My 83 linked brakes

[dan filipi]

About 6 months back my rear brakes went all the way down with no pressure so I rebuilt them with new seals.

They worked fine for a few weeks then started fading again.
I suspected the new seals got damaged because I saw some corrosion in the master cylinder bore.
Well I'm not so sure about that now.

Recently I found the pedal was coming up and bumping the metal engine cover I put on ages ago.
The cover was preventing the pedal from coming up all the way. Odd, never did that before and far as I can recall it wasn't doing that after the rebuild and while I was pump bleeding them.
There were no other adjustments made to the pedal height or the cover.
I'm missing something of course.

Anyway, after taking the cover off I found the pedal came up another 1/2 inch.
This got me to thinking that maybe the piston wasn't drawing in enough fluid for it to pump properly.
A road test proved that wasn't the case. Pedal still dropped too far.

Suspecting there was still air in the system because these linked brakes can be tricky, I picked up a vacuum bleeder from Harbor freight and bled both front and rear which brought the pedal back up and the brakes work good with a nice firm pedal.

It's got me to wondering now what happened before and if they're going to fade out again like before.
Guess miles and time are the only way to know.

I have a 82 MC jpwinger sent me that I'm going to install as a test.
The hookup looks exactly the same but the 83 MC is "special" in that the piston is a bit larger, longer I think.
The assumption is it's larger to pump more fluid required for the linked brakes.
Well my test will prove or disprove that.
If the 83 linked will work with prior years MC then that will open up replacement possibilities for this year because the 83 MC is getting rare.

 

[joedrum]

cool good to know it pumped up....

 

[scdmarx]

This can easily become confusing. I know I struggle with it because I've dealt with changing worn parts more than reinventing the wheel. Think "use it or lose it".

If you're getting air in the system, the only cure is to find out where and remedy that problem.

I'm not sure what you mean by the piston is longer. Do you mean it's longer taking up more volume? Or it takes a longer stroke?

According to Pascals law, the way I understand it, relative to the surface area in the caliper, the smaller the surface area in the master cylinder, the greater the pressure will be multiplied in the caliper. And of course it works the same in the opposite as well.

Now while this may seem like you're gaining something for nothing, understand that this pressure increase will be countered by lesser volume being transferred.

As you apply pressure at the brake pedal, the MC piston pushes the fluid into the caliper, applying force to the pads against the rotor. But as the MC meets the end of it's travel and runs out of volume, naturally pressure at the caliper piston will cease to increase. I'm sure the linked brakes on the 83 using a smaller piston bore on the RF has everything to do with this balance.

Hmmm, am I doing it again? :doh:

Sorry I don't have education enough to work the formula. I guess the bottom line is a smaller MC will increase brake pressure for as long as you have volume. Be careful not to lock up the wheels.

 

[dan filipi]

Air getting reintroduced into the system, I hadn't thought of that.
Hmm.

Where are the likely places air could come in?

 

[scdmarx]

Air getting reintroduced into the system, I hadn't thought of that.
Hmm.

Where are the likely places air could come in?

Well, in my experience, most times there will be tell-tale signs of fluid leaking out as well. Screw in or o-ringed fittings. Air can squeeze through a lot easier than fluid, so it don't have to a be very big leak at all. Applied fluid pressure being much greater than air pressure, all it takes is little gulps of air over long periods of time to eventually build into a larger bubble. Another way that might be more hard to find is seals at the MC or the wheels. Seals are usually made to retain the fluid in one direction. When the lip points toward the fluid side, by design, may be able to draw air back the other way. Especially if trying to seal over a corroded or pitted surface. Or just old and tired seals that have lost enough elasticity. I mostly run into this when trying to find an elusive leak on air conditioning systems. As everything cools down and contracts at night while you sleep...so do the seals.

And of course the obvious, allowing the reservoir to get too low as pads wear and such.

 

[82a]

read a thread (with nasty pix) that was about the splitter (aka pressure control valve) being shot causing air leaks and parts were n/a

https://www.goldwingdocs.com/forum/viewt ... 7&start=25

So im rebuilding a 1100 for a friend and i couldn't get the rear and rt front to bleed i opened the splitter valve and i guess its meant to have rubber o rings in it . As you can see mine did at one time . This is a sealed unit so there no rebuild kit for it and as mother Honda no longer make the part the only thing to do is to unlink the brakes .

 

[joedrum]

hmmm all got to say is linked brakes work great in gravel and is worth fixing right ...the porporsioning valve seems just right for my 83 interstate ...brakes stable in gravel cant think of a better test for the system ... :laptop: :mrgreen:

 

[griz]

On my 83 Neked, I had air trapped at the line connection under the shroud. I took the caliper off of the leg with the line attached and hung it above the bike to try to get the bubble to move. I finally did, but also discovered that the internal sleeve in the line was collapsed. That is the line that runs down the length of the leg. I could not find a replacement line so I replaced both front lines with stainless braided line for a Valkyrie. So now both front brakes work like old school (at the same time). With the addition of a rear rotor replacement, the brakes work great. Even on gravel at a corner. Also remoed the retired line from the valve to the clip mount near the neck. Didn't need to leave the unused on the bike.