probably stupid brake question

hey guys, i've started working on the brakes on my rebuild project here, and i have a quick question.

front brakes on a 81 xj750 rh seca, dual calipers.

the piston is basically a cup, and it was set up with the open part of the "cup" facing the brake pads, is this correct? I ask because the service manual seems to depict it the other way around.

It looks like i'm going to be rebuilding the brakes and master cylinder for piece of mind here, any tips or advice is also appreciated!

The brakes were sticking and not allowing the front wheel to really turn by hand, couldn't get a full rotation in without the friction stopping it.

 

also one more question, it says i should lubricate the caliper piston with hydraulic fluid, thats brake fluid correct?

 

Question 1: Yes, the open end of the piston goes against the pads, the solid bottom of the piston goes in first.

Question 2:
Brake fluid is the best brake parts cleaner I have found.
You will need lots of q-tips

Statement 4: If the brakes weren't releasing, it was probably a plugged relief valve. Make sure you get a strand of wire or some other such thing to clean that port out really good.

 

No, brake fluid is brake fluid and hydraulic fluid is hydraulic fluid.

You're going to need a nice new jug of brake fluid anyway (buy the big one) so use that. Stick to DoT3.

 

and of course nobody ever thought a brake system was a Hydraulic system . I mean seriously , a hydraulic systems uses a fluid that compresses to push or a pull a shaft or piston and a brake system uses a fluid that compresses to pull or push a shaft or piston . I just cant imagine how you got it mixed up Fitz

@ groundswell listen to TSkaz

 

There's a CRITICAL Differences in Hydraulic Fluid and Brake Fluid.
Petroleum Based vs. Non-Petroleum Based, too.
Heat tolerances.

Hydraulic Fluid is not blended to be as resistant to Heat as Brake Fluid.
Could damage Brake Seals.

Quality Brake Fluid should not expand nor boil when subjected to high temperatures.

You can use Hydraulic Fluid as a substitute for Fork Oil.
Not Brake Fluid.

 

Grease for the SLIDING PIN, the sleeve the bolt fits through to mount caliper to caliper mount.

Every other spot in the system you want to use nothing but brake fluid.

Lube the piston up with brake fluid, place it in position, square it up, and tap into place. I used a small piece of 1x4 and lightly taped into place. It should slide right in.

It is true that the brake system is a hydraulic brake system, but brake fluid and hydraulic fluid are definitely NOT the same. Ricko and Fitz are correct.

Also, just an FYI, if you have some detail painting to do, such as I did on my MC, and need to remove spots of paint, a brake fluid-soaked rag works wonders. It's a great paint stripper.

 

Hydralic fluid will also destroy all the rubber components of the braking system, you can believe me on this one as I went and found out the hard way. That was a lesson.

 

Sounds like after rebuilding calipers and master cylinder all problems will be gone. The locking sounds like the master cylinder isn't sucking back fluid.to reduce pressure on the pads.

 

thanks so much guys, that was my biggest concern, that the brake fluid eats away at rubber seals.
so i suppose i'll use hydraulic fluid for re-assembly? because of the rubber seals along the piston? thats what i'm thinking.

edit: answer found in recent similar post about the piston pitting.

things were moving pretty fast with my re-assembly till i hit the brakes, found out my master cylinder is kinda rusty inside, taking the circlip out tomorrow morning to find what the inside inside holds. here's hoping i won't need a whole new master cyclinder, doesn't look like xj4ever carries one for the 81 xj750 rh seca

 

NOOOOO use brake fluid lol sorry my sacrcastic post was aimed at Fitz for his non explanatory reply .
Hydraulic fluid is fine for just smearing on the seals and pistons for re assembly but as your going to have a bottle of brake fluid handy for the sytem afterwards then just use the brake fluid .
So
1, dismatle and clean thoroughly
2, go over pistons with scotchbrite or 1500 grit paper and polish if needed
3, install new seals , Old ones can be used if they are in good condition but its best practice to use new ones.

4, smear seals and pistons in brake fluid and slide them home . The piston should push in releatvely easy , if it doesent, take it out and start again as if its tilted at all then it will cause a bind , you will feel when you get it right.

put it all back on the bike and the teach yourself how to bleed brakes . Its a pain in the George Bush but when you get it right its quite rewarding

 

Hydraulic fluid IS NOT fine for smearing on anything in the brakes; depending on its formulation IT CAN DAMAGE rubber seals.

Use fresh, clean BRAKE FLUID to do the final cleaning and re-assembly lubrication of brake parts. Brake fluid doesn't destroy brake seals; other types of lubricants can react with brake fluid in adverse ways.

Just use brake fluid.

 

This is getting good...I'm going to go get some popcorn.

 

I use Hydraulic brake fluid.

 

alright, i'll find some hydraulic brake fluid ha, the damn manual keeps referring to it as hydraulic fluid, and i just keep looking at that bottle i use in the jack,. alright, brake fluid, dot 3, and i'll drop it. thankyou

 

Just to clarify. Brake fluid and Hydraulic fluid DO NOT compress, they are non compressible fluids. That's how they do what they do and why when you have air in the lines, which WILL compress, your brakes are soft. The manual is calling brake fluid hydraulic fluid because it IS hydraulic fluid it's just a special variety designed to take the heat.

You can clean your MC and your whole system with a little time and patience.

My MC looked like someone baked a cake inside it and burnt it-used 'deep creep', some scotchbrite and q-tips and after it looked better. The little hole in the base is what relieves the pressure.


This thread has got to be close to a record for # of posts in 24hr, yes?