500psi T-Bird Calipers

[chuzie]

I'm starting to think the DIY braided lines are the issue.

They weren't DIY. Bought em from one of the major vendors like 200 years ago. Even have the fancy clear plastic coating encasing the braided.

 

[nvrstuk]

Hope this is an EZ fix tomorrow when the new lines (parts) show up.

 

[chuzie]

FAIL!
Still have 500 psi or less at the caliper.
Still doesn't stop well.
I just don't get it y'all.

One thing I did notice, before I tossed my tools across the shop, is with the line lock engaged and measuring pressure at the caliper, I can achieve 2000+psi with multiple pumps of the pedal and zero indication of bleed down over 30 seconds.

With the line lock disengaged, I can barely get to 500psi with the pedal all the way to the floor.

Also, the pedal goes all the way to the floor. Like I really have ZERO pedal feel. Not sure if that's a hydroboost thing or not. Also seems to take a couple seconds for the pedal to return.

The only thing I haven't changed is the braided line from the frame to the axle. If you recall however, I was able to achieve 2500psi measured at the tee which is when I eliminated it as a possibility.

I'm at a loss my friends.

 

[ntsqd]

Is the line-lock plumbed backwards? Doesn't sound like it, but......

So you can pump up the system to 2ksi or so with multiple pedal pumps while the line-lock keeps the pressure from bleeding down. That tells me that something is metering the system. What haven't you plumbed around or replaced in the front brake system?

I think you mentioned that you had taken the line-lock out of the system, and that had made no change? I'd be seriously inclined to simplify the front brake plumbing as much as possible for right now. Complicate it later, get it working first.

 

[nvrstuk]

What a freakin' buggar!! Dang!

Line lock- sorry I forgot that you mentioned it before and...

I had MULTIPLE failures bleeding the brakes and having pedal using every method of bleeding imagined back on my build thread from 2017. As an ex brake tech from a GM dealership I was frustrated as it was keeping me from going to Moab after 10 months of 14-19 hr days.... ANYWAY, the line lock was dying and I didn't know it but after swapping UP to a 1.334" dia MC it could force enough fluid at enough pressure it eventually allowed me to bleed them

I pulled it out and replaced it with a Mico-lock last spring and no issues bleeding it.

After all that typing- pull the line lock & bypass it and try it again is my suggestion. (unless like TS mentioned you've done that)

 

[lars]

Speaking to @ntsqd's comments and advice, something just occurred to me. Maybe it's been mentioned before, but if you run out of fluid volume as the pedal hits bottom before the line hits full pressure, you will never get there.

One thing noted previously- by @Broncobowsher maybe?- is that with the bleed screw straight up, there is actually a substantial air volume above the bleed port inside the caliper. The bleed port on the inside bore of the caliper is roughly tangential to the piston. In other words, the bleed screw needs to be at the top, pointed horizontally (I think that's stock mounting but it's been awhile). Otherwise you'll never get all the air out. If you are compressing lots of air and the pedal bottoms before you have compressed it, you'll be stuck at a lower pressure.

 

[chuzie]

Is the line-lock plumbed backwards?

No, I have had it backwards previously and it wouldn't hold pressure.

What haven't you plumbed around or replaced in the front brake system?

At this point, everything is new except the frame to axle hose.

I think you mentioned that you had taken the line-lock out of the system, and that had made no change?

Correct, but I was only measuring for pressure when line bypassed, not flow via volume from bleeding.

Complicate it later, get it working first.

Agreed 100%

I pulled it out and replaced it with a Mico-lock last spring and no issues bleeding it.

I'm running an old school Mico. It could be failing and need a rebuild.

After all that typing- pull the line lock & bypass it and try it again is my suggestion.

Will do.

...is that with the bleed screw straight up, there is actually a substantial air volume above the bleed port inside the caliper.

Ya, I stopped that vertical bleeding nonsense after it was mentioned. Bleeder horizontal as designed.

Tomorrow I'll bypass line lock again and test for both pressure and flow. I may also fabricate a line to bypass the frame to axle hose for testing purposes since getting a replacement on the weekend ain't gonna happen and my sanity is on the line

Thanks fellas

 

[nvrstuk]

I don't follow how he could have with all the parts connected- 2,000psi at the mc, 1500 psi at the flex hose but only 500 or so psi at the bleeder.

1- Back to wondering how you can lose 1,000psi (2500 dropping to 1500psi) from the fitting on the mc thru hard line only?? Correct? Or was that 1,500 psi measurement thru some flex line??

2- How can you have 1500 psi at one end of a line and 500psi at the other end (2ft apart) when you still have liquid (brake fluid) coming out? Doesn't matter where the air is in the system there shouldn't be that kind of a drop after 3 minutes of holding your foot on the pedal. Pressure should equalize right? come on mechanical engineers...



Here's Chuzie's original 1st post:

"Trying to troubleshoot the T-Bird calipers on my 77. They SUCK, but why?

Running T-Bird up front, Explorer discs in back, 1-1/8 MC and WH Hydroboost.

2500 psi @ MC
1500 psi @ transition from hard line to caliper flex with one caliper disconnected. (note this it not at the tee above the diff but at the junction near the coil spring bucket.
500 psi @ caliper bleeder

Tried bleeding with caliper off knuckle and bleeder at 12 o'clock to ensure no air = still 500 psi
Soft line not kinked.

What are my potential culprits here? No much left but flex line, banjo and caliper.

Considered a partial blockage in the line, but that should eventually yield more than 500 psi with repeated pumps, no?"


We've got to eliminate something... flex lines are now "out" although after typing this your post popped up so the FRAME flex lines are still the old ones??? Hmmm, do you have a short metal line you can just loop de loop around to by-pass those rubber frame flex lines?

How about connecting the calipers as direct as possible to the mc ports? See if you can eliminate everything between the new calipers and the mc. Might be some funky fitting tho for the Tbird caliper.

Excuse me for possibly missing this earlier but how are we positive it's not the rear brakes?

 

[chuzie]

I don't follow how he could have with all the parts connected- 2,000psi at the mc, 1500 psi at the flex hose but only 500 or so psi at the bleeder.

1- Back to wondering how you can lose 1,000psi (2500 dropping to 1500psi) from the fitting on the mc thru hard line only?? Correct? Or was that 1,500 psi measurement thru some flex line??

2500 directly at mc port

1500 was at frame to axle hose tee above axle measured at driver port (caliper and hose disconnected) with passenger side caliper still connected.

Once passenger side was disconnected and plugged, 2500 was achieved.

Hmmm, do you have a short metal line you can just loop de loop around to by-pass those rubber frame flex lines?

How about connecting the calipers as direct as possible to the mc ports? See if you can eliminate everything between the new calipers and the mc.

Yep, exactly what I'm thinking too.

Excuse me for possibly missing this earlier but how are we positive it's not the rear brakes?

Absolutely not.
I'll plug that port on MC and test as well. I plugged it previously but only to ensure mc was bled and test pressure. Never test front pressure with rear plugged.

 

[nvrstuk]

Yeah, totally plug/disconnect the rear b4 any flex hose in that circuit that could be influencing what we are working on and retest the front again and after replacing those front flex hoses. Course you might need to test them after replacing that last flex hose.

Below is from post #67

What haven't you plumbed around or replaced in the front brake system?

At this point, everything is new except the frame to axle hose.

 

[Broncobowsher]

I know this isn't GM brakes that are known for needing caliper clearance. But since they are oversized calipers, have you checked if there is any clearance issues to the knuckle?
Or the sliders are bound up and not traveling like they should?

 

[lars]

I don't follow how he could have with all the parts connected- 2,000psi at the mc, 1500 psi at the flex hose but only 500 or so psi at the bleeder.

1- Back to wondering how you can lose 1,000psi (2500 dropping to 1500psi) from the fitting on the mc thru hard line only?? Correct? Or was that 1,500 psi measurement thru some flex line??

2- How can you have 1500 psi at one end of a line and 500psi at the other end (2ft apart) when you still have liquid (brake fluid) coming out? Doesn't matter where the air is in the system there shouldn't be that kind of a drop after 3 minutes of holding your foot on the pedal. Pressure should equalize right? come on mechanical engineers...



Here's Chuzie's original 1st post:

"Trying to troubleshoot the T-Bird calipers on my 77. They SUCK, but why?

Running T-Bird up front, Explorer discs in back, 1-1/8 MC and WH Hydroboost.

2500 psi @ MC
1500 psi @ transition from hard line to caliper flex with one caliper disconnected. (note this it not at the tee above the diff but at the junction near the coil spring bucket.
500 psi @ caliper bleeder

Tried bleeding with caliper off knuckle and bleeder at 12 o'clock to ensure no air = still 500 psi
Soft line not kinked.

What are my potential culprits here? No much left but flex line, banjo and caliper.

Considered a partial blockage in the line, but that should eventually yield more than 500 psi with repeated pumps, no?"


We've got to eliminate something... flex lines are now "out" although after typing this your post popped up so the FRAME flex lines are still the old ones??? Hmmm, do you have a short metal line you can just loop de loop around to by-pass those rubber frame flex lines?

How about connecting the calipers as direct as possible to the mc ports? See if you can eliminate everything between the new calipers and the mc. Might be some funky fitting tho for the Tbird caliper.

Excuse me for possibly missing this earlier but how are we positive it's not the rear brakes?

Think about it this way, Brian. If the volume of fluid he has to move (arguably, not a whole lot) to take up all the clearance, hose swelling, piston motion, blah blah blah is more than he has moved when the brake pedal is bottomed, then he will never get to (1500, 2000, whatever) psi. He will only get to what he reached when the pedal bottomed. Somewhere, additional fluid volume beyond what he's getting is required. Question is what is sucking up the additional volume. I had nearly the identical brake setup for years, decades even, and never had this problem. Somewhere an evil brake gremlin is sucking up fluid volume. It's the only thing that can explain this. There is no fluid pressure regulator in the system, which would be the only other explanation.

 

[ntsqd]

Since the frame to axle hose is the only thing left of the original system I'm looking hard at it.

 

[ksagis]

FAIL!
Still have 500 psi or less at the caliper.
Still doesn't stop well.
I just don't get it y'all.

One thing I did notice, before I tossed my tools across the shop, is with the line lock engaged and measuring pressure at the caliper, I can achieve 2000+psi with multiple pumps of the pedal and zero indication of bleed down over 30 seconds.

With the line lock disengaged, I can barely get to 500psi with the pedal all the way to the floor.

Also, the pedal goes all the way to the floor. Like I really have ZERO pedal feel. Not sure if that's a hydroboost thing or not. Also seems to take a couple seconds for the pedal to return.

The only thing I haven't changed is the braided line from the frame to the axle. If you recall however, I was able to achieve 2500psi measured at the tee which is when I eliminated it as a possibility.

I'm at a loss my friends.

Not sure if something I noticed when battling my brakes gremlins is related but passing it on in case useful.

When I had bad brake bleed (not hydrobleed), it seemed like brake pedal returned slow. When I finally sorted out brake bleed, it seemed like pedal returned faster. There were a few other things changed too like going from 1 1/8 to 1 1/4” MC and tightening up gap between booster pushrod to MC cup, but feel like thats neither of those would affect pedal return speed.

Also, going back to a thread from @nvrstuk a long time ago. we sure your MC bore is big enough?

Edit: you don’t have large gaps between pads and calipers post brake pedal release, correct?

Second Edit: do you recall as you checked pressure further down system of the pedal went farther and farther? Might tell us something if so.

Third edit: I caught up on the thread and see now that Brian’s root cause was subsequently attributed to line lock and not the MC bore size.

 

[chuzie]

I know this isn't GM brakes that are known for needing caliper clearance. But since they are oversized calipers, have you checked if there is any clearance issues to the knuckle?
Or the sliders are bound up and not traveling like they should?

I will check that today. Of note, I did, and have previously needed to tap the lower part of the calipers to encourage them to enter lower arm of the knuckle. They definitely don't just plop into the knuckle without resistance.

When I had bad brake bleed (not hydrobleed), it seemed like brake pedal returned slow. When I finally sorted out brake bleed, it seemed like pedal returned faster.

I didn't have this slow pedal return when I was running manual brakes so I'm uncertain if that's a function of hydroboost or another issue in the system. I'd say it takes about 5 seconds for the pedal to fully return to rested position.

There were a few other things changed too like going from 1 1/8 to 1 1/4” MC and tightening up gap between booster pushrod to MC cup,

I recall there was a need to adjust the little nipple on the end of the push rod on the vacuum boosters and a tiny adjustment could make a big difference. I didn't adjust it on the hydroboost though. Maybe that would be worth investigating.

Also, going back to a thread from @nvrstuk a long time ago. we sure your MC bore is big enough?

Not completely sure, but somewhat confident. WH told my that's the size they'd sell me for my configuration.

Edit: you don’t have large gaps between pads and calipers post brake pedal release, correct?

I'll check

Second Edit: do you recall as you checked pressure further down system of the pedal went farther and farther? Might tell us something if so.

Adding to the list

 

[ntsqd]

When I first put H-B on Snowball I had a slow return as well. I'll need to go thru the thread to see if I posted what fixed that, but I'm thinking that the whole PS/H-B system needed more bleeding. One tech that I talked to suggested drilling out the spittor fitting to increase the flow, but I figure that Bosch knew what they were doing when they made that fitting with the restrictor in it and I'd leave that for when I'd run out of all other options. I never did drill it.

If you don't have a tool like this one; buy or make one. It will make setting that push-rod's length MUCH easier. Pay attention to the tool's rod diameter & nose radius on the m/c vs. the those dims of the end of the H-B's push-rod. You may need to modify the rod to make it duplicate the H-B's push-rod nose.

Ultimately the m/c bore size will determine the maximum possible system pressure at any particular pedal effort, but that is more about the very subjective pedal feel than this problem. The m/c bore would need to be beyond Huge for it to not be able to generate enough pressure, and we know that it can because at the outlet ports it already does generate enough pressure. Leave this for later if/when you want to tune how the pedal feels once the system is working as it should.

 

[chuzie]

I know this isn't GM brakes that are known for needing caliper clearance. But since they are oversized calipers, have you checked if there is any clearance issues to the knuckle?
Or the sliders are bound up and not traveling like they should?

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.

 

[ntsqd]

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?

 

[chuzie]

How are you measuring the line pressure?

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[nvrstuk]

Responding to Lars post on decreasing pressure - - The part about swelling lowering the pressure and increasing volume needed I totally understand but what I didn't understand was how it could happen w/o the hoses (or something swelling to increase the volume like someone had mentioned before your posts. Guess I didn't read that post and understand what they meant and mainly the fact that ALL flexible hoses hadn't been replaced yet

I had thought mistakenly that all rubber hoses had been replaced so that's where I was coming from. Thx