Post-mount brake blocks
Post-mount brake blocks
Many cantilever brakes, some V brakes, and many older centre pull brakes use so-called 'post mount' brake blocks. Brakes which are configured thus usually allow a far wider range of rim widths vs boss spacings/arm geometries to be accommodated, since the post mount allows the brake block to be swung at any angle relative to the brake arm. Perhaps surprisingly you can still buy inserts which fit both mafac 4-stud and 5 stud patterns (eg from Kool stop) but most other brake users either use a moulded all-in one brake block or some kind of more modern holder/insert system. So what is available?
In moulded all in one brake blocks the Aztec control block is pretty good value
about £4 a pair from many outlets. They are nicely made with aluminium posts. Fibrax sell an almost identical looking brake block too. The compound isn't super-soft though; to get a softer compound you need to spend a bit more, eg on kool stop salmons. Other makers offer soft compounds too, but not all are very hard wearing.
All in one brake blocks have two main disadvantages;
1) the brake blocks need to be realigned when a new set is fitted (which is fiddlier than it needs to be with many post-mount brakes) and
2) when the brake blocks wear out, it isn't obvious that you have reached the end and the results can be incredibly destructive; inside the brake block there is usually a die cast (zinc or aluminium) frame; this quickly causes severe rim damage if it is allowed to contact the rim. There is usually a line on the brake block indicating the wear limit, but a good a rule of thumb is that once the grooves in the brake block are gone, you are living on borrowed time. Obviously if the brake block is set at an angle to the rim it will wear through at one corner first, before the rest of the brake block has become badly worn.
If you want to find out where the metal frame is inside such a brake block, you can poke a pin into it and see how deeply it is set into the material. It is rarely more than 1-2mm below the bottom of the grooves.
If you use holder/insert type brake blocks you can change inserts without disturbing the alignment. You can also wear inserts down until the holder is almost touching the rim, and you will be able to see when you have reached 'the end' without having to guess or risk your rims.
Holders which accept 70mm 'XTR type' V-brake inserts are available from several different manufacturers. Of these the least expensive is usually the Clarks CP522 set, which includes spare inserts. The supplied inserts are not super soft but are not rim wreckers either.
What doesn't seem to be readily available in 70mm post-mount is a holder which uses a centrally mounted (rather than offset) post. Offset 70mm brake blocks don't fit every bike, and sometimes contribute to squealing etc.
Another hard to find item is a post mount holder which accepts the shorter shimano 'road' inserts . Kool stop make their 'cross' brake blocks and they are nice enough, but 'cross' is a pretty good description of me when I am asked to pay over £20 for a set of brake blocks
Recently I have become aware of Clarks CP453 which I would expect to be a lot more reasonably priced. However I can't find it for sale at retailers, so I don't know how much they actually cost. Anyone?
cheers
In moulded all in one brake blocks the Aztec control block is pretty good value
about £4 a pair from many outlets. They are nicely made with aluminium posts. Fibrax sell an almost identical looking brake block too. The compound isn't super-soft though; to get a softer compound you need to spend a bit more, eg on kool stop salmons. Other makers offer soft compounds too, but not all are very hard wearing.
All in one brake blocks have two main disadvantages;
1) the brake blocks need to be realigned when a new set is fitted (which is fiddlier than it needs to be with many post-mount brakes) and
2) when the brake blocks wear out, it isn't obvious that you have reached the end and the results can be incredibly destructive; inside the brake block there is usually a die cast (zinc or aluminium) frame; this quickly causes severe rim damage if it is allowed to contact the rim. There is usually a line on the brake block indicating the wear limit, but a good a rule of thumb is that once the grooves in the brake block are gone, you are living on borrowed time. Obviously if the brake block is set at an angle to the rim it will wear through at one corner first, before the rest of the brake block has become badly worn.
If you want to find out where the metal frame is inside such a brake block, you can poke a pin into it and see how deeply it is set into the material. It is rarely more than 1-2mm below the bottom of the grooves.
If you use holder/insert type brake blocks you can change inserts without disturbing the alignment. You can also wear inserts down until the holder is almost touching the rim, and you will be able to see when you have reached 'the end' without having to guess or risk your rims.
Holders which accept 70mm 'XTR type' V-brake inserts are available from several different manufacturers. Of these the least expensive is usually the Clarks CP522 set, which includes spare inserts. The supplied inserts are not super soft but are not rim wreckers either.
What doesn't seem to be readily available in 70mm post-mount is a holder which uses a centrally mounted (rather than offset) post. Offset 70mm brake blocks don't fit every bike, and sometimes contribute to squealing etc.
Another hard to find item is a post mount holder which accepts the shorter shimano 'road' inserts . Kool stop make their 'cross' brake blocks and they are nice enough, but 'cross' is a pretty good description of me when I am asked to pay over £20 for a set of brake blocks
Recently I have become aware of Clarks CP453 which I would expect to be a lot more reasonably priced. However I can't find it for sale at retailers, so I don't know how much they actually cost. Anyone?
cheers
Last edited by Brucey on 27 Sep 2020, 8:10pm, edited 1 time in total.
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Post-mount brake blocks
Are you psychic? That's just what I was exploring after reading the other thread.
: - )
Jonathan
: - )
Jonathan
Re: Post-mount brake blocks
Fibrax 'surestop' brake block ASH298
Also available in red (ASH298R)
cheers
Also available in red (ASH298R)
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Post-mount brake blocks
Also, Swisstop RAT. Now only in original black but I have some of the green compound.
Re: Post-mount brake blocks
That lot take me back. Perhaps it is just that I now know the tricks to make adjustment easy, but I always found those post mount jobbies very fiddly to tighten up without them going out of alignment. The modern vee-brake style allen key alternatives seem like a doddle in comparison.
Re: Post-mount brake blocks
I never found it that bad to adjust the brake blocks in post mount brakes (I had BR-AT50 and similar on several bikes at one stage, so it was a regular occurrence) . However using cartridge type brake blocks means that it is no longer an issue even if you find the adjustment awkward, because you only need to do it the once.
My hack bike (post mount cantis) has been through at least five or six sets of XTR type inserts and I have not had to touch the holder adjustment; easy peasy.
cheers
My hack bike (post mount cantis) has been through at least five or six sets of XTR type inserts and I have not had to touch the holder adjustment; easy peasy.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Post-mount brake blocks
One interesting devolpment in cantilever post blocks are adjust in place style such as these TRP units
https://trpcycling.com/product/inplace-adjust-f/
Allows you to adjust the pad angle on brake designs where the angle is fixed eg. froglegs. There's an allen key on the end of the posts which secures the pad holder to the post, and some cup/cone fittings to adjust angle. I'm sure I've bought some that were much better value than the TRP items above
https://trpcycling.com/product/inplace-adjust-f/
Allows you to adjust the pad angle on brake designs where the angle is fixed eg. froglegs. There's an allen key on the end of the posts which secures the pad holder to the post, and some cup/cone fittings to adjust angle. I'm sure I've bought some that were much better value than the TRP items above
Re: Post-mount brake blocks
like this?
they look like a good idea (eg for old Mafac cantis etc) but I have not seen them in the flesh.
cheers
they look like a good idea (eg for old Mafac cantis etc) but I have not seen them in the flesh.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
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- Posts: 2876
- Joined: 9 Jun 2008, 8:06pm
Re: Post-mount brake blocks
Adjusting these is never easy but the following will help:
1. All mounting hardware must be very clean and dry, except...
2. The threads of the eye bolt must be lubricated so the nut binds it all together without rotating the pad out of alignment
3. Turn the cable adjuster out a few turns and set the pads up against the rim. Then turn the cable adjuster back in to achieve clearance. You cannot use a third hand tool or similar as the studs will push straight through the eyebolts.
It is worth buying the Cross Pads just to avoid doing this every year on a commuting bike.
In terms of geometry, pads further out on their studs give higher MA with most brakes but you risk squeal, so it's a compromise.
1. All mounting hardware must be very clean and dry, except...
2. The threads of the eye bolt must be lubricated so the nut binds it all together without rotating the pad out of alignment
3. Turn the cable adjuster out a few turns and set the pads up against the rim. Then turn the cable adjuster back in to achieve clearance. You cannot use a third hand tool or similar as the studs will push straight through the eyebolts.
It is worth buying the Cross Pads just to avoid doing this every year on a commuting bike.
In terms of geometry, pads further out on their studs give higher MA with most brakes but you risk squeal, so it's a compromise.
Re: Post-mount brake blocks
In the past some post mount brake shoes were M6 threaded with a sleeve thread locked over to increase the diameter to 7mm for the post mount size.
Like these from my scrap bin.
Like these from my scrap bin.
At the last count:- Peugeot 531 pro, Dawes Discovery Tandem, Dawes Kingpin X3, Raleigh 20 stowaway, 1965 Moulton deluxe, Falcon K2 MTB dropped bar tourer, Rudge Bi frame folder, Longstaff trike conversion on a Giant XTC 840
Re: Post-mount brake blocks
Presumably the core is made from strong steel while the outer casing is softer to allow some "bite"?
Re: Post-mount brake blocks
Still got one set of brakes using these pads, on my old Dawes simply because the brake posts are too close together to allow later cantis with V-brake pads.
Still hate setting them up with pad angle, reach and height varying simultaneously when the nut is slackened off. I like the holder/insert idea to avoid this hassle. Trouble is, as the pads wear and the brake arms move towards the rim the mechanical advantage decreases while the pads wear unevenly with the top edges wearing fastest while the lower edge tends to move past the rim braking surface, so I can't see that re-adjustment can be avoided during the life of the pads.
Also anything apart from Koolstop salmon pads seems to rip chunks of aluminium out of my braking surfaces.
Used Aztecs years ago but more recently they've been horrendous at clogging up with chunks of ali from the rim. Either the compound's changed or modern rims are chocolate?
Still hate setting them up with pad angle, reach and height varying simultaneously when the nut is slackened off. I like the holder/insert idea to avoid this hassle. Trouble is, as the pads wear and the brake arms move towards the rim the mechanical advantage decreases while the pads wear unevenly with the top edges wearing fastest while the lower edge tends to move past the rim braking surface, so I can't see that re-adjustment can be avoided during the life of the pads.
Also anything apart from Koolstop salmon pads seems to rip chunks of aluminium out of my braking surfaces.
Used Aztecs years ago but more recently they've been horrendous at clogging up with chunks of ali from the rim. Either the compound's changed or modern rims are chocolate?
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- Posts: 2876
- Joined: 9 Jun 2008, 8:06pm
Re: Post-mount brake blocks
The most rim-eating pads I've used were Clarks red ones. Full of metal chips when removed, and a front rim lasted 18 months. Pad material is a delicate balance: soft enough to have high friction, but hard enough not to embed grit or rim wear particles. The answer to all "what rim brake pad" questions is usually Kool-Stop salmon.
Re: Post-mount brake blocks
I've used clarks red and there was zero pick-up of swarf over several sets. Did you use your brake blocks on a new rim by any chance?
My theory is that whatever brake blocks you use first on a new rim (especially with machined brake surfaces) are the ones that pull most swarf out of the rim, and that not all rims release the same amount of swarf. The reason for this is that swarf gets embedded into the machined surface of the rim and the extent to which this happens depends on (unknown, uncontrollable) details of the machining process.
Pretty much any brake block that is fitted as OEM on bikes has a bad rep for swarf, and I think this is the main reason.
cheers
My theory is that whatever brake blocks you use first on a new rim (especially with machined brake surfaces) are the ones that pull most swarf out of the rim, and that not all rims release the same amount of swarf. The reason for this is that swarf gets embedded into the machined surface of the rim and the extent to which this happens depends on (unknown, uncontrollable) details of the machining process.
Pretty much any brake block that is fitted as OEM on bikes has a bad rep for swarf, and I think this is the main reason.
cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~
Re: Post-mount brake blocks
That's interesting... and testable.
How about getting two different pairs of blocks and putting one of each on a new rim. Then swapping to the other pair?
Jonathan
How about getting two different pairs of blocks and putting one of each on a new rim. Then swapping to the other pair?
Jonathan