Rear caliper question???

[stevbd]

When I hear hanging up or dragging I think not releasing completely. That is what confused me.

Fair point. @2012Boss302 does refer to dragging but if that is the case it seems odd that both rear calipers are dragging equally, plus according to his inspection nothing is amiss and the rears have even temp and wear. Dragging or not, the evidence is that the rear brakes are getting hotter than the front. That combined with the opening comment about the rear brakes "locking" at the track leads me to think this is more of a brake bias issue than a frozen caliper/dragging issue. Which of course would be exaggerated with the upsized rear GT500 rotors. As mentioned I am curious about front brake pads, if he is using R12 in front also I think that will be another clue.

 

[2012Boss302]

How long were the R12s on the car and what fronts were you using?

I'm using Gloc R16 on the front and R12 on the rear. Both sets of pads were new for this track day. I bought the pads from OP Tim. They were already heat cycled out of the box. I still took it easy on the first couple of laps of the first session

The rear NEVER locked up before the front. I didn't start diving into this until May 18th. The track day was May 4th. It lost the brake pedal at the end of the fourth session of a four session day. When I say it "lost the brake pedal", I mean it went straight to the floor. It kinda pumped up so I didn't wreck the car

 

[2012Boss302]

Another question?? What provides the front to rear brake bias on a factory equipped ABS car??

I am under the impression the master cylinder supplies pressure and some front to rear delay to the ABS pump. Again I am under the impression the ABS pump should be where the pressure adjustments are made.

I hope that's clear? It kinda is in my head....

In other words, the ABS pump is the same as a proportioning valve in a non ABS equipped car. Thoughts???

 

[EF1]

I'm using Gloc R16 on the front and R12 on the rear. Both sets of pads were new for this track day. I bought the pads from OP Tim. They were already heat cycled out of the box. I still took it easy on the first couple of laps of the first session

The rear NEVER locked up before the front. I didn't start diving into this until May 18th. The track day was May 4th. It lost the brake pedal at the end of the fourth session of a four session day. When I say it "lost the brake pedal", I mean it went straight to the floor. It kinda pumped up so I didn't wreck the car

We are running nearly identical brake set ups except I have switched from Motul 600 to castrol srf fluid. I have not experienced the accelerated even wear of the rear pads. When Zi have had heat/wear issues it has been one sided and traced to advance track or a sticky caliper. The even wear snd temps from left to right are puzzling since dragging issues are usually not experienced equally from side to side. A previous poster mentioned parking brake not fully releasing as a potential cause. He may be on to something. It will be interesting to hear if you figure this out or if it was a one time occurrence and disappears on its own.

 

[TennTex]

Check the guide pins. They may be hanging up and not letting the pads fully release. I recently cleaned and re-greased mine on my S550. One of the 2 pins has a rubber "band" on one end. Found a tip online to trim the width of it a bit to reduce grab potential.

 

[stevbd]

@2012Boss302 In your first post you asked, has "anyone ever have both rear calipers lock up ONLY on track??"
Then in your post #22 you stated, "the rear NEVER locked up before the front."
Then you say you LOST the brake pedal as it went to the floor, during which event I assume no brakes were locking.
I'm not trying to be difficult but I'm just not quite understanding exactly what happened. Did your rear brakes lock up or not? Did the fronts lock up?
Some of this sounds like a front-rear bias problem. But then your other statements make it sound like dragging rear brake calipers? Can you say a little more about which it is? If the car is just sitting in neutral on a very slight incline, will it roll?

 

[2012Boss302]

dragging rear brake calipers? Can you say a little more about which it is? If the car is just sitting in neutral on a very slight incline, will it roll?

Dragging a lot.

Also just to be clear. Since I screwed the rear pistons in to install my street brake pads, they have not been dragging yet. I find it odd that it only did this on track. Heavier braking maybe???