Severe brake pull

[CamWeiss]

Hey guys

So... I'm starting to get a little frustrated with this one.
I put a new set of Hawk HP+ pads in before I went down to the 'States for an autocross. Flushed and bled the brake lines, and bedded the pads on the way to the ferry.
Everything was working fine. The brakes were fine on the way down, they were just fine (but a bit toasty warm) at the track, and they were fine on the drive home.

Due to the cracked wheel, I swapped over to my swirlies w/ all seasons on them this morning. It's the only change to the car. And it's been pulling like an SOB all day under braking. The harder the braking force, the harder the pull, and the passenger wheel locks prematurely. If I hold the wheel straight, it pulls to the passenger side. If I let the wheel go, I can feel the car want to pull but the steering wheel rotates about 10 degrees to the left.
At first, I thought it was a bad suspension peice allowing the wheel to have excessive camber or toe under braking, but I had a good feel around and everything felt tight. The wheel bearing has a bit of play, but I'd say it's within tolerance. I had a buddy hang out the window, and he couldn't see anything amiss with the geometry. He did note a few sparks coming from the brakes on that side, I obviously couldn't check my side. I'm almost inclined to write that off as a product of the high metal content of the Hawk pads.
I pulled that front right corner apart, nothing was amiss. Pads were wearing evenly (Although there was significantly more brake dust and heat on that side, a 75 degree spread over a half dozen moderate 80-40 slowdowns). Rotors are not heavily worn or grooved. I did notice a bit of transfer from the rubber piston boots onto the pad backs, as if a bit had melted on.


So... I'm stumped. When everything appears normal but is obviously amiss, what do you do?
Rebuild calipers? I'm inclined to try all the simple stuff first as I'm very tight for time these days.


PS - I checked and set all tire pressures. It's not that.

[Jordan Kruger]

I think any sparks would be a result of the hp+     but the problem you have sounds like a really sticky caliper and/or slide pins.

[CamWeiss]

As part of the disassembly, I greased the slide pins.
I don't think it's a sticky caliper, it would drag and maybe pull when you're off the brakes. When I'm on the brakes, the problem occurs.

[Chad Giffen]

sounds like a bad caliper.

[Dan Harshey]

Sounds like a stuck piston in that caliper, especially if its creating excessive brake dust.  Pull the Caliper off and try and push the piston back.  Everything may have been good before you went to Packwood, but all that heat from the autox could easily cause an issue.  I had it happen after a Solo Sprint event, on a rear caliper.
Edit:  I've also seen brake pull happen when control arm bushings have play, but it doesn't sound like your situation.

[Robert Vorley]

+1 Dan. I ran mine until one day I lost brake pressure due to fluid leaking out of the offending piston. I realized what had happened and drove without using the brakes the rest of the way home.

It turned out to be a broken seal that was seizing a piston and eventually allowing fluid to leak past it, particularly  when braking.  Prior to that I had some of the same symptoms as you are having, pulling, heating up, excessive dust. This was on a Ssbc dual piston big brake kit.

[CamWeiss]

These, as well, are the "big brakes".

I know the drivers' side pistons move freely, I'll take apart the passenger side tomorrow and see.

What are my options for rebuilds? If the rubber seal can't take the heat, do I have options for something that can?

[Robert Vorley]

In my case I had the inconvenience of having to get them from back east, and since the expedited shipping cost more than the new seals I got an extra set, for next time. I haven't heard of upgradable seals, just upgradable calipers. gl

[Dan Harshey]

The rubber seals should be able to take the heat Cam, they probably distorted or melted because the caliper was stuck partially on and the brakes never had a chance to cool down.

[Jason Gilbert]

These, as well, are the "big brakes".

I know the drivers' side pistons move freely, I'll take apart the passenger side tomorrow and see.

What are my options for rebuilds? If the rubber seal can't take the heat, do I have options for something that can?

JNZ Tuning has an oem rebuild kit that comes with everything you need to rebuild your calipers,except the pistons. Call Ziggy @ RTM, he can probably get you the kit as well.

[John Hartman]

brake line Cam.

If the pistons move in the caliper and the slide pins are free, and the pads are not really siezed in place, its the line.

What happens is that the inner layer of the brake line breaks down adn then starts to come apart.  The material will have an end bend inwards.  The force of your foot and the booster will force the fluid out and push the caliper and pads against the rotor, but the piece of offending rubber acts like a one way check valve and will not allow the fluid back up the line and it holds the caliper tight.

Eventually it will let the fluid back.  Sometimes it even happens quickly like in a few seconds, but sometimes it takes quite a while.

Time for some stainless braided lines 

It CAN be a bad proportioning valve as well, but its less common as that is just a ball and spring and if your fluid is even remotely clean its usually pretty good.

[CamWeiss]

Someone else I was talking to also mentioned brake lines today. I'm not discounting it, but the brakes don't continue to drag, it's only when I'm on them that they are misbehaving. However, perhaps I'm looking at it the wrong way. Maybe one caliper isn't giving enough bite?
I dunno.

I'm not sure about the proportioning valve. I would effect front to rear bias, not side to side. I think?

Anyway, I think I'll look into rebuilding the calipers and replacing the brake lines with stainless.

[Remi Raymond]

Just had a lightbulb go off about this Cam: If you had just done a race day what if you just boiled your fluid in one spot and you have an air lock situation going on? Bleed your brakes!

[KevinBuckham]

Here's my bets (in order):
1) Bent slider pin (you lubed it fine, but it's bent and it's causing the caliper to not release properly)
2) You used low temp lube, and a pin is totally stuck now that you used them with heat.  The majority of the caliper lube you will find doesn't have a high enough temp rating for even autox use.  This lube WILL turn into a blackish mess next to the pin and prevent it from moving at all.  No lube is better than that crap if you are going to race.
3) Seized piston
4) Brake lines

If you are stumped, come see me, or I can come see you and we can inspect the calipers.  I've been through h@xoring DSM brakes too many times.

Here's a simple test for you to see if one caliper is stuck:
Pull the wheel, attach a hose to the bleed screw and crack open the bleed screw  (might want to drain that hose somewhere besides your nice black paint too).  If you open it enough and release the line pressure you should be able to wiggle your caliper in and out along the slider pins.  This only works if the pads pistons are compressed, but you can sometimes do this by just cracking the line and moving the caliper in and out by hand.  If not, pull the lock pin, rotate the caliper up and compress the pistons (use a tool).  Then put the caliper back in place (both lock and guide pin installed with proper torque) and it should slide freely in and out as you move it by hand.  If it's stiff or one pin grabs you will immediately feel it.  (Obviously if you couldn't compress one piston you also found your problem.)

When I ran DSM calipers I kept around a set of guide and lock pins as I inevitably bent them after a driver training or Solo sprint race.

Doing this will test the pins and pistons.  I'd replace the lines anyway.  Our cars are old.

[Trevor Robinson]

I know the fluid was flushed and bled.  Its possable there is some moisture in the lines still that crept in there if the fluid has been open or old or... anyway...

new fluid again is a possable fix.  I have had the unfortunate experience of replace a set of rubber lines thinking exactly what john said about being a 1 way check valve and not allowing the pison in the caliper to retract. 

BUT  i have had the brakes bled  but not all the old fluid was replaced (still some traces left in the master), and the brake calipers heated up causing the fluid to heat up causeing the caliper to apply pressure to the pads locking them on the one side....

full fluid replacement by sucking out all the fluid from the master and then new fluid all the way down with a vacume bleed.  was the only cure. even after parts where replace calipers lines etc.