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Unread 02-06-2016, 08:12 PM   #1
wingless
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Front Brakes - Minor Dragging

The front brakes failed big time on my '94 ZJ a few weeks ago.

Both calipers locked up while I was driving home. I stopped as soon as possible. It was night and both rotors were glowing red. I waited to let them cool, then continued the short distance home, using the parking brake to stop.

Both rotors and pads were toasted. I also swapped the calipers and hoses.

The vehicle now has: new front wheel bearings; new CV joints / axle half shafts; properly torqued hub bearing to axle shaft nuts; cleaned and properly lubed steering knuckle ledges; new rotors; new pads; new calipers w/ new correct-length mounting bolts, lubed per the FSM; new hoses and properly bled brake system.

The sudden major drag is gone. There is a very minor drag now. A squeek, squeek, squeek when I drive down the road. I park, then feel the rotors and they are warm w/ virtually no usage. Both are squeeking and both are warm.



According to the FSM these are the common causes of brake drag:
  • loose or damaged wheel bearing - brand new wheel brearings, properly torqued per FSM
  • siezed or sticking caliper or wheel cylinder piston - brand new calipers
  • caliper binding on bushings or bolts - new bolts and cleaned ledges, lubed per FSM
  • incorrect length caliper mounting bolts (too long) - new bolt lengths measured, length okay
  • loose caliper mounting bracket - torqued per FSM
  • misassembled components - they look okay to me...
  • misadjusted brakelight switch - not yet checked
  • binding brake pedal - not yet checked
  • master cylinder internal fault - help requested
The FSM says the brake pedal is a serviceable component. I have not yet yanked or serviced mine.

The FSM says to replace not reuse the brake pedal bushings and says to replace not reuse the shaft nut (in bold in the FSM).

Q1) - Has anyone done the brake pedal service and did they replace or reuse those parts?

Q2) - Any clues on the switch adjustment?

Q3) - How is a good versus bad master cylinder determined?

Q4) - What else can I check to fix this minor front brake drag?




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Unread 02-06-2016, 08:23 PM   #2
ZeeJay1997
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Does the 94 have a proportioning valve?

BTW, the suspension looks great.
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Unread 02-06-2016, 08:30 PM   #3
wingless
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Quote:
Originally Posted by ZeeJay1997 View Post
Does the 94 have a proportioning valve?
According to the FSM: "A dual reservoir master cylinder and a combination valve and are used for all applications. The combination valve contains a brake pressure differential switch, a front brake metering valve and a fixed rate rear proportioning valve.


Quote:
Originally Posted by ZeeJay1997 View Post
BTW, the suspension looks great.
Thanks, I just yanked the front axle, sanded off all the rust, sanded then painted the Up Country springs and shocks, replaced all the control arms, replaced all the bushings, replaced and painted all the steering linkage. I also did a front end alignment. I haven't yet replaced all the missing jounce bumpers, they all disintegrated. I am also going to replace the spring seats.

The ball joints have not yet been replaced. I wanted to see where the front end alignment fell to see if the adjustable ball joints were required. I now know that the adjustable ball joints will permit me to set the alignment to dead nuts on, versus close to properly aligned, where it is now.

It was very loose and floaty on the highway. Now it is tight.
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Unread 02-06-2016, 09:10 PM   #4
wingless
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This image shows the new calipers, rotors, pads and hoses.

The Cardone Powder-Coated Remanufactured Calipers were used, along w/ the Raybestos Performance R-300 Rotor and the Raybestos Ceramic Advanced Technology Pads.

The goal was superior performance and better appearance than stock.



Last edited by wingless; 02-06-2016 at 10:44 PM.. Reason: Fixed Link
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Unread 02-06-2016, 09:37 PM   #5
ZeeJay1997
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Does your FSM say anything like this...

CAUTION: If new caliper bolts are being installed,
or if the original reason for repair was a drag/pull
condition, check caliper bolt length before proceeding.
If the bolts have a shank length greater than
67.6 mm (2.66 in.), they may contact the inboard
brake shoe causing a partial apply condition. Refer
to Figure 14 for the required caliper bolt length
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Unread 02-06-2016, 09:40 PM   #6
wingless
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Quote:
Originally Posted by ZeeJay1997 View Post
Does your FSM say anything like this...

CAUTION: If new caliper bolts are being installed,
or if the original reason for repair was a drag/pull
condition, check caliper bolt length before proceeding.
If the bolts have a shank length greater than
67.6 mm (2.66 in.), they may contact the inboard
brake shoe causing a partial apply condition. Refer
to Figure 14 for the required caliper bolt length
Yes, verbatim.

My new caliper bolts were measured and found to be less than the maximum length.
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Unread 02-06-2016, 10:00 PM   #7
ZeeJay1997
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After I re-read about the proportioning valve, I gathered it affects only the rear brakes and warning light. So the bolts seemed a likely suspect.

Maybe a combination of pad/rotor thickness? Since they are both Raybestos it doesn't seem likely but stranger things have happened.
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Unread 02-07-2016, 08:08 AM   #8
coralman
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Have the same set up on mine and it will occasional squeek when backing out of the driveway in the morning but never constant. I'm shooting in the dark here but I would test the runout of the rotors. Might be difficult to do due to the design of the slots but sections are clear.
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Unread 02-07-2016, 11:26 AM   #9
wingless
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Quote:
Originally Posted by coralman View Post
I'm shooting in the dark here but I would test the runout of the rotors.
The Raybestos Performance R-300 Rotors are brand new. They are specified for 0.002" lateral runout, not yet checked.
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Unread 02-07-2016, 11:29 AM   #10
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Quote:
Originally Posted by wingless View Post
According to the FSM these are the common causes of brake drag:
  • loose or damaged wheel bearing - brand new wheel brearings, properly torqued per FSM
  • siezed or sticking caliper or wheel cylinder piston - brand new calipers
  • caliper binding on bushings or bolts - new bolts and cleaned ledges, lubed per FSM
  • incorrect length caliper mounting bolts (too long) - new bolt lengths measured, length okay
  • loose caliper mounting bracket - torqued per FSM
  • misassembled components - they look okay to me...
  • misadjusted brakelight switch - not yet checked
  • binding brake pedal - not yet checked
  • master cylinder internal fault - help requested
The FSM says the brake pedal is a serviceable component. I have not yet yanked or serviced mine.

The FSM says to replace not reuse the brake pedal bushings and says to replace not reuse the shaft nut (in bold in the FSM).

Q1) - Has anyone done the brake pedal service and did they replace or reuse those parts?

Q2) - Any clues on the switch adjustment?
The brake pedal assembly was removed, cleaned and lubricated per the FSM.

There was no effect on the minor brake drag noise. There is an A/V clip at the end showing the operational noise.

Note the the FSM states the pivot shaft nut should not be reused. It has distorted threads, used for thread locking. I used Loctite red on the threads w/ the same nut.

The only thing remaining in the FSM list is the master cylinder fault. How is this checked?

  • loose or damaged wheel bearing - brand new wheel brearings, properly torqued per FSM
  • siezed or sticking caliper or wheel cylinder piston - brand new calipers
  • caliper binding on bushings or bolts - new bolts and cleaned ledges, lubed per FSM
  • incorrect length caliper mounting bolts (too long) - new bolt lengths measured, length okay
  • loose caliper mounting bracket - torqued per FSM
  • misassembled components - they look okay to me...
  • misadjusted brakelight switch - brake switch adjusted per FSM
  • binding brake pedal - brake pedal lubed per FSM - okay
  • master cylinder internal fault - help requested


Brake Pedal Installed - Showing Push Rod Pin Clip





Push Rod Pin Clip - Small Screwdriver Releases Tang, Then Slide Off



Brake Pedal Bushings and Shaft - As-Removed



Brake Pedal Bushings, Shaft and Pedal - Cleaned - Note, the shoulder bushings are thin and delicate, handle w/ extreme care







Brake Pedal Bushings Lubricated





Brake Pedal Switch Plunger Extended - Ready for FSM Installation Steps



Brake Pedal and Switch Installed and Adjusted per FSM



Operational Brake Noise A/V Clip - Note that it sounds the same when the vehicle is operated in normal orientation, as well as the sideways orientation shown in the clip.
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Unread 02-07-2016, 11:41 AM   #11
coralman
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Reason I say that is makers do blow it once in a while. I seem to remember that jeep says if runout is too great rotors need to be turned on vehicle. Seems a bit goofy but I see the logic. Another thing is caliper rebuilds don't go according to plan either. But here is the kicker, I did the DRB bleed on mine when I rebuilt the suspension and steering. Mine {brand new mopars, but new old stock} hung up badly. I never could exactly pin what caused them to do so, but I changed the calipers, flushed the heck out the lines and they worked normally. I don't know if the DRB loosened some gook up in the lines or what. New everything short of the master cylinder went into the original effort.
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Unread 02-07-2016, 11:55 AM   #12
ZeeJay1997
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There may be a better way of doing it but if I suspected the MC was not releasing line pressure, I would pump the brake pedal a few times, then crack a bleeder to see if the brakes still drag. That would tell you if fluid pressure is causing it.
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Unread 02-07-2016, 12:01 PM   #13
coralman
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I think I did that when mine did and they would release. But as soon as you hit them they would do it again. So fluid fluid pressure is very much worth looking at.
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Unread Yesterday, 07:22 AM   #14
wingless
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The bleeder was cracked and it still squeeked.

The calipers, rotors and pads were removed w/ the brake hose connected.

The caliper piston was pumped out w/ the brake pedal, then pushed back in.

The system was reassembled.

The hydraulic system was bled again.

It still squeeks.
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Unread Yesterday, 08:23 AM   #15
JonS
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Were the sliders cleaned and lubricated with silicone grease? Do they slide freely?
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