Frustration

[alexis291]

Greetings,

does anyone have experience of splitting a 4-pot Brembo calliper and successfully putting it back together? I know everyone says you shouldn’t do it but I had to split one of mine to get a stuck piston out. Try as I might, I can’t get the damned thing to seal now. I’ve had it apart several times and tried different bolt torques and clamping sequences but it still weeps brake fluid. It’s only an o-
ring between two flat faces so it can’t be that difficult - can it?

[The Mighty Gryphon]

I know this is a stupid question(consider the source), but is it a new o-ring?  Even if it is, have you tried another one?

I have noticed that in a lot of the designs on these bikes, there is minimal o-ring compression.  The oil filter cover is another one I have had to deal with.  Sometimes I have to try two different(new) o-rings to stop the seepage there.  The slightest bit of warpage or damage to the surface results in a leak.

[alexis291]

Good point, and yes it is a new O-ring. I can’t try another one because I only have one of that size unfortunately. I have others of the same diameter but not as thick. The one I have came from motorworks and is intended for these callipers. I’ve done a good visual check of the joint faces and given them a light rub with 1000 grade wet and dry. Visually they look fine without any blemishes or damage. I can’t help feeling it’s something to do with the clamping force because the O-ring is not positioned between any of the bolts.


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[stokester]

Greetings,

does anyone have experience of splitting a 4-pot Brembo calliper and successfully putting it back together? I know everyone says you shouldn’t do it but I had to split one of mine to get a stuck piston out. Try as I might, I can’t get the damned thing to seal now. I’ve had it apart several times and tried different bolt torques and clamping sequences but it still weeps brake fluid. It’s only an o-
ring between two flat faces so it can’t be that difficult - can it?

I've read the same thing regarding Brembo calipers, possibly on the Airhead list.  It is advised not to split them because you will never get them back together without leaking as they are pressed together using industrial machines and you will not be able to duplicate the process.

[rbm]

I've read the same thing regarding Brembo calipers, possibly on the Airhead list.  It is advised not to split them because you will never get them back together without leaking as they are pressed together using industrial machines and you will not be able to duplicate the process.

If the callipers were never intended to be split and rebuilt, then why does Motobins offer an internal O-ring for sale?

[Filmcamera]

I have split mine various times and have not had an issue with them leaking afterwards. Just make sure you clean the mating surfaces carefully and also get any gunk out of the ring the o-ring sits in.

[Scott_]

I have to shake my head in wonder, some places sell the Brembo caliper rebuild kit that comes with pistons, seals, and o-rings, but NOWHERE in the instructions does it give the bolt torque for re-assembly of the caliper halves.......

For me I've been lucky and not had to split one to replace pistons and seals, but surely someone has to know the correct assembly torque if you do have to split them. I understand this is a different issue than the halves being warped from heat and no longer flat and true, where no amount of torque will correct that.

But if someone were to go to the trouble(expense) of having the caliper halves lightly surface honed and trued back up, it would be nice to know the correct assembly torque.

[alexis291]

Thanks filmcamera that’s encouraging!
rbm, although Moto works sell the O-rings they also advise on their website not to split callipers. Clearly it can be done successfully and four bolts and one O-ring shouldn’t really present much of a problem, however there’s obviously some knack to it.

[Laitch]

But if someone were to go to the trouble(expense) of having the caliper halves lightly surface honed and trued back up, it would be nice to know the correct assembly torque.

Is this it? This page is from the K1 K100RS manual on this site.

[The Mighty Gryphon]

My Clymer Manual in chapter 14 on page 647 lists the torque as follows:

Outer bolts: 5-10 N-m  and 3.6-7.4 ft.lb

Inner Bolts: 25-35 N-m  and 18.4-25.8 ft.lb

It specifies installing and torquing the two inner bolts first followed by the outer bolts with Loctite(?!).

It makes sense to me to have more torque close to the o-ring to allow any warpage or thermal expansion to work away from the sealing surface.

[Enfield]

I split all mine and sodablasted Them etc. Did have a minor leak of brakefluid... but it stopped after a couple days... i used the White grease from the pistons on the o rings as Well.
Chr


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[stokester]

Thanks filmcamera that’s encouraging!
rbm, although Moto works sell the O-rings they also advise on their website not to split callipers. Clearly it can be done successfully and four bolts and one O-ring shouldn’t really present much of a problem, however there’s obviously some knack to it.

I frequently refer to Rob Fleischer's BMW site for instruction and recommendations on how to do tasks.  Although much of the info deals specifically with Airheads he has a section on K-Bikes and there are some components shared.


Here is what he has to say about Brembo brakes: -> [size=78%]http://bmwmotorcycletech.info/brakes.htm[/size]


"Split caliper halves ONLY when really needed!  In some instances, you can NOT remove the piston fully without splitting the caliper.  If you are overhauling Brembo calipers, if the kit does not come with the 10 x 6 x 2  O-ring, do not separate the halves, unless you get the proper EPDM  O-rings ahead of time.   When you try to reassemble the parts, small distortions from tightening the bolts (new ones in the kit) will sometimes let the calipers leak.  I first resurface the caliper halves by using very fine grit sandpaper, upside down on a very flat hard surface, using equal pressure & figure eight's, and changing hand positions often on the part.   This all takes time & labor.  I HIGHLY recommend you do NOT separate halves unless you MUST.  Be sure the O-ring area is clean.  If things are poor, you best purchase a brand-new caliper, unless you KNOW what you are doing, or can follow directions exactly!"

[alexis291]

Thanks all.
Laitch and Gryphon - those torques are what I first used. They are given in the Clymer manual. Thanks for taking the time to look.
Stokester - my plan tomorrow after a restless night of dreaming about brake fluid is to rub down the calliper halves on a flat plate. That should show up any high spots. A visit to my friend who has a selection of o rings will be next.

[stokester]

Thanks all.
Laitch and Gryphon - those torques are what I first used. They are given in the Clymer manual. Thanks for taking the time to look.
Stokester - my plan tomorrow after a restless night of dreaming about brake fluid is to rub down the calliper halves on a flat plate. That should show up any high spots. A visit to my friend who has a selection of o rings will be next.

I realized after posting that your brakes are not exactly like the ones he was referring to but the concept should be the same.


Keep us updated on your progress.

[Martin]

Try running a straight edge at various angles and directions across both surfaces of the caliper. If you don't have a straight edge a good quality steel ruler, if it is straight can be utilized.
Regards Martin.

[The Mighty Gryphon]

Get a piece of plate glass.  Stick a sheet of 2000 grit wet or dry on it with water and lightly wet sand the surface.  Follow that with a good flush with 93% rubbing alcohol to remove the water from the parts.

Take your time and work in figure 8's as someone else mentioned.

[alexis291]

Keep us updated on your progress.

I will. Big push tomorrow. I’m hoping to go to work on it on Tuesday!

[The Mighty Gryphon]

Keep in mind that brakes are one of the last things you want to do a rush job on.

[Scott_]

Is this it? This page is from the K1 K100RS manual on this site.

It's probably pretty close. The 1100 bmw manual says not to split the halves so obviously they don't list a torque value.
I did finally find a table in the clymer section for the late model 1100's.
Hopefully I won't ever have to split any......

[Laitch]

Live in hope; die in despair.

[alexis291]

Well I'm afraid to say that this problem has beaten me. After spending two days trying to fix it I have given up and ordered a 2nd hand (assembled!) caliper from ebay.

What I discovered when investigating is that the caliper mating faces were not flat and that the faces on the two halves are distorted differently - one side was bowed end-to-end and the other had a saw-tooth profile. I rubbed both sides down by hand on a flat plate and the pattern left by marking blue is shown in the photo. The port between the halves where the o-ring sits is in line with the bleed nipple so obviously there is uneven clamping across it. This is not surprising when you look at where the bots are. The shape of the caliper is such that only the inner two will hold it together and seal it, and the outer two appear to be there just to stop the caliper from spreading under pressure.

When I torqued up  the two centre bolts there were gaps of 0.0015" around the edges of the caliper, and doing up the outer bolts made little difference. Someone did write in a previous answer that these calipers may be pressed together before bolting up at the factory and that may be the case. If I had time to machine the faces and re-cut the o-ring groove that may work but I need the bike back on the road!

I have a spare caliper (also split) and I tried putting my new seals and pistons into this but it also leaked in exactly the same place. So unless you have a lot of time and possibly a milling machine, the moral of the story is - don't split your calipers.

PS Would anyone like to buy a bag full of brake caliper halves ?