Cycling UK Forum

Any suggestions where i can obtain the allen headed bolts that secure V-Brake arms to pivot studs . Mine have gone rusty .

I have a couple in my bits box - PM me your address details and I will pop them in the post in the morning

George

scotsmanincumbria wrote:I have a couple in my bits box - PM me your address details and I will pop them in the post in the morning

George

PM sent .

while we're talking about these bolts, I have a question for the experienced mechanics reading this topic! I have just put together a lovely tourer, which uses pivot brakes, and boy did I get tired of twiddling that allen key, getting the 25mm-ish long bolts on and off - do they need to be that long? I'm thinking of cutting them down somewhat to save twiddling-time... then it occurred to me that the pivot braze-on might depend on the full length of the bolt for structural integrity, thus it might not be a good idea to cut the bolt down - any comments?

simonineaston wrote:while we're talking about these bolts, I have a question for the experienced mechanics reading this topic! I have just put together a lovely tourer, which uses pivot brakes, and boy did I get tired of twiddling that allen key, getting the 25mm-ish long bolts on and off - do they need to be that long? I'm thinking of cutting them down somewhat to save twiddling-time... then it occurred to me that the pivot braze-on might depend on the full length of the bolt for structural integrity, thus it might not be a good idea to cut the bolt down - any comments?

Your closing comment answers the question - if you think of the strain that grabbing the wheel rim takes you can see why.

As an aside to that ... there's also an interesting question that would relate to disc brakes and carbon (front) forks ... the stopping vs leverage/fulcrum must be quite a strain?

Rob

simonineaston wrote:- do they need to be that long?

When I built up a bike recently I was short of the 'proper' bolts for my cantilevers, but used some dome-headed brake-block bolts that I found in my bits box. Worked fine for a few weeks until I bought some mini-Vs (to solve squealing) which came with much longer bolts, which were a bit tedious to fasten all the way in.

In case anyone asks, I doubt that the short bolts were so short that they were the cause of the original squealing. But I suppose I do feel more confident now I've got the longer bolts; especially on the front brake.

Ray

I think I'll stick with the full-length... I've never know Shimano (or in this case, Tektro!) supply more metal than they need to, so I think it would be safe to assume the bolts need to be that length. Thanx folks.

simonineaston wrote:I think I'll stick with the full-length... I've never know Shimano (or in this case, Tektro!) supply more metal than they need to, so I think it would be safe to assume the bolts need to be that length. Thanx folks.

That's sound advice . For safety sake alone,i would use what the manufacturer supplies or recommends,particularly where brakes are concerned .

Drake wrote:

simonineaston wrote:I think I'll stick with the full-length... I've never know Shimano (or in this case, Tektro!) supply more metal than they need to, so I think it would be safe to assume the bolts need to be that length. Thanx folks.

That's sound advice . For safety sake alone,i would use what the manufacturer supplies or recommends,particularly where brakes are concerned .

I have had brake cable pinch bolts fitted to new brakes where the bolt heads snapped off as soon as I tried to nip up the cable. These people are not infallible....if something looks wrong, check it out.
I have a vague idea canti. mounting bolts are longer now than they were 20 or 30 years ago, but all the bits are......somewhere!!

robgul wrote:

simonineaston wrote:while we're talking about these bolts, I have a question for the experienced mechanics reading this topic! I have just put together a lovely tourer, which uses pivot brakes, and boy did I get tired of twiddling that allen key, getting the 25mm-ish long bolts on and off - do they need to be that long? I'm thinking of cutting them down somewhat to save twiddling-time... then it occurred to me that the pivot braze-on might depend on the full length of the bolt for structural integrity, thus it might not be a good idea to cut the bolt down - any comments?

Your closing comment answers the question - if you think of the strain that grabbing the wheel rim takes you can see why.

As an aside to that ... there's also an interesting question that would relate to disc brakes and carbon (front) forks ... the stopping vs leverage/fulcrum must be quite a strain?

Rob

Is this the logic for Thorn putting their brake on the back of the fork,so everything in in compression not tension?
It,to me,looks unattractive though.

http://www.sjscycles.co.uk/thorn-nomad- ... prod27191/

breakwellmz wrote:Is this the logic for Thorn putting their brake on the back of the fork,so everything in in compression not tension?
It,to me,looks unattractive though.

http://www.sjscycles.co.uk/thorn-nomad- ... prod27191/

I think the reason Thorn put the brake bosses on the rear of the fork had a lot to do with the introduction of self energising brakes at the time which were generally only available for rear brakes only. Thorn found them very effective for stopping tandems. (This was in the days before V brakes made an appearance). Also by using the brakes in a reverse action with a cable actuator (dont remember the proper name of this but various manufacturers made them including tektro - sometimes called a brake booster) made for a neater cable route than normal.

Going backto the thread (sic) about bolt length - i believe that 90% of the load is carried on about 2 threads only so there is no reason to have excesively long bolts. The recommendation is for bolts to be at least as long as their diameter.
See this link http://www.roymech.co.uk/Useful_Tables/ ... Calcs.html
However it could be that a longer bolt provides a reinforcing action in the Pivot which may explain why they are generally so long.
No doubt some engineering expert will be along soon to shoot me down.

About 15 years ago (early-mid 1990's) Shimano introduced longer pivot mount bolts for their cantilever brakes (no Vs then) to reinforce the pivot. They had found that cheaper bikes with their brakes on sometimes had the pivot boss fail, so they lenghtened the bolt to reinforce the pivot to reduce this risk.

You need to calculate the minimum thread engagement, this program will do it, but you need to change some of the input values (I don't think cantilever bosses are made of cast iron):

http://www.tribology-abc.com/calculators/e3_6e.htm

Edit: Here's the link to the wikipedia guide on bolt gradings http://en.wikipedia.org/wiki/ASTM_F568M

simonineaston wrote:I think I'll stick with the full-length... I've never know Shimano (or in this case, Tektro!) supply more metal than they need to, so I think it would be safe to assume the bolts need to be that length. Thanx folks.

In case you want to fit a mini rack that attaches to the bosses maybe?
The mounting brackets can be 5mm thick.