Front brake service / set up 400/4 advice please

[Rozabikes Tim]

Just getting my 400 up and running for pre resto check for any gremlins.

Motor running suprisingly well bar some primary chain and camchain noise. Dare not ride it far as front brake useless even by sohc standards! I know this is well covered on the forum but can't easily find relevant posts. Can someone point me to best post or just advise from experience.

Tim

[Nurse Julie]

All I can tell you is that it has a floating caliper, and mine needs adjusting every 50 miles or so due to squeeking on braking. New pads fitted about 5k ago. Not the worse bike I have ever owned for braking, that was an old 750 Bonneville. With the CB400/4 just pull the lever in on Tuesday if you want to come to a halt on Saturday at 3pm 

[mike the bike]

Make sure the pads are free to move, likewise the caliper pivot.  Grease the pivot with Copaslip or something similar.  Bleed the brake.  Fitting Stainless brake hoses makes a difference.  Use PTFE tape on the bleed nipple threads so it doesn't seize.

[Rozabikes Tim]

Surprisingly pivot arm moving great, piston side of caliper  really stiff. On stripping, pad corroded on back plate sides / ditto in front of caliper round contact area with it. Piston pitted so either replace now or clean up and see, then do proper job on resto. From what I read, new pistom from DS and genuine Hionda seal. I know copaslip can be used on pins etc on more modern and car calipers. Is a smear of this ok or a no no on sides of pad back plate?

[kent400]

All good advice here, I too wasn't too happy with the front brake performance and genuine Honda brake
pads improved performance. Keeping the disc clean with a frequent clean with brake cleaner spray also seems to help. The corrosion on the piston to caused by moisture within the brake fluid so it does need to be changed every three years or so. Alternatively change to silicone brake fluid which does not absorb moisture and before anyone says it's not compatible with the various seals after 15 years of using it following master cylinder/calliper rebuild all is fine. Still on the original hoses. Also it won't damage paint and we all know what a mess can be made when bleeding the front brake.   

[AshimotoK0]

I found an old article on this ... tried to photo it as no scanner at the mo.

[ Guests cannot view attachments ] [ Guests cannot view attachments ] [ Guests cannot view attachments ] [ Guests cannot view attachments ]

[Johnwebley]

give both the caliper and piston a complete strip down and clean,

 make sure the seal groove is clean,replace the seal ,(it should only cost about $4) as the seal and how it flexes is the
heart of how disc brakes work,

 assemble carefully,ensure the pads move freely,use copa grease around the pad will (should ) cure the squealing ,

 bleed,and see what happens,it should be SO much better

[Rozabikes Tim]

Absolutely what I was looking for chaps. Experience based advise always the best! Looks like a good article Ash, great if you could scan when available again.

What a marvelous forum!

[mike the bike]

If, after all the TLC outlined above you're still not happy with the brakes,  I would recommend a master cylinder repair kit.

[Rozabikes Tim]

If time allows I will sort next weekend. Just want to be able to get it to stop this side of Xmas (if I apply the brakes now -per Julie  ). As I say, just a pre resto shake down. If cant get it acceptable short term, recon I will go for a stainless piston and genuine seal per ebay link below.  Anyone here used them?

http://www.ebay.co.uk/itm/262018047322?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[Rozabikes Tim]

Went for it and bought piston and seal kit. Also silicone based fluid as suggeted. Hopefully get out to the garage at weekend. Told esssential to get rid of all  residual conventional fluid. Any tips on flushing? Thinking meths then air line?

[K2-K6]

As I understand it generally with calipers the seal operates in a very particular way which you need to make sure it's able to do.

The groove in the caliper body has the face (back face looking into the bore) at 90 degrees to the the bore the piston travels in. The front face (the one nearest to you which you can't see) is at a small angle which is leaning outward towards you.
When the piston is at rest with no pressure on it the the seal sits square to both the piston and the back of its groove. When you use it, as the piston moves outward it drags the seal with it but the seal in the deepest part of the groove remains static. Because of the slope on the groove is in the direction of piston travel, the seal deforms in cross section to a parallelogram shape rather than a square section. Then when you let go of the brake lever it's the seal deformation that as it recovers back to its original square section that retracts the piston into the caliper. This is absolutely vital to the caliper functioning as it should.
If the piston fails to retract then the pad is always applied gently to the disc. It's this status that gently glazes the pad and makes it squeal, also reducing it's ability to generate friction and voila,  crap braking is the result.

The taper in that seal groove is where corrosion builds up as it has no additional seal to protect it. The seal becomes held static by the corrosion filling up its movement space so that when you use the brake the piston is forced straight past the seal without deforming it,  so no retraction takes place and it just drags all the time.
To make it all work properly,  that seal groove has to be scrupulously clean,  the seal needs to be of the right material/dimensions and you may want to assemble it with brake specific rubber grease.

[RGP750]

K2-K6 Great info there , thanks for that.
Understanding the full function of a design really helps when restoring anything.

[Trigger]

And as I have said before : treat it as a whole system, just changing or looking at one part will not help. You have to go through the lot if you want everything to work as it should.

[Rozabikes Tim]

Fab info chaps.

Any specific checks on flushing system for silicone fluid change?