help, brakes get hot and drag

[LurkTheKoukiHatch]

I have a 93 240sx with dba 4000 series slotted rotors and hawk hps pads.
after some aggressive driving, the pads sound like they are dragging. continue pushing hard and the pedal will get stiff, and the noise is constant. driving with minimal braking allows them to cool and the problem ceases. the problem will also stop if the car is parked for 2-3 minutes. i have pulled them apart and re-lubricated all components several times, but nothing was binding, and the caliper piston retracts normally. it did not happen with the old standard rotors and pads, but has been a problem since i put the new equipment on. (along with SS brake lines and flushed with motul 5.1 fluid)
I don't believe i am overheating the brakes, because it doesnt take very long to make this problem occur, and the pedal never gets mushy.
Any insight into what the hell is going on would be great. so far my theory is front calipers, but i dont know why other than its the only part that hasnt been replaced yet. (rear calipers have been replaced, and there is no issue with them, but thats not proof)

[Tower240sx]

try eliminating one change at a time, I'm thinking put stock pads in and see if problem goes away.

how much pad is left on the stock pads?

are the hawk pads too thick, with the new rotors is there clearance at full piston retract for the assembly to grow with heat? (no more than .010-.020 should be required)


is the pedal adjusted to the correct height? if it doesn't come all the way up to near the internal stop i don't think it can vent line pressure from expansion to the master cylinder

Welcome aboard BTW

[LurkTheKoukiHatch]

stock pads when removed were at approx. 30-40%, they've long since been tossed. ive been driving on the new setup for about 4 months now, but the hps pads have shown little sign of wear (maybe at 90-95% as of now)
the caliper piston is no longer fully retracted, so i would assume there is some room to grow (if i am understanding your question correctly)
the pedal feels great under normal and spirited conditions, very firm, and begins to clamp after very minimal free play (except when i create this problem, then the pedal has 0 free play, and feels like i have no vacuum booster)
ill order some oem pads and see if that makes any difference, i suppose...at least i could compare thickness?
i really appreciate your input, thanks!

[Matt93SE]

how hard are you driving when this happens?
a hard pedal and no brakes is pad fade or a failing booster.
A soft spongy pedal is fluid fade where there's air bubbles in the lines that's caused the fluid to expand. as you press on the pedal, it compresses the air pockets first, then starts moving the piston.

how long since a front caliper rebuild?
the seals are designed with a tiny amount of spring to them so when you let off the brakes, they retract and pull the pads away from the rotor slightly. When the seals get old, they get hard and stop retracting like they should, causing your brakes to drag when they get hot. Mine were so bad on my car, it took 4 people to push the car through tech after a race. rebuilt the calipers with new seals and you can push the car with one arm again.


Motul DOT 5.1? eek. Motul is usually good stuff, but I'm wondering if the 5.1 is the problem.. Our cars were designed around a DOT 3/4 fluid. just grasping at straws here, but I prefer ATE in my race car and Valvoline Synpower in a street car.


I'd also take a closer look at your brake booster. it's near 20 years old now and they can do strange things when they get old and cranky. it could be on its way out.

[LurkTheKoukiHatch]

im driving pretty hard, but for a short period of time when this problem occurs. i feel as though the brakes shouldn't be overheating this easily, just based on how the old stock setup performed under similar conditions.

i have no idea when the last time the front calipers have been rebuilt. this is the direction im leaning towards as well, but i was hoping to avoid replacing them because i want to go z32 with my 5 lug conversion sometime in the future. I have rebuilt calipers before for someone else, but i didnt want to do it on mine without knowing how to gauge the condition of the honing...unless im overthinking it?

a frozen caliper such as you described suggests that the caliper wouldnt retract at all, correct? a few minutes of calm driving or stopping my car completely allows everything to return to normal, which is why this is so confusing to me. I pull the car into my shop to check/relubricate, and everything has free range of motion, including the caliper piston which retracts normally. Maybe when the piston expands from heat, it snags on...something; then when it cools and contracts, its free again? It doesn't really add up, but my gut feeling is the calipers are the problem

after a short talk with a hawk pads tech, he said he didnt really know what was going on, but is sending me some new pads just in case. i'm blown away with how good their customer service is, but we both agreed we didn't think the pads are the culprit.

I really really doubt the Motul 5.1 is a problem, unless you can give me a reasonable explanation as to why it might cause this issue.

the brake booster is possible as well, but why should it care if the brakes are hot or not?

thanks for the input i really appreciate it! 2 very useful responses in less than 24 hours? this forum kicks ass!

[Tower240sx]

the 5.1 fluids are glycol based just like the 3/4 fluids so there is no compatibility issues there, Matt may not have known about the "newish" 5.1 dot standard (not silicone fluid)

[Def]

Its probably Motul RBF600. Good fluid, it's what I use.

[LurkTheKoukiHatch]

i was thinking of running rbf600, but you have to change it a lot more often, so i figured the 5.1 was overkill enough haha

[Matt93SE]

the 5.1 fluids are glycol based just like the 3/4 fluids so there is no compatibility issues there, Matt may not have known about the "newish" 5.1 dot standard (not silicone fluid)

Nope. I looked it up before I said anything. I still don't like it, even though it's supposed to be compatible. ;)
anything that says "DOT 5" anywhere on the label, even if it's 5.1 I'm going to avoid. :D

[hai1206vn]

I had a similar problem for a while. Pedal would stiffen and calipers would not release; this happened at random time without any pattern. Pulling the vac hose to the booster restored everything immediately. The culprit was a bad booster.

[Tower240sx]

Nope. I looked it up before I said anything. I still don't like it, even though it's supposed to be compatible. ;)
anything that says "DOT 5" anywhere on the label, even if it's 5.1 I'm going to avoid. :D

Hater^

How far in the back woods are you in Texas boy,

Embrace the new technologies, I won't make you change your brake fluid in the tractor.

[Matt93SE]

ATE is good enough for those sausage eaters in Germany, it's good enough for me. ;)

and my tractor doesn't use brake fluid. it's all hydraulic fluid. Sad part is I use better oil in it than I do in the 240....

[WorkInProgressK]

ATE FTW. I like the 3 years or if your start boiling, your fluid needs a change :D.

[Def]

i was thinking of running rbf600, but you have to change it a lot more often, so i figured the 5.1 was overkill enough haha

RBF600 absorbs water very slowly compared to most glycol brake fluids. Plus even with it a little wet it won't boil on the track on pretty much any car.

I change mine every 6 months and it's never given me problems on track. Cheaper than most other fluids when you look at the cost over time.

[Def]

Nope. I looked it up before I said anything. I still don't like it, even though it's supposed to be compatible. ;)
anything that says "DOT 5" anywhere on the label, even if it's 5.1 I'm going to avoid. :D

Dude... seriously?


It's just a higher temp spec for DOT 3/4.

[Matt93SE]

Dude... why?

I usually run Valvoline Synpower in my car and bleed it once a year or so, flush every 2-3 years. and I've never had a fluid problem.

so why pay $20+ a quart (figure in shipping too since you don't just pick it up at Autozone) when the $7.99 stuff works just fine?

:D

But yes, I get your point. I just have no need for it, so I poke fun at the guys who think they have to spend 5x as much for brake fluid.

[Tower240sx]

This fanboi I work with (manonegra) has a backstreet hooker that gets him OEM porsche fluid that comes in silly german cans and he loves it, (i think he puts it in his coffee)

^
No content relative to discussion

[Def]

Dude... why?

I usually run Valvoline Synpower in my car and bleed it once a year or so, flush every 2-3 years. and I've never had a fluid problem.

so why pay $20+ a quart (figure in shipping too since you don't just pick it up at Autozone) when the $7.99 stuff works just fine?

:D

But yes, I get your point. I just have no need for it, so I poke fun at the guys who think they have to spend 5x as much for brake fluid.

I've boiled that stuff before, so I'll pass(yes it was fresh, it was at Road Atlanta where it was about 125 mph (speed limiter) to 40 mph, and the pedal would sink just a bit more eat lap until it finally just dropped).

I feel fine giving a light flush to the Motul every 6 months then bleeding it well at the beginning of the next year.


I'm sure when my S13 Chumpcar gets up and going and is also hamster powered it'll be fine on whatever brake fluid I can buy in a big jug from the junkyard for 99 cents too. :D

[T-Rex]

I have seen the slider pins start to hang up when they get worn. It could be that the heat aggravates this condition causing them to not allow the floating portion of the caliper to release.

You made need a rebuild kit, and change out the pins.

[LurkTheKoukiHatch]

when i did the brakes, one slider pin was binding pretty bad, but i was able to clear the bore of the bracket and clean the slider pin back to a shine. they all move freely now (at least when its cool enough to touch). if i replace the calipers, ill be sure to get loaded just to be safe though. i hadn't thought of the slider pin possibility yet, thanks!

[Tower240sx]

if i replace the calipers, ill be sure to get loaded just to be safe though.

I, as a rule, only work on cars when I'm loaded

[LurkTheKoukiHatch]

update: got the brakes smoking hot and pulled directly into my shop...while still smoking, the wheels spin freely, and the front wheel bearings seem to have a little bit of play when hot...then when they cool down, the play goes away to almost nothing. the passenger front is brand new, and its doing it a bit less...but still...WTF?!

[Matt93SE]

when you installed the bearings, how much did you torque them to?

[LurkTheKoukiHatch]

torqued to factory spec. don't recall the number now. why would the play go away when it cools as well?

[LurkTheKoukiHatch]

I, as a rule, only work on cars when I'm loaded

unless im at work, i tend to follow this rule as well haha

[Tower240sx]

HaHa I'm the boss

So

Yeah,

gotta love california


do a search for wheel bearings here and see all the problems everyone has had, consensus seems to be torque to 200 or so, or the bearings fail,

seems to me the bearings should be tighter when hot unless the spindle is somehow hotter than the bearings by quite some amount, I'll have to ponder that one

[LurkTheKoukiHatch]

torqued the pants off the wheel bearings. passenger side with the fresh bearing didnt budge with 250 ft lbs dialed up on the torque wrench, but got a little extra movement from my impact lol. the driver's side seemed pretty loose..maybe had 60 ft lbs on it, and it got 250 + the impact...the noise returned, but it seemed to require a little more aggression before getting noisy, and i didnt continue pushing, so i didnt get the brakes to smoke or anything...im wondering if i am just beating the hps pads too much, and they cant take it...but kind of hard to imagine 5-6 consecutive heavy braking deceleration would be enough to thwart "high performance" pads...

[Matt93SE]

5-6 would be enough for an HPS if you have enough power and are stopping from fast enough, hard enough.
i.e. a 250+hp car doing consecutive 100 to 20 stops would toast an HPS.

[LurkTheKoukiHatch]

well im lucky if i have 150whp, and digging in hard from 60-80 to about 20, so yeah...i can scratch that one off...

[PoorMans180SX]

What kind of brake lines are you running?

It sounds like the inner lining on your lines are separating and causing a check-valve effect inside your brake lines.