Brake Disc Flex

Ralli///Art GS · 08-29-2004, 08:52 AM

When I get on the binders after exiting a tight corner (pulling over 1G according to my G-tech meter) the brake pedal almost goes to the floor. Pressing the brake again yeilds normal stopping power. The only thing I can think of that would cause this would be the brake disc moving and pushing the piston back into the caliper. The energy from pressing the pedal is used to push the brake pad back up to the surface of the rotor. I can not notice a handling problem or hear anything odd. I also checked the wheel bearings and can not feel any play. Has anyone encountered this problem before? If the wheel bearings are fine is it just that my bearings/uprights are not up to the task of driving that hard? Does anyone make upgraded wheel bearings?

Suspension Mod List:
1994 Eclipse GS

KYB AGX (set on 2 front, 3 back)
H&R Springs
Full Poly bushing Kit
Front and rear strut tower bars
RRE SS brake lines
Axxis Metal Master Pads
Yoko AVS ES100's, 215-45-ZR17
Remanufactured halfshafts

URMachines · 08-29-2004, 09:56 AM

sounds to me like you have some hydraulic problems. check out your master cylinder for bubbles and do a brake fluid flush.

f8ldzz · 08-29-2004, 07:07 PM

Even if your brake discs flex axially, it has nothing to do with the braking dynamics.
Under braking, the wheel/tire/brake rotor is turning.
The brake caliper clamps the brake rotor and it induces an opposite force in the circumferential direction.

Multi-piston brake calipers are self adjusting to the location of the brake rotor.
Floating brake calipers do the same, albiet in a different manner.

You're looking in the wrong direction for your problem.
It's either your brake hydraulics is bad (brake master, brake lines, or brake caliper piston o-ring seals) or you have a heat dissipation problem.

URMachines · 08-29-2004, 08:37 PM

do a proper fuild flush and replace with DOT 4 fliud. that will solve the problem. it is your hydrolics

GRiDRaceTech · 08-29-2004, 08:56 PM

Quote:

Originally posted by Ralli///Art GS
(pulling over 1G according to my G-tech meter)

1.0g cornering with those suspension mods and tires? More proof that G-tech isn't a bonafide performance meter. (Although it can be useful.)

Definitely sounds like hydraulic problems.

URMachines · 08-30-2004, 07:56 AM

yea 1.0g is a bit much especially for a FWD with no LSD or high grip tires but if you love to drive, and do it well, more power to ya

Parry · 08-30-2004, 08:10 AM

is this happening when you are breaking at idle, or is the car wound up?

Ralli///Art GS · 08-30-2004, 11:53 AM

1.06 G's is instantaneous, don't concider it skid pad number. I just upgraded the brake lines and flushed and filled the whole system, that's why i don't think it's a hydraulic problem, I'll do it again when I get some time, but the brakes feel fine unless I exit a tight corner, and then get on them. I'm not talking about mid corner braking, i'm talking about after the corner on a straight section.

blargonator · 08-30-2004, 02:26 PM

before you spend anymore money i have this idea.....buy second hand stuff from another DSM because i noticed you have one. (my brother has a 91 GS) my brother and many other dsm owners know that dsm parts are readily availiable. my brother knows a guy who has 3 dsms and another who has 9 (they are not shoes!) but just a idea. do you still have the stock NA engine?

Parry · 08-30-2004, 02:34 PM

This is odd...

If it was the master cylender it would do it at low rpm or idle when the vaccuum was down in my experiance. That's why I asked about that.

I'm really not too sure. That is very strange, sorta out of my league.

Check and see if it is rpm-related (aka vaccuum related) in any way I guess.

Do you know what a bad master cylender feels like?

f8ldzz · 08-30-2004, 04:17 PM

Bad master cylinders can make no hint that they are bad.
In best case, it'll start leaking fluid.
I've seen them leak no fluid at all but still managed to be bad.
How did we find out?
We replaced it and it fixed all our braking headaches.

Did you replace your brake master cylinder recently?
Even "new" brake master cylinders are bad out of the box!
We've had best luck with brand new brake master cylinders from the dealer.
Units that are rebuild from big chain auto parts stores - i.e. AutoZone, Pep Boys, Kragen / Schucks / Checkers - are inferior in quality versus the dealer stuff.

08-29-2004, 08:52 AM	#1
Ralli///Art GS Battle Ready. Join Date: May 2004 Location: RI Posts: 132	Brake Disc Flex When I get on the binders after exiting a tight corner (pulling over 1G according to my G-tech meter) the brake pedal almost goes to the floor. Pressing the brake again yeilds normal stopping power. The only thing I can think of that would cause this would be the brake disc moving and pushing the piston back into the caliper. The energy from pressing the pedal is used to push the brake pad back up to the surface of the rotor. I can not notice a handling problem or hear anything odd. I also checked the wheel bearings and can not feel any play. Has anyone encountered this problem before? If the wheel bearings are fine is it just that my bearings/uprights are not up to the task of driving that hard? Does anyone make upgraded wheel bearings? Suspension Mod List: 1994 Eclipse GS KYB AGX (set on 2 front, 3 back) H&R Springs Full Poly bushing Kit Front and rear strut tower bars RRE SS brake lines Axxis Metal Master Pads Yoko AVS ES100's, 215-45-ZR17 Remanufactured halfshafts

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08-29-2004, 09:56 AM	#2
URMachines Registered User Join Date: May 2004 Location: East Prov,RI Posts: 131	sounds to me like you have some hydraulic problems. check out your master cylinder for bubbles and do a brake fluid flush.

08-29-2004, 07:07 PM	#3
f8ldzz Registered User Join Date: Aug 2004 Posts: 185	Even if your brake discs flex axially, it has nothing to do with the braking dynamics. Under braking, the wheel/tire/brake rotor is turning. The brake caliper clamps the brake rotor and it induces an opposite force in the circumferential direction. Multi-piston brake calipers are self adjusting to the location of the brake rotor. Floating brake calipers do the same, albiet in a different manner. You're looking in the wrong direction for your problem. It's either your brake hydraulics is bad (brake master, brake lines, or brake caliper piston o-ring seals) or you have a heat dissipation problem.

08-29-2004, 08:37 PM	#4
URMachines Registered User Join Date: May 2004 Location: East Prov,RI Posts: 131	do a proper fuild flush and replace with DOT 4 fliud. that will solve the problem. it is your hydrolics

08-30-2004, 07:56 AM	#6
URMachines Registered User Join Date: May 2004 Location: East Prov,RI Posts: 131	yea 1.0g is a bit much especially for a FWD with no LSD or high grip tires but if you love to drive, and do it well, more power to ya

08-30-2004, 08:10 AM	#7
Parry Registered User Join Date: May 2004 Posts: 894	is this happening when you are breaking at idle, or is the car wound up?

08-30-2004, 11:53 AM	#8
Ralli///Art GS Battle Ready. Join Date: May 2004 Location: RI Posts: 132	1.06 G's is instantaneous, don't concider it skid pad number. I just upgraded the brake lines and flushed and filled the whole system, that's why i don't think it's a hydraulic problem, I'll do it again when I get some time, but the brakes feel fine unless I exit a tight corner, and then get on them. I'm not talking about mid corner braking, i'm talking about after the corner on a straight section.

08-30-2004, 02:26 PM	#9
blargonator Registered User Join Date: Jun 2004 Location: michigan Posts: 406	before you spend anymore money i have this idea.....buy second hand stuff from another DSM because i noticed you have one. (my brother has a 91 GS) my brother and many other dsm owners know that dsm parts are readily availiable. my brother knows a guy who has 3 dsms and another who has 9 (they are not shoes!) but just a idea. do you still have the stock NA engine?

08-30-2004, 02:34 PM	#10
Parry Registered User Join Date: May 2004 Posts: 894	This is odd... If it was the master cylender it would do it at low rpm or idle when the vaccuum was down in my experiance. That's why I asked about that. I'm really not too sure. That is very strange, sorta out of my league. Check and see if it is rpm-related (aka vaccuum related) in any way I guess. Do you know what a bad master cylender feels like?

08-30-2004, 04:17 PM	#11
f8ldzz Registered User Join Date: Aug 2004 Posts: 185	Bad master cylinders can make no hint that they are bad. In best case, it'll start leaking fluid. I've seen them leak no fluid at all but still managed to be bad. How did we find out? We replaced it and it fixed all our braking headaches. Did you replace your brake master cylinder recently? Even "new" brake master cylinders are bad out of the box! We've had best luck with brand new brake master cylinders from the dealer. Units that are rebuild from big chain auto parts stores - i.e. AutoZone, Pep Boys, Kragen / Schucks / Checkers - are inferior in quality versus the dealer stuff.