disc brake post facing - carbon forks

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hoogerbooger
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disc brake post facing - carbon forks

Post by hoogerbooger »

I think we have a disc post facing/alignment problem on my Missus's bike at the front forks.

I presume refacing is possible on carbon forks ? but I presume I will need to go back to the bike shop?

As far as I can see it is not my attempts to set the caliper alignment. But shout if I'm missing something:

It's a Pioggia disc carbon fork with TRP Spyre on original Spyre 160mm discs. Have had rub and judder problems. Disc is plumb straight. On new pads can't remove the rub/judder in operation, or get a sensible clearance without rub. With time rubbing reduces (with pad wear presumably)

On googling I found this link to a TRP advice on rubbing issues with Spyres:
https://www.youtube.com/watch?v=1T2RLgQoyvs

Here is a picci of a pad I've just taken out:
disc wear.jpg
hopefully shows the uneven wear top to bottom. The other pad is much less obviously uneven top to bottom but noticeable uneven front to back.

I tried centring on new pads again, via loosening mount bolts, then with with brake held on, re-tightening. Noticeably on the last bit of tightening on the lower post there is a visible movement of the caliper, tilting it outwards. I tried loosening and repeating 3 times and each time the same happened. When I then look down at the light gap between disc and pad it appears wider at the rear and a bit uneven top to bottom ( unless I'm just imagining it, having seen the pads !)(difficult to get a good view & remove parallax issues)

Like this it rubs, unless I back-off on the cable adjuster a good wack, and no point trying to centre with the caliper adjusters as it's off front to back. If I do a bit of loosening and physically push outwards the caliper on the lower post, when I tighten, I can get it a tad better aligned with less rub/judder, but not remove it. This is what I did with the last set of pads ...with it wearing in I presume, until it didn't rub.....but the pads end up as described/shown above.

The forks came sprayed to match the frame. I removed the caliper to check if there was excess paint on the post end. It is covered in paint. I can't tell if it's been faced or whether the calliper has just marked the paint, but it does not obviously look the issue, in that both ends appear flat when a steel ruler edge is taken across them. However, unless my head is playing games, when I eye-ball or put a steel ruler edge across both posts at the same time, It does look like the lower post is angled a bit outward.

So I have got to the point where my QED is the lower post ( or both posts) need facing. However, I would appreciate any advice on anything else I should check before going back to the shop as we've had the bike for 18 months, which was a frame replacement after a crash, but I sourced the replacement matching front wheel, which the shop declined to do trying to sell us a set. so I am anticipating the possibility of some banter from the shop.

Advice appreciated.
old fangled
S2L
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Re: disc brake post facing - carbon forks

Post by S2L »

That wear is a lot better than I ever had on my disc braked bikes when I used TRP brakes.
Valbrona
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Re: disc brake post facing - carbon forks

Post by Valbrona »

Not many shops would have facing equipment. A framebuilder might be the best option. Just don't file them.

Before resorting to facing try cup and cone washers under the heads of the fixing bolts, for which you might need a pair of longer bolts.
I should coco.
Stevek76
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Re: disc brake post facing - carbon forks

Post by Stevek76 »

cup and cone washers as used on the bb7s may help, but might also move the caliper too far out.

another option is to use some sort of sheet material to space out the desired gap between the pads and rotors as an alternative to the hold the brakes method.
The contents of this post, unless otherwise stated, are opinions of the author and may actually be complete codswallop
gregoryoftours
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Re: disc brake post facing - carbon forks

Post by gregoryoftours »

Its very unlikely that the mounts were faced on the fork when new, so it might well need doing, and sounds like it does. It's not something that would be done as part of a PDI so you'd have to pay for it. The post mounts are threaded aluminium so it is perfectly possible to face them. It's also quite possible that's the caliper pistons aren't completely parallel. I had this problem with a spyre caliper of my own.
S2L
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Re: disc brake post facing - carbon forks

Post by S2L »

gregoryoftours wrote: 4 May 2021, 6:08pm It's also quite possible that's the caliper pistons aren't completely parallel. I had this problem with a spyre caliper of my own.
This...
If you isolate the caliper and look at how the pistons move, it's not the nice parallel action you would expect. As I said earlier, I never had pads wearing homogeneously... neither with the TRP, nor with other calipers.
It's one of the reasons I gave up on disc brakes on road bikes... just a the industry went the other way.
hoogerbooger
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Re: disc brake post facing - carbon forks

Post by hoogerbooger »

Ah ha...." possible....calliper pistons aren't completely parallel" . Thanks for this...which is getting me thinking, particularly with the one pad having uneven wear top to bottom and the other mainly front to back. Having done some more reading on the forum and elsewhere I have found a 2014/15 US recall notice which says:

In the December notice, TRP said, "The Spyre caliper uses a dual piston design in which ball bearings move within opposing ramps. We have discovered that in a specific scenario, the balls can be forced from the ramps if the actuator arm is fully activated to its stop with excessively worn or no pads installed.

"The effect is that the one or more of the balls can jump from its position within its respective ramp, resulting in a reduction or loss of braking force."

Thursday's CPSC report explained the failure this way: ""The brake cable actuator arm can over-rotate, dislocating parts, causing the brake calipers to fail. Lack of brakes results in loss of control and a crash hazard, posing a risk of injury to the rider and others.”


(!!! Our Spyres are of the right age, coming on a bike built originally up by Condor in spring 2015).

This is it seems ( reading elsewhere) associated with a clicking sound.......which indeed we have had on this brake when the pads are worn and lever travel high. Progressing to 2 clicks with further wear/arm travel. With the clicks there was not a great loss of braking power, but one pad could be seen to move back in a bit.....so seems a good candidate for the click cause.

Whilst I think the movement of the whole calliper outwards when I tighten on the lower post( described in OP), seems odd and I don't think should happen if the posts were aligned, I may have two problems and one/other/both sides of the caliper may not be aligned, or might be just a caliper post issue.

I can't quite work out if the clicking brake issue we have had means balls will remain out of place in the caliper when new pads are put in and brake arm/travel is re-set.... as the clicking stops, when travel is reset. If they remain out of place it may be the cause of alignment issues......if balls have return to the right place now, then probably not.

However, I think, I may have to dismantle the caliper/clean/carefully grease & see if this makes any difference: have found videos/guidance:

https://www.youtube.com/watch?v=N1Isb1vpENk

https://singletrackworld.com/forum/topi ... ild-guide/

(If that does solves the issue, sounds like I need to make sure the calliper lever arm doesn't travel too far & I probably need to use the brake pad adjuster screws in set up and not just the cable barrel adjuster ( but I am aware they tend to work loose, which is why I wasn't)).

Any other advice welcome
Last edited by hoogerbooger on 6 May 2021, 2:03pm, edited 1 time in total.
old fangled
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531colin
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Re: disc brake post facing - carbon forks

Post by 531colin »

Isn't it the case that with any ball bearing type caliper you need to use the pad adjusters because they can run out of travel if you back the cable adjuster out too far?
PH
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Re: disc brake post facing - carbon forks

Post by PH »

Have you swapped front and rear callipers? That might not be the answer, but it might help clarify the question.
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elPedro666
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Re: disc brake post facing - carbon forks

Post by elPedro666 »


Sounds annoyingly like you may have a few small issues adding up to something more Image

531colin wrote:Isn't it the case that with any ball bearing type caliper you need to use the pad adjusters because they can run out of travel if you back the cable adjuster out too far?
I had a pm off Brucey about this once, after mentioning how I set up my BB7 using the cable adjustment to determine when the pads make contact (to give me the best possible leverage at max braking power); there's no certainty the same applies to TRP but it does seem like possibly an easy solution.

Basically, what he explained to me is that the pads effectively 'reset' (or perhaps re-seat) within the caliper when they fully retract, so using the cable tension rather than the pad adjustment prevents this and can lead to uneven pad wear, reduced performance and even premature wear/failure of the caliper.

Just one more thing for your list! Image

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531colin
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Re: disc brake post facing - carbon forks

Post by 531colin »

elPedro666 wrote: 6 May 2021, 10:18am Sounds annoyingly like you may have a few small issues adding up to something more Image

531colin wrote:Isn't it the case that with any ball bearing type caliper you need to use the pad adjusters because they can run out of travel if you back the cable adjuster out too far?
I had a pm off Brucey about this once, after mentioning how I set up my BB7 using the cable adjustment to determine when the pads make contact (to give me the best possible leverage at max braking power); there's no certainty the same applies to TRP but it does seem like possibly an easy solution.

Basically, what he explained to me is that the pads effectively 'reset' (or perhaps re-seat) within the caliper when they fully retract, so using the cable tension rather than the pad adjustment prevents this and can lead to uneven pad wear, reduced performance and even premature wear/failure of the caliper.

Just one more thing for your list! Image

I'm a trendy consumer. Just look at my VOG-L09 using hovercraft full of eels.
Sorry, I wasn't clear....I'll try again!

I think all ballbearing type calipers have 3 ballbearings, which "at rest" sit in little "detent" cups in the actuating cam and the pad adjuster/fixed part of caliper.
When the cam turns, the ballbearings are no longer in the bottom of the cups and they push the brake pad(s) against the disc.
So the cam always needs to return to the "at rest" position, otherwise at best you will lose some pad travel, and at worst the ballbearings will come out of the cups and you may completely run out of travel and the ballbearings may move out of position.

The calipers where both pads move have 2 sets of all this stuff in the same amount of space as calipers which move just one pad, so the ballbearings are smaller and there is possibly less room for error.
hoogerbooger
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Re: disc brake post facing - carbon forks

Post by hoogerbooger »

Colin: I see this now and I believe this is part of our problem here.

By not using the pad adjusters the caliper actuation arm has ended up travelling further than it is meant to do.....by adjusting otherwise. The barrel adjuster doesn't seem the biggest culprit as it has limited range in extra cable take, it's adjusting on the cable clamp , which I confess I have done.

It may be we have one or two balls on one side of the caliper not in position now...... + possibly a post alignment issue. I intend to take it apart, clean, inspect etc, but the Missus wants to go back to Condor 1st, in case it is a batch covered by the recall ( I presume not as we were not contacted)
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hoogerbooger
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Re: disc brake post facing - carbon forks

Post by hoogerbooger »

oh...and yes: swapping the front and back calipers seems like a good plan to test the post alignment vs caliper function question
old fangled
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