Explorer rear discs: not working at all! Thoughts???

[chuzie]

Where can i obtain brake lines for these explorer brakes? I know i can use stock but what are other folks running? I don't know what else to change to make them work.

 

[plumbdoctor]

If you are talking about the flex lines to calipers... I bought mine from jegs, if your looking for local, you might have to still use stock, if that helps
I haven't followed your thread too much, but I had issues at first, but mine turned out to be the fronts , one bleeder wouldn't seal, so it bled fluid going down the road. Thank god the exploder s were working. All good now

 

[chuzie]

Yep flex. Im using stock and i need to eliminate them as culprit since they are old. Thx. Don't suppose u have a part number to save my lazy ass the trouble of searching.

 

[chuzie]

Found this http://m.summitracing.com/parts/cur-6013e

Perfect.

 

[plumbdoctor]

Yep, those look the same... Go for it

 

[broncosbybart]

Chuzie, I used those lines on an 8.8 swap in the TJ. They worked great. I bent/flared my own hard lines.

 

[chuzie]

Im at the end of my rope with this swap. I just want my brakes to flippin work!

 

[chuzie]

Found this http://m.summitracing.com/parts/cur-6013e

Perfect.

Junked the old Explorer lines with these and made my own hard lines. Still no brakes.

Just to recap....

T-bird calipers in front stop just fine. Rear explorers will continue to spin while in drive and jacked off ground at idle.

New 1-1/8" MC (700psi at both ports)
New booster (verified operational)
No prop valve
98 Explorer rear discs with new pads and lines
700psi at caliper
No line swelling
Vac at 14
New fluid throughout
No leaks

This brake issue has become my nemesis. I remain faithful someone out there has a solution.

The discs were redrilled by a buddy for the 5x5.5 pattern. Is there any way if the work is off even in the slightest it could cause no braking ability? I don't see how though.

Does anyone know of a writeup on the explorer disc swap I can reference to ensure I have crossed all my T's and dotted all my I's?

 

[Apogee]

If you have 700 psi at the caliper, assuming you're testing at the bleed screw port, and everything still spins, then there's something wrong with the caliper or the pins and pad abutment brackets (PABs) they mount into. Are these new or used components? Do the caliper guide pins slide freely in the PAB? If the piston is seized in the caliper body, you'll get no braking. If the caliper guide pins are seized in the PAB, then the piston should still push on one side of the rotor, the caliper body just won't slide freely to pull the outboard pad equally and oppositely.

Your brake functionality has nothing to do with the wheel pattern in the rotors, so you can cross that off the list IMO.

 

[chuzie]

You lost me at PAB and I can't find any info to that reference online. School me and I may be able to provide a better response.

Can you point out a PAB on a picture?

I assume the pins are the two long bolts that I secure the caliper with which allow it to free float?

Everything was originally all used but after 129 posts of brake hell, The calipers, discs, and backing plates are only original parts left.

I have watched the piston extend from the housing when caliper is removed. I think at one point I posted a video supposedly showing the calipers moving slightly upon application. That was with 250psi. Would a new video be helpful now that I am up to 700psi?

 

[Apogee]

The pad abutment bracket, or PAB, is also commonly referred to as a "caliper bracket". These are what hold the pads and transfer the brake torque from the pads into the backing plate/axle/knuckle or whatever they're bolted to, so that the calipers can float and are only responsible for squeezing the pads against the rotor. If you would like a picture, search Google images for a Dorman #619111.

The Explorer rear caliper has a 48mm [1.89"] piston diameter, which equates to a piston area of 2.80 square inches. At 250 psi, that means that there would be 700 pounds of clamping force on the rotor, and at 700 psi that will equate to 1960 pounds of force, so unless you're running a brake pad compound with the coefficient of friction of an ice cube, nothing should be spinning at either of those pressures, leading me to think that there may be something wrong with the caliper assemblies.

If you haven't already, I would suggest that you remove the caliper body with the two smaller caliper mounting bolts that tie into the guide pins, then remove the pins and grease boots for inspection. The pins should be well lubricated and slide freely in the holes in the PAB. Once all that looks good, I would stroke the pistons in the calipers to make sure they're not hanging up due to corrosion or anything else. Use a block to make sure that you don't overextend the caliper piston and have someone apply the brakes. The piston should smoothly and freely slide outward and inward when you use a clamp to push it back into the bore...make sure you have plenty of fluid in your MC reservoir when doing this since you don't want to run it dry when extending the pistons, otherwise you get to bleed everything again.

Speaking of bleeding, how does the pedal feel? Is it high and firm or something else?

 

[chuzie]

Ahhhhh. Gotcha.

I pulled the calipers and the pins float nice and smooth. I removed them to clean and lube. Stuck a piece of wood in caliper and the piston does actuate.

Here is a new video of both static and dynamic.

3 parts to video.
actuating with truck off
actuating with truck on in park
actuating with truck on in drive

I am concerned with the movement in drive. Check it out...

http://youtu.be/CtbpZAvWEhc

 

[chuzie]

Forgot to mention. I also put the dial indicator on the rotor. It seems to be slightly warped at about .050.

Notice how when I hit the brake while in drive it stops briefly, the pressure fluctuates, then the rotor continues to turn.

 

[DirtDonk]

The movement in the video is a lot more than .050" from what I can see. More like .125 or so.
Is it the rotor, or is the axle flange bent? Or is it just loosely assembled? I see lug nuts, so assume that they're holding it tight. Could something be stuck between the two surfaces causing all that runout?

Even though the caliper floating should sill clamp tightly even with oscillations, I can't help but think that it at least has something to do with some things.
It doesn't look like it in the vid, but that much runout would very easily press the pistons back into the caliper body each time you let off the brakes, which would in turn cause the rears to have have more travel before clamping the rotor each time.

Just an observation. Doesn't really appear to be the case in the image, but it's hard to tell. And it can't be good, no matter what it does or doesn't cause!

Paul

 

[chuzie]

Combined my last 3 posts.

I agree the movement in the video is significantly more than what I measured on the rotor which leads me to believe something else is going on here.

The axle flange seems secure. I cannot move it up/down or in/out by hand. Pulled the caliper and rotor to measure the axle flange. The circumferential surface varies no more than .003" and the mounting surface varies no more than .005".

I will take a look at the passenger side for similar issues. I would think if the spacer ring was out of place, the backing plate would more too. The 4 axle housing flange bolts are tight.

There has been an awful vibration which I thought was a out of balance tire but rotation did not seem to change it. I wonder if this has something to do with it.

Thanks for the input. More to come.

---------------

I recorded a video with caliper and rotor removed from the driver's side. Observe no wobbling while in drive both with and without the passenger brake applied. I did have a block of wood in the removed driver's caliper to ensure effective braking.

Also recorded a video of the passenger side with wheel removed and lug nuts installed on rotor. There is movement similar to the driver's side but not as severe.

I think we can eliminate the axleshafts as players here unless I am missing something completely. Just can't figure out where all this movement is coming from and if it has anything to do with the braking problem or is completely unrelated.

Anything else I should test? Maybe I could take the driver's rotor and have it turned? I really think if it was severely warped, I would feel it in the brake pedal. We also do not see fluctuating pressure on application which points to warpage as a non-issue

---------------
Upon further inspection of the rotor I see that it is not seating fully on the axle flange.

It seems to be displaced outboard of the flange a distance equal to the length of the shank of the wheel stud.

Measurements:
Wheel stud shank dia: 0.520"
Wheel stud shank exposed length: .120"
Wheel stud thread dia: 0.490"
Rotor hole size: .550"

The stud holes in the rotor should be large enough to fit over the shank of the stud and allow it to sit flat on the axle flange; however, if the 5x5.5" pattern is not dead on perfect, I can see how it would prevent seating.

Three questions:

1.) Does the rotor need to seat flush against the axle flange?

2.) If so, does anyone see a negative aspect to me making the holes in the rotor larger to accomplish this?

3.) What implications does this issue have with respect to my braking issue, if any?

 

[Apogee]

1. Yes, without a doubt the rotor needs to seat flush against the flange.

2. If the rotors are hub-centric (which would be ideal), then it doesn't matter how large the wheel stud holes are so long as they clear the wheel studs. If they're not hub-centric, I would buy or machine a hub-centric ring to make them hub-centric. Depending on how the rotors were converted to the 5x5.5" wheel pattern, the accuracy of the hole pattern should be taken into consideration since it sounds like that may be in doubt.

3. As stated by Donk, excessive runout of the rotor can cause piston knockback, which obviously negatively impacts caliper performance.

Since it sounds like you have a mag base and dial indicator, I would first enlarge the wheel stud holes in your rotors to 9/16 or 5/8, then make hub-centric if it isn't already, then install and measure runout. Index the rotor on the wheel stud pattern to see if it changes any...something you can get lucky and find a position where the runout of the axle flange and the runout of the rotor cancel one another out. For street applications, I generally like to see less than .004" total indicated runout (axial), however you can get away with more of off-road rigs with knobby tires, although I'd rather not. If there isn't any "happy place", then you can always remachine the axle face, the rotor, or both...or if you have access to an on-car brake lathe, you could do it in place.

 

[toddz69]

Three questions:

1.) Does the rotor need to seat flush against the axle flange?

2.) If so, does anyone see a negative aspect to me making the holes in the rotor larger to accomplish this?

3.) What implications does this issue have with respect to my braking issue, if any?

Wow. I think you've found something. I'll let Apogee give you the real answers since he's the pro with this stuff but a few of my thoughts.

1. Yes, the rotor should be flush against the axle flange, in my opinion. The strength of the clamped connection depends on the rotor being flush against the flange. If I'm correctly visualizing what your current configuration looks like, you're imparting a much larger shear stress on the wheel studs than what is expected/preferred.
2. You could enlarge the holes but then you'll probably have some/more radial runout of the rotor. Personally, I'd cough up some $$ and get some rotors from Currie that you know are drilled correctly.
3. The runout I'm seeing in that video (and it's severe) is likely causing piston knock back, which as Paul noted, will result in having to do at least an extra pump of the brake pedal when you apply the brakes and can also contribute to a wonky pedal feel.

I'm fairly certain the vibration you've been feeling from the rear is probably caused by what you see in the video.

Todd Z.

 

[chuzie]

I agree with all three of you 100%.

Before I pass the point of no return by drilling, I flipped the rotor over and installed in backwards. It fits over the shanks of the studs perfectly and lays flush to the axle flange. Something else is preventing it from mating correctly.

The inside of the back of the rotor, where the hat mates to the disc, there is a slight chamfer along the circumference. I believe this chamfer is coming in contact with the outer circumference of the axle flange and preventing it from mating flush.

Ran a bead of tape around the outer circumference of the axle flange and installed the rotor. Markings confirm this is my contact point.

Either the axle flange circumference is too big or the bevel is too big on the rotor. Either way, something has to go. I am more inclined to grind the circumference of the axle flange before I begin to compromise the integrity of the rotor.

Agree / disagree?

 

[toddz69]

Agree. In fact, you might be able to run the truck in drive and kiss the edge of the axle flange with your grinder at the same time and take just enough off pretty quickly.

Todd Z.

 

[chuzie]

Combined last two posts.

Had to grind a ton of material to get the rotor to fit but I finally got the driver's side installed and mated flush with the axle flange.

The majority of the runout is gone and what remains appears to be a warped rotor.

Runout measurements:
Outer pad area on disc: .015"
Inner pad area on disc: .020"
Inner hub area: .010"

I think having it turned will eliminate the rest of the wobble but still no brakes.

Before I waste my money on turning these rotors, is there any reason to suspect these calipers are bad somehow? We determined the piston extends, they have pressure, and the sliders are sliding. Can I justify buying new calipers?

----------

Ground down the passenger side. Noticed the axle is slightly bent, causing about .013" runout. Thanks Yukon chromos!

Anyway, final runout on passenger side is about 0.030" which is a combination of a warped rotor and bent axle.

So, I have a;; but eliminated the death wobble from both sides we saw in the video and we can eliminate the remainder with turning rotors and replacing a bent axle.

Still no brakes though.



Can anyone call in a favor and get me some divine intervention?