1974 TX650 Front Caliper Dragging/Locking Up

[Thedawkter]

Good Afternoon Everyone,

I am having a very peculiar issue with my 74 TX650. The completely rebuilt front brakes are locking up.

To ensure my brakes would work well and I wouldn't have any issues, I bought a new master cylinder, a caliper rebuild kit, new pistons and new pads.

I cleaned the caliper extensively, ensured the new pistons went in properly with the new gaskets, put on new brake pads, and bled the whole system.

Once the system was bled and the breaks were pumped up, they hold very tight. Not tight enough that you can't move the wheel, but close. Much tighter than the typical accepted slight drag, at least to my limited knowledge.

The only thing I did not replace was the caliper itself, the bleeder screw, and the brake lines.

Now my first thought is it must be the lines, so I did the standard test of cracking the bleeder and seeing if it frees it up. It did not.

The ONLY thing that gets it to free up, is to continue to bleed it. After a few pumps up and down, it releases the pressure back to slight drag. As soon as the bleeder is tightened and the brakes are pumped up, its locked.

So I thought that the issue must be in the caliper, and I tore it apart 3 more times and got no change.

Then I thought maybe the new pads just need broken in, so i took it for a ride and the front rotor got up to around 200 degrees F, which to me seemed really high for casual riding.

Got home and lifted the front tire, and it is just as locked as it was, no change.

Before I buy any more parts, I wanted to see what you all thought. Thank you in advance for your insight.

 

[5twins]

There are a couple small holes in the master cylinder between the piston area and the reservoir. One lets fluid into the piston area when you pull the lever, the other lets it bleed back into the reservoir when you release the lever. It sounds like that return hole may be blocked or partially blocked. It's the smaller of the two so it's more prone to getting blocked.

 

[Thedawkter]

There are a couple small holes in the master cylinder between the piston area and the reservoir. One lets fluid into the piston area when you pull the lever, the other lets it bleed back into the reservoir when you release the lever. It sounds like that return hole may be blocked or partially blocked. It's the smaller of the two so it's more prone to getting blocked.

Just went down and checked that out. I used a small piece of safety wire to make sure it was completely clear, and then carefully pumped it with the cap off, and it is pumping fluid back into the Master. The brake fluid is also completely clean and clear.

 

[DogBunny]

The brake lines!!! You said you did not replace the brake lines. If you're running original, or old rubber brake lines, I guarantee that's the problem. When you squeeze the lever, those rubber lines expand. When you let off of the lever, they continue to be pumped up, creating the drag you're experiencing. Buy new lines. I suggest braided stainless steel, unless it has to look original. Virtually impossible for stainless lines to expand.

 

[Thedawkter]

The brake lines!!! You said you did not replace the brake lines. If you're running original, or old rubber brake lines, I guarantee that's the problem. When you squeeze the lever, those rubber lines expand. When you let off of the lever, they continue to be pumped up, creating the drag you're experiencing. Buy new lines. I suggest braided stainless steel, unless it has to look original. Virtually impossible for stainless lines to expand.

Okay so even though the pressure is not released when the bleeder screw is cracked, you still think it is brake lines? I thought that if it released when cracked it would be brake lines, but it isn't doing that.

 

[gggGary]

When you took the caliper apart did you remove the rubber seal from each piston bore and clean out all the spooge that lives in the groove behind them?
Is the rotor centered in the caliper slot? Thinking maybe an alignment or spacer issue between wheel, rotor and caliper.

 

[Thedawkter]

When you took the caliper apart did you remove the rubber seal from each piston bore and clean out all the spooge that lives in the groove behind them?
Is the rotor centered in the caliper slot? Thinking maybe an alignment or spacer issue between wheel, rotor and caliper.

Yes I removed, cleaned out the grooves, and replaced the rubber seals. There was a lot of crud there, but I cleaned it all out.

I was concerned with a centering issue, but the rotor is perfectly centered. All stock spacers are present on the wheel. This bike is completely stock.

 

[5twins]

You can get the stainless lines with a black covering so they'll look somewhat original, if that's what you're after. I replace them on any old bike I'm working on. I've encountered enough bad ones over the years to know they're probably bad. I never encountered your issue, usually just a soft and/or spongy lever feel no matter how much bleeding is done.

 

[Thedawkter]

You can get the stainless lines with a black covering so they'll look somewhat original, if that's what you're after. I replace them on any old bike I'm working on. I've encountered enough bad ones over the years to know they're probably bad. I never encountered your issue, usually just a soft and/or spongy lever feel no matter how much bleeding is done.

That’s the thing, they feel great, just a bit too great!

 

[gggGary]

Well you are stumping me good here. Are your certain the passages in the bleed screw are clear?
There is such a thing as collapsed inner wall in brake lines.

 

[Thedawkter]

Well you are stumping me good here. Are your certain the passages in the bleed screw are clear?
There is such a thing as collapsed inner wall in brake lines.

Yes, I checked those. It does leak a bit around the threads when tight, but I didn’t think that would give me this issue.

I just removed the master cylinder completely, and it did not free anything up. So the problem must be in the caliper. I just cannot figure out where or what.

I will tear it apart again tomorrow and see what the situation is. Can anyone think of what I should look for? Should the calipers be honed?

 

[kopcicle]

We need a pic of brake lever and adjustment screw.

 

[gggGary]

What pistons, caliper, seals, are you using? With the caliper off the fork, or wheel off, do both pistons pump out (and can you retract them) easily? There are several internal passages with seals between the caliper halves are they all clear?
A flat bar (round the sharp edges off an old flat blade screw driver) twisted between the pads should retract the pistons without excessive force.
Use the old pads if there's any fight to the system.
I'm wondering if an "out of spec" part is causing piston binding.
Cuz if everything you say is true that's about the only answer that fits.

 

[Thedawkter]

What pistons, caliper, seals, are you using? With the caliper off the fork, or wheel off, do both pistons pump out (and can you retract them) easily? There are several internal passages with seals between the caliper halves are they all clear?
A flat bar (round the sharp edges off an old flat blade screw driver) twisted between the pads should retract the pistons without excessive force.
Use the old pads if there's any fight to the system.
I'm wondering if an "out of spec" part is causing piston binding.
Cuz if everything you say is true that's about the only answer that fits.

Im using the caliper rebuild kit from Mikes, and the pistons from Mikes. both pistons pump out, but I cannot say they retract easy. I cannot retract them with my hands.

The internal passages are clean and clear.

I am thinking that you may be right though. With the caliper split in half, should I be able to push the piston back in relatively easily? Obviously with no fluid in the system but still lubed from the brake fluid.

 

[gggGary]

Yes no more than moderate two thumb pressure should do it.

 

[Raymond]

I With the caliper split in half, should I be able to push the piston back in relatively easily? Obviously with no fluid in the system but still lubed from the brake fluid.

You should be able to push the piston back even with fluid in the system. If the piston doesn't push back easily, that would seem to explain the binding. Piston too big for the bore? Or corrosion on the bore making it too narrow?

 

[gggGary]

Well it's mikesXS...........
funky rubber seal?
You still have original seals?

 

[gggGary]

You should be able to push the piston back even with fluid in the system. If the piston doesn't push back easily, that would seem to explain the binding. Piston too big for the bore? Or corrosion on the bore making it too narrow?

with the seal out the piston should have zero resistance to sliding in out.

 

[Thedawkter]

Let me get it pulled apart again and go through it. Ugh I’m so tired of spilling brake fluid everywhere!

I will let you know what I determine. If I still have the old rubber I will give it a try.

 

[Mike G]

If you find the Mike's seals are the problem (seems pretty likely) and you don't want to reuse the old ones you can still get them new from Yamaha.(cost more obviously) I got mine from PartShark.com.

If it's just as stiff with the old seals then that would point to the pistons being bigger O.D.