Secret Incantations for GT front brakes ?

TripleBlk · Aug 28, 2008

The situation :

99 Mustang GT - all stock, installed Motorcraft pads on front wheels. All components clean, no leaks seen at the caliper pistons or boots , slider pins greased with very expensive caliper grease, caliper bolts torqued to specifications.

Yet, the driver's side caliper still wants to stick. Entire wheel was smoking hot. I could cook a slab of bacon on this brake disc after a short drive ! I used a genuine disc pad spreader tool to compress the piston. Is there something I'm missing ? Are these caliper pistons sensitive to being compressed manually ? I have the FSM (factory service manual), but there's no clue in there. Thanks in advance for any help.

FineLineMtrsprts · Aug 28, 2008

Sounds like your caliper is sticking. Replace it.

TripleBlk · Aug 28, 2008

FineLineMtrsprts said:
Sounds like your caliper is sticking. Replace it.

Good thinking there. But , the caliper was not sticking prior to my pad replacement . Thanks for the reply. The issue is that the caliper is now sticking after being "pressed/.squeezed in" for clearance for the new pads. Is this not the right thing to do, or is there some secret procedure I'm not aware of ?

That's why I put the "incantation" stuff in the subject line. Maybe Ford should update the procedure ?

FineLineMtrsprts · Aug 28, 2008

I think you are reading into why it happened a little too much. You car is going on 10yrs old..parts fail. When you pressed the pistons in it may have failed and it not releasing like it should. Replace the caliper,problem solved.

TripleBlk · Aug 28, 2008

So, my caliper magically failed because I had the knotty muscles in my forearms to screw the caliper pistons back in ?

Is the brake system sensitive to " back pressure" ? Does the bleeder screw need to be cracked ?

This in the "incantation" I am referring to. Thankd.

Mustang5L5 · Aug 28, 2008

TripleBlk said:
So, my caliper magically failed because I had the knotty muscles in my forearms to screw the caliper pistons back in ?

Yes. Pressing the piston into the bore could have damaged the bore, scratched the piston or did something else internally that results in the piston sticking.

But yes, with ABS systems they generally want you to crack a bleeder screw when you push the pistons in, but it sounds to me like yours is a mechanical failure of the caliper.

You can try repressing it and see if it sticks, or just replace it

Kman92 · Aug 28, 2008

Maybe..just MAYBE.Your Rotor is warped??long shot..but IM drunk as well.

FineLineMtrsprts · Aug 28, 2008

IF the rotor was that was that warped you would know it by looking at it. TripleBlk you are seriously reading way to much into this. Yes what you did could have made the part fail...

TropicMustang · Aug 28, 2008

You Might have too much fluid. did any fluid come out of the resivor when you were changing the brakes.

forum155pl · Aug 28, 2008

replace caliper.. it happends all the time.. i just ran into this idenical problem in my truck not too long ago

BobHyatt · Aug 28, 2008

TripleBlk said:
The situation :

99 Mustang GT - all stock, installed Motorcraft pads on front wheels. All components clean, no leaks seen at the caliper pistons or boots , slider pins greased with very expensive caliper grease, caliper bolts torqued to specifications.

Yet, the driver's side caliper still wants to stick. Entire wheel was smoking hot. I could cook a slab of bacon on this brake disc after a short drive ! I used a genuine disc pad spreader tool to compress the piston. Is there something I'm missing ? Are these caliper pistons sensitive to being compressed manually ? I have the FSM (factory service manual), but there's no clue in there. Thanks in advance for any help.

It is possible that you have a caliper issue. As the pads wear, the pistons extend outward to keep slight tension on the pads. If you get some water under the rubber boots on the caliper piston, you can get rust. When you press the piston back in, this rust can cause sticking. Cheap way out, remove the piston by unbolting the caliper and let a friend slowly press the brake pedal to push the piston out. Take some crocus cloth and clean the piston and bore, oil with brake fluid and reassemble and the sticking might be gone. Otherwise, replace the caliper. They are not expensive.

steve_stang2003 · Aug 28, 2008

TripleBlk said:
The situation :

99 Mustang GT - all stock, installed Motorcraft pads on front wheels. All components clean, no leaks seen at the caliper pistons or boots , slider pins greased with very expensive caliper grease, caliper bolts torqued to specifications.

Yet, the driver's side caliper still wants to stick. Entire wheel was smoking hot. I could cook a slab of bacon on this brake disc after a short drive ! I used a genuine disc pad spreader tool to compress the piston. Is there something I'm missing ? Are these caliper pistons sensitive to being compressed manually ? I have the FSM (factory service manual), but there's no clue in there. Thanks in advance for any help.

I had EXACTLY the same problem when I did my brakes for the second time a couple of weeks ago.
Brakes were working fine, lubed pins with proper grease etc.
I've been doing this for 30+ years BTW.

Test drive and the drivers side was cooking with bacon!

Jacked car up and wheel was difficult to spin.

Took it apart again and put it back and it worked fine for a couple of days until it started dragging again, not as bad though.
This time I replaced the caliper, which understand was working fine until I replaced the pads.

1. System was NOT opened.
2. Pins lubed and cleaned and looked fine.
3. Everything torqued to spec.
4. Nothing obvious wrong
5. Gentle pushing back piston and it went in fine with no binds.

I think Mustang5L5 is on to something.

Technically we are supposed to crack the bleed screw when compressing the piston because dirty fluid tends to collect down at the caliper end and we are in effect pushing back this dirty fluid into the ABS system which is not good.

Also as the brakes wear, obviously the piston is riding on a different portion of the metal within the bore. Pressing it back maybe causes it to scratch on a ridge that may form or something like that.

I know that on GM cars after replacing very worn down pads the master cylinder tends to develop leaks because the bore is riding on a different section of metal.
Very common in GM cars so maybe something similar happens with the calipers on Fords?

I say replace the caliper with a PBR rebuilt or better yet go for the Cobra kit!
I'm still kicking myself for not doing it when I had the problems because overall the price difference would not have been *that* much.

I've talked to a number of people who have had this exact problem with Mustang brakes for some reason so maybe it's common on the older cars as they age.

I've never seen it on any of my GM or Dodge cars though but they have their own set of quirks.

HTH!

BlownFiveLiter · Aug 28, 2008

Take the caliper back off of the rotor and hit the brake pedal to pop the piston out of the bore. You can also do it with compressed air, but make sure your fingers are clear in either case. Inspect both of them for any rust, or imperfections. If you find any that look fixable, hit the piston and the bore with some fine emory cloth and rinse it clean with some fresh brake fluid. My left rear caliper was seized after 99,000 miles of use on original pads, but I've gotten 6 more years out of it so far, after doing this.

281CI · Aug 29, 2008

had this same problem. took piston out of bore and it looked fine. the problem was where the piston seal sits in its groove on the aluminum caliper there was white corrosion from moisture/brake fluid. i took some small screwdrivers/metal picks and scraped it all out and it was fine.

TripleBlk · Aug 29, 2008

Thanks very much for all the replies ! It sounds like many of you all have "been there", so my plan is:

Pop the pistons out of the "bad caliper" , clean, and re-assemble , and re-test. According to the FSM I have, I won't have to bleed the whole system, just that one caliper that needs to be disconnected.

I'll try to post pics of what I find : dirt, ridge, rust, whatever.

:SNSign:

steve_stang2003 · Aug 29, 2008

TripleBlk said:
Thanks very much for all the replies ! It sounds like many of you all have "been there", so my plan is:

Pop the pistons out of the "bad caliper" , clean, and re-assemble , and re-test. According to the FSM I have, I won't have to bleed the whole system, just that one caliper that needs to be disconnected.

I'll try to post pics of what I find : dirt, ridge, rust, whatever.

:SNSign:

Sounds like a plan!!

Just make sure to keep an eyeball on the master cylinder fluid reservoir so that it doesn't go dry.

looking forward to the pics!

TripleBlk · Aug 29, 2008

OK, here's the situation :

Removed caliper, and had assistant pump brake pedal. One of the caliper pistons eased on out , slowly. The other remained stuck ! I re-inserted the piston which came out into the bore and used my trusty disk pad spreader to try and force the balky piston out. No dice. I have to admit defeat at this point , and I ordered a new caliper from NAPA.

A couple of surprises :

The aluminum caliper on my 99 GT is made by "PBR", I guess they are the prime vendor for brake parts for Mustangs of 1999, at least.

The pistons are NOT steel, they are some kind of phenolic resin design. I guess this design is OK, as the resin will never rust. Beware compressing this type of piston when doing a pad change, obviously.

I have attached some pics ; hopefully it will help some other Stangnet member in the future !

Mustang5L5 · Aug 29, 2008

PBR is a brake supplier based in Australia. They supply brake calipers for dozens of OEM calipers. They make the Cobra calipers, Corvette calipers and a ton of GM and Ford truck calipers..as well as other applications

The rear calipers are made by Varga, which is based in Brazil.

danongentry · Aug 29, 2008

I've had the caliper lock up on me twice. Once in my old ranger and once in my grandmother's F150. Both fun, although the oil pump went at the same time on the F150 so it was slightly more fun.

Also, mmmmmm...brake bacon

flymikemc · Jan 3, 2010

I did the brake conversion on my 89 and have the 99 PBRs also. Both front brakes are putting slight pressure on the pads making them hard to turn. If one of them were doing it I would think that a caliper is stuck but both are. Could the Master cylinder be holding pressure on them? If so what can I do. I would hate to go through the trouble of putting new ones on if it doesn't fix it. Any thoughts? Thanks.

Secret Incantations for GT front brakes ?

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