Author Topic: Brembo rebuild  (Read 305 times)

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Offline Chippitt68

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Brembo rebuild
« on: September 19, 2018, 03:37:20 PM »
Iím rebuilding the front calipers on my 2010 ultra. Bikers choice seals and pistons. They seemed very snug going in. Throughly cleaned calipers and lubed seals and pistons with dot 4 brake fluid.  Bled brakes and drag is pretty severe. When I opened them up, there was a milky look to the fluid. The pistons had a ring of black dirt around the edge that hits the pad.  Very light scoring on pistons. Iíve never done bike calipers before,  but have done car calipers. I either did something wrong, or the bores were damaged. New calipers?

Offline topcat3815

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Re: Brembo rebuild
« Reply #1 on: September 19, 2018, 03:50:08 PM »
Id go with new calipers. Whats your life worth

Online Maddo Snr

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Re: Brembo rebuild
« Reply #2 on: September 19, 2018, 04:11:40 PM »
The MoCo manual says they're not re-buildable and to replace them. I guess there's a reason for that...but...I've rebuilt dozens of Brembo calipers over the years, usually using Nissin seals and pins. Make sure the calipers get NEW slide pins, that the bores are lightly honed and cross hatched and the new pistons are sized to the bore. Oversized pistons will interference-grab, undersize pistons will cock-grab.

Also, ensure 100% that your seal kit has the correct compatibility for the intended fluid fill. (DoT rating) I re-done plenty of 'new' work where seal swell has occurred due to incompatible seals/fluid.

I know it's the other end, but I always kit the M/C when re-building calipers to ensure that the back seal of the M/C hasn't swollen. That wil always cause the pads to drag if the M/C can't depressurise due to seal drag. Ensure your M/C kit has a fresh return spring, a fatigued spring can cause pad drag as well.

Causes of pad drag:
1) S/C seals too big
2) S/C pistons over/under sized
3) pad hangers catching on slide pins
4) broken M/C return spring
5) swollen M/C back seal
6) gunk in S/C bores
7) lipping of S/C bores
8) S/C seals have cupped during installation
9) over-swelling of seals due to incompatible fluid

There's a check-list for you Chip. All the best mate.

Cheers, Pete.
« Last Edit: September 19, 2018, 04:58:01 PM by Maddo Snr »

Offline Chippitt68

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Re: Brembo rebuild
« Reply #3 on: September 19, 2018, 05:19:23 PM »
Thanks maddo 🥃Appreciate you taking the time. I think Iím gonna buy new calipers. Iíll just put the oem  ones back on, unless there is a better option, thatís not gonna cost an arm and a leg
« Last Edit: September 19, 2018, 05:32:54 PM by Chippitt68 »

Offline ecir50

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Re: Brembo rebuild
« Reply #4 on: September 19, 2018, 06:20:47 PM »
milky may be air, I would throw your old cleaned parts back in if they don't look damaged and retry. If it works if you want pull back apart and compare parts for the obvious.

Online PoorUB

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Re: Brembo rebuild
« Reply #5 on: September 19, 2018, 07:47:41 PM »
At $200 each I would rebuild them, normally it isn't that difficult. try a different source for seals.
I am an adult?? When did that happen, and how do I make it stop?!

Offline klammer76

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Re: Brembo rebuild
« Reply #6 on: September 19, 2018, 08:36:05 PM »
I converted my 2002 front and rear back in 2016. I used QTM seals at the time, no longer available but believe willy shiney sells a seal kit. What I had read before doing mine was the after market pistons were not very good. Do a search for my thread on the rebuild, it's here some where. FSG is also a wealth of knowledge. You can get new take offs on ebay cheap all the time. I also used a light smear of NAPA sil-glide on the seals as instructions said not to use brake fluid FYI. My OE seals were actually fine. Pistons were a snug fit but went easy once properly lined up. Make sure to clean everything with denatured alcohol (I also used electrical contact cleaner on the calipers).

Offline Chippitt68

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Re: Brembo rebuild
« Reply #7 on: September 20, 2018, 02:52:47 AM »
I cleaned up and reused the pistons. I did not note which pistons came from which bores tho, probably should have done that. The seals looked square to me, some have a slight angle. Iím using dot 4 fluid, thought dot 5 was a no no on the seals. Anyhow, found brand new calipers on new castle Hd for $141 a piece. On their way. Thanks for all the replies.

Offline klammer76

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Re: Brembo rebuild
« Reply #8 on: September 20, 2018, 04:33:55 AM »
I cleaned up and reused the pistons. I did not note which pistons came from which bores tho, probably should have done that. The seals looked square to me, some have a slight angle. Iím using dot 4 fluid, thought dot 5 was a no no on the seals. Anyhow, found brand new calipers on new castle Hd for $141 a piece. On their way. Thanks for all the replies.
The seals are square.

Offline topcat3815

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Re: Brembo rebuild
« Reply #9 on: September 20, 2018, 05:47:15 AM »
 You did the right thing buying new ones.

Online PoorUB

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Re: Brembo rebuild
« Reply #10 on: September 20, 2018, 08:29:38 AM »
I guess I still don't know why it would be a bad deal to rebuild them. Brake calipers are about as complicated as a brick. As long as you can get quality kits and know what to look for I would rebuild them.

If you are not comfortable, I realize everyone is at a diffent skill level, then relace them.
I am an adult?? When did that happen, and how do I make it stop?!

Offline Chippitt68

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Re: Brembo rebuild
« Reply #11 on: September 20, 2018, 02:02:59 PM »
UB, I agree itís not a bad deal to rebuild. I cleaned everything and put it back together. The pistons were very difficult to push in. Two were stuck when I pulled em off the bike. My feeling was itís better to get new ones since I havenít done these before. Iíll mess around with them after I get my bike on the road. Maybe hone bores and rebuild. Your right about the comfort level, im not there yet.

Online Maddo Snr

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Re: Brembo rebuild
« Reply #12 on: September 20, 2018, 02:28:22 PM »
Chip, there's a fellow on US EBay who rebuilds HD Brembo callipers professionally. They're about 1/2 the price of fresh ones and painted corvette red (if that floats your boat).

Maybe worth a look...

Offline FSG

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Re: Brembo rebuild
« Reply #13 on: September 20, 2018, 02:36:35 PM »
I'll need to check my notes from back when I did the HD Brembo thing,
but just from memory the pistons are 34mm in diameter, they and the square seals
are used in a wide range of 2 and 4 piston calipers that Brembo make for the OEM
markets other than HD.

The best source I found for them was at the KTM Parts Counter, KTM actually do list
and supply parts to rebuild the Brembo Calipers on their models.

Online PoorUB

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Re: Brembo rebuild
« Reply #14 on: September 20, 2018, 03:55:18 PM »
UB, I agree itís not a bad deal to rebuild. I cleaned everything and put it back together. The pistons were very difficult to push in. Two were stuck when I pulled em off the bike. My feeling was itís better to get new ones since I havenít done these before. Iíll mess around with them after I get my bike on the road. Maybe hone bores and rebuild. Your right about the comfort level, im not there yet.

If the pistons were stuck the bores are probably corroded up, a light honing would fix that, but beings the body is aluminum it won't take much. Also you need to take a good look at the groove for the seal and make sure it is clean. Any build up of corrosion you need to clean out carefully or pitting, toss 'em. The pistons need to be spotless around the diameter. Any pits or scratches and they are junk. The fit of the pistons is not overly critical, as long as the piston moves easily in the bore.

You can buy lube for the pistons and seals, just make sure it is compatible with the brake fluid you will be using.

I might be wrong, but I don't think the seals care which fluid you use, just make sure the complete brake system is flushed and clean if you switch to a different type of fluid.

The best thing you can do to avoid brake rebuilds is to flush the fluid every couple years. Get the moisture and contaminates out!
I am an adult?? When did that happen, and how do I make it stop?!