Novakane 

I'm sure there's been plenty of discussion about threaded to threadless conversions but I didn't find anything that covered my particular concerns.
I have a 23" 1979 Raleigh Grand Prix frame - pretty common stuff, it had totally thrashed paint and a lot of rust thus I de-rusted it and found little paint intact - so I sanded it down and found it was generally good shape under that mess so I'm re-painting it and deciding how I might build it back up a bit differently. It's a common frame, doesn't have any sentimental value and has already been paint stripped so although I'm a vintage nerd, this particular one holds no concerns to trying to keep it original lol.

I was considering changing out the front fork for a threadless model, particularly one that has disk brake mounts and was also considering either a 700C or more ideally a 650B conversion for the wheel set.
I might stick some north road or similar upright position bars on there and make it less road-bike and more casual/comfortable for longer rides.

I know that I will need to source a fork with a 1" stem to fit - but I seriously doubt anyone has ever made a disc brake fork for a vintage 27" wheel size since nobody is putting disk brake hubs on 27" rims (I assume, because ... why would you?)
I have found that there are 700C disc forks available in 1" ... But what I don't know is:
- if putting a 700C fork on a bike intended for 27" is going to cause any serious issues? Presumably the whole bike will end up tilted forward by a few mm due to the forks being shorter
-- or do I just need to find a certain length of fork to compensate for the difference? Is spacers under the head tube a thing?
- most of these forks are straighter than the original, but do seem to have a forward rake, does the axle end up in the same place generally, will I still have the proper clearance?
-- is there a certain angle I should be looking for or avoiding for this application?

I'm not totally committed to it being a disc fork - that may be a unicorn, but it's the general of "will the conversion work with a 700C fork on a vintage frame?" and "what factors should I be concerned with when shopping?"

3alarmer 

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...in general, the tilting forward problem usually takes care of itself, when you match up both wheels as 700c.
I would shop around online and see what shows up as a 1" threadless headset these days, before I got too far down the road on this.

For a while, those were difficult to find. Threadless didn't really take off until steerers were going to 1 1/8". But they did make some.

The rake/trail thing is hard to predict. Your new fork might turn out to handle better (or worse), than the original. Try to stay as close as you can to the original. in terms of trail.

Leisesturm

Ffinding a threadless fork steerer tube in 1" will be quite a trick.

base2 

What would be wrong with obtaining a threaded fork & cutting the threaded area off. Wouldn't the unthreaded (shank) area of both types be the same diameter ?

It would have to be quite a long unthreaded area, though.

base2 

1 inch threaded to threadless conversion headset invented by a BF member.

Iride01 

Is your current fork in good shape? Just find a person that does brazing or silver soldering and have them cut the steerer tube off a few inches above the fork crown and then use the unthreaded part of a steerer tube from some other junk fork to have brazed on to the stub of the fork you wish to use. You just need to fashion a union out of another small section of steerer tube by splitting the tube and making it smaller to fit inside the steerer tube where they will be joined.

You might get less naysayers about this if you go to the Framebuilders forum and ask. For certain you need to have this done by someone that is competent in brazing and this type metal work.

As for the headset, you'll have to look, they are out there, but not in great quantity or selection. However the treaded headset on my '78 Raleigh Competition GS seemed like it'd work for a threadless with a little modification. I never found out though as I bought a new bike and that project when by the wayside.

HillRider

Cane Creek still offers a 1" threadless headset in their 40-series. I have one on a mid-90s Litespeed frame I converted to threadless.

70sSanO

It appears that once upon a time 1" 700c disc compatible forks were available. The market, or lack of, probably lead to their demise.

https://www.bikeforums.net/bicycle-m...atability.html

John

Novakane 

Thanks for all of the replies. After some searching, I found that I could find such a unicorn fork (1" threadless with disc brake attachments for 700c) but - it would run me about $500 to get it and that seems prohibitive for a project like this, yikes!
There are some reasonably priced 700c forks available for 1" threadless but most are lacking in fender braze-ons which really limits the usefulness.

I do still have the original threaded fork.
I guess it's probably going to be easiest to just stick with that one and if I do want to use threadless parts up top I can just get a quill adapter, it doesn't seem likely I'm going to easily get a disc brake on this bike, maybe I'll look into hub brake options.
Thanks again!