Just how do you convert an f1 to twin disc

[JonnyHonda]

Hi all, have you seen the gallery, there are two cool CB750 F's in there, with dual front disc conversions.

Has anyone actually done the conversion themselves, and how? :blink:

Also would this affect the insurance as being  \"Modified\"

[TheCamel]

You swipe the front off of a '78?

[lordmoonpie]

I've just done this conversion for my CR750 project. I'm not entirely sure it'll be the same for the F1 as I'm a K series man myself but I would think it should be?! You simply use a K series hub if the F1 doesn't have bolt holes straight through and mounting shoulders for twin discs (most models do for the USA market). You'll then need a second disc, six longer bolts to hold both on the hub and a right hand fork leg off a twin disc USA model. The right hand caliper is just a standard left hand one reversed on the same caliper mount. If you use the normal K series caliper hanger of the plain hinged blade, you just re-use a right hand one. It's less pretty because the brake line then bolts into the caliper on the leading edge so isn't symmetrical. If you want to use the old K0 type caliper hangers you either need a genune CR750 parts kit or get a mirror image of the right one machined - very expensive. Other than that, there's nothing else to do - it's really straightforward!

[leonardo269]

Hi, I have done the conversion on a K7 which i just an un-sporty version of the your F1.
The F2 had twin disks so getting an F2 front end may be a route to go (although I havent done this).

The way I have done it is to first buy an extra cb750 caliper and disk to match the existing one. When fitting the disks you will need longer bolts (I think they are 110mm). the chrome speedo cover has to go and you have to carefully drill & screw the speedo drive (screws flush) in place to the wheel. This is tricky -  you do not what to drill into the bearing! when this is done the speedo drive will sit in place and will just about miss everything!

Next fit the wheel and the caliper arm. (the adjustment screw locknut fits on the inside of the stanchion).

The caliper arm must be in a similar position to the one on the other side. This means taking a file to the mounting lugs on the stanchion until the disk pads lie flat to the disk.

You will need an extra brake line connecting from the extra caliper to the master cylinder.

Finally you will need a dual disk master cylinder that is capable of pumping out enough fluid for the two calipers. Connect your two brake lines to the master cylinder with a double banjo bolt and 3 copper washers. Typical bikes to go for are twin-disk Nighthawks, Gold-wings or a good one is CX500 as they are cheap. Make sure that you get one with a mirror boss integral with the master cylinder.

Brake levers that are the wrong colours can either be replaced (if possible) or polished to the ally and the ends dipped in black rubber paint

Bleed the brakes and away you go. B)

If I have made any of this sound easy , beleive me it isnt. It takes a lot of time searching for bits on eBay and head scratching to overcome some of the problems, but you do get a much better front brake at the end of it all.

I declared this mod on my classic insurance (Footman James) and it was no problem. (I guess they think that improving the brakes is not something they ought to discourage!):woohoo:

I have also included a file I found on the internet when I did mine that you may find useful.

Oh by the way before you do anything with brake fluid, cover you tank with plastic or better still remove it - brake fluid gets everywhere and is the best paint remover you can get. :sick: I even had to put bubble wrap around the throttle grip because the slight contamination of brake fluid on my hand was causing the rubber to melt!

Regards

Ray

Post edited by: leonardo269, at: 2006/11/17 22:47

[leonardo269]

Hi, I have done the conversion on a K7 which i just an un-sporty version of the your F1.
The F2 had twin disks so getting an F2 front end may be a route to go (although I havent done this).

The way I have done it is to first buy an extra cb750 caliper and disk to match the existing one. When fitting the disks you will need longer bolts (I think they are 110mm). the chrome speedo cover has to go and you have to carefully drill & screw the speedo drive (screws flush) in place to the wheel. This is tricky -  you do not what to drill into the bearing! when this is done the speedo drive will sit in place and will just about miss everything!

Next fit the wheel and the caliper arm. (the adjustment screw locknut fits on the inside of the stanchion).

The caliper arm must be in a similar position to the one on the other side. This means taking a file to the mounting lugs on the stanchion until the disk pads lie flat to the disk.

You will need an extra brake line connecting from the extra caliper to the master cylinder.

Finally you will need a dual disk master cylinder that is capable of pumping out enough fluid for the two calipers. Connect your two brake lines to the master cylinder with a double banjo bolt and 3 copper washers. Typical bikes to go for are twin-disk Nighthawks, Gold-wings or a good one is CX500 as they are cheap. Make sure that you get one with a mirror boss integral with the master cylinder.

Brake levers that are the wrong colours can either be replaced (if possible) or polished to the ally and the ends dipped in black rubber paint

Bleed the brakes and away you go. B)

If I have made any of this sound easy , beleive me it isnt. It takes a lot of time searching for bits on eBay and head scratching to overcome some of the problems, but you do get a much better front brake at the end of it all.

I declared this mod on my classic insurance (Footman James) and it was no problem. (I guess they think that improving the brakes is not something they ought to discourage!):woohoo:

I have also included a file I found on the internet when I did mine that you may find useful.

Oh by the way before you do anything with brake fluid, cover you tank with plastic or better still remove it - brake fluid gets everywhere and is the best paint remover you can get. :sick: I even had to put bubble wrap around the throttle grip because the slight contamination of brake fluid on my hand was causing the rubber to melt!

Regards

Ray

[leonardo269]

Hi it turns out that I cant send you this file as it is in word format.

Anyone who wants a copy - just email me:-

rmdl17239@blueyonder.co.uk

Regards

Ray