Author Topic: Front Brakes Stick and won't Retract  (Read 27127 times)

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Rainmaker

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Front Brakes Stick and won't Retract
« on: November 18, 2006, 09:20:04 am »
There are many posts all around the SOHC forum that talk about front disc brakes that stick or do not retract when brake lever is released. The evidence is obvious.  The bike is hard to push around or you sense the drag when coming to a stop.  Another symptom is the front disc rotor gets very hot and discolored.  This article attempts to consolidate all the tips, tricks and techniques that took me a considerable amount of time searching throughout the forum and putting to practical use.

*  In most cases purchasing an aftermarket front disc brake rebuild kit and replacement pads will be the best way to fix the front brake sticking problem.
*  If you want to trouble shoot it as is then try these various techniques:
1.  prop bike up on main stand.  Have your girl friend or wife sit on back part of the seat. If she's heavy enough, this should raise the front tire off the ground.  (I'd avoid any comments to her at this point). Alternatively, use a small jack and a piece of 1x board to gently jack up the bike at the exhaust pipes just enough to raise the front wheel off the ground. If it doesn't free spin or is stuck then you have the sticking brake problem.
 2. first try to adjust the swing arm left to right tolerance.  Use a 10mm wrench to loose nut and turn slot screw in or out until front tire moves freely. If that doesn't do it then your in for a bigger job.

<== 10mm nut for disc caliper brake swing arm on right......14mm nut for removing caliper on left

3. loosen (but don't remove yet) 10mm nut on brake line going into the front disc brake caliper. Catch any dripping fluid and wipe off painted surfaces.
 4. remove both 14mm bolts that clamp the caliper left side and right side sections to the disc brake swing arm.
 5. finish removing 10mm brake line fitting nut and drop inside and outside halves of the caliper.
 6. from the left side of the caliper, empty out brake fluid from inside piston housing through the brake line hole.
 7. remove brake pad (puck). If it's stuck there may be your problem.
 8. wrap the left side of the caliper in a towel and on your work bench with the piston facing down, blow a short burst of compressed air into the brake line hole. Be carefull here. There are horror stories about blowing the piston out of the housing at high speeds break things along the way. Save your face at all costs....wear your helmet with shield down  ;D The gentle application of compressed air should force the piston out and a bunch of messy brake fluid as well.  If it doesn't come out with air you can try the grease gun method which is more safe but leaves you with a yuk of a mess to clean out of the caliper housing and passages (see Stuck Caliper Piston in Tips and Tricks section).  Another method I've used in extreme cases where the brake has heated up to very high temperatures due to sticking, is heating the outside of the caliper housing with a propare torch. Get it hot but not hot enough to warp the housing or melt the silicon-rubber seal inside. Use welders gloves and once good and hot, it should blow out with compressed air. I've seen very badly corroded calipers where I had to use both heat and a rubber mallet to tap the piston out.
9. once the piston has popped out, check the exterior sides for pits.

<=== clean out this groove to make sure the ring seal seats flush inside.

11. Check the groove for deposits and corrosion.  Likely there will be something there.....just enough gunk to raise the seal high enough outta the groove to prevent the piston from retracting and causing the sticky brake symptom.
12. you can use a dremel tool with a brass rotory brush to clean out the insides of the groove.
13. clean the surface of the inside edge of the caliper where the brake pad/puck would sit. Use 800 grit w/d sandpaper.

<== clean this surface to prevent puck / brake pad binding.

14. some of us reuse the old pads if they are still reasonably good. Regardless, if you're going to use your old ones or new, turn the puck around backwards to make sure the pad material fits inside the groove you just polished.  I have found that sometimes the pad has distorted to the point where it catches on the inner surface of the caliper hence causing the sticking problem.  If it doesn't fit without binding, use a file and remove material from the pad until you can slip it in and turn it 360 degrees without binding.

<== insert puck / brake pad backwards to check for clearance.

15. Once you've got your surfaces clean, you're ready for reassembly. Coat your new rubber seal with brake fluid and insert inside the ring groove of the caliper.  May sure it seats correctly and is not twisted (that would be hard to do but you never know). Apply a bit more brake fluid around the ring seal and insert your new or cleaned up piston back inside the caliper. The solid end goes in first. It should slide in fairly easily by applying pressure with both thumbs pushing it inside.
16. Install new or reused brake pad on top of piston metal end in first. If you have squeaking front brakes, this is the time to put a dab of brake anti squeak between the piston and the puck (this works for me). Make sure you use just a bit and don't get any on the surface you just cleaned.
17. Inspect the inside caliper half to make sure the pad wear is within tolerance (note the red line). Now is the time to clean up that half prior to re-assembly.
18. Reassemble in reverse order, reconnect your brake line and fill your master cylinder 1/2 way with brake fluid.
19  Bleeding front brakes is another whole topic with dozens of ways to do it best. I've tried a lot of them including using one of those Mighty Vacuum bleeders. I find that I spill more brake fluid if I'm trying to recover the old fluid so I just bleed letting it run out the bleed screw down the caliper and into a plastic pan. If you wipe down the fluid off the caliper face with mineral spirits, the paint isn't effected.  My method: Leave M/C cover on loosely and pump slowly at the brake handle.  Hold pressure on the handle and open the bleed screw. Don't let go of the handle before re-tightening bleed screw. Repeat over and over until no more air comes out just fluid.  Check your fluid level in the M/C between each cycle. When only fluid comes out and you have enough brake resistance at the handle, tighten down bleed screen and top off M/C fluid and tighten cover.
20. Now the test....with the front wheel off the ground, you should have free spin on your wheel.  Apply the brake and it should stop. Release the brake and you should have free spin again. If you need to reseat the pads.......take a thin blade putty knife and tap that in between your rotor and brake pad on the outside. You may need to readjust the swing arm to find that perfect spot that keeps the pads from contacting the rotor.

Note: I have inquired via the SOHC forum about front brake caliper piston differences between the years.  Apparently, the piston part number for CB750F '76
CB750A '76, CB750A '77 - '78, CB750K '77 - '78 is different from the earlier years. Keep that in mind when ordering.  However, in what seems like an exception to the rule, my very stock and unmodified 1978 CB750K has the same sized pistons that are used in all the early year SOHC CB750Ks. 
 


Rainmaker

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Re: Front Brakes Stick and won't Retract
« Reply #1 on: November 18, 2006, 09:25:29 am »
I was hoping the pictures would line up inside the text but I guess I don't know how to do that. The 'Post a New Topic' dialogue wasn't too friendly (at least for me). 

USN20

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Re: Front Brakes Stick and won't Retract
« Reply #2 on: November 18, 2006, 10:32:02 am »
Nice write-up for those pesky Honda brake calipers that we sometimes encounter!   ;)

Offline eurban

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Re: Front Brakes Stick and won't Retract
« Reply #3 on: November 18, 2006, 11:44:16 am »
The typcial SOHC master cylinder has a two holes in the bottom of resevoir.  One is relatively large and is easy to see.  The second pin prick size hole is easy to miss and can get clogged very easily.  If this hole is clogged or partially blocked it will keep the hydraulic system from relasing pressure properly when the brake lever is released.  This will cause the brakes to stay locked or to drag.  Most of those 30+year old master cylinders are in need of a rebuild . . . . .

Offline mrbreeze

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Re: Front Brakes Stick and won't Retract
« Reply #4 on: November 18, 2006, 11:47:29 am »
Before doing anything,you should make sure the tiny passageway in the bottom of the reservoir is not blocked.If it is,your brake will not release.Take the cap off of the master cylinder.You should put a sheet of plastic underneath before doing this to prevent spilling brake fluid on painted surfaces. Down in the bottom of the reservoir are 2 holes. The tiny one (compensating port I believe it is called) is the one you after. Take a #1 guitar string (the real fine one) and run it in & out of that hole.Then gently pump the lever to see if you get any action.Don't reef on the brake lever with the cap off or you will squirt brake fluid all over. This may or may not be the cause of your problem but is the easiest thing to check first.
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Offline Hockers Choppers

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Re: Front Brakes Stick and won't Retract
« Reply #5 on: November 19, 2006, 09:08:14 am »
If you take the system all a part and clean it VERY well. I recommend putting dot 5 brake fluid back in it. It won't corrode the inners up like dot 3 does. and you can pour it all over the bike and it won't hurt a thing!!
The thing about common sense is that, it's not that common.

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Offline ElCheapo

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Re: Front Brakes Stick and won't Retract
« Reply #6 on: November 20, 2006, 09:00:36 am »
The questions come to mind:

Is your rotor thick enough?
Are your pads worn down to the last 10%?

I ask these because these two combined will make the piston stick in its bore as it gets over extended.. 8) Just an idea. I hope you find that it is something else.
Contact me for affordable rotor drilling services at $55 each rotor. Same day service on CB750/CB500/CB550 rotors. Next day on everything else.

Rainmaker

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Re: Front Brakes Stick and won't Retract
« Reply #7 on: November 26, 2006, 11:05:24 am »
El Cheap-o: Responding to your input. I agree with your tips too and consider them further things to consider given a sticky brake scenario.  Please realize that this article began as a help article and only a hypothetical problem.  So being the article initiator, I'm adding the following things to check when brakes do not retract.

1. check tiny pin-hole in that brake's master cylinder. There are two; small one and a bigger one. Simple test to see if that was causing the sticking problem would be to open the bleader valve. If the brakes release, it could be your M/C. Unclog the tiny holes at the bottom of the MC by removing all the fluid and run a guitar string end (high E works) through the hole to the bottom cleaning out gunk.

2. Check to make sure Disc Rotor meets thickness tolerance (anybody know what that is?) and that disc pad is 10% or better. Usually there is a red line on the pad(s) that indicates minimum wear mark.

3. Avoid piston pitting by draining entire system and replace with DOT5 brake fluid.

Offline Hockers Choppers

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Re: Front Brakes Stick and won't Retract
« Reply #8 on: November 26, 2006, 01:07:15 pm »
dot 3 and 5 do not mix, So make damn sure the 3 is all out first. I take the system completly apart and clean all the parts with brake clean. All the rubber parts will need extra care. Alcohol works great. While you have it apart, I'd replace the brake lines with stainless braided lines. There are some on ebay cheap ;). The minumum thickness should be stamped on the rotor.
The thing about common sense is that, it's not that common.

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Offline Drewery

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Re: Front Brakes Stick and won't Retract
« Reply #9 on: December 11, 2006, 09:11:32 am »
I had difficulties for months (maybe even a year) with my front disc sticking. I tried everything to figure out why but without success. Then one day when I replaced the fork oil I realized that I had uneven levels in the forks. I have straight handle bars and it was always difficult to get the oil in the forks without spilling some of it without taking the forks right off the bike. Once I got the levels exactly to spec - no more sticky front brake.
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Offline kuyarico

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Re: Front Brakes Stick and won't Retract
« Reply #10 on: December 11, 2006, 11:50:30 am »
I had difficulties for months (maybe even a year) with my front disc sticking. I tried everything to figure out why but without success. Then one day when I replaced the fork oil I realized that I had uneven levels in the forks. I have straight handle bars and it was always difficult to get the oil in the forks without spilling some of it without taking the forks right off the bike. Once I got the levels exactly to spec - no more sticky front brake.

How exactly does uneven levels of fork oil cause a brake to stick?

Offline Hockers Choppers

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Re: Front Brakes Stick and won't Retract
« Reply #11 on: December 11, 2006, 02:49:11 pm »
I think he meant the tubes were at different heights in the triple clamps. Causing the rotor to bind in the caliper? Front wheel bearings must be pretty loose also to do that.
The thing about common sense is that, it's not that common.

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phylo101

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Re: Front Brakes Stick and won't Retract
« Reply #12 on: December 12, 2006, 02:27:43 pm »
Hi all. Unfortunately, when the Forum format changed a while ago, my posts on this subject went too. I've riddent the same K7 for 16 years now, including three years when it had to be pressed into service for 9 hours a day despatching. There are a number of little tweaks that eradicate this problem ENTIRELY and also greatly improve the braking of the standard system - with no miracle cures required.

The first is the discovery that MOST aftermarket brake pads WILL bind no matter what cleaning regine is applied to the caliper....for the VERY simple reason that while they may be manufactured to the correct tolerances - THEN the factories apply that thick gloopy paint to them! I've tried every bradn of brake pad under the sun, and discovered that about 90% suffer from this problem - including sadly the BEST pad for regular high-speed use that will NOT wear your rotor prematurely, the EBC either "organic" or with sintered bronze added.This is the pad of choice here in Ireland/UK, which as you know has a rotten climate! So as well as very longlasting, and preserving your rotor - gives excellent wet-weather performance.

BUT to make it, and many other perform properly with NO binding - you have to remove all trqaces of paint from around the edge of the "sliding" pad in the piston side. Dress down with a file then polish with wet-and-dry paper, and don't forget the little groove as well! You'll know this is a correct fit when you can insert the pad, turn the caliper half upside-down....and it falls out!

Now, assemble the whole caliper on the bike "dry" - you'll find out what I mean by that in a minute. loosen off the adjuster bolt for the tension spring....and rattle the caliper in your hand! Nice and loose? now, tighten slowly until there's JUST enough clearance for it to still rattle a fraction in your hand as you wobble the caliper. Tigten the locknut.

Now, disasemble the caliper again, and smear a LITLE brake-friendly grease (Girling used to do this in little tubes) or Copaslip around the outside edge of the active pad, the area youve just cleaned of paint. Alternatively, you cnan smear it around the sides of the pad's housing in the active caliper half. Reassemble, fill with fluid and bleed as normal.

You will have a brake that doesn't rattle above the noise of the engine, and doesn't bind.

Now, the miraculous cure for bad braking, whihc however may persist....

Notice how slack the lever is in your hand? there seems an awful lot of lever play before the brake bites? In fact if you wobble the lever back and forth in your finger and thumb you find half its travel is taken up before it bites?

Remove the lever from the master cylinder. Take a small copper coin and dress the edges until its a loose fit up in the round hole where the master cylinder piston is, and would fit between the "heel" activating cam part of the lever and the top of the piston. Reassemble and pump the lever a few times. See how the slack has gone? and the lack of clearance now is the coin's OWN way of not floating around! There should however still be a LITTLE free play left; if there isn't disassemble and dress one face of the coin down slowly on a piece of flat wet-and-dry. Reassemble.

P.S. you CAN if you want lube in there with Copaslip or brake-fiendly grease, but its not necessary - the copper coin will be "self-lubricating"!

IF you do all of these in association with a stainless braided brake hose, you will have a two-finger brake that is also perfectly controllable and progressive. A LOT of the lack of feel of these old brakes is actually down to you having to force the pads onto the rotor AGAINST THE BINDING which does after all affect the pad in BOTH directions!!!! A lot of folk forget that!

A final warning - get used to you new brake! It will be VERY effective!!! Make sure your front tyre is decent quality and "sticky", because the brake will now test it to the limits of adhesion, something you'll not expect from a Honda Four brake.

Regards, Phylo

Offline CrisPDuk

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Re: Front Brakes Stick and won't Retract
« Reply #13 on: December 25, 2006, 08:48:00 pm »
Instead of using compressed air (very dangerous), or a grease gun (very messy) to force the piston out of the caliper body, why not just use the brake lever? If you remove the two bolts holding the caliper halves to the pivot arm the caliper body will be free to move away from the disc face as you work the brake lever. Continual working of the lever (whilst checking the fluid level) will eventually cause the pad, then the piston to pop out. In my case, accompanied by a huge accumulation of road crud that was causing the edge of the pad to stick to the caliper bore!

My compensating port on the MC was also blocked, that one took a while to figure ???

Whilst we're on this subject, how the hell is a person with normal sized hands supposed to get the circlip out that retains the MC piston? Especially after it's been sat there in all weathers for nearly 30 years :(
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Offline Terry in Australia

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Re: Front Brakes Stick and won't Retract
« Reply #14 on: January 31, 2007, 02:59:57 pm »
Alcohol works great.

Very true Hocky, I've been drinking a lot of alcohol this week due to the frustration abounding from my twin disc conversion.

So far I've changed two calipers, (bead-blasted, new seals, and new pads) and 3 master cylinders (all of which came off bikes with brakes that worked fine) and each time I think I've got it fixed, I come back with a smoking disc.

Tonight I'm gonna change the fluid (again) with dot 5, strip and re-clean the calipers, remove any paint on the edges of the new pucks which may be contributing to them perhaps binding in the calipers, modify the hole in the swingarm so that the screw and spring can be fitted,(this is a twin disc conversion on a set of K3-K6 forks) and if none of the above works, I'm gonna insure it and burn the bastard! Ha ha, Cheers, Terry. :)
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Offline Hockers Choppers

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Re: Front Brakes Stick and won't Retract
« Reply #15 on: January 31, 2007, 03:46:29 pm »
Yes Terry, These bikes are #$%* on the liver!!!! :-\ :-\
The thing about common sense is that, it's not that common.

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Offline sandcastcb750

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Re: Front Brakes Stick and won't Retract
« Reply #16 on: January 31, 2007, 05:49:46 pm »
I have read the posts about stuck front disks. I agree with all, however, I find one big culprit.

The brake pad near on the piston side is stuck in the caliper. I used hydraulic pressure fron the master cylinder to carefully push the brake pad out. Being careful not to force the piston out. I removed sufficient material to allow the pad to drop into caliper. Then the problem went away.

The piston / force, I believe, causes the seal to rotate and allow the outward movement. Pits in the piston may cause leaks. Movement is short.


Offline Terry in Australia

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Re: Front Brakes Stick and won't Retract
« Reply #17 on: February 01, 2007, 03:15:02 am »
Yep, it seems that the pad sticking in the caliper body's main cause is insufficient gap between the pad and the caliper, I confirmed that the pad was indeed stuck in mine, so I tapped it out, then used the MC to pump the piston right out, cleaned the bore, coated the seal with brake fluid and reinstalled the piston, cleaned the pad backing plates (I did both calipers) and removed all traces of paint off them, coated the outside edges with a thin smear of copper-grease and reassembled and bled them.

They now seem a lot better, but it was 9 pm and getting dark (even though it was still a pleasant 80 deg F outside) but as my ice was melting in the jug of JD and coke on my bench, I retired inside for the evening. Tomorrow, I'll take it for a blast and see if I've had a win, ha ha! Cheers, Terry.  ;D 
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Re: Front Brakes Stick and won't Retract
« Reply #18 on: February 06, 2007, 06:49:08 am »
I had a similar problem with the fit on the pads.  Just needed to increase the the size of the half round recess for the locator pin and pad quit hanging.  Dremel tool with small round grinding stone works great.

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Re: Front Brakes Stick and won't Retract
« Reply #19 on: March 24, 2007, 03:44:01 pm »
Heres a tip that could save you a lot of time and money.  Before you go out and spend a bundle on trying to fix your front brakes take a ride at around 20 mph and stand up, lean over the front of the bike and look at your tire.  If you notice even a tiny wobble in your tire that means your rim is out of shape.  When you hit the brakes with an untrue rim it will eventually seize up your brakes.  So even if you rebuild them they may work for a month or so but eventually the same thing will happen and you'll be back at square one.  I know this from having this exact problem on my 81 650c.  My rim was bent when the jackass tire guy down at my local cycle shop put on a new tire for me.  I rebuilt my brakes twice before figuring out the problem.

Offline Terry in Australia

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Re: Front Brakes Stick and won't Retract
« Reply #20 on: March 24, 2007, 10:48:40 pm »
Heres a tip that could save you a lot of time and money.  Before you go out and spend a bundle on trying to fix your front brakes take a ride at around 20 mph and stand up, lean over the front of the bike and look at your tire.  If you notice even a tiny wobble in your tire that means your rim is out of shape.  When you hit the brakes with an untrue rim it will eventually seize up your brakes.  So even if you rebuild them they may work for a month or so but eventually the same thing will happen and you'll be back at square one.  I know this from having this exact problem on my 81 650c.  My rim was bent when the jackass tire guy down at my local cycle shop put on a new tire for me.  I rebuilt my brakes twice before figuring out the problem.

Why is that mate? The disc is mounted on the hub, not the rim, so if the rim is bent it shouldn't affect the "true-ness" of the disc? I've owned and ridden plenty of old bikes with wobbly rims, with no brake problems at all. Cheers, Terry. ;D
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Re: Front Brakes Stick and won't Retract
« Reply #21 on: March 25, 2007, 12:05:35 pm »
Well im no expert and this is just a theory.  But at high speeds i believe the wobble in the rim in transfered to the rotors as well.  I am pretty sure of this seeing as how after rebuilding my brakes twice i finally replaced the rim and all is well.  But again its just something to check and im no expert.

Offline clarkjh

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Re: Front Brakes Stick and won't Retract
« Reply #22 on: March 25, 2007, 04:18:43 pm »
Well im no expert and this is just a theory.  But at high speeds i believe the wobble in the rim in transfered to the rotors as well.  I am pretty sure of this seeing as how after rebuilding my brakes twice i finally replaced the rim and all is well.  But again its just something to check and im no expert.

Did you just replace the rim or the whole wheel assembly?  If the whole assembly you might have had bad bearings that got replaced with the rim.  If just the rim, then something wasn't setup correctly when put together.

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Offline CrisPDuk

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Re: Front Brakes Stick and won't Retract
« Reply #23 on: March 25, 2007, 06:57:30 pm »
I can see where 81cb650C is coming from with this. I've never experienced it on a bike, but we have hd the situation on the rally car where we've bent a wheel at the rim, and the vibration created is transferred back through the hub to the rotor. Swap the wheel at the end of the stage and all is well again. Apart from us now owning another £100 worth of scrap aluminium ::)

In our case It's usually caused pad knock-off, rather than stick though, which is 'interesting' when you're on a dirt track, pulling nearly 100mph, between two rows of trees and there's a 2nd gear corner rapidly approaching :o
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81cb650C

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Re: Front Brakes Stick and won't Retract
« Reply #24 on: March 26, 2007, 04:22:48 pm »
Well im no expert and this is just a theory.  But at high speeds i believe the wobble in the rim in transfered to the rotors as well.  I am pretty sure of this seeing as how after rebuilding my brakes twice i finally replaced the rim and all is well.  But again its just something to check and im no expert.

Did you just replace the rim or the whole wheel assembly?  If the whole assembly you might have had bad bearings that got replaced with the rim.  If just the rim, then something wasn't setup correctly when put together.

James