Tektro r538 rear caliper... on the front?

I was given a Tektro r538 rear brake caliper that I assumed to be the same as the front and intended to use as such but I've just realised the bolt is too short.

So is it possible to use a rear caliper on the front or is it completely inadvisable/foolish/impossible/dangerous?

Do you not just need a different bolt?

sheldon brown says it is OK, so it must be....just be careful that it stays tight....and will only work if you have forks with enough diameter to take it....

I've done so by using a V brake pad allen key nut which tightens up against the inner face of fork crown-2 years in and I'm still alive

Snotty, a different bolt yes, but an unusual one with two different sizes of threads and a particular head. I found one in an old front caliper that works. It involved dismantling the caliper which was rather fiddly but it's together now. I'll keep an eye on it to make sure nothing works loose.
Why are these things never simple?

http://www.sjscycles.co.uk/problem-solvers-xl-caliper-brake-mounting-bolt-for-carbon-thick-nut-each-prod18239/

rather than a new bolt which shimano sells for extortionate money you could try a longer recessed nut that will reach further into the fork and engage with the shorter bolt..

the above link is to one up to 30mm, but if you need longer you can go to a specialist hardware store like clerkenwell screws and they should be able to sort you out.

the only problem you may run into is that some forks have an internal lip that prevents a longer nut reaching far enough into the fork to interface with the shorter bolt.

just poke a toothpick / pencil in there to feel if there is a lip that would obstruct a longer nut reaching the bolt.

A brake is primarily a safety device. There are already enough things that can go wrong with them. If brakes fail, the consequences (face plant, soiled underwear, hospital food, life in a wheel chair) are not really worth the small savings made, so I would just buy a new brake or at least the correct pivot bolt.

+1 for 790's solution - especially if you're running a rear brake on a steel fork - as long as you're getting 4 turns of thread engagement you'll be fine

I tend to favour 6 full turns of engagement - that threaded coupling is in tension and the only thing between you and smashing into the back of a lorry.

On the other hand, R538s are so cheap that it's hardly worth bothering

I tend to favour 6 full turns of engagement - that threaded coupling is in tension and the only thing between you and smashing into the back of a lorry.

On the other hand, R538s are so cheap that it's hardly worth bothering

+1
Brake pivots are normally M6 x 1mm pitch which with a standard nut (5mm deep) means a minimum of 5 threads (or turns if you like) must be engaged. If the whole nut isn't engaged, the stress on the engaged threads is greatly increased, making stripping of the threads more likely. Bearing in mind the thread is in tension during braking, the whole set up could suddenly turn ugly when the caliper gets ripped out....