Topic: 1975 CB400/4 Front Brake Upgrades

[NikoLovell]

I recently hopped back on my 1975 CB400/4 after 2 years of riding modern bikes and the front brake is not cutting it. I have searched the Internet for possible bolt on upgrades, but found nothing. Have any of you found a solution to improve the brakes on this bike?

[bryanj]

Special cast slider for twin discs but it still wont be as good as modern bikes, if you think the 400 is bad try a drum braked triumph 500

[newday777]

Welcome aboard the forum NikoLovell from southern NH.

The shortest route will be to take apart the master cylinder and caliper and fully clean them out of any crud(especially to carefully scrape out the groove the seal the caliper piston seal resides in so it has full motion), put in rebuild kits, a new caliper stainless piston if needed, and buy replacement stainless steel brake hoses so you get full pressure transfer to the caliper piston to brake far better than the flexible rubber hoses(especially if they are the old original rubber hoses to the bike).
That will give you much better front braking and keeping the stock appearance.
The next level is to have the rotor drilled and surfaced by someone like Godffery's Garage(a member on here, in Wisconsin)

The stock 400F fork legs are only set up for a single disc system but there are a little better forks and brakes in the 80s.
This thread link is about changing the forks to early 80s front end with the a single disc, dual piston caliper and drilled disc. He gives you the parts references needed and pictures. Read through the thread start to finish for some great upgraded front brakes and bigger diameter forks(better handling). Again, put on new Stainless Steel hoses for best braking performance.

http://forums.sohc4.net/index.php?topic=178947.0

Next level would be to change the front end to an inverted fork system of a GSXR or Niga type with dual discs, which would be at a higher cost and full modification process. Cognito Moto might have the upgrade triple tree and stem conversion already figured out?? I haven't got those details.

Keep this thread of yours going on the progress through replies on the route you go with to keep all the information together. (Bookmark this thread to keep easy access for it. If you haven't yet, click the notify button to get emails with links on replies that come in as it isn't automatically set on this forum, you have to set it manually.)

BTW, Go to the new members section of the forum and introduce yourself and your bike and ideas on it. Pictures of how you got it and history of the bike is always welcome. (And change your location in your profile to an actual location as others in your area might be able to help you out when in a bind or have knowledge of parts availability locally). I'll be following along on this as I have a friend here with a 76 400F that we worked on it last Saturday and found he has to replace the right fork leg because of a busted fender mount casting (or get it welded and shaped to repair it)
Lots of great help and peeps on this great forum. Again,  welcome aboard 😀.

[newday777]

Here is Godffery's link for drilling and resurfacing the rotor

https://godfferysgarage.com/

[RAFster122s]

You will spend over $1000 to do a modern right side up or upside down for with modern calipers and master cylinder. Likely closer if not above $1500.

[jonda500]

Change the master cylinder for one with a smaller diameter bore/piston, or just simply learn to grab the brake lever right at the end for more leverage! John

[jakec]

New reproduction caliper and piston, and MC. New SS braided lines. New pads and resurface and drill disc. I did all this and mine is very good.

[Quattrocilindri]

I recently hopped back on my 1975 CB400/4 after 2 years of riding modern bikes and the front brake is not cutting it. I have searched the Internet for possible bolt on upgrades, but found nothing. Have any of you found a solution to improve the brakes on this bike?

Yes, the braking on this vintage bike does not even come close to modern bikes, as you found out after 2 years of riding modern machinery. And that is the dilemma: assuming that your original set up works and is maintained as designed (modern pads, effective master cylinder and caliper, modern hoses, etc.) one cannot simply ride this old bike the same way as a modern machine, which is more powerful, handles better, and has better brakes. I have owned a 400f and now a 350F, and I find their brakes adequate, but certainly not spectacular. So, I just take it easy on them, not expecting much more than their original performance (and limitations).

[scottly]

Change the master cylinder for one with a smaller diameter bore/piston,

1+ The stock 14mm master too large for a single 38mm caliper.

[jonda500]

Change the master cylinder for one with a smaller diameter bore/piston,

1+ The stock 14mm master too large for a single 38mm caliper.

The only way to get better leverage and therefore a noticeable improvement is to use a smaller master cyl bore, larger caliper bore or add a second disc - none of the other suggestions will take it much beyond the original mediocre performance, John

[RAFster122s]

The original discs, even drilled won’t give you modern brake performance…never gonna happen, the smaller diameter master cylinder is a step in the right direction. Combine that with the Teflon braided stainless hoses, 2nd caliper, drilled disc (better wet braking performance), and changing the caliper brake pad material to a semi-sinter compound and you will achieve much better braking performance. You will never achieve the braking capacity of modern cars and trucks, so give yourself additional room for brakimg. I know in big cities you will get frustrated repeatedly by other drivers taking your room you are trying to maintain as excessive because they have no clue why you are giving what they view as room for them to get in front of you.
I see even modern MC riders following close and think to myself they are playing a dangerous game and they will lose sooner or later and blame others for their lack of defensive driving.