change)
- Pedal min height from floor
-- Engine ON = 2.25"
-- Engine OFF = 1.25"
- 1500 psi direct from MC to caliper using a 15 foot coiled steel line

No observed no air bubbles in the PS reservoir in case anyone is wondering.
Pads appear to be in light contact with rotor when brakes not engaged. I can still turn rotor and there is not a noticeable gap.

Why am I losing 1000 psi when plumbed directly to the caliper?
If I assume each caliper is absorbing 1000 psi, then net 500 psi measured at each seems to make sense since the pressure would balance between the two, correct
2500 MC
-1000 caliper
-1000 caliper
-------------
500 leftover between the two?

As far a volume is concerned, if I'm getting the same volume from both the MC and the caliper, I'd say there's no restriction in the lines but, barring some issue with the calipers binding, I can't help but think I need a larger MC although I swear people running Explorer rear discs and T-Bird front discs are using 1-1/8"

Next, I'll bypass the frame to axle line with the large steel line and see what measurements I get just to rule out the hose once and for all.
Also need to really look at how the caliper is moving in the knuckle.

But if the caliper is grounding out on the knuckle, the outer pad won't have contact with the rotor. As pressure builds the piston will press the inner pad to the rotor and the rotor can flex. This will be a point where there is expansion (fluid flowing with minimal pressure increase). That is why I was suggesting checking caliper clearance.

Are y'all suggesting if I remove the pads and mount the caliper, it should slide laterally by hand?

 

[ntsqd]

No, what he's saying is that if the caliper body is coming into contact with something that hard-stops it, that then the caliper piston will flex the rotor. In doing so this creates the expanding volume that Lars was talking about. It's an excellent point. My wet thumb in the wind impression is that it may only be marginally enough to give you the results that you're getting, but that it definitely needs to be checked and immediately eliminated if it's found to be happening.

When plumbed together neither caliper 'absorbs' partial pressure. Assuming that there is nothing between them that meters or regulates the pressure they both should be seeing full line pressure as measured at the m/c port. Said differently, if the pressure at the m/c port is 1500 psi then both front calipers should also have 1500 psi at their bleed screws.

As for the caliper's sliding ease, they should slide with little to no effort while also not having much slop in their mounts. If they don't slide easily then the inner pad will wear out at a greatly accelerated rate.

 

[ksagis]

Another thought... I think it's safe to assume I've NEVER had decent brakes since acquiring the Bronco is 2000 (yes, sad and unacceptable). That said, I likely have no reference for what proper clearance and movement / travel should look like on this rig. I'm guessing I should pull the pads and make sure the caliper can move laterally, but am I looking for a certain level of resistance, or lack thereof? Paint me a picture please.

My take from data collection from various well balanced setups would be a pedal stroke of 1.5 to 2 inches is what most would say is a nice configuration. Anything more is indicative of poorly bled brakes or mis-matched calipers to MC, etc. I'm now at 2 inches at my rig and still poking around.

Random thought since I know you said you're a one man band. Point your phone at the caliper and record a video o see if things are flexing or binding. Or get two phones and do a face time. (necessity is the mother of invention)

 

[ksagis]

- 1500 psi direct from MC to caliper using a 15 foot coiled steel line

Gonna check the obvious question, you are sure you got a good bleed on this configuration? If so, this points directly at caliper issues.

And these are the new calipers?

 

[chuzie]

No, what he's saying is that if the caliper body is coming into contact with something that hard-stops it, that then the caliper piston will flex the rotor. In doing so this creates the expanding volume that Lars was talking about. It's an excellent point. My wet thumb in the wind impression is that it may only be marginally enough to give you the results that you're getting, but that it definitely needs to be checked and immediately eliminated if it's found to be happening.

Makes sense. I see no evidence of this happening though. The caliper travels freely along the knuckle when the retainer is removed and the pads rest flush against the rotor. Additionally, removed the pads to ensure additional movement area is available as they wear down.

When plumbed together neither caliper 'absorbs' partial pressure. Assuming that there is nothing between them that meters or regulates the pressure they both should be seeing full line pressure as measured at the m/c port. Said differently, if the pressure at the m/c port is 1500 psi then both front calipers should also have 1500 psi at their bleed screws.

Totally agree. I was more trying to convey that whatever issue is sucking up the pressure here, it is being dissipated at the calipers at a rate of 1000 psi per caliper which then leaves a net system pressure of 500 psi.

As for the caliper's sliding ease, they should slide with little to no effort while also not having much slop in their mounts. If they don't slide easily then the inner pad will wear out at a greatly accelerated rate.

The old outboard pads are worn 50% more than the inboard.

My take from data collection from various well balanced setups would be a pedal stroke of 1.5 to 2 inches is what most would say is a nice configuration. Anything more is indicative of poorly bled brakes or mis-matched calipers to MC, etc. I'm now at 2 inches at my rig and still poking around.

So I'm moving 3.5" of pedal. Not sure what that equates to in rod movement.

Gonna check the obvious question, you are sure you got a good bleed on this configuration? If so, this points directly at caliper issues.

And these are the new calipers?

I'm 95% sure. Bled em till no more air comes from the caliper bleeder.
Calipers are brand spanking new as of yesterday.


I was going to bypass the frame to axle hose, but considering the 2500psi measurement we had at the hose tee above the diff with calipers removed along with the pressure drop on a direct hard line configuration from the MC to the caliper, I think it's safe to eliminate the frame to axle hose.

Something is happening at the caliper. It's either the caliper or the knuckle in my opnion.
What's a reliable method to test the caliper OFF the knuckle?
I have a bunch of 1/4" plates I can stack in the caliper instead of a 2x4 so we can eliminate any compression. Can also remove the pads as an added measure.

 

[ksagis]

Something is happening at the caliper. It's either the caliper or the knuckle in my opnion.
What's a reliable method to test the caliper OFF the knuckle?
I have a bunch of 1/4" plates I can stack in the caliper instead of a 2x4 so we can eliminate any compression. Can also remove the pads as an added measure.

Metal plate was exactly what I was going to suggest. Or take the caliper off knuckle and rotate to an exposed area of rotor (If you have that)

 

[chuzie]

Doesn't get any more direct connect than this boys. 700psi at the caliper directly off MC. Someone explain this madness.

 

[Oldtimer]

Check OD of rubber hose with a micrometer, at rest, and at pressure.
The only other flexible item in the picture is the caliper housing its self, and it looks like a stout casting.

 

[ba123]

Doesn't get any more direct connect than this boys. 700psi at the caliper directly off MC. Someone explain this madness.

I stopped reading this thread for a bit but coming back.

First off, I think you're losing yourself in the numbers when you should just be thinking about braking. I like to over analyze things as well, but...

You have two lines coming off the master cylinder. Pressure is going to go the easiest way out.

I think this might be more your master and your whole setup vs the "where am I losing pressure" issue. Although, just cause you didn't get any more air out, doesn't mean you don't have any more air in there.

Get a pressure bleeder or borrow one, or a reverse bleeder...whatever someone has near you. Normal bleeding process sucks and is only enough for "ok" brakes in a lot of cases. A motive pressure bleeder is what I have. It's no outrageous and well worth it and you can use it on ANY vehicle.

***also, just cause a caliper is "new" doesn't mean it is perfect. I had to return a newly rebuilt Tbird caliper cause the threads on the bleeder were not perfect.

 

[ksagis]

Doesn't get any more direct connect than this boys. 700psi at the caliper directly off MC. Someone explain this madness.

Is that a flex line in the path but that’s needed due to needing a banjo to connect to caliper. Is it a new flexline?

Maybe get this or fab one to rule out the flexline?

BrakeQuip BQ1020R

 

[ntsqd]

Was it me, I'd scare up a -3AN banjo adapter and some -3AN tube nuts and sleeves so that you can take the flex line out of the plumbing.

I built a pressure bleeder using a calibration gas bottle (a dead fire extinguisher would work instead), some tubing, and a low pressure air pressure regulator. ~5 psi air in the top of the brake fluid in the container, and the tubing is submerged below the fluid level, which is connected by hose to the bleed screw. This allowed me to push fluid in from the bottom, and by going slowly it pushes the air out of the m/c reservoir.

 

[chuzie]

Check OD of rubber hose with a micrometer, at rest, and at pressure.
The only other flexible item in the picture is the caliper housing its self, and it looks like a stout casting.

New hose and no flex as measured with caliper

Although, just cause you didn't get any more air out, doesn't mean you don't have any more air in there.

You're absolutely right, but in this last test, were dealing with 10" of hard line, another 10" of hose and a caliper; nothing else in the system. I imagine that caliper would need to be mostly full of air to compress 2000 psi, no? Good call on the pressure bleeder. I should have one anyway so now I have an excuse.

***also, just cause a caliper is "new" doesn't mean it is perfect. I had to return a newly rebuilt Tbird caliper cause the threads on the bleeder were not perfect.

I can't assume the new calipers are good, however this is the 3rd set of calipers put on this rig that have acted the same exact way. Maybe I need to go buy lotto tickets.

 

[ba123]

Was it me, I'd scare up a -3AN banjo adapter and some -3AN tube nuts and sleeves so that you can take the flex line out of the plumbing.

I built a pressure bleeder using a calibration gas bottle (a dead fire extinguisher would work instead), some tubing, and a low pressure air pressure regulator. ~5 psi air in the top of the brake fluid in the container, and the tubing is submerged below the fluid level, which is connected by hose to the bleed screw. This allowed me to push fluid in from the bottom, and by going slowly it pushes the air out of the m/c reservoir.

Haha, my first bleeder, I built out of a pressure sprayer and someone borrowed it and I forgot who, but I never got it back (I can guess and that guy is no longer a friend)! I like your extinguisher idea but still might be easier using a pressure sprayer and they’re cheap.

@chuzie , the one thing that does bother me about your pic of the calipers above is how much the calipers are extended with only that tiny piece of metal there. Maybe it’s just me, but I’d have something sized closer to that of a rotor.

So, you’re saying that on that other line, there is nothing other than a blocked brake line? Maybe one last try of blocking the passage completely and measuring the front outlet and then measuring at the bleeder? If you’re losing a bunch of pressure with that test then I would bet there is some blockage or some air.

 

[chuzie]

the one thing that does bother me about your pic of the calipers above is how much the calipers are extended with only that tiny piece of metal there. Maybe it’s just me, but I’d have something sized closer to that of a rotor.

Look closer. There's two big 1"+ cast plates from my hydraulic press sandwiched in there. That piece of .125 flat was just to take up the last bit of space so I didn't have to deal with retracting the piston to get the caliper reinstalled.

So, you’re saying that on that other line, there is nothing other than a blocked brake line? Maybe one last try of blocking the passage completely and measuring the front outlet and then measuring at the bleeder? If you’re losing a bunch of pressure with that test then I would bet there is some blockage or some air.

You lost me with the nomenclature. Which other line / passage are you referring to please?
Both front and rear MC ports are yielding 2500psi with and without the opposing port blocked.

 

[ba123]

Look closer. There's two big 1"+ cast plates from my hydraulic press sandwiched in there. That piece of .125 flat was just to take up the last bit of space so I didn't have to deal with retracting the piston to get the caliper reinstalled.

Ahhh, crap, now I see. I kinda glanced and those look like brake pads if you just glance!

You lost me with the nomenclature. Which other line / passage are you referring to please?
Both front and rear MC ports are yielding 2500psi with and without the opposing port blocked.

I mean what do you get if you completely block off this port:

 

[chuzie]

I mean what do you get if you completely block off this port:
View attachment 937549

2500 psi without caliper
500-700 with caliper
Played that game this morning

 

[ksagis]

Was it me, I'd scare up a -3AN banjo adapter and some -3AN tube nuts and sleeves so that you can take the flex line out of the plumbing.

I built a pressure bleeder using a calibration gas bottle (a dead fire extinguisher would work instead), some tubing, and a low pressure air pressure regulator. ~5 psi air in the top of the brake fluid in the container, and the tubing is submerged below the fluid level, which is connected by hose to the bleed screw. This allowed me to push fluid in from the bottom, and by going slowly it pushes the air out of the m/c reservoir.

Minor thread highjack…

Follow up on this for my knowledge and maybe benefit others, I’ve only used AN style on 37 degree flares. Are you indicating they sell 45 degree ferrules and bnuts too? (Seem to recall brake lines are not 37 degrees). Or are you thinking to use a male to 37 male adapter at MC?

Thanks for knowledge.

 

[ba123]

If you did that, and those are your results, then you have a problem.

Line is the same, so it not the line, right? Looks new anyway.

Has to be either some weird thing with the pressure gauge, some air in the line, a connection, or blockage.

You should be able to remove the caliper and clear it out with compressed air. I would just leave those stoppers in there so you don’t push out the piston. Take the bleed screw completely out…maybe something will come out.

@ksagis you can use whatever you want to make a connection, 37/45…as long as the other side is the same. It’s all what you choose. And a banjo is a banjo regardless of what’s attached to it.

 

[gnpenning]

While I couldn't find it when I went back, I thought you isolated one front side?? If so did you isolate both fronts independently?

Seems like awhile back we had a thread where the rebuilt calipers had issues with the bleeder screws and pulling air back into the system?

What part of Washington are you in. I have a pressure bleeder you could borrow.