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Braking Clinic

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oscarb2b View Drop Down
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    Posted: 07 Apr 2022 at 21:23
I’m in the process of recommissioning my Gen1 4 pad calliper RSV and hoping to cure some braking woes. 

They’ve never been the best brakes, suffering from a vibration/warping sensation when used anything over 60% force. Not too bad at low speed just hard braking. I put another set of (admittedly second hand) Brembo discs on but with similar symptoms. 

Now I’ve got the bike nearly MOT ready, I took the nearly new SBS pads out, popped the pistons out and gave them a good clean with brake cleaner. I also cleaned the disc bobbins and made sure everything was free. 

Whilst I want to sort the brake judder long term, I think I need to focus on the huge amount of drag I seem to be getting. If I spin the front wheel (after correctly aligning and torquing everything up) I’m getting only half a wheel of free spin before it comes to a stop. There’s definitely some drag there. 

I really can’t remember if I’ve done the seals before it got laid up, but I know the fluid and everything in the system
Is 5 years old. 

So what would you do first? I’m assuming the pistons aren’t returning nicely and dragging on the disc. So am I right in thinking that’s either a piston or two in bad condition or seals that have swelled over time and not allowing free movement? 

Thoughts appreciated 


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426hemi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 426hemi Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 01:32
With vibration how clean is the disc mounting face on the wheel? Take the discs off and scotchbrite the mounting surfaces also on the dragging how full is the reservoir, if it’s to full it will cause drag.
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oscarb2b View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oscarb2b Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 07:18
Thanks I hadn’t thought about cleaning behind the disc mounting surfaces. 

Fluid wise the reservoir is around 50% full I would say. Whatever I’ll do next I’ll change fluid (as with everything else wet on the bike) but wonder if seals or pistons could be part of the issue here 

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Post Options Post Options   Thanks (0) Thanks(0)   Quote wigginsjp Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 07:46
They could be an issue yes, especially if you didn’t replace the seals 5 years ago? 
If you haven’t, they would be at best 19 years old by now, so due a replacement in my opinion 


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Post Options Post Options   Thanks (0) Thanks(0)   Quote oscarb2b Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 08:21
Yea I really can’t remember! 

I’ve owned the bike for a few more years before it was laid up so I’m thinking the seals are at least my ownership old. Even if I did change them 5 or so years ago they’ve been sat for ages with old fluid next to them so Im guessing there may be some swelling with the brake fluid taking on water atmospherically? 

What do people use - OEM seals or aftermarket? 

I twisted a few of the sticky pistons with pistons pliers when I cleaned them and did notice a bit of surface damage to one of them so thinking the pistons might also be needing attention 

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426hemi View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 426hemi Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 10:11
I’ve had a few parts from this company.
https://addictionmotorsport.co.uk/brembo-replacement-parts#s1
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oscarb2b Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 10:56
Thanks. 

Is changing the seals a splitting the caliper job or can they be done without splitting them? 

When I got the pliers in there it was fairly tight so wondered if you would be able to get the pistons out without splitting...

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Post Options Post Options   Thanks (0) Thanks(0)   Quote blacklines Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 12:09
You can get the pistons out without splitting the calipers. It is really tight and fiddly on these 4 pad calipers though. The noggins the pads sit on make it pretty tight compared to most modern 2 pad calipers. You've got piston pliers I'm guessing?

I think you are right in that sorting the sticky pistons is your first job. Because even if there's a disc problem that needs fixing, having dragging pads is only going to cause the problem again on new discs. 

When you have cleaned the calipers and pistons, use a bit of this stuff (Technicqll PTFE brake assembly lube) on the seals and a bit on the part of the pistons that are behind the seals. £3 for a tiny tube but it's enough to do 2 calipers with more to spare. You don't want it (or anything) on the exposed pistons as they'll only just get all gummed up. But it does help make things super slippery. 

I find these calipers do get really sticky very quickly. Even having stripped and cleaned them, it only takes a day on track for them to start to stick again. So I tend to clean the pistons after each day. After my recent day the wheel would barely turn at all. The disc was heavily coated in pad material, but the pistons were also sticking and dirty with brake dust. 

This is after cleaning the pistons:



You can see it now continues to spin a bit after letting go. Where before it'd stop almost instantly. But it still wasn't great. Adam reminded me about the old Dave Moss fork alignment trick. Thought that was just for radial calipers but gave it a go anyway:
1. Remove calipers and push pads right back in on both of them.
2. Loosen all 4 pinch bolts at the base of the forks. 
3. Give it a bit of a bounce and confirm the forks are moving freely without additional stiction.
4. Lift front back onto the stand.
5. Tighten calipers back onto the forks. The wheel should still spin nicely because the pads are pushed back in and not in contact with the rim.
6. While spinning the front wheel, pump the brake lever until the pads are again seated against the disc. 
7. Tighten all pinch bolts.
8. Test forks still free of stiction.
9. Test spinning the wheel now the pads are primed against the disc.

That gave me a subtle improvement, but it all helps right.

 

As mentioned above, you can get dragging if the reservoir is too full. But you can also somehow end up with a pressure buildup at the master cylinder. I've had luck before just cracking the MC bleed and also brake banjo bolts. You know there's some pressure there if fluid doesn't just seep but sort of gives a little shart of brake fluid. 

Can't comment on the judder, but that should help with the drag. Then it might just be pad material buildup on the discs. Or warped discs. But if you first get the wheel spinning you can then see what problems you are left with.
Owen
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oscarb2b Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 12:33
Cheers Owen appreciated. Can't believe how much difference the fork allignment made. I did actually try this myself but may not have done it as per your list, so will give it another go. The only thing you didn't mention was whether you need to loosen the axle nut as well as the pinch bolts to align them properly? 

Re brake pistons. Yes i've got piston pliers. The nagging thought in my mind is that i'll want to do the seals to rule out any foul play but it's not like they are leaking. 

So the assembly grease is safe to go the wet side of the piston? Do you think it's worth popping all the pistons out, cleaning, new fluid, bleeding and aligning. Or would you go a step further and do seals? I've got no leaks as far as i'm aware.

Cheers


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Post Options Post Options   Thanks (0) Thanks(0)   Quote blacklines Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 13:04
Originally posted by oscarb2b oscarb2b wrote:

Cheers Owen appreciated. Can't believe how much difference the fork allignment made. I did actually try this myself but may not have done it as per your list, so will give it another go. The only thing you didn't mention was whether you need to loosen the axle nut as well as the pinch bolts to align them properly? 

Re brake pistons. Yes i've got piston pliers. The nagging thought in my mind is that i'll want to do the seals to rule out any foul play but it's not like they are leaking. 

So the assembly grease is safe to go the wet side of the piston? Do you think it's worth popping all the pistons out, cleaning, new fluid, bleeding and aligning. Or would you go a step further and do seals? I've got no leaks as far as i'm aware.

Cheers


No need to loosen the axle. With the axle torqued up to spec, there is still room for the forks to slide side to side a very small amount. So if you completely relax off the pinch bolts it allows them to find a more comfortable position. If they've been held at a bit of an angle by the pinch bolts then it'd give some stiction in the forks because they can't move in a straight line. They have a kink. But also because the calipers are fixed in place on the fork legs, they'll be at an angle too. So the pads would be constantly rubbing due to being out of parallel. 

I wonder sometimes whether you could just leave the pinch bolts loose and floating. There must be some safety concern to that. But really, once you've set them perfectly central and then tightened the pinch bolt it should be good until you next remove the wheel. The problem is just caused by tightening the pinch bolts when the forks are a little out of shape.

What you could do - which'd be double work on the calipers - is do all the cleaning etc and reassemble without the dust seals in place. If that fixes the issue then you know it was because the dust wipers had swollen. Which they had a bit on my bike. I was probably the first to touch the brakes since 2003. 

I have some seals (pyramid I think it was from memory) but as the actual seals themselves were fine I just left the dust wipers out. I only do the occasional summer ride and track day on the bike so there's no danger of road salt etc getting in there. Only thing to watch for is you don't just push the pistons back in when changing pads. Because any built up pad material on the pistons would get pushed past the seal and could get lodged in there. 

If the seals are the problem (they may be) then it'll be the dust seal that's the issue. The actual seals would last much longer as they're constantly in brake fluid and not exposed to the elements. But if you're buying a full replacement set you might as well change them all I guess. 

You could try first just cleaning the pistons one at a time by rotating with piston pliers and cleaning the exposed bit. Repeat 8 times for all pistons. If that doesn't do the trick then you could try popping the pistons out, giving them a good clean and then re-priming the system without the dust seals in. Or just you just skip the first two steps and go straight to replacing all seals. 

Yeah the assembly grease is safe to go on the wet side of the piston. I'd avoid getting it on the dry side though, only because dust will stick to it. Though it'll clean off. 
Owen
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Post Options Post Options   Thanks (0) Thanks(0)   Quote oscarb2b Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 13:29
Thanks I’ll give that a go - probably whip the dust seals out to rule them out of the equation. Like you I generally only ride in the sunshine and on track so not too worried. 


Here’s a link to the current free spin. It actually seems better than when I left it?! Strange. Looks somewhere in between your two clips 

You can hear the drag though!

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Post Options Post Options   Thanks (1) Thanks(1)   Quote IanG Quote  Post ReplyReply Direct Link To This Post Posted: 08 Apr 2022 at 21:22
Another thing to consider with tight pistons is the possibility of corrosion in the grooves behind the seals

I've had it happen on one of my calipers,the seal is fine but when you remove the seal and clean the groove you find a build up of very localised corrosion where the plating/anodizing has failed. In my case this had actually left quite an impression in the the seal and it was applying a localised additional pressure on the piston.

Not really likely to be your problem but it's something to check for when replacing or checking the seals.

I've got seal kits from Powerhouse? in the past,I think they were genuine Brembo kits but cheaper than Ape stealers at the time.
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Looking forward to the next track day
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Post Options Post Options   Thanks (1) Thanks(1)   Quote badapple Quote  Post ReplyReply Direct Link To This Post Posted: 09 Apr 2022 at 00:12
Just to add when you go through the wheel alignment procedure when you get the pads to hit the disc the calipers should be slightly loose and you keep the lever pulled as you nip them up then torque as normal Thumbs Up
I started out with nothing and I've still got most of it left
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