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Old 04-13-2010, 10:53 AM   #1
newclutch
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Default pad knock back

I just tracked my 03 WRX yesterday with the new motor and giant big brakes. It stopped like on a dime but I was getting pad knock back and was pumping the brake at the 5 marker and then slowing the car at the 2-1/2 marker. The brake pedal normally has 4" of travel. The brakes engage at the three inch mark, just right for toe/heeling. But yesterday they engaged at the 3-1/2 inch mark and I pushed them to 3-3/4. The pedal is about bottomed out. What can I do to remedy this? When I pumped twice and then braked all was perfect but that is not the fast way around a track. master cylinder is original. 119,000 miles
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Old 04-13-2010, 11:48 AM   #2
MasterKwan
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Wheel bearings.
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Old 04-13-2010, 11:58 AM   #3
Dutch Scooby lover
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Change the fluids, and bleed the brakes.
You seem to have multiple problems, pad knockback is just one of them.
The "needing to press the pedal further for the same braking" is indicative of air in the system, either due to unproperly bled brakes, or from boiling the (too old) fluid.
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Old 04-13-2010, 01:59 PM   #4
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Depending on what kit you have, you may be able to use different rotor mounting hardware to allow for more float and you can also install knockback springs behind the pistons to keep them from staying retracted after corner induced hub flex. Full float hardware will cause the rotors to rattle around when driven on the street and knockback springs will cause the pads to always drag slightly, so they are not ideal for street driven cars. Ultimately, the hubs and bearings are the issue, but its just a way of life for 5x100 cars.
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Old 04-13-2010, 02:22 PM   #5
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How about pumping the brake with your left foot while going down the straight, right foot to the floor. That way you won't be giving up anything in the braking zones.
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Old 04-13-2010, 02:41 PM   #6
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Quote:
Originally Posted by REX8 View Post
How about pumping the brake with your left foot while going down the straight, right foot to the floor. That way you won't be giving up anything in the braking zones.
That's what I've always done. Quick tap down the straights and it's all good into heavy braking zones.... not sure my competitors like it though.
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Old 04-13-2010, 02:43 PM   #7
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Quote:
Originally Posted by Dutch Scooby lover View Post
Change the fluids, and bleed the brakes.
You seem to have multiple problems, pad knockback is just one of them.
The "needing to press the pedal further for the same braking" is indicative of air in the system, either due to unproperly bled brakes, or from boiling the (too old) fluid.

Fresh fluid and pads and I've bleed brakes over 20 times per year for the last 5 years. I didn't screw it up.

Mr. KWAN, New bearings will solve my problem for a year or two? This would be a good fix that I can do. I put in new bearings at 60-65,000 miles or so.
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Old 04-13-2010, 02:50 PM   #8
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Quote:
Originally Posted by newclutch View Post
Mr. KWAN, New bearings will solve my problem for a year or two? This would be a good fix that I can do. I put in new bearings at 60-65,000 miles or so.
No, I think he is referring to the '05+ STi wheel bearing conversion.
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Old 04-13-2010, 03:15 PM   #9
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It depends on what kind of tires you run. If you're on street tires, new wheel bearings will probably last a season or 2. On real R-comps, you might need to do it every couple months.

WRX's are known to have weak wheel bearings. The STI bearings are larger both front and back than the WRX ones. My comment was just suggesting that the knockback is primarily caused by the wheel bearings. The really nice thing about STI front wheel bearings is you can change them at the track in about 30 minutes if you need to.

What kind of fluid do you use?
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Old 04-13-2010, 04:00 PM   #10
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ON the car now are Michilin PS2 but I used Michilin cups before. Fluid is ATE I have another set of street tires when the PS2s are destroyed. Continental Sport contact 3s. This is my DDriver so I might not run R compound on this car. I have a more track worthy car for extreme fun.The brake are 355 x 32 six piston BREMBOs front and 2 piston BREMBOs rear 316 x 20. Pads are Pagid RS-29.
Fluid boiling is not my problem.
I'll get new bearings.
thanks
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Old 04-13-2010, 07:10 PM   #11
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My dealer says $145.00 for seals and bearings for one side front x 2 if I do it myself. $290.00

Dealer says $500.00 labor each side + above parts = $1,300.00 for them to do it. Special tools to press off old and press on new. Bend over.

How hard by myself? anyone done this?
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Old 04-13-2010, 07:50 PM   #12
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Quote:
Originally Posted by newclutch View Post
My dealer says $145.00 for seals and bearings for one side front x 2 if I do it myself. $290.00

Dealer says $500.00 labor each side + above parts = $1,300.00 for them to do it. Special tools to press off old and press on new. Bend over.

How hard by myself? anyone done this?
Search "hub shark". You can make a puller to get the bearing out with the hub on the car for $15 or so from home depot. Might need a 3-jaw puller (rent for free from autozone) to get the race off the hub. As well as a slide hammer (again, rent for free).

And don't buy your parts from Subaru.
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Old 04-13-2010, 08:12 PM   #13
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Quote:
Originally Posted by generalee69 View Post
That's what I've always done. Quick tap down the straights and it's all good into heavy braking zones.... not sure my competitors like it though.
I do it at the same spot coming into each braking zone, so I hope people have taken note of that.

Quote:
Originally Posted by newclutch View Post
My dealer says $145.00 for seals and bearings for one side front x 2 if I do it myself. $290.00

Dealer says $500.00 labor each side + above parts = $1,300.00 for them to do it. Special tools to press off old and press on new. Bend over.

How hard by myself? anyone done this?
Upgrade the hubs/knuckles while you're at it. Then you shouldn't have to worry about removing bearings.
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Old 04-13-2010, 09:36 PM   #14
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I agree but, it's not that cheap to upgrade for a WRX. You could do what I did and drop a complete STI drivetrain in... Was a fun project if tedious.
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Old 04-14-2010, 12:40 AM   #15
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Quote:
Originally Posted by MasterKwan View Post
It depends on what kind of tires you run. If you're on street tires, new wheel bearings will probably last a season or 2. On real R-comps, you might need to do it every couple months.

WRX's are known to have weak wheel bearings. The STI bearings are larger both front and back than the WRX ones. My comment was just suggesting that the knockback is primarily caused by the wheel bearings. The really nice thing about STI front wheel bearings is you can change them at the track in about 30 minutes if you need to.

What kind of fluid do you use?
Not all the STi bearings are bigger, the 04's use the WRX bearings.

I've been extremely lucky in my 04 STi on R-comps (Hoosier Koni Challenge)... 12 race weekends plus another 6 or 8 track days on the original wheel bearings (56k miles). Just to be safe though, I carry a spare set of front hubs with fresh bearings installed to the track (because I know it's a matter of when, not if).

To the OP on a "how to" -- http://forums.nasioc.com/forums/show...+wheel+bearing
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Old 04-14-2010, 10:38 AM   #16
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we also just did the conversion on our 04 car.... feels like a new car. really
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Old 04-14-2010, 11:13 AM   #17
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Tap those brakes with your left foot before heavy braking point, then heel-toe downshift, turn in, trail brake, power on at apex, and exit the corner. I am sure you do these things anyway, but it was worth mentioning.

This is the cheapest way to upgrade your brakes and eleviate your pad knock problems!

Seriously though, make sure your fluid is fresh and bled recently. The WRX's have poor braking feel in general, good pads help that (Carbotechs,hawks, ect.) but our consevative 2-stage brake boosters just create a poor mushy feeling all around. I have heard of people upgrading to units with more initial boost.

EDIT:

Bearing are not too bad to replace yourself. You can take the whole hub off (knucle and all) and use a simple press from harbor frieght to get the bearings and race out. Then perform the opposite, pressing the bearing and seal into the hub. Don't forget to use the good grease. Good luck!
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Old 04-14-2010, 12:23 PM   #18
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[quote=jc8587;30403816]Tap those brakes with your left foot before heavy braking point, then heel-toe downshift, turn in, trail brake, power on at apex,

I usually brake, turn in and power on well before apex and run the slip angle with throttle steer.For me trail braking is corners with slow exits, ie ; decreaceing radius, or short straight to a more importaint corner

Seriously though, make sure your fluid is fresh and bled recently. The WRX's have poor braking feel in general, good pads help that (Carbotechs,hawks, ect.) but our consevative 2-stage brake boosters just create a poor mushy feeling all around. I have heard of people upgrading to units with more initial boost.
Stopping power of my set-up is unreal, I just want to be floored until I need the brakes. MUST FIX problem, not band aid symptom
EDIT:

Bearing are not too bad to replace yourself. You can take the whole hub off ( Don't forget to use the good grease. quote]
The dealership said bearings are greased internally packing not necessary, just seals.
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Old 04-14-2010, 12:33 PM   #19
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[quote=MasterKwan;30398521]I agree but, it's not that cheap to upgrade for a WRX. You could do what I did and drop a complete STI drivetrain in... Was a fun project if tedious

I upgraded suspention and brakes and wheels and tires only for the first 104K miles. Now I have dumped more on motor than I paid for car brand new. I demand fun with no more money outlays.

You are correct "oh great Karnac the Magnificent" no new hubs
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Old 04-14-2010, 12:36 PM   #20
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Quote:
The dealership said bearings are greased internally packing not necessary, just seals.
Some people here pull the bearings apart and replace the grease with "better" grease. They claim better results.


Quote:
Now I have dumped more on motor than I paid for car brand new.
I know people who've done that and the motor lasted two track days. Just say'in... I did the complete STI swap for $7000. Find wrecked STI and start swapping. I'll bet you spent more than that on your motor alone.
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Old 04-14-2010, 01:42 PM   #21
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Quote:
Originally Posted by MasterKwan View Post
Some people here pull the bearings apart and replace the grease with "better" grease. They claim better results.




I know people who've done that and the motor lasted two track days. Just say'in... I did the complete STI swap for $7000. Find wrecked STI and start swapping. I'll bet you spent more than that on your motor alone.
I always have a smile on my face when I see someone only doing trackdays with a modded motor. Save your coin for brakes and tires..
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Old 04-14-2010, 01:54 PM   #22
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I know people who've done that and the motor lasted two track days. Just say'in... I did the complete STI swap for $7000. Find wrecked STI and start swapping. I'll bet you spent more than that on your motor alone.

My first tune was only 18lbs and an 8,000 red line. I had a $20.00 problem that took out my motor but a very well known Company stood behind their product and bought me a new built short block. This tune my tuner pulled my timing and I am only 300 hp 325 tq @ 16 lbs. 7,500 red line. I lost 25 horse but power delivery is very smooth, less raw. Pulls hard from 3500 to 6200 , oil temp never got above 190 and oil pressure was 88- 95 lbs. Exhaust temp was holding at 1,600 degrees. (on a cool 65 degree day) I also run 5 gal. of 100 oct. and 5 gal. of 93. I do not think I could be more safe. If I blow up, I will never mod again. I am overbuilt to the hilt.
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Old 04-14-2010, 02:44 PM   #23
generalee69
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Quote:
Originally Posted by MasterKwan View Post
Some people here pull the bearings apart and replace the grease with "better" grease. They claim better results.
I've had a theory for awhile now (just based anecdotally on people I've talked with) that the bearing issue is more due to the rate of impact than overall heat/force input.

I think this because it seems like people who autocross and track their WRX's and 04 STi's have more of an issue with bearing failure. The guys I've talked to have tried the high temp grease and still have problems... leading me to believe it is not solely a temperature problem.

It's like tossing the car around during an autocross generates side loading faster. The bearings can handle the load ok, but not the sudden impact of force.

So between the beating the bearing takes during an autocross and then the heat (and high loads) they see on the track is enough to cause them to fail prematurely.

Edit: There's a thread on here where a guy back East was using the piston anti-knock back springs and was pretty happy with them. I think they are relatively cheap... The caliper rebuild kits aren't too bad either. Just run cheap street pads when DD, because you'll probably go through them more quickly.
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Old 04-14-2010, 04:18 PM   #24
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It doesn't help that I've 10mm spacers in the front so the brakes will clear my cheap wheels. I usually run 5mm spacers with my good track wheels. As soon as I get them painted they will be on for the summer. I went through a few winters in Chicago with a heavey coating of brake dust so they looked terrible. I sand blasted them clean over the winter and now I need to paint them.
I stayed off the curbs last Monday because it upset the car too much.
So I do'nt think I beat on the bearings, I leaned on them pretty hard though.
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Old 04-14-2010, 04:33 PM   #25
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Quote:
Originally Posted by newclutch View Post
I know people who've done that and the motor lasted two track days. Just say'in... I did the complete STI swap for $7000. Find wrecked STI and start swapping. I'll bet you spent more than that on your motor alone.

My first tune was only 18lbs and an 8,000 red line. I had a $20.00 problem that took out my motor but a very well known Company stood behind their product and bought me a new built short block. This tune my tuner pulled my timing and I am only 300 hp 325 tq @ 16 lbs. 7,500 red line. I lost 25 horse but power delivery is very smooth, less raw. Pulls hard from 3500 to 6200 , oil temp never got above 190 and oil pressure was 88- 95 lbs. Exhaust temp was holding at 1,600 degrees. (on a cool 65 degree day) I also run 5 gal. of 100 oct. and 5 gal. of 93. I do not think I could be more safe. If I blow up, I will never mod again. I am overbuilt to the hilt.
That oil temp is too cool. You need to play with the oil weight to get it hotter. What weight oil are you running?

-Duncan
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