Author Topic: I just don't get why it won't work!! Front Brake and Fork questions (Read 10860 times)

manjisann · « **on:** October 28, 2008, 04:23:15 PM »

I have a 73 CB500 K2. When I bought it back in april-ish I took it for a ride and got about 50 mpg. It had a couple knocks in the steering, so I replaced the steering stem bearings with All Ballz tapered ones. I also had to replace the fork oil seals, and apparently when I was putting my right fork (the one without the caliper on it) back together I didn't screw the damper rod in all the way or something because when I took the front tire and brake off and pulled on that fork the bottom came off with a nice bit of oil spilled everywhere. Anyhow, I have steadily been losing mileage, and at last fill up I was getting about 22 - 25 mpg. Other than adding a 4-2 exhaust, I haven't done anything other than mess with the front end that would account for such horrible gas mileage.

I completely disassembled the forks and put new seals on them (again) and replaced the screw and washer that hold the damper to the bottom of the fork. I also put in about 3/4 of an inch of washers on the top of the springs of each fork to stiffen them up a bit ( I read about this in one of Hondamans posts.) I tightened everything down this time ( I try to only make a mistake once

) and put the forks back on and made sure they were level with eachother.

I also completely rebuilt my brake master cylinder with new parts OEM parts. While I had it disassembled, I JB welded a brass brush to an aluminum rod and cleaned the piston area of the MC real good. I also cleaned the caliper and the little groove where the rubber seal goes in the calper. I blew out all the lines and that three way junction to ensure everything was clear, and even was sure to clear the two holes in the MC bowl. I reassembled everything real careful, being sure to coat all the rubber piston parts with new clean brake fluid to get a proper seal ( except for the caliper seal, I left that dry, was this a mistake?) I got brand new EBC brake pads from Z1 that fit my bike and put those in, since the previous ones had been worn crooked.

I have now reassembled it and bled the lines so the brake level is pretty solid. With it all assembled I could maybe get the front wheel to spin one rotation. If I open the bleeder, it oozes fluid pretty good. I read where someone had a fender cause everything to go cockeyed, so I have removed my fender and put the brake and wheel back one but I still can only get 2 to 2.5 revolutions before it stops. I am at a bit of a loss at this point as to what is causing my problem. I have read a bunch of posts on the subject and even posted a few of my own, so I have a reasonably good idea of how this is all supposed to work. With the brake caliper piston pushed back and the stationary side not touching, the wheel will spin several revolutions before coming to a stop, but once I use the brake once and release it, I am back to only a couple revolutions before it stops.

So I have concluded that first, my fender is kinda bent so I need to figure a way to straighten it out, and second that my caliper piston is not retracting like it should. I assume the wheel should spin pretty freely, and then when the brake is pressed, the caliper piston squeezes against the rotor and forces the stationary pad to come in and engage the rotor. I REALLY don't want to completely disassemble the MC and everything again, as I don't know what to look for. Is this normal with new pads? I ask because this was very much like the problem I was having before that prompted me to rebuild the MC and caliper in the first place. Anyone have any suggestions?

Please forgive the lengthiness of the post, I am just trying to put in as much info that I think may be relevant as possible. Thanks for any help.

Brandon

nickjtc · « **Reply #1 on:** October 28, 2008, 04:31:54 PM »

A slightly sticking brake would account for the poor fuel consumption, but I would have thought that you would be able to tell if this was a cause because the disc would get very hot.

Unless the replacement pads are significantly thicker than stock OEM then the piston must be hanging up in its bore, somehow.

Anyone else??

scunny · « **Reply #2 on:** October 28, 2008, 04:34:22 PM »

as for your wheel not spinning freely, I would pull the caliper off and the wheel should rotate for a while not just a few turns.
how are your wheel bearings ?

HondaMan · « **Reply #3 on:** October 28, 2008, 06:35:43 PM »

Like Scunny said, or at least, adjust the space between the pad and the disc (with the adjuster screw) for the required .004"-.008" clearance, then see how it spins. Also, misalignments (minor) between the two fork legs can cause axle curve, which can bind the bearings (it doesn't take much!). Make sure both end caps are on the same way (originally the gaps were to the front, make sure the flat faces meet and tighten those before the clamping sides).

Brake bleeding: get a long (24" or more) length of tubing (I use clear) and stick it onto the bleeder nipple, and raise the end of the hose to about the height of the manifold on the steering tree, and catch the drips. Loosen the brake reservoir cap (to let air in) and crack open the bleeder nipple, then leave it set for 15-20 minutes. Watch it for bubbles, that's the drill. I've found this will bleed these brakes better than any other method. The type of master cylinder piston used will tend to pull air back up the lines if pump-and-bleed methods are used, and that ends up taking much longer.

shoemanII · « **Reply #4 on:** October 28, 2008, 08:14:15 PM »

i don't think it's that unusual for a wheel to spin a couple of revolutions before it stops (end of 3rd paragraph). take your bike out for a ride, then come to a stop using only the rear brake. if the front discs are cool, or maybe just slightly warm, you don't have a problem.

if your brakes were dragging enough to cut your MPG in half, there'd be smoke somewhere. i'd look elsewhere for that solution. .015
bobp

mrbreeze · « **Reply #5 on:** October 28, 2008, 08:52:05 PM »

After you do what everyone here has said to do...and the brake is still hanging up....clear out the tiny port in the bottom of your master cyl. reservoir. Thats what was wrong with mine.

Hush · « **Reply #6 on:** October 28, 2008, 09:02:13 PM »

Cheers for the clever bleed idea Hondaman, I was just about to bleed my 650 brakes the old way.
That idea alone should be in the FAQ's section.

crazypj · « **Reply #7 on:** October 28, 2008, 10:34:57 PM »

Make sure the pivot is completely free swinging. I've seen loads of 'sticking calipers' that were either bad adjustment or seized pivots
PJ

jason teamshralp · « **Reply #8 on:** October 28, 2008, 11:19:09 PM »

Quote from: manjisann on October 28, 2008, 04:23:15 PM

... Other than adding a 4-2 exhaust, I haven't done anything other than mess with the front end that would account for such horrible gas mileage.

Check your brakes for rubbing as stated above but, it maybe that your fuel mixture is screwed up with the change in exhaust. I know sometimes when you change exhaust you have to re-jet your carbs. I'm not an expert but just my 2 cents.

manjisann · « **Reply #9 on:** October 29, 2008, 04:33:46 AM »

Does the pivot pin come apart so that it can be cleaned an lubed, or do I just hose it down with WD40? It feels like it pivots smoothly, but I had wondered if it could be a contributing factor as well. I will also go back over all the suggestions when I get home.

Thanks a ton everyone for all your suggestions!

Brandon

crazypj · « **Reply #10 on:** October 29, 2008, 07:28:11 AM »

You have to remove 3 bolts to get it off bike.
Its pretty normal to use some 'gentle persuasion' with a hammer and drift

I usually tap 6x1mm for a grease nipple when I get them apart (I like to keep 'metric bikes' metric)
PJ

manjisann · « **Reply #11 on:** October 29, 2008, 08:56:00 AM »

It comes off the bike just fine, I was wondering how one cleans the actual pivoting part. Are you saying you can put a grease nipple in the top of it so that the grease will go into the swiveling hinge part?

Thanks,

Brandon

manjisann · « **Reply #12 on:** October 29, 2008, 09:00:23 AM »

Quote

as for your wheel not spinning freely, I would pull the caliper off and the wheel should rotate for a while not just a few turns.
how are your wheel bearings ?

Yes, with the caliper off it will spin significantly longer, several revolutions longer.

Quote

Like Scunny said, or at least, adjust the space between the pad and the disc (with the adjuster screw) for the required .004"-.008" clearance, then see how it spins.

Is this clearance between the stationary pad (the one not on the piston) and the one on the piston? I will check this with a gauge when I get home, hopefully my little feeler set goes this small

Bodi · « **Reply #13 on:** October 29, 2008, 01:49:36 PM »

You don't really need a feeler, just push "in" hard on the caliper to press the piston in. The caliper should move side-to-side a wee bit through the full revolution of the wheel, the back pad must not touch the disc.
My experience is that the drag comes from one of two things. There's air in the system somewhere - the MC pulls back a tiny bit of fluid when you release the lever, to retract the piston slightly. Any air will nullify this action, the bubbles shrink under pressure then just expand again when the fluid is pulled back. Bottom up bleeding works best for me, just using the piston as a reservoir (pumping it out with the caliper split then forcing it back in with a C-clamp). Pressure bleeders work the same way while absorbing cash for their purchase. The other problem is the caliper seal groove. It gets corroded and even a new seal won't let the piston slide freely enough. You have to go to extreme efforts to rerally clean out that groove. A bronze brush wheel on a dremel tool is the only thing I've found that works. A dentist type mirror lets you see in the groove.

manjisann · « **Reply #14 on:** October 29, 2008, 04:17:30 PM »

I have about 4 feet of clear tube. When I open the bleeder nipple, a little bit of fluid wells up at the base. I loosen the MC cap to let the air in and a small amount of micro bubbles will come out of the bleeder. I waited about 15 -20 minutes the first time, closed the bleeder, tightened the MC cap and pumped the brake handle, and the same thing happened. The wheel went from spinning freely, to only spinning a couple revolutions.

I then will open the bleeder again, and press against the caliper to move the piston back in and small micro bubbles, and some bigger ones, maybe the size of a period on the keyboard. As before, when I loosen the bleeder, maybe half a turn, a little bit of fluid wells up at the base. I am pretty sure it is not leaking from the base of the tubeing as it was pretty tough to get on. Could this be the source of all the micro bubbles, or is there just a lot of small pockets of air? I have done this 3 or 4 times now. Do I just need to keep topping off the MC and keep bleeding this way?

I have also just been emptying the fluid into a jar, this is correct right, I shouldn't be forcing it back into the piston?

I have tried several small adjustments of the adjusting screw, and it hasn't made a lot of difference.

Quote

Its pretty normal to use some 'gentle persuasion' with a hammer and drift

Are you saying to hammer the little pin out that the caliper arm pivots on?

Quote

The other problem is the caliper seal groove. It gets corroded and even a new seal won't let the piston slide freely enough. You have to go to extreme efforts to rerally clean out that groove. A bronze brush wheel on a dremel tool is the only thing I've found that works. A dentist type mirror lets you see in the groove.

I cleaned this out with a brass dremel brush and cleaner, so I am 99% sure it is clean (the one percent is because I have obviously missed something, hence my brake isn't working quite right

)

Quote

clear out the tiny port in the bottom of your master cyl. reservoir. Thats what was wrong with mine.

Already done this, so I am really sure this isn't the issue. I had read about this in another posts.

Quote

Also, misalignments (minor) between the two fork legs can cause axle curve, which can bind the bearings (it doesn't take much!). Make sure both end caps are on the same way (originally the gaps were to the front, make sure the flat faces meet and tighten those before the clamping sides).

Hondaman, I read about this in one of your other posts so I am pretty sure it isn't the end caps. I also don't beleive the forks are tweaked, as I can take a straight rod approx the same diameter as the axle and put it in there. I then put a level on it, and when the forks are pointed as if you are riding straight it shows level. Does this rule out tweaked forks?

Quote

Posted by: scunny
Insert Quote
as for your wheel not spinning freely, I would pull the caliper off and the wheel should rotate for a while not just a few turns.
how are your wheel bearings ?

Yeah, it will spin quite well. I think my bearings need to be replace, and that is on my to do list in spring, but I am pretty sure this isn't the major problem.

Thanks again for everyones help!! I can take pictures if anyone wants.

Brandon

mlinder · « **Reply #15 on:** October 29, 2008, 05:19:01 PM »

you have to clear the bubbles out. Some do it by just continuing to pur dot3 into the MC and bleeding the system. I do that a bit, but then i just tighten everything up and go ape#$%* fast on brake lever, pulling it in and letting it out as fast as possible, for 15 minutes to half an hour. This moves the air bubbles into the MC. Be sure to stop and look in the MC every couple minutes, as the air moves up, dot3 level goes down... If you dont have enough dot3 in there, you can start pumping air back in.

manjisann · « **Reply #16 on:** October 29, 2008, 05:39:05 PM »

Ok, it sounds like I am on the right track, just more air in there than I thought. I also took apart the little pivot point and put it in my drill press and polished it up a bit and am installing a grease nipple, so that will get rid of that variable.

Sorry if this is a dumb question, but as I was out working on my bike I wondered. When putting the front wheel on, to ensure I don't tweek, the axle or forks, should I lower the bike onto the wheel? I have been just putting my foot under the wheel and lifting it that way and then tightening things down like that. Is this wrong?

If anyone else has any suggestions or comments, please feel free. Thank you again to everyone who has already replied.

Brandon

mrbreeze · « **Reply #17 on:** October 29, 2008, 06:46:46 PM »

OK...you have cleaned the groove where the seal in the caliper lives. You have cleared the tiny port in the reservoir (did you clean the tiny one? There are 2 ports.Clean them both.Especially the tiny one.Use a fine wire or guitar string). With the front wheel up in the air....turn the wheel and turn the caliper adjusting screw in till the wheel locks.Back it off (I believe a quarter turn). The wheel should spin freely.Hit the brake and release it .It should still turn freely.If not....open the bleeder on the caliper.If it now moves freely....you haven't cleaned the compensating port out good enough.

HondaMan · « **Reply #18 on:** October 29, 2008, 07:10:09 PM »

Quote from: Hush on October 28, 2008, 09:02:13 PM

Cheers for the clever bleed idea Hondaman, I was just about to bleed my 650 brakes the old way.
That idea alone should be in the FAQ's section.

I'm just basically lazy...

manjisann · « **Reply #19 on:** October 30, 2008, 11:29:30 AM »

Quote

With the front wheel up in the air....turn the wheel and turn the caliper adjusting screw in till the wheel locks.Back it off (I believe a quarter turn). The wheel should spin freely.Hit the brake and release it .It should still turn freely.If not....open the bleeder on the caliper.If it now moves freely....you haven't cleaned the compensating port out good enough.

I have opened the bleeder and it will ooze out, but when I spin the wheel it is the same, only about 2 revolutions, and no noticible increase in brake fluid coming out of the bleeder.

I am beginning to think I must still have air in my lines, so I am going to try what Mlinder said and pump the brake for a bit with everything tighened up. If that doesn't do it I will kind of alternate between Hondamans method and Mlinder's and see if I can get the air out of both ends. Hopefully in an hour or two I will be posting about my success!

Brandon

manjisann · « **Reply #20 on:** October 30, 2008, 11:32:13 AM »

Oh, Mlinder, I read about your accident and wanted to say I am glad to read you are back and on the mend! Thanks for taking the time to give me your advice.

And again, thanks to everyone else, this really is the best forum for motorcycle wisdom!!

Brandon

mlinder · « **Reply #21 on:** October 30, 2008, 11:37:58 AM »

Did you replace the litte rubber seal in the groove of the caliper? Old ones can cause the piston to not retract all the way. And did you adjust the width? It's the bolt that is down there on the calipers.
Remember, without riding, the disc pistons will be touching the disc after it's used. You should ride around the block a couple times, use the back brake to stop in your driveway, then put the front up again and spin the wheel. See how it behaves after that.

crazypj · « **Reply #22 on:** October 30, 2008, 11:48:20 AM »

Quote from: manjisann on October 29, 2008, 08:56:00 AM

It comes off the bike just fine, I was wondering how one cleans the actual pivoting part. Are you saying you can put a grease nipple in the top of it so that the grease will go into the swiveling hinge part?

Thanks,

Brandon

Just drill and tap the alloy , somewhere around middle, at slight angle outwards so it's easy to get grease gun on it
PJ

manjisann · « **Reply #23 on:** October 30, 2008, 12:53:17 PM »

Quote

Did you replace the litte rubber seal in the groove of the caliper? Old ones can cause the piston to not retract all the way. And did you adjust the width? It's the bolt that is down there on the calipers.

Yes, that was one of the first things I replaced when I was trying to track down what was happening.

Quote

Just drill and tap the alloy , somewhere around middle, at slight angle outwards so it's easy to get grease gun on it
PJ

Did it last night and reassembled today with new rubber seals. It slides pretty smooth now.

Quote

Remember, without riding, the disc pistons will be touching the disc after it's used. You should ride around the block a couple times, use the back brake to stop in your driveway, then put the front up again and spin the wheel. See how it behaves after that.

Ok, will do.

One more question. After I have tightened my bleeder, and have pumped the brake a bit, there is a small amount of brake fluid around the base of the bleeder. I am really pretty sure it isn't leaking from the clear hose I have attached to catch the stuff, so I can only assume it is coming up from the threads. I assume this is not normal right? Could that also be contributing to the piston not retracting as it should?

Thanks again all, I'll get her reassembled and ride her around the block a few times and then let you know what happens.

Brandon

SKTP · « **Reply #24 on:** October 30, 2008, 02:37:14 PM »

My front brake is acting much the same way (1978 CB750K)...I gave up and my bike's at the mechanic's right now...is there and after-market caliper option? It really seems to be a crappy front brake design...

News:

Author Topic: I just don't get why it won't work!! Front Brake and Fork questions (Read 10860 times)