Author Topic: Caliper Repair for a dry system. (Read 8402 times)

schmidbc · « **on:** April 17, 2005, 08:08:25 PM »

After a lot of work I'm entering the home stretch. However, I cannot seem to get the front caliper on my '76 CB750f-1 to come apart. I'm hesitant to force it too much for fear of damaging the piston or any other sensitive (...expensive) internal part.

The system is dry and has been for a number of years. Please help! How can I disassemble this unit to rebuild it?

n9viw · « **Reply #1 on:** April 17, 2005, 08:20:00 PM »

The first time the piston seized on my '76 550k (came to me seized, actually), I filled the MC, unbolted the caliper from the arm, and pumped away until the piston came out. I dressed the piston and cylinder with 400-grit wet-dry sandpaper, cleaned out the gasket channel, and put it back together.
The second time it seized, it had sat for 2 or 3 years and the seals in the MC were toast, so that route was out. I removed the caliper completely, and used a rubber-tipped blow gun on my 120PSI air compressor to blow air into the brake line port. Bruised my palm, but the piston came out! Yee-owch. Dressed it out the same way, but put in a new gasket this time. That was two years ago, and it's still going strong.
I think the trick to these systems is, although they weren't originally outfitted with it, the use of DOT-5 fluid. It's non-hydroscopic, so you don't have to worry about moisture corroding the inside of the cylinder. You have to make sure you get EVERY trace of DOT-3 fluid out of the system before you put in the new stuff, because the two aren't compatible, I think the DOT-3 causes the DOT-5 to degrade.

Gordon · « **Reply #2 on:** April 17, 2005, 08:24:59 PM »

Are you having trouble getting the two pieces of the caliper separated, or is the problem that the piston is stuck inside the caliper?

Gordon

kghost · « **Reply #3 on:** April 17, 2005, 08:35:49 PM »

Remember DOT-5 is silicon based. Better have good rubber or it will leak. On the plus side the DOT-5 just makes the paint shine instead of like DOT-3 where it eats it.

schmidbc · « **Reply #4 on:** April 17, 2005, 08:50:25 PM »

The two halves of the caliper come apart easily. The piston is stuck inside the caliper with what's left of the brake pad still attached.

If I do go ahead with DOT 5 what's the best way to ensure the system has been flushed of the DOT 3? Just bleed it like mad?

kghost · « **Reply #5 on:** April 17, 2005, 09:59:16 PM »

Naptha

cbsevenfifty · « **Reply #6 on:** April 18, 2005, 02:23:28 AM »

Try putting a grease nipple into wear the brake fluid pipe goes in (leave the bleeder nipple in) and pump some grease into it.Worked for me a couple of times.

Bob Wessner · « **Reply #7 on:** April 18, 2005, 03:37:23 AM »

I second the grease gun approach, worked like a charm for me. You have a good cleaning to do afterwards, but you're going to clean it all up anyway.

Quail "Owner of the comfortable k8" · « **Reply #8 on:** April 18, 2005, 07:03:13 AM »

I you were my paying customer I would first drain gravity bleed then put in the dot five, then flush with methel alcohol if you feel the master cones are going dry add more dot five. Gravity drain flush with dot five and bleed. 100 overkill and has never failed. The way I do it for me : Gravity drain add dot five pump a can through. Go in house. Come out of house look at leaks convert back to dot 3 go back in house watch the rest of CSI. My point: you can over do anything but if time and money are not a problem do it right.

SCJIM · « **Reply #9 on:** April 18, 2005, 08:00:28 AM »

--------------------------------------------------------------------------------

i speak from experience here so here goes...

I've had to rebuild my front breaks completly.

first: remove the calipers and pull out the pistons

THE WAY I DID THIS WAS WITH A PAIR OF LONG HANDELED PLIERS AND A VICE.
I GRABBED THE EDGE OF THE PISTON WITH THE PLIERS AND SPUN IT
UNTILL IT WAS SLOWLY BACKING OUT. WORKING IT BACK N FORTH
THE SEAL ON THE INSIDE OF THE CALIPER HAD ADHEARED TO THE SIDES OF THE PISTON
ON THE FIRST TWIST I FELT THIS BREAK LOOSE THEN AFTER IT WAS EASYER TO MOVE.

keep track of what parts came from what side. better yet do one side at a time. in the caliper theres a single rubber seal try to remove without dammaging it. or if it is already go get a caliper rebuild kit. you will need a cylinder hone to smooth off the inner walls of the caliper.
second: youll need to get some 1000/2000 grit emory cloth. lay emory cloth on a table and with a fiew drops of oil on it, rub the piston on the emory cloth until the surface is smooth all the way around. ""DO NOT JUST RUB IN ONE SPOT OF THE PISTON!"" keep rotating the piston to keep the sanding equal.

third: replace the inner seal into the caliper "new or old" and coat the piston and inside of the caliper with a little motor oil. press in the piston 3/4 of the way back into the caliper. next replace the boot cover to the piston and attach to caliper. now compress the caliper all the way

fourth: reassemble the calipers on the forks

fifth: ""BLEEDING"" attach a clear tube about 19 inches long to the bleeder nut on top of the 10mm wrench that you will need to open n close the nut with. "box end my pref." drop the other end of the tube into a jar or cup of break fluid. make sure the end is submerged in the fluid.

now fill the master cylinder and begin...

open nut, squeeze break, close nut, release break.

you will see the bubbles move slowly, but be patient.

repeat untill ALL you can see moving in the tube is fluid.

now do the other side the same way.

have fun.

Jim in South Carolina

rob · « **Reply #10 on:** March 16, 2006, 08:33:48 PM »

I've removed a siezed piston by hooking it directly to the master cylinder and using brake fluid to pump it out, worked like a charm. I've also gone to the gas station and held the air compressor up to the brake line port, listen to n9viw's advice: the piston comes out like a rocket! If your worried about damaging the piston, I would say that using the master cylinder to pump the piston out is the way to go: you'll be lubricating things with brake fluid, and moving the piston out at small increments, and then not blasting it out when it finally comes. Just be ready to clean up all the fluid.

To comment on SCJim's advice, the "open nut, squeeze break, close nut, release break " of bleeding the brakes is exactly the method that I typically used. The other day I was bleeding my brakes with my brother, who is an automotive mechanic, and he said that on cars they use a method of, "squeeze several times (4-10), then hold them squeezed. Open the nut (quick pause), close the nut. repeat." It did appear that doing it this way seemed to get the air out faster than the other way.

Also, since your taking your brakes apart anyway, inspect the piston seals, pads and any other replaceable while your in there. Easier to just rebuild your brakes once right than having to do it frequently.

Hope the rebuild goes well,

Rob

techy5025 · « **Reply #11 on:** March 16, 2006, 08:59:07 PM »

I second (third?) the recommendation on Dot 5. We had a long thread on this a while back
and no one could put forth a reason NOT to use it.

Also when it comes time to bleed the brakes, they make a replacement for the bleed
fitting that has a one way check valve in it. You back the fitting off one or two turns
and then proceed to squeeze the brake level as you normally do. The check valve
will only let fluid out and not air in so you don't have to do the tighten/loosen bit. When
all the air is out you re-tighten the fitting and it acts like a normal fitting.

I would toss the pads regardless of how good they look. Mine had brake fluid embedded
that greatly reduced their effectiveness....hard to tell by looking. You need to coat around
the piston with silicon grease when you reassemble the caliper to avoid this.

Good luck,

Jim

crazypj · « **Reply #12 on:** March 16, 2006, 10:58:42 PM »

If you want a reason not to use dot 5 think of this. Its hydrophobic, yes? where does all the condenstion your going to get go? to the lowest point. destroys the caliper after a few years unless you dismantle and flush ever year or so ( I found out the hard way that it isnt fit and forget) Could always blame the British weather and my riding style I guess
PJ

techy5025 · « **Reply #13 on:** March 16, 2006, 11:18:50 PM »

Not sure exactly what you mean. Dot 3 absorbs and retains moisture...Dot 5 (silicone) does not.

How can moisture get past the fluid to the bottom on the caliper? Are you saying past the ring
seal in the caliper?

Jim

TwoTired · « **Reply #14 on:** March 17, 2006, 01:18:03 AM »

The process works like this.
Humidity (water) in the atmosphere.
Each time you open the master reservoir to check fluid level, air gets in.
When the temp inside the master reservoir falls, the water condenses out (just like the outside of the beer bottle).
Since water is heavier than DOT 5 and doesn't mix, it collects at the bottom of the fluid system (the caliper).
The oxygenated water corrodes metals.

I thought systems designed to use DOT 5 had sight guages for this reason. You only open the system to add needed fluid and even then a rubber diaphram on the cover removes all or most of the air that enters the reservoir during the maintenance proceedure.

Cheers,

eldar · « **Reply #15 on:** March 17, 2006, 07:39:16 AM »

Well dont most of us usually replace our brake fluid every spring? If you bleed things good and have a good seal and use the silicon brake grease, you should not have a problem with water anywhere. Dot 5 has worked good for me and caused no added corrosion anywhere. I just pull my brake apart every spring to clean it and put in new fluid. I figure it is my only front brake so I better treat it right so it is there when I need it. However, I now need a new bleeder screw and caliper seal. Does honda still carry these?

Bob Wessner · « **Reply #16 on:** March 17, 2006, 08:20:30 AM »

Quote

I now need a new bleeder screw and caliper seal. Does honda still carry these?

Yes, or at least they did for my earlier 750 last year.

kaceyf2 · « **Reply #17 on:** March 17, 2006, 09:13:57 AM »

Just reading Some of the answers given here made me want to post.....
First off..grabbing hold of the end of the piston and "just twisting till it comes free" Yep thats FINE AS LONG AS YOU INTEND TO THROW THAT PISTON AWAY! why? because your going to chew all the chrome up on the edge of the piston, which makes it rust ,which travels back past the seal and its only time before it seizes /leaks!
Secondly, sorry an all that bUT what A LOAD OF BULL about silicone brake fluid having negative points! NO IT DOESN't !! NOT AT ALL.
May I point you in the direction of (a) Mr.Chris rushton (cb750 sandcast VJMC) and his mate Max ( IT WAS HIS K2 FEATURED IN THE CB750 STORY By Mick Duckworth) Chris rides his cb750 on a near daily basis,(and travels from yorkshire to Scotland most years and back on it!) Both he and his cb750 have been regularly featured in "Tansha" (VJMC Bi-monthly members mag) among other classic bike mags. Max, to The best of my knowledge Has an example of cb750 K0, K1,2,3,6,8 (and more that i dont know about.)
Both Max and Chris "Turned me on to silicone brake fluid" some time ago, they have used it in their own cb750,s since time began (I think mAX SAID TWENTY YEARS HE HAS BEEN RUNNING IT IN HIS BIKES) With no problems at all, and I do not mean JUST no probs with the silicone fluid,I mean no probs with the brakes!! Except for the very, very occasional change of seal,(not due to rusty dirty brown sludge like with the NON silicone brake fluid) NOT because it had seized either, BUT BECAUSE AFTER SO MUCH TIME IT HAD WORN OUT NATURALLY!!!!
How many can say that?
"nonhydroscopic"

Great! Thats what we want! (ooh deary me , a little tad of water in the bottem,probably got there through either a worn out seal or leaking banjo-bolt or nipple anyways OR a leaky master cylinder cap -seal!

WEIGH THAT OFF AGAINST THE ROTTING BROWN RUSTY FOREIGN _OBJECT LADEN - PAINT REMOVING GUNGE THAT NON SILICONE BRAKE FLUID CAUSES.....AND THE DANGER THIS CAUSES TO YOU AND YOUR BIKE!!!!!

THis is why you get pistons that are difficult to remove, chrome missing, leaking, DANGEROUS.

You may ONLY have one life (who knows) whenyou pull that brake lever at ninety plus MPH DO YOU WANT IT TO WORK EVERY TIME? ALLWAYS ? NO IFS OR BUTS?

This is what to do, get rid of the old non silicone brake fluid.....
open up your calipers, clean them out, pay particular attention to where the seal sits...This is where the build up of years of alluminium oxide is gonna be. stopping the piston moving freely,by not allowing the seal to sit correctly in the caliper...Its where the air meets the seal/meets the old fluid/meeets the alluminium.....
You will not find it easy to get in there with any form of rubbing paper.....get a dremal or the like and select a BRASS repeat BRASS (softer than alluminium) wheel, and GENTLY go round the seal groove.
REMOVE ALL oxidisation, but no more!

BUY NEW SEALS, DO NOT REUSE OLD ONES, they are cheap,you are not!
I can buy stainless banjo bolts for a fiver and also stainless nipples for less,these will not rust or rot.
I can buy STAINLESS pistons for cheaper than D>SILVER sells his for (The ones that you have just binned because the chrome came off and the bits jammed your brakes up remember)
These stainless pistons should last you forever! and at just fifteen pounds each thats great.
Fit the new seals, fit the new stainless pistons, fit the silicone brake fluid, and if you done it right, You will never, ever have another #$%*ty brake problem, I GARAUNTEE it........Do this, and you will thank me for ever!

In a few years time, when a seal wears out and you leak silicone fluid on your newly painted mags, you will LAUGH, because it has just made them shiny!

When you go to take the piston out and it just pops out as intended (AND as stated in manual!) You will laugh again, and when the new seal just goes in and so does the old stainless piston , STILL looking shiny and new after all those years, and when you test your brakes after the ten - minuite seal refit you just done,.......... believe me you will laugh........

Because you aint gonna have seen any dirty -rusty-stinking gunge laden -corrosive - paint stripping fluid, because you took the correct option all those years ago, or maybe listened to someone who had and learned offa them! ( like I did, Thanks Chris AND MAX)
Its great to have brakes that are perfect, and will stay that way ,because you can ride faster, knowing that a tiny squeeze stops you every time.
Dont botch it guys, we wanna see you all around for years to come.

crazypj · « **Reply #18 on:** March 17, 2006, 09:33:49 AM »

Quote from: techy5025 on March 16, 2006, 11:18:50 PM

Not sure exactly what you mean. Dot 3 absorbs and retains moisture...Dot 5 (silicone) does not.

How can moisture get past the fluid to the bottom on the caliper? Are you saying past the ring
seal in the caliper?

Jim

OOOOH,
didnt realise so many people felt so strongly about this.
The condensation gets in through the top diaphram and migrates to the bottom. As I said, when it was first on the market it was treated as 'fit and forget (what all the reps told us) did'nt need to change every year. With DOT3/4 we knew it absorbed moisture and needed changing.
BTW I've been working on motorcycles for almost 38yrs,(september) still learning but I do know an awful lot of stuff. started on Honda's in 1968

eldar · « **Reply #19 on:** March 17, 2006, 11:00:07 AM »

If water gets in the top, you have a leak and thus a bad seal. With a good seal, water will not get in. Thats why it is called a seal. If water can get in, then so can air.

kacey, let go of the throttle a little. On my piston and probably others, there is a part that actually pushes against the pad. it is NOT chrome and gripping that part with pliers will not hurt the piston in anyways. This part is always open to dirt and water and such.

also crazy, lets not get into years working on bikes. Years means nothing. I have seen people who worked on farm equipment for decades and always have problems cause it was not correct. I have changed engines on cars with no manual and have never had a problem and I have only done it a couple of times.

basically just because you have done it a long time might not neccesarily mean you are doing it right.
Fine if you want to put in things you have tried and what worked and did not work but years does not mean much.
My 78k is my only bike, yet everytime I work on it, it gets better.

dusterdude · « **Reply #20 on:** March 17, 2006, 12:54:23 PM »

thats cause you da man eldar.

crazypj · « **Reply #21 on:** March 17, 2006, 01:55:38 PM »

Water molecules will migrate through the rubber over a period of time,including the brake lines. Its part of the reason the DOT3/4 gets so bad, not just the water vapor/ condensation. Teflon lined (Aeroquip, et.al) dont have the same problem but they do have other problems ( like the stainless steel braid cracks and punctures liners) I have seen several do this. I was also an MOT motorcycle inspector in Britain before I moved to USA.

mick750F · « **Reply #22 on:** March 17, 2006, 05:47:21 PM »

This link used to be in the FAQs. Either I couldn't find it or it's been removed. It's some facts and opinion about brake fluids. http://shotimes.com/brakes/part5.html

Mike

eldar · « **Reply #23 on:** March 18, 2006, 09:38:48 AM »

again, over time. how much time? tires and brakes, the 2 most important things on a bike. How long do you go before servicing your front brake? If you do it every spring, you wil have no water build up. simple as that. It is your safety after all.

crazypj · « **Reply #24 on:** March 19, 2006, 07:19:00 AM »

Quote from: eldar, Master of the K8 Thunder! on March 18, 2006, 09:38:48 AM

again, over time. how much time? tires and brakes, the 2 most important things on a bike. How long do you go before servicing your front brake? If you do it every spring, you wil have no water build up. simple as that. It is your safety after all.

I think your missing the point of my reply. I dont remember the exact time period, around 2 to 3 yrs or so.
A couple of people who have posted replies understand what I'm saying
When DOT 5 first came on the market it was touted as the best thing since sliced bread, a total fit and forget solution. It turns out it wasnt so and needs to be changed just as regularly as conventional brake fluid. Problem is, when you change it you DONT get any water in the system out (it sank to the lowest point, remember) So, if you use dot 5 you have to strip calipers down to check them
The 'new' DOT 5.5 is probably better for fast riders as it has a higher boiling point (but its 'conventional' glycol base)
The main reason to use DOT 5 is the fact it doesnt damage paintwork.
I have worked in motorcycle dealers for years, I'm Honda and Suzuki trained and have worked on thousands if not tens of thousands of motorcycles. Unlike most, I studied for this career and still do.
CrazyPJ

I would also add to tyres, brakes. Wheel bearings, steering and suspension.

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Author Topic: Caliper Repair for a dry system. (Read 8402 times)

schmidbc

schmidbc

rob

eldar

eldar

eldar