Honda-SOHC
SOHC.co.uk Forums => CB350/400 => Topic started by: Ken4004 on January 12, 2026, 12:15:15 PM
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Hi everyone I have a question about the the cb 400 four front brake , I know that the front brake on this model is not great but after fitting a new master cylinder a new set of hoses and fully bleeding the system the brake lever can be pulled back to within 15mm of the handle bar grips.
I believe it’s probably due to the hoses expanding under pressure as you can feel them expanding under pressure.
The answer would probably be to change the hoses for some stainless steel braided hoses to stop this flexing but how much difference does it really make to the effectiveness of the brakes by upgrading the hoses basically is it worth it ?
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In October 2020, like yourself, I replaced evrything except the disc. These were all original type (NOT OE), fittings, so no braided steel hoses etc. Even now, when I apply the front brake, it is a very firm, nearly hard feel, and I'm sure that if I felt brave or daft enough I could lock the front wheel. If your flexi hoses are new, and you can feel them expanding, then I would send them back and try another brand. Make doubly sure that you have bled the system properly, quick check is to rapidly pump the handlebar lever, if it firms up th en you have air in the system. Check with some blue workshop paper round every joint to see if there are any leaks. Finally, make sure that you have adjusted the caliper to give the accepted minimum clearance between pad and disc. Sorry, cannot remember the figure. Get it sorted before you even think of taking it out on the road mate.
PS Have just found my old purchase details, my pipework I bought from Legend
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Hi Tricky thanks for the advice , no I wasn’t going to take it on the road as it is but just wanted to know what is normal, I cannot pull the lever right up to the bars but within 15 mm and I am pretty sure all the air is out.
I bought the hoses from Wemoto in Brighton so would have thought they should be reasonable.
I will check out all the set up again and see if I can get any more air out and see where I am after that.
Thanks again regards Ken
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"I know that the front brake on this model is not great "
Old wives tale courtesy of the internet. Per road test data from then/now the 400F had the same stopping distance from speed as current middleweight standard Honda's.
more info... (you can take a look at the whole thread if interested)
https://www.sohc.co.uk/index.php/topic,29559.msg285797.html#msg285797
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Quite possibly true Mike. Until it rains that is. Then it's pull and pray time. The other main difference is how it's setup. Brand new it would be ok, as it wore however it got worse, the new ones don't do that due to different design. For it's age it's a ok system, better with another disc fitted though.
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Difficult to twin disc a 400 as no mountings on second slider, i believe there were some castings made years ago for it.
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My 400F is my primary ride in the UK so it's seen a lot of use. I've ridden in the wet - though not pouring rain - and my best "statement" about the brakes overall is that I don't even think about them when riding. After doing the re-work AND the break in procedure for new pads that you (OddJ) so kindly posted back then, it stops with no issue/concern when I need it to stop! :)
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Bedding new pads in correctly can dramatically improve these old systems. Whilst the 400 isn’t that easy to twin disc the 500/550/750 which use the same setup are. I could lock the front wheel on my 500 if I used it hard. I did find the stainless steel discs suffered with water film and severely impacted braking performance as a result. However this was 30 odd years ago and things might have improved since then.
Glad to hear it’s working well for you Mike.
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As Mick says they do feel wooden with virtually no feel even when set UK correctly.
The last 400/4 I worked on had air trapped in the line that refused to budge. In the end I pull the lever back as far as I could and zip tied it to the handlebar, took the reservoir cap off and left it overnight, it worked.
As for the new rubber lines, I'm pretty sure genuine Honda items actually contain steel braiding sandwiched between two layers of rubber and they shouldn't expand.
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One of the not uncommon features regarding older vehicles, (2 or 4 wheels), is that nowadays they are being driven by people of all age groups, so there are differing expectations as to what is an acceptable level of performance. Being an old 'wrinkly git' I was brought up with the idea of firm/hard braking required firm/hard input from the driver. This method, when used with a well set up hydraulic or mechanical system gave great feedback through the lever/pedal. My first vehicle with a so-called powerful brake was a 1969 CB250 with a twin LS front brake, which I soon learnt not to apply too suddenly!! Bloody useless though when trying to stop the bike rolling backwards down a slope. I never had a car licence until I took my test in 1969 on a London Transport bus. Very satisfying, but the early type air brakes felt peculiar at first, it was just like pressing your foot on a firm rubber ball. Because there was no mechanical connection between the pedal and the brake shoes, the only feedback you got was from the seat of your pants. ABS had not been invented then, so I was taught the art of cadence braking on the skid patch in West London. Moving on, my present car, a 14 year old Peugeot is the first car I have owned with ABS. The irony of this being that 3 days ago, the ABS warning light illuminated, and stayed on. To me this is not too much of a problem, as it still possesses a working brake system like I have been used to. BUT!!! it will not pass the MOT. My GB250 is fitted with one of those 2 piston front calipers, which yes, is quite powerful, but has a vastly different lever feel to the 400, quite soft in fact. When I took it for its MOT, I queried it with the tester, and he replied that it was a perfectly set up brake. I realise that I have deviated somewhat from the original post, so, is there any progress on the offending front brake? It'll soon be spring, when the dust sheets can be removed from the bikes and placed over the model railway!! Stay safe everyone.
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Tricky, the abs light is frequently a wheel sensor covered in crap or failing, trouble is you may need an expensive scanner to tell you which one!
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Thank you got everyone’s input, I will try pulling back the lever and leaving it overnight as suggested by Dave and see what difference that makes.
As I said previously and people have commented on is the fact that I am comparing a 50 year old bike with a modern bikes brakes , things have come along way in 50 years.
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Oh yes, go and see if you can ride a Triumph T110 from 59 then you will never complain about the 400 again!
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To bleed the brakes I always remove the top of the reservoir and rubber diaphragm and just pull the lever back quite small amounts a few times in fairly quick succession. BUT you have to be be gentle to ensure the fluid does not shoot out. The bubbles will appear. Turn the handle bars full lock the other way and keep repeating. I didn't get any success with just pulling the lever right back. But did have one that still had what I thought was too much movement and fitted another spare M/C to improve it.
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Thank you got everyone’s input, I will try pulling back the lever and leaving it overnight as suggested by Dave and see what difference that makes.
As I said previously and people have commented on is the fact that I am comparing a 50 year old bike with a modern bikes brakes , things have come along way in 50 years.
The best way will be to pull the lever back and whilst you do so open the bleed nipple and then close it whilst keeping the lever pulled back. Once the nipple is closed allow the lever to return and then pull it back to the handlebar, zip tie it overnight but make sure you wrap a cloth around the handgrip otherwise the zip tie will cut into it.
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Great advice from everyone but please let me know how far you can pull your brake lever back before it becomes difficult so the gap between the handle bars and the lever as I said be for mine geo is around 15 mm just interested to see what gap other people had after bleeding their brakes.
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...I pull the lever back as far as I could and zip tied it to the handlebar, took the reservoir cap off and left it overnight, it worked.
That, and gently tapping on all the lines and hoses with the (plastic) handle of a screwdriver to dislodge the adhered micro-bubbles in there...
I'm pretty sure genuine Honda items actually contain steel braiding sandwiched between two layers of rubber and they shouldn't expand.
Again I concur...
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Great advice from everyone but please let me know how far you can pull your brake lever back before it becomes difficult so the gap between the handle bars and the lever as I said be for mine geo is around 15 mm just interested to see what gap other people had after bleeding their brakes.
My 400 has the DS replacement master cylinder, I use Silicone brake fluid, the flexi pipe was new in 2021, the gap between the bar grip and the lever at it's closest point is 4 cms with the lever pulled in hard.
Its a really solid front brake, not spongy.
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At rest
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Emergency stop
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At least 15 year old OEM hoses and MC rebuild kit. And using DOT 5 brake fluid
Regards
Dave
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My experience of the inside of the Honda brake lines was that the braiding was not steel, more like nylon or even cotton. It was white looking iirc. I could watch the lines expand under pressure, which is why most got braided stainless steel lines back in the 70s.
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Thanks for the info everyone looks like I need to do some rework but will start with another brake bleed .
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After the brake bleed, and assuming you have new brake lines that won't be expanding when you apply the brakes, bed in a set of NEW, brake pads properly and you will likely be happy with the front brake. Bedding in the brakes takes some effort, it's not a matter of just going out/applying them a few times. It is not really necessary on modern brakes but it will make a DRAMATIC difference/improvement on these brakes. I suggest the Vesrah Organic pads which were best of 5 different compound pads I tried when I restored my 400's front brake.
Here is the bedding-in procedure I followed, it was posted on the site by OddJ in Aug, 2023:
"Clean the brake disc off with brake cleaner to remove any existing pad transfer material, a gentle rub with some fine wet and dry won't hurt either. Then take the bike out and do 15 gentle brakes from 30mph and then a 2 mile cool down followed by another 15 or so from around 45mph using moderate brake pressure followed by another 2 mile cool down run, then stop to see how the discs look. You should clearly see some pad transfer, it's a sort of blue/grey mist on the surface of the disc, then do 15-20 full on braking sessions from around 65-75mph, dropping the speed down really quickly but rolling off when around 10mph and then back up to speed later, followed by a 5 mile cool down run."
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Thanks Mike great advice , I like the sound of the bedding in the brakes process.
Looking at all the advice I have had there must be air still in my brake lines so will end a couple of hours at the weekend to try and get it out.
I have bleed my brakes many times on my Triumph 1050 triple with no issues at all but I have always started with a filled system and used my myti vac to draw through new brake fluid and just top up the reservoir only normally takes me 15 to 20 minutes with no drama but with new pipe work and master cylinder there’s lots of air trapped everywhere.
Anyway I’ll get there again just a little patience needed.
quote author=Mikep328 link=topic=32445.msg315691#msg315691 date=1768827108]
After the brake bleed, and assuming you have new brake lines that won't be expanding when you apply the brakes, bed in a set of NEW, brake pads properly and you will likely be happy with the front brake. Bedding in the brakes takes some effort, it's not a matter of just going out/applying them a few times. It is not really necessary on modern brakes but it will make a DRAMATIC difference/improvement on these brakes. I suggest the Vesrah Organic pads which were best of 5 different compound pads I tried when I restored my 400's front brake.
Here is the bedding-in procedure I followed, it was posted on the site by OddJ in Aug, 2023:
"Clean the brake disc off with brake cleaner to remove any existing pad transfer material, a gentle rub with some fine wet and dry won't hurt either. Then take the bike out and do 15 gentle brakes from 30mph and then a 2 mile cool down followed by another 15 or so from around 45mph using moderate brake pressure followed by another 2 mile cool down run, then stop to see how the discs look. You should clearly see some pad transfer, it's a sort of blue/grey mist on the surface of the disc, then do 15-20 full on braking sessions from around 65-75mph, dropping the speed down really quickly but rolling off when around 10mph and then back up to speed later, followed by a 5 mile cool down run."
[/quote]
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Spent a wet afternoon in the garage looking at the front brake and after trying to bleed them again I noticed some brake fluid drips at the lever where it touches the plunger/ master cylinder.
I have therefore decided to take the master cylinder apart to inspect the seals and all looks ok so seals are not damaged they are the correct way around and there are no scores that I can see in the bore .
I took the parts to my local bike shop and he inspected all the parts and couldn’t see anything wrong but did comment about the quality of the master cylinder seal kit I used.
I must admit it wasn’t an original Honda kit which are £65 but one From Wemoto in Brighton at £18.00, anyway to cut a long story short I have asked the bike shop to order me another kit which is going to be £35.00 instead of the £18 I spent on the last kit so hopefully it will be a little more successful .
A friend of mine at work had a favourite saying “pay cheap pay twice “ so this could be a good example lesson learned.
I will also take the brake assembly with me to the bike shop so they can check to bore because I don’t want to take it apart again, I don’t mind most of the rework but getting that circling out is a Pain.
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FWIW, when I did the work on my front brake I replaced all parts with genuine Honda parts. I figured that since the brakes are a critically important component I did not want anything but Honda parts, regardless of price. This included removing a new aftermarket caliper piston a shop had installed for the previous owner just a few months prior. But since the brake was TERRIBLE and essentially useless when I bought the bike, I figured the shop didn't actually test the brakes, just installed some new parts/new fluid, made sure the lever felt firm and that was that.
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Well I am glad to say my front brake is now really good , as soon as the lever is pulled in pressure is felt at the brake lever immediately so all good.
So the issue with the leak was a small scratch inside the master cylinder bore so I polished it out with fine emery paper and flushed it clean.
I bought a better quality master cylinder repair kit fitted it and then re bleed the brakes which took about an hour, I would say if you pull hard on the brakes now the gap between the brake lever and handle bars is now 40 mm instead of 10 to 15 mm, I believe the movement is due to a little flex in the brake calliper which is to be expected but I just check tightened the caliper bolts so all is good.
So now just have to bed in the brake pads.
I really appreciate everyone advice and hopefully should be on the road once the weather improves , I just need to go over the whole bike again and check everything is tight and correctly assembled ( shake down) I might even take it into the local bike shop and get them to do an MOT test even though it doesn’t require one anymore just in case I have forgotten something better safe than sorry.
I expect like me your all glad this saga is resolved your probably sick of hearing about it.
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One thing I find occasionally helpful when I feel I've bled as best I could and it still feels a little spongy.... tie the lever to the handlebar, so everything is under some pressure, then tap the lines starting at the bottom (questional benefit, but what the heck)... leave it overnight. Lever will likely be firm in the morning, meaning air bubbles migrated up into the reservoir. A quick squirt should confirm no air.
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Hi Razerman while bleeding the brakes I did a combination of tapping the hoses and the continued with the bleeding, I will however have another look tomorrow but it really is very firm at the moment so I think I have cracked it
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Well done ken. Not everyone chiming in to this thread doesn't mean we're not engaged. We're probably making notes in case it happens to us!
Regarding any micro bubbles left in there, once they get to the top you can usually remove them by just gently working the lever by about 10 cm a few times, you will see them coming out one of the tiny holes in the reservoir.
Regards
Dave
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Hi Dave
Yes I have noticed this already and will keep as you say pumping the lever slightly to encourage the last of the air out of the system.
With regards to the leak I had the scratches I found in the bore were hard to see but luckily not too deep so we’re relatively easy to polish out.
If I replace the master cylinder on any future bikes I will probably inspect the bore surface with a lot more care , this time I also used lint free clothes to wipe all the components and the bore as any imperfections or dirt present will damage the seal.