Topic: Seized brakes and bouncing speedo

[spmc]

Two issues I'm facing right now... Just wanna make sure I'm right in what I plan to do...

So the speedo keeps bouncing around so I was gonna take the cable off and give it a good lube job... Just wd40 or would marvel mystery oil be a better choice?

Also while I was riding yesterday the back brake seized up on me, luckily I was in a neighbourhood and a nice guy let me use an adjustable wrench to release the pressure. They seemed to work fine after that so my thought is that it was something blocking the return hole. So I was planning to flush the system with a decent amount of fluid before buttoning it up and bleeding it.

Sound like the right moves?

1977 CB750f2

[navydad]

Cable could be causing the speedo bounce. Remove the inner cable, it should pull right out. Wipe it down and get any dirt or rust off and then I used a light grease on mine, but anything is better than nothing. How old is the brake line? I ask because the inner liner can break down on older lines and cause the problem you are having. Looks good on the outside, but bad on the inside. If the return hole is blocked it sounds like a good system cleaning is on order.

[ekpent]

Yes if you were able to release the pressure with the bleed valve look at the return hole in the master or a collapsed rubber line.

[PeWe]

Bouncing speedo is first sign of cable soon to stop work as I have seen on my bike. Replace it.

[Remcod]

Or the damping oil is gone, quite normal for its age. Can be solved by gauge restorer or self but difficult with silicone oil. Better check cable first

[2wheels]

Dont use wd40.  It is not a lubricant.  I just use motor oil, but that may not be the best either.

[RAFster122s]

Don't want to use oil products on a teflon lined or cables. Specific cable lubes...some do not use petroleum products to lube the cable. Oil products will cause the cable to deteriorate.  Honda cables are superior to the aftermerket cables (motion pro, etc)

Others have addressed the hose or mc issue. You would want to consider braided stainless steel teflon lines if the hoses are bad. It really improves brake feel and performance.

[spmc]

Thanks for all the input guys! I should have mentioned, aftermarket gauge, which did work fine until the original speedo cable gave out, this new cable was a motion pro I believe that I ordered and it did sit for 6-8 months before I actually installed it, so maybe something got goofy inside. Will relube with the mystery oil and see how that fairs.

ALSO should have mentioned I did go to braided steel hoses already, and rebuilt the master cylinder so I don't think it would be anything in the line, maybe just something got in the system while I was putting it together. Will see how I fair with a good cleaning and flushing.

[RAFster122s]

The MC then may have a blocked port, unless the pads are misaligned and that can prevent them from retracting if they are binding.
The MC has a very tiny hole that can get blocked...there are threads about it with photos.
Is the MC std or did you change it to a different style.
David

[spmc]

Just to add a resolution to this thread in case someone stumbles across it later with a problem, it was indeed the very small hole in the master cylinder.

You'll have to remove the master cylinder connector, the nipple/bolt thing that leads to the reservoir and there will be two holes, one looks like a little dimple but you should be able to see the smallest of holes, we're talking SMALL. Thought I could get away with some spare brass wire I had but that was too thick. Had to go with the High E string of a guitar as others have suggested. Keep on pushing and prodding until you can get it clear through, then take it through the open end and give it some back and forth to make sure it's nice and clear.