Topic: New front caliper or complete front brake set?

[78CB750F1]

My front brakes on my CB750 F1 are useless - I believe it is a combination of worn front wheel bearings (being replaced) and a stripped bleeder screw that is preventing me from bleeding the lines.  I will be installing a modern master cylinder assembly, removing the brake light pressure switch and using stainless steel line to try and get the best front braking performance possible.  I tried extracting the stripped bleeder screw on  front brakes but it is too damaged.  I need to replace that part of the caliper and could use some advice.  A local supplier provides a rebuilt part of the front caliper (top photo).  However, they also offer a full double disc conversion set for another 100 euros that includes a reconditioned disc (bottom photo).  I am considering requesting a complete left side set to replace my current system - is it worth the extra money to get the full reconditioned setup?  Do front discs wear considerably and require replacement? 

[Clyde]

The F1 brake is slightly better than the K0-K6 brake as it has a slightly larger caliper piston. The master cylinder is the same on both bikes.
The F1 caliper also uses different mounting bracket. Note the two bolts entering from the outside on the F1 whereas the early caliper uses two allen/hex head bolts from the inside and they are spaced differently. Also the location of the bleeder screw is different
The photo you have of the dual disc setup shows the early K caliper and first model bracket/arm(K0-K2) which will not fit on your forks. The actual caliper on the K did not change until the K7 when the F1 caliper was used for both the K7and K8. An K0-K6 caliper could be fitted if you use a later K bracket and arm. The F1 caliper uses a different arm to suit the caliper as compared to the K3-K6, but the fork bolt layout is the same for the K3-K6 and F-F1, so if you use the matching arm bracket with the caliper they can be substituted.
I am not sure what master cylinder you are using (ie what bore), but if it is bigger than the std MC you will lose some leverage and perhaps some performance.
Reasonable braking can be achieved if you overhaul the caliper with a new seal and also the MC with a new kit. If your brake hoses are suspect I would replace with braided ones. Bleeding is obviously critical
Make sure the arm swings smoothly and is lightly greased- they have a tendency to seize especially if used in wet and/or salty weather.
Most of the discs I have seen are not worn very much, but they do tend to glaze up and this can be removed by light sanding.
Hope this helps (after reading this It seems like it may confuse?)
Clyde

[78CB750F1]

Thanks Clyde - you are right, the kit pictured is for the earlier K series but the same kit is available for the F and later K series.  I didn't realize that the bore of a replacement master cylinder had to match the original - what size should I be looking for?

[SteveD CB500F]

I think Clyde was talking about the bore of the brake caliper (not the master cylinder)

You can use any M/C you like as long as you can match up the banjo bolts to the (new) brake lines.  Some on here have used modern (CBR etc) M/Cs with good results.

[Clyde]

The smaller the bore of the master cylinder the higher the pressure you can generate and this pressure is duplicated at the caliper piston. The larger the bore the  less pressure but more volume. A master cylinder gives a leverage effect which is equivalent to the ratio of the area of the caliper piston divided by the area of the master cylinder piston or about 7.3 for a standard setup (38mm piston and 14mm MC). This becomes about 5.8 for a 5/8" MC with a 38mm caliper piston
With twin discs you need to be able to move more brake fluid (two caliper pistons), hence a larger bore, but you have double the braking area which more than compensates for reduced leverage
As with most things it is a compromise. If you plan to use twin discs I would, given the choice, go for a 5/8'" master cylinder (like the CB900/CB750F2/CBX and most modern master cylinders). If I had a std single disc setup I would stay with the smaller master cylinder (14mm bore). I have used a small master cylinder with twin discs, but would not recommend it unless you go to all braided brake lines.
I have also used a CB900 MC with a single disc setup and although theoretically it should be worse, there was not a lot of difference.
Hope this is of some help
Clyde

[Gabus]

Braided brake lines improved the feel on my F2. The lever still has some movement before it gets firm, but it's firm now and never was with OE brake lines.