Anyone ever had a line lock fail and degrade braking? - Hot Rod Forum : Hotrodders Bulletin Board
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Old 09-20-2006, 09:48 PM
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Anyone ever had a line lock fail and degrade braking?

Was driving along when some aggressive braking caused what I thougt was brake fade, but it didn't go away... So I bled the mess out of em several times, and replaced a MC, calipers were already new, and adjusted the pushrod form the boster a few times, etc...

Still no better until the last test drive, it was still acting the same, I couldn't even get em to lock up unless I was going slow, like 20-30 MPH and slammed the mess out of em and they finally locked. Just before I got back to the house I heard/felt a small click/minor pop at the stop sign and the brakes started draggin really bad! So I had to drive darn near a mile to the house with what felt like half the brake pedal depressed, stopping a few times to let em cool a little. All four were smokin' when I got back to the house...

I was wondering if perhaps the line lock was stuck half open or something because now that I think about it, it seemed like I had full travel of the pedal, absolutely no air in the lines that I could find... So I'm wondering if maybe I should call/email the line lock folks to see if this might have been an indication of a stuck line lock or something???

I'm also wondering if maybe maybe the booster is the culprit? Like perhaps the pedal rod wasn't jivin' up with the booster pushrod???

So somethin was magically dislodged in the line lock, or something mechanically snapped back into place with the booster???

Any ideas?

The pedal did get all the way to the floor when I had the problem, but it was pretty much already this way when it was working fine earlier; but when the magic "fix happened", the pedal would barely go down after whatever it was corrected itself... I call it a magic fix because I prolly had the booster rod too far out at this point and I assume if I shorten it back to where it used to be it would work fine again????
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Old 09-21-2006, 12:36 PM
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a lot of the things u came up with are logical and should be checked, also due u have proportional valve in the system?? check by changing or neutral setting if adjustable..gl
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Old 09-21-2006, 02:57 PM
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Quote:
Originally Posted by sizemoremk

Was driving along when some aggressive braking caused what I thougt was brake fade, but it didn't go away...
What quality pads do you have and are the rotors glazed?

Quote:
So I bled the mess out of em several times, and replaced a MC, calipers were already new, and adjusted the pushrod form the boster a few times, etc...


Quote:
Still no better until the last test drive, it was still acting the same, I couldn't even get em to lock up unless I was going slow, like 20-30 MPH and slammed the mess out of em and they finally locked. Just before I got back to the house I heard/felt a small click/minor pop at the stop sign and the brakes started draggin really bad! So I had to drive darn near a mile to the house with what felt like half the brake pedal depressed, stopping a few times to let em cool a little. All four were smokin' when I got back to the house...
This sounds more like a malfunctioning combination valve (or M/C) if all four were dragging. The LINE-LOC is only plumbed to the front, right?

You need to give the type of car, type of brakes, any brake system modifications, etc.

To properly adjust the pushrod, you either need the shop manual or directions from the supplier of the replaced parts.
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Old 09-21-2006, 03:26 PM
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Specifics are not OEM...

Its a 1990 Tbird SC originally equiped with a Teves IV ABS system that was starting to fail.

It now has a non-ABS 1990 Tbird booster, with a 1993 crown vic master cylinder. This is a common swap for the Tbirds as the ABS untis are getting old and no quality replacements are available. The Crown vic master was used becasue it is a conventional (non-diagonal setup as was the tbird did use the diagonal setup) and the vic unit has the same size bore and stroke as the tbird unit. I have also upgraded to 99+ Mustang dual piston brake calipers in the front. The pads are Advanceautoparts ceramic pads...


Now I assume that the something has “snapped into place” mechanically if it was the booster; or “magically dislodged” if it was the line lock…

I adjusted the booster rod out, and it seemed to be fine for pedal travel; but if something in the booster was stuck in a shortened position, it makes sense that the pedal travel was OK. Now assume the whatever was “stuck in a shortened position” came unstuck, the booster rod would now go further into the master cylinder; which is why I am thinking that the brakes began to drag when whatever snapped into place allowed correct travel of the booster pushrod…

As I think more, if the line-lock was stuck in a partially shut position, it seems like without a piston to move the fluid into the fluid would have nowhere to go, so the pedal would not move??? Or am I wrong and could a partially stuck linelock perhaps slow the fluid travel enough to give brake fade???

I’m kinda leaning towards the booster…

The proportioning valve is a stock unit.

As for the brakes being glazed, this happened kinda suddenly and without that much aggressive braking, I did a few 5-8 second WOT "runs" but they were spaced pretty far apart during a backroads cruise... Can glazing happen that quickly? Now they may very well be glazed after them suddenly clamping down last night, so what do you do if the pads are glazed??? It might be a good time to swap to some greenstuff pads or something...
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Old 09-22-2006, 10:03 AM
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Yep pit can happen. Circle trackers use Line locks installed backward to shutoff brakes sometimes.

I 've seen em go bad and cause all sort of weird malignancies.
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Old 09-22-2006, 12:38 PM
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Quote:
Originally Posted by sizemoremk

Specifics are not OEM...

Its a 1990 Tbird SC originally equiped with a Teves IV ABS system that was starting to fail.

It now has a non-ABS 1990 Tbird booster, with a 1993 crown vic master cylinder. This is a common swap for the Tbirds as the ABS untis are getting old and no quality replacements are available. The Crown vic master was used becasue it is a conventional (non-diagonal setup as was the tbird did use the diagonal setup) and the vic unit has the same size bore and stroke as the tbird unit. I have also upgraded to 99+ Mustang dual piston brake calipers in the front. The pads are Advanceautoparts ceramic pads...
Hey! Thanks for the education. It shows I have not been keeping up (still stuck in the fifties)...

My thought is that the push rod is not adjusted correctly, and not allowing the brakes to completely release. On this brake upgrade (and I am sure whoever came across this method is knowledgeable) did he check to see if the BIRD and CROWN combination valves (metering {front disc-rear drum}-pressure differential-proportioning) are the same if one application is diagonal (should be different plumbing)?

The below is from the 1992 FORD SHOP MANUAL (earliest late model I have);

Quote:
Dual Brake System


Brake Vacuum Booster Push Rod-to-Master Cylinder

The vacuum booster has an adjustable push rod which is used to compensate for dimensional variations in an assembled booster. The push rod length is adjusted after each booster power unit has been assembled in production. A properly adjusted push rod that remains within the booster after it was assembled in production should never require a service adjustment.

A booster that is suspected of having an improper push rod length will indicate either of the following:

l A push rod which is too long will prevent the master cylinder piston from completely releasing hydraulic pressure and cause brakes to drag.

l A push rod which is too short will increase brake pedal travel and cause a clunk or groaning noise from the booster.

If necessary, a booster push rod length can be verified with a push rod gauge using the following procedure:

The gauge cannot be copied from the text but the MIN/MAX lengths are given below)

1. Without disconnecting the brake tubes, disconnect the master cylinder and set it away from the booster power unit. The master cylinder must be supported to prevent damaging the brake tubes.

2. With the engine idling, gauge and adjust the push rod length. A force of approximately 22 N (5 lb) applied to the push rod with the gauge will ensure that push rod is seated with power unit.

MIN 5.84MM (0.23 INCH)
MAX 6.22MM (0.245 INCH)

3. Install the master cylinder on the booster. Gradually alternate the tightening of the retaining nuts to 18-34 N-m (14-25 lb-ft).
The dual piston caliper upgrade is nice isn't it? Being a SC, I assume the rear are disc also? Do you think you have the proper bias with the front upgrade?

The pads (and rotors) can be glazed (and rotors burnt-hot spots) just by the brakes dragging. Also compare prices on RAYBESTOS ceramic and rotors. A lot of discount store branded parts are CHI-COM.

Now, all of this is assuming that the LINE-LOC is installed properly (and is of good quality) in the front brake circuit.

How did you overcome the diagonal plumbing? Re-plumb at the combination valve?

Let me know what you find.
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Old 09-22-2006, 01:27 PM
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Well, it was working fine for severla months before this happened. like I say, all of a sudden I got the brake fade I was discussing. After screwing with it, and also re-adjustnig the pushrod out a few threads, it still acted exactly the same. THEN after my last test run, there was a click, and the brakes did not begin to drag until that click happed... I don't know if the click was something mechanically snapping back into place with the brake booster, or if it was just the pedal being moved, or maybe the click I heard was was more mental and I thought I heard a click when the brakes suddenlt grabbed like they did??? It on;ly happened once, and I guess I was not pyaing enough attention

Anyways, I am not familiar with the inner workings of the booster, so i don't know if it is even possible for the pedal rod or pushrod to machanically bind in there??? So I went and got a remanned booster yesterday, but it wasn't painted black, so I painted it and figured I'd leave it for the weekend...

As for the swap stuff, the 93 crown vic had the non-diagonal setup, the 90 tbird had the diagonal setup. The vic booster would not fit in the tbird, so we use the 90tbird booster, with the 93 CV MC. The vic MC had the proportioning valve attached to the MC, and it remains. The line lock is just after the MC before the split to the two front calipers. IIRC, the line lock was directional, and I did "try it out " once or four times on my street tires, and it seemed to work fine each time.

The dual piston calipers did seem a bit better, but not drastically, I beleive this is more of something for the guys that like the twisties, and autocross and such... Prolly not sa noticable for the striaght line guys (like me)... The biggest difference is the pad surface area is alot bigger which allows better heat dissipation, and increases the life of the pads and rotors. The tbird is bad about warped rotors, and it was time for both, so I went ahead with the dual piston jobbies. I am wrestling with the idea of going with the stainless lines to the calipers, but the only source that has them in stock without a 4-6 week wait wants $160...

As for the glazing, if they are glazed, do you mean they must be replaced? Or is there something I can do to em? But maybe I wasn;t clear, the draggin only occured for about a mile, and I stopped for a minute 3 time sot let em cool off a little...

Thanks guys!
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Old 09-22-2006, 02:13 PM
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If the pads are glazed, they can usually be sanded (surfaced) and reused. If the rotor is glazed, it needs to be cut and if any hard (blue) spots remain, replaced.

See what happens with the booster replacement and ascertain correct rod adjustment and get back.
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