Honda CB 900 brake question

dhermesc

Well-known Member
We bought an old (1985) Honda CB 900 to run parts to the field - actually in great condition. Much cheaper than running a 10 MPG pickup around.


Previous owner put new brakes on the front and rear that's turned into an issue. After he put the brakes on he never rode the bike - he had bought it with the intention to ride but his wife talked him out
of it (he was 70 years old). Just sitting the front brake tightens up and eventually its locked. My son thought it was fixed and parked it in our shop and I went to roll it to another spot and couldn't
because the front brake had locked up. In order to move the cycle you have to bleed pressure off it. (has twin disks - both brakes tighten) If you bleed it off and take off down the road on it immediately
begins to build up pressure and the front brake will lock up - sending the rider over the handle bars (actual event). The temporary solution has been to open the bleeders and just run it with the back brake
and no front brake. With all the fluid bled of the front brake doesn't build up pressure. With only the back brake the stopping distances are a bit long and we need to get it working again.


Anyone have an idea what is goin on with this? It is filled with Dot 3 brake fluid - as per the reservoir directions. Right now its empty so it can be used.
 
I would talk to a motorcycle shop or find a Honda motorcycle forum. Sounds like a bad brake line or master cylinder.
 
Master cylinders need to retract behind a compensating port to relieve line pressure. The primary cup may be deteriorating and swelled to be too long, but it is usually an adjustment between the piston and the actuating link to the lever. 1.5mm needed to assure full piston retraction. Wrong parts can do it, as can sticky piston, or lever with restricted travel. Jim (2 Honda owner)
 
Thank you. Just needing a place to start. It seems like such a weird issue that when it did happen it would attract a lot of attention.
 
I have a 1982 CB900 that I rebuilt the front calipers and master cylinders. I'll look at it today to see if there is anything that would be obvious that might need adjusted. Your year could be off a bit. They did not build a CB900 in 1985. It was produced from 80-82 and in 83 went to a CB1000.
mvphoto97535.jpg
 
You could be right on year. My son bought this from the 70 year old man for $600 and figure he couldn't go wrong - I haven't even seen the title yet.
 
It looks just like the one in your picture. It has the 5(or is it 6?) speed two speed transmission set up.
 
No help with your brake issue, I remember something like that happening years go to a Honda 400F bike I owned. Eventually took it to a shop, not sure what he did but he fixed it. One of those 900's just finished being auctioned off on the Hemmings online auction site, I'm sure you'll like to read this link. Somebody got a beautiful bike at a decent price I'd say, especially considering it had only 10,000 original miles. I always wondered about that dual-range gearing system Honda used. I think just adding a 6th gear would have been simpler and just as good. I'm sure a lot of the gear combinations in the two ranges were very similar. Anyways, here's the auction link ....
Untitled URL Link
 
What's the yellow ride in the background. When you mention the 1100 showing up in '83 that you refer to, was that an 1100 version of the custom (which I think yours is) or the CB1100F sport bike? The 1100F's were available up here in Canada, I think it might have been one of the Hondas that never made it to the US, not sure about that. They were a monster bike for their time, I would have loved to own one but settled for a Yamaha 750 Seca which was OK but it wasn't an 1100F.
 
Oops, I shoulda said 1000 Custom (which you referred to), not an 1100 Custom (in '83). For me, it was the golden era for motorcycles.
 
The Yellow ride is my 2001 Honda S2000. My summertime fun car. The other bike is my 1985 Honda 700c Shadow. It's my main bike but only has 14,000 some miles on it.
I looked at my CB900 and did not see any adjustment to the master cylinder plunger.
The 900f was a sport bike I don't believe it had the dual transmission. I agree that 6 speeds would have been more practical. I mainly just use low range then when I'm up to speed shift it up to high range like 6th gear. My 85 Shadow has 6 speeds and 6th is over drive. SEE Wikipedia for info.
 
I would get some kits for both the master cylinder and wheel calipers. On these old bikes the rubber parts, boot and seals get hard. I have had to rebuild my 85 Shadow and my 71 CB 450 in the last few years. They work perfectly now. My Shadow has hydraulic clutch too that I had to rebuild it was leaking on the slave cylinder.
 
I've seen very few of those Honda sports cars ..... I've been told that they had a big dose of power and also they are VERY sought after by collectors and are climbing in value. I think I remember your Shadow being one of the victims of the extra taxation in the US on imported bikes that were over 700 cc at the time and as a result those middleweight bikes down there were all 700 cc in size. Do you remember that? Up here they continued to be 750's like elsewhere on the planet. The 1100 F's ..... if there was ever a better looking bike I can't remember one.
 
check the return port in the master cyl reservoir. Often gets gunked up and needs a little small puncture wound with a torch cleaner. It will do the same as the brake lines swelling shut. I would also put a rebuild kit in the calipers. Corrosion behind the square edge seals binds the pistons. Next time you need to move it rap the calipers with a rubber mallet and I bet you it rolls freely.
 
"Puncture with" not wound.... there s two small holes in the mcyl, the smaller is the relief.
 

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