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Under chain stay U brakes

Posted: 28 Jul 2020, 7:52pm
by nez
We have an old Saracen Blizzard with a peculiar 1980s 'under the chain stay' braking arrangement. Essentially it's a U brake like the ones you'd find on BMX. Of course setting that sort of brake depends on the spring-back and that's nearly impossible to adjust properly on the el cheapo U brakes I bought at first. Is there a 'go-to' marque of U brake which is reliable and of decent quality?

Re: Under chain stay U brakes

Posted: 28 Jul 2020, 9:31pm
by rualexander
Not particularly peculiar, they were standard on most mountain bikes back in the late '80's.

Dia Compe one available on ebay https://www.ebay.co.uk/itm/183848897686

Re: Under chain stay U brakes

Posted: 28 Jul 2020, 9:42pm
by zenitb
Key thing to check is that you are not using v-brake levers .. sounds like U brakes used the same ones as cantilever brakes used to use .. with a different leverage ratio. Sheldon Brown has a section on them that might be helpful ? https://www.sheldonbrown.com/canti-u.html

Re: Under chain stay U brakes

Posted: 28 Jul 2020, 9:45pm
by nez
Thanks for these hint. I don't think mine are any good - I watched set-up videos on Youtube and people def have more spring resistance than I can raise on them.
Thanks

Re: Under chain stay U brakes

Posted: 29 Jul 2020, 8:53am
by PT1029
Some makes of U brake had the Dia Compe style centering method, loosen the boss bolt, turn the inner bit that had the spring in it (usually use a cone spanner for this) and the retighten the boss bolt. This applied to both sides, so you could set the springs on both sides too slack, giving poor spring tension.
If you look at the e bay link, you can see the spanner flats on each pivot, just below the cable end cap/XCE label.
You will also get poor spring tension if the boss pivots are rusty/gunged up, in which case they'll need cleaning/greasing.

Re: Under chain stay U brakes

Posted: 29 Jul 2020, 12:53pm
by Brucey
PT1029 wrote:…..You will also get poor spring tension if the boss pivots are rusty/gunged up, in which case they'll need cleaning/greasing...


if...???? :shock: :shock:

what is this 'if'....?

I remember shopping for a new MTB when these were 'the latest thing'. Needless to say I "politely declined" (*) the offer of a similarly equipped machine and happily bought the 'old fashioned' previous year's model which had the brake on the seatstays... I thought the U brake was an absurd idea for typical UK conditions and that is how it turned out. Hopeless things.

(*) I think I may have come within a hair's breadth of telling the salesman to " **** off and stop talking b******s"….

However they can be made to work OK for at least, ooooh, five minutes or so provided the springs are correctly set up and the pivots are greased.

If we see photos of the parts, advice on correct setup can be given.

cheers

Re: Under chain stay U brakes

Posted: 29 Jul 2020, 3:04pm
by nez
I was young and easily led. I’ll post a picture when the bike is next here -maybe the weekend. I am the amateur mechanic for my grown up kids bikes... when they are born no one tells you ´and in nearly 40 years you’ll still be fixing their bikes’

Re: Under chain stay U brakes

Posted: 29 Jul 2020, 4:28pm
by rualexander
I used a Saracen Trekker mtb converted for touring use with drop bars etc. for 20 years between 1989 and 2009.
Travelled all over the world with it in all sorts of weather and road conditions.
It had a U brake under the chainstays, never any problem really.

Re: Under chain stay U brakes

Posted: 29 Jul 2020, 6:28pm
by Pneumant
There ought to be a thread for spurious parts fitted to bikes by marketing departments :roll: The U brake lasted a year or two on MTBs with consumers wising up long before they were dropped. Sadly I was not one of those people and owned a 1987 MTB with a Dia Compe U Brake. This brake was perfectly placed to collect mud / filth/water requiring far more (regular) TLC than a seatstay mounted cantilever set. Brake performance no better than a cantilever either, if anything it felt like a big spongy centrepull brake which is, in fact, exactly what it was .

Re: Under chain stay U brakes

Posted: 29 Jul 2020, 6:40pm
by nez
I agree with those who 'diss' the U brake located under the bottom stay - but the trouble is I don't see a way of replacing it with, say, a cantilever without paying for posts to be brazed elsewhere - probably equalling the value of the bike. Interestingly on those weird little trick bikes that use them nowadays the rear brake is often located under the upper stay. I'm hoping I've added a picture found on t'internet to demonstrate.

Re: Under chain stay U brakes

Posted: 29 Jul 2020, 9:27pm
by cycle tramp
...Are still available, at least for BMXs. I guess in many ways the u-brake came about because in many ways putting a pair of brake bosses on the chain stay (usually considered more stiff, than the seat stays) and closer to the braced area would mean there's less braking force lost by frame deflection...
..in theory anyway..
..I guess in practice the design only worked in sunny America where mud was relatively unknown... here in muddy blighty things might have been some what different as the brakes collected every piece of crud thrown up by both the front and back wheel....
..however in bmx land the design has improved and developed - most of the designs seem to have the adjusters, operated by scanners and fixed on the 'bolt' (or non-frame) side of the brake arms (if that makes sense). Who knows with a decent set of mudguards to keep them clean u-brakes could be one of the ultimate rim brakes for touring bikes...

Re: Under chain stay U brakes

Posted: 11 Aug 2020, 2:20pm
by nez
IMG_0416.JPG
Finally - photos. From which you may judge the bike doesn't live with me...
I have made the brakes work but whatever I do I can't make them spring away from the rim with some vim and vigour. What I'd really like to do is replace them with something else, but I don't see any other form of brake working down there any better

Re: Under chain stay U brakes

Posted: 11 Aug 2020, 2:25pm
by Jdsk
nez wrote:I have made the brakes work but whatever I do I can't make them spring away from the rim with some vim and vigour.

What do they do without the cable attached ? And what do the pivots feel like when you work them by hand? (See above.)

Jonathan

Re: Under chain stay U brakes

Posted: 11 Aug 2020, 2:29pm
by nez
They're not bad at the hand-pull. The pivots are clean and greased. A lot of people would say 'there's nothing wrong with those' I think, but I put the bike back on the road for a mechanically incompetent and skint son, so I don't want to leave him with brakes which are a bit cr*p.

Re: Under chain stay U brakes

Posted: 11 Aug 2020, 3:00pm
by Pneumant
Assuming you have the L & R springs matched to the caliper arms?! To adjust & if memory serves me correctly use a spanner on the hex to move/tension the caliper arm away from the rim then tighten the cap bolt.