Anyone know thread pitch for brake line bolts ?

[pearljam724]

I'd appreciate the help.

[Coyote]

I assume you are talking about the banjo bolts. If so, they are 10mm diameter and the pitch is 1.0mm

[pearljam724]

Yes, sir. Thank you. Coyote, these caliper have yet to be sorted out. They are giving me an absolute fit. I have one more thing I'm gonna try and if that doesn't work. I'm gonna fit one caliper off of my 550 just to have front brakes. Then deal with the 750 calipers later. Banjo bolt has nothing to do with any of this.

[GT750Battleship]

Hi,sounds like you're still having brake dramas ? If calipers have been sorted to you're satisfaction,clean,new seals,pistons not seized etc,then maybe the problem is with the master cylinder & fluid not returning through the line,I've read about this being a problem...a little hole in the master cylinder gets blocked with crud,& stops fluid flow.I sure someone on here can explain it better than me
Cheers,
Roger.

[pearljam724]

I don't believe it's the master cylinder, as I have used 2 that worked fine prior. If the master cylinder was the problem, I wouldn't be able to build up pressure. I've yet to look further, than what I did a couple of days ago. At that time I removed the o rings on the pins, cleaned and sanded all paint from inside the pad retaining grooves and greased those areas. Removed the dust boots that surround the pins just in case they were causing the pins to hang up. Put plenty of antiseize on the entire length of the pins. And I was very careful in making sure the both side of the calipers were tighten without putting a bind on them. Tightened them little by little one pin equally to the other and making sure all pins were the same torque. The pistons are fine, they are extracting without the slightest problem. They just won't relax enough to free the pads. I believe it's one of 2 things. Either I seated the seals incorrectly not allowing the pistons to relax enough away from the rotors. But, the seals don't leak. Or I installed allan bolts to replace the phillips that hold the pads on the opposite side of the pistons. Those allans were the same exact diameter and length. But, unlike the oem phillips. I didn't put lock washers under them. I haven't investigated those 2 things. But, I'm going to. I reused the original pads that worked fine prior to taking the calipers apart. Cleaned, pistons, etc. No rust on them.

[yeadon_m]

If the calipers do float easily on their two pins so that you can slide them back and forth with light finger pressure, then despite your findings to date, I would vote for a master cylinder issue.
I believe if the smallest of the two relief holes is blocked, it will pump very well, so the brakes will come on, but they will be slow to release or won't release at all.
Good luck!
Mike

[GT750Battleship]

Cheers Mike....I knew you could explain it so much better than me
My brakes have never been better after overhauling the calipers recently,I was embarrassed by what I found inside!!, my Fettling skills are slipping...I must look at the brakes more regularly
Cheers,
Roger

[Suzukidave]

+1 on the thought the return hole in the master is blocked , the hole is tiny ( as small as 1 strand of a wire brush ) so if the brake lines were not new and maybe had particles in them from before the brake work was done it could be reblocking any master you may try . I would say if there is any possible way there could be bits in the lines is to flush them with clean brake fluid .

[Vintageman]

To prove which it is:

Squeeze brake lever so they come, and then release lever. If stuck on, next, loosen hose to master cylinder banjo bolt a bit to relieve any pressure. Also try at caliper.

Do brakes free up then? If so caliper OK. Master Cylinder little hole or piston check valve not opening.

Are both caliper sticking or one?


Mike S

[pearljam724]

To prove which it is:

Squeeze brake lever so they come, and then release lever. If stuck on, next, loosen hose to master cylinder banjo bolt a bit to relieve any pressure. Also try at caliper.

Do brakes free up then? If so caliper OK. Master Cylinder little hole or piston check valve not opening.

Are both caliper sticking or one?


Mike S

I'm all ears. I'm gonna mess around with them more on Thursday. When you say loosen master cylinder banjo bolt. Do I do that after I have released the lever or do I need to hold the lever with pressure applied ? The only way they will free up, is if I loosen a little torque from the 2 caliper allan pins. Both calipers will seize. All of my lines are brand spanking new. New fluid, etc. I can bleed nearly 100% of air out of the system through the reservoir. I have the lid and the diaphragm off. I shake all the lines too loosen any air bubbles, while turning the handlebars side to side and letting the master cylinder to point down, etc. I have no problem applying the brakes with ample pressure. It's just that the pads won't relax away from the rotors. They will clamp down very tight. What is the piston check valve ? Are you talking about the bleeder valve on the caliper ?

[Vintageman]

pearljam724

I would start with the brake free, apply lever, release lever (sticking right?) then immediately loosen banjo bolt to relive pressure... should be none at lever side

In theory the caliper rubber piston seal/ring is spring and what pushes piston it back as you know. I would also say the spring in master cylinder must helps some too. However, fluid can't be compressed so it must flow backwards back into reservoir for a return. If it does back off significantly when doing this it somehow must involve the master cylinder?

Piston check valve is the stuff in master cylinder. Look at it. There is the metal ram with tiny hole in the end if i recall and I think that end has a washer or flap (check valve). Check valve closes when you squeeze but, should bask off some to allow fluid return from calipers and line expansion (and hand lever to return mainly). Also the rubber piston cups due to shape/ design block flow one way and relax the other some. I think there are two and work in opposite directions. I have never seen a good write up on theory, but some fluid has to pass in reverse to allow fluid to retract from caliper and expanded line.


It is odd about those caliper sliding bolts.
Maybe next to try do not torque Allen head so tight, just as a test, in case deforming casting.

I think only the pad near piston needs to slide freely.

When stuck I think you could shake or hit calipers with rubber mallet and see if frees it up. if it does then not stuck fluid in lines but some mechanical binding at caliper halves or pad.

One other idea is to take caliper off. Just half with piston. Squeeze lever a tadd, let go, the whole time watching piston come out a little and see if it moves back a little. Also can you push back caliper piston easy with C clamp?

Bleeding is freaking nightmare. Take the round metal plate out from bottom of the master reservoir ala two screws. The reservoir is transparent and you can now see if air bubbles are caught under it. It seems like the plastic gets bowl shaped and bubbles have hard time getting to hole in center to escape. The dang bubble jump from big hole to little hole in master cylinder and just cycle: with metal out you can see if this is the case. It was for me.


I have f'd with dang hydraulic brakes and clutches and a pain in the Arse. I sure like the simplicity of cables and mechanical levers.

I hope this give you something else to try and may give you some more ideas.

[pearljam724]

Thanks, Vintageman. Yes, I tried loosening the allen pins to see if it will still lock up if I reapply the brakes. Doesn't work. The funny thing about bleeding air from the system. I figured as long as I could bleed all air out the system through the reservoir only. There would be no need to crack any banjo bolts or bleeder screws on the calipers. As long as the lever feel was not spongy. I can do that without the slightest problem. That's how most bike master cylinders work. Maybe the GT master is different ? I'm going to take the plate off the reservoir on Thursday and see what the holes are doing. But, like I said. I can't imagine that being the problem if I can get all air out of the system by no spongy lever feel.

[Suzukidave]

A easy test to see if it is in the caliper is to pull the brake lever till as you say the calipers lock tight to the disk , put a bleeder tube to the bleeder valve on the caliper and then loosen the bleeder . When the line pressure releases through the bleeder and the caliper relaxes off the disk you know then its in the system above the caliper , if the caliper stays fixed tight to the disk then its a problem in the caliper .

[dyrberg123]

I have just had a hanging fron caliper on my GT380, i rebuild the caliper, fitted it Again, bleeded it and it seemed to behave as intented. But after a short drive it got worse and worse. Fortunately i had an adjustable spanner so i loosend the bleeding screw and it took out preassure. I took the bike home, and yes it was the small return hole in the master cylinder that was blocked. Took it apart, and cleaned the small hole with a drillbit - now it Works.

[Vintageman]

Its not that you have air, its the fact the fluid won't retract maybe.

You can do as Suzukidave said earlier. That is easy.

If it frees, you can try at master in case something with hoses or splitter and see if it still frees

So if it frees after both of these test fluid not returning at master cylinder for example.

If it does not free something with calipers.

If it is caliper try some ideas above. for example I think if you look at just piston you would see it retract a tad. I mean separate caliper so you are looking at just the piston as you apply and release brake lever. if it retracts then something else with pins or pad for example. If it does not something with piston/seal/bore

Nothing to do with air in line. That would be a separate matter. sorry for talking about both at once