New to CB400 four and new here! Front brake improvement?

[Oddjob]

There is also a strong spring on the adjusting bolt to make sure the fixed pad moves away from the disc when the pressure is released.

I am however in disagreement with Bryan regarding cleaning the slot for the seal, a Dremel is ideal for this job, it's what you put on the end of it that matters. The abrasive discs I use will remove alloy, the crud that collects in the slot is hard but it's no match for the discs, I wouldn't use the most abrasive ones though, a 220 one should work to do the heavy work and then go up to 400 and 800 to finish off the slot.

I'm currently restoring a CB550 rotor cover that's been down the road and has some bad gravel rash on it, it's about 80% done and was restored using those discs, I'll post pics of it when finished and I'm sure you'll be surprised just how good these discs are for cleaning alloy, the inside of a caliper body for instance will look new after some light brushing with these discs and they are cheap, you can get around 27 pieces for £8.

https://www.ebay.co.uk/itm/314692515911?hash=item494522b847:g:oUQAAOSwoBRkpjs3&amdata=enc%3AAQAIAAAAwLV96za6Q43eRYqm8FJ6aiJrsd%2BoMDHOxQUCd77uPlqr9YduV6EDM17ZrfMDX6jnnJhylJvKR90AJgHLjPHwrkhs2j%2BKIIjLCKrpYplPDH1a7R5jztAskFfgw%2FTCRL78iyBS2Er3JP7H2oBUbNa90OZ4E8Isk1%2FmIYGOC98SI%2Fp8oUD2u%2BagCp5sDrIYTLYJgPTSNje1fip332tY7CmXh59xmm7dt8l87qnj66y1tpnqAIHIDjOhz2OBK6zbii3Dzg%3D%3D%7Ctkp%3ABk9SR6DyiM2zYg

[robvangulik]

I am with Bryan on this, any brush you use only polishes the crud, and as those discs, as you say, will remove alloy, the risk to remove more than just the filth is always there.
It is only one groove per caliper so how much time can you save by doing it mechanically in stead of by hand?

[Oddjob]

They aren't particularly aggressive Rob, sure they'll take alloy away if left there too long but they really only remove a few microns. Hence why I said not the most aggressive type which is 80 grit, that would remove any crud in there no problem at all, it wouldn't TBH do any particular damage if used lightly either. I've been using these for a long time now and know exactly what they are capable of and how to use them, I'd say anything pointed like a dental pick for instance stands a far higher change of damaging the alloy than these discs, as you can't really see inside the slot your sort of guessing how much is still left in the corners and how hard to use the pick. I've used these discs on my calipers and the result was really good, super clean and no damage visible.

[Trigger]

Bryan is correct, no brush will get in the corners, so a nice angled pick cleans them in good order for a replacement seal 

[robvangulik]

I've been using the same tool for the last 40+ years, an adapted wheel spoke with two almost 90° bends and a flattened end, doesn't damage anything but scrapes dirt out of any corner without getting my hands in a knot

[Laverdaroo]

Abrasive discs every time for me. There might only be one but the crap in that groove can be atomically welded in there that a pick simply won’t shift.


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[Mikep328]

In doing further research, I found an instance where an owner of a couple of 400s noted that one had poor brakes while the other is OK.  Both were OEM but there was no info re if they had different type of pads, etc.  So maybe one was adjusted better/had more aggressive pads.

I have ordered two sets of pads - a sintered set and an organic set.  I don't know what type/brand is in the bike at the moment but they have a different color backing plate to either of the two I have ordered so it's probably different than either of the pads I purchased.  I am thinking that if different pads don't improve performance, I am going to purchase a Brembo MC with a 12mm piston and, assuming it makes the huge difference I expect, regretfully adopt the non-OEM look.

[McCabe-Thiele (Ted)]

The 500 has the same front brake I believe - fitting Brembo Pads worked fine for me on my 500. 

I guess it all depends on expectations - if you ride a modern twin front disc bike you will never be happy with the standard 400 set up.

[Mikep328]

Yeah, might be chasing windmills here...but my 400's brakes have to be noticeably better than they are right now to ride routinely and safely on normal roads with typical traffic/situations. 

I'll advise if I find any improvement with either of the different pads.

[McCabe-Thiele (Ted)]

My base for motor cycle brakes were the old drum brakes on British bikes. When I had my XJ900 the brakes were just fantastic but so was the performance. With my 400 the brakes were so much better than my Aerial Leader with similar performance.

[Mikep328]

Question...re the fixed pad/swingarm...

When the fixed pad is adjusted to have the minimum clearance is that spring on the adjusting bolt supposed to push the fixed pad/swingarm back to the established clearance?

This morning I found that even if I adjusted the bolt to provide far too much clearance, so I could move the caliper back/forth maybe 8-9mm by hand, once I applied the brakes and then released the lever, the swingarm/pad did not move back to the 8-9mm clearance.  I had to push the caliper inward to re-establish the clearance.  Is the spring supposed to be strong enough to do that?  It doesn't seem to be very strong - easy to compress with my fingers.

Further... I pulled the caliper bolts to determine the type of pads.  They appear to be sintered pads.  No idea of the brand but "JB CR FF" is stamped on the backing plate.  Don't know what that means.   The pads are quite thick so appear to have very little mileage/use but there are grooves worn into the pads though the rotor is perfectly smooth.

[Bryanj]

Sounds like that pivot pin is starting to sieze up, the bracket needs to be super free

[McCabe-Thiele (Ted)]

Bryan is correct about the pivot. plus the pads will be pushed away from the disc by a high spot to provide clearance.

[Mikep328]

Thanks guys...

I checked and the pivot pin/swing arm is very free/moves with no effort at all if the adjusting bolt is loosened to provide some clearance and I physically push the caliper in which forces the active pad back into the caliper and creates the clearance.  But it won't return to that clearance on its own once the brakes are applied/released.  The spring cannot force the active pad back into the caliper to "open up" the clearance.  I suppose it doesn't really matter - it's common for disc brake pads to JUST touch the rotor even when the brakes are not applied but if the 400's pads are supposed to stay in light contact with the rotor, what's the point of the spring? 

[Oddjob]

The spring is not there to force the active pad back into the caliper Mike, it's there to push the arm backwards so that when the active pad retracts the arm moves away from the disc allowing the clearance needed to stop the brake dragging. It's the piston seal that pulls the piston back into the caliper, as the piston moves out the seal distorts, it's this distortion that applies pressure to the piston and the seal trying to retain it's shape that pulls the piston back. It could be that the piston is pulling back but the pad is not, the pad should be just ever so slightly loose in order for the arm when it's being pushed back by the spring pushes the pad back into place.

If you remove the caliper and test the arm you'll find the spring is plenty strong enough to push any movement to the left back again, maybe test that and see if the spring has lost it's tension or maybe it's the wrong spring.