Where to start with front brakes?

Ok, so I have poor braking on the front with my xj750. I feel like I get little to no braking power until the handle is fully depressed, and then all of a sudden it will lock up the wheel.

To be clear, the pad have plenty of wear left on them, so it's not like that is the issue.

I forced myself to replace the rear brakes before I put this bike on the road, so I have a ton better stopping than the PO who suggested that I slow down by engine braking only.

So I have a couple of questions...

1) I think that I should probably start by replacing all of the brake fluid. I'm not entirely sure where to start this process. Do I open the MC cover and disconnect the two hoses to the calipers, and drain all that fluid, then reconnect, refill at the top and bleed each caliper until there are no bubbles and the brake fluid is clean? Is there some other way to go about this that is better?

2) I read some people saying that a vacuum system is worth it's weight in gold, so I might swing by harbor freight and pick that up. Does this just connect on to the bleeder nipples and keep me from having to push the brake lever myself and loosen and tighten the bleed screws?

3) How do I know if there is more work to be done. As in how do I know if I need to rebuild the MC or the two calipers. Yeah Chacal has the parts I would need, but is the first step to change all the fluid and then see if I still am unhappy with the braking?

Thanks for any help guys. I am learning a lot through fixing these things, and I guess hydraulic brakes is the next step in the process.

 

Hi unreal.
You are talking about the single most important piece of safety equipment on the bike. For the cost, I would get re-build kits for the MC and calipers. As for the pads, they may have plenty of wear left, but does not mean they are working as they should. If they are old or glazed, they will usually have greatly reduced efficiency. Did the PO say when he last did the front brakes?
Also, what shape are the rotors in? Heavily grooved, smooth?
What you are describing does not sound like a fluid issue. The usual issues with fluid are low fluid (Loss of braking effeciency), or air in the lines (spongy). These IMHO would not cause the sudden lock up. My first suspect would be the calipers.
Don't play with your life over $100, it not worth it..
As for the vacum system, I don't use one, but have in the past. Yeah, they are a great tool and can make it a lot easier.

 

You'll have to rebuild the calibers NOW. My guess is that the pistons in the caliber should be renewed, there are probably rust on them so they will not slide freely. Buy some Steel Braided Brake Lines.

 

#1 is best answered by #2. With a vacuum pump (they really are worth it) you simply hook up the the pump at the caliper, open the bleed screw, pull the handle back and tie it and let the pump suck all the fluid out. It goes quite quickly, just follow the old fluid with new (keep adding to the reservoir, don't let it suck air) and you'll minimize the amount of bleeding necessary.

#3: Yes, by all means replace all the fluid, bleed the system and see where you're at. HOWEVER: OLD pads, no matter how good they look, should be replaced. They can crumble and "chunk" when put through a few heat cycles. I also agree that it sounds like you need to at the very least pull the caliper off, clean everything thoroughly, and see if the piston is moving, etc. Calipers aren't difficult to rebuild, there's just the piston and a couple of seals-- the cleaning is the most important part and it's also the biggest PIA. Think dentistry.

Finally, a note on using the vacuum pump to bleed the brakes: Once you're done with whatever work you're doing, the system is full of new fluid and you're ready to actually bleed the brakes, the vacuum pump can help drive you crazy. It will pull minor amounts of air around the bleed screw which, of course, appear as bubbles in the line. A couple turns of teflon tape on the bleed screw (be careful not to cover the holes) will alleviate this issue. Personally, I always do the final bleed the old fashioned way, by hand. And don't forget to re-bleed after the first couple hundred miles.

*Final note* Members have posted that Harbor Freight's vacuum pump is not necessarily brake-fluid resistant. You can get a real Mity-Vac brand at almost any auto parts store, Sears, or from chacal. I got mine off Amazon; the "real" one isn't damaged if it gets some brake fluid in it. They're NOT expensive, the one at HF is almost the same price.

 

I guess I still would like to know, how do you know when you need to rebuild calipers and the mc?

 

IMHO

Bleed them first, if they drastically improve, you're good till winter or need a new front tire and then you can check the caliper and master cyclinder.

 

that depends on the maintenance they've had, on a 30 year old bike you don't know so you should assume the worst
brake fluid absorbs water right out of the air, as it does it gets a brown color
the water corrodes aluminum and steel then the seals deal with aluminum oxide, rust and ozone and ultraviolet
but that wasn't the question
starting with everything new 2 sets of pads, change fluid, inspect everything
3rd set of pads inspect everything, 4th set of pads or 4 years rebuild it all
hows that sound ?

 

sounds like a wizard speakin, LISTEN to the wizard. 100 bucks in parts is not worth your life and never will be. the piston sounds as if its stickin due to the sudden LOCK UP of the brakes. sure sign of hydrostatic intrusion. THINK and u will be safe. dont think and u risk your very life as if we dont do that everyday we saddle up anyway. BE SMART.........

 

If you are going to get a Vacuum Pump; then you might as well go Whole Hog!

Take-out the Pads.
Pump the Lever and get the Caliper Pistons moving out.
Remove the Whole Caliper Assembly.
Take-out the Caliper Pistons
Carefully extract the Caliper Piston Seals from the channels inside.

Using a Scraping Tool ... Scrape perfectly clean of any build-up ... All the Caliper Seal Channels.

(You can make a great Tool or two by cutting, heating and bending an old CB Radio Antenna. Do some heating and Blacksmithing and you can make a Tool to clean-out the channel without any problem)

Scrape the channel down to bare aluminum.

Toothbrush scrub the Seals
(New Seals is a better idea)

With the Calipers Overhauled ... you won't be wasting time if they need it.
If you never did them before ... they need it!

 

Yamaha actually recommends the the master cylinder and the brake calipers be rebuilt every 2 years.

 

Hi Chacal... I'll be emailing you about getting some parts for rebuilds... you haven't been keeping track of how much I've spent with you have you? Where's my frequent shopper card? I've been looking in the mail for it.

Ok, so here's what I did today. I went out and bought a quart of dot3 brake fluid and a plastic mityvac from Pepboys for $35. I pulled out the bleeder screws, wrapped 3 layers of teflon tape on the threads, and put them back in. This let out a lot of brake fluid from the right side, and not that much from the left... did the right first though.

Then I figured out how to hook up the mityvac and got to work. Covered the tank with two plastic bags, and set the vac and cracked the right seal. After a couple minutes opened up the MC and it was empty making that sucking straw noise... oops, oh well no biggie. Filled the resevoir and kept going. I kept bleeding the right side for quite a while, and after a while I figured the air bubles must have been coming from the bleed screws not being sealed well enough. So I sealed that side up (fluid was clear by then) and started the other side.

No real bubbles ever came out the other side, but not much liquid was coming out either (this isn't the bleeder screw cuz I blew that out while I was putting on the teflon tape). When I figured I was done, I sealed it back up, topped off the resevoir and closed that back up too.

So then I put away my tools and tried it out. No real difference. I guess that the brakes locking up the front tire is a bad description. I just don't get much significant braking power out of them unless I have the lever all the way in, and even then it's not what I expect... I've got my 550 with better braking power on the front wheel with just one disc. I know there is more weight on the 750, but I still think there is a problem.

I am taking it pretty seriously guys. If you notice, I've put these as the next thing I have to do to the bike. I don't feel like I have enough braking power yet, and I'm trying to fix it. I really don't need people telling me about how I could die.

Well next step is probably to rebuild the calipers and the MC. I know I've gotta do the same job I did today again after I finish, but I know that the 550's brakes were pretty much fixed by bleeding out the lines and topping off the fluid.

Ok so could someone describe spongy brakes to me?

 

ok guess that part may have been unecessary,and we all KNOW whats involvd with riding. Good Luck with your rebuilds and lt us know whats happening. thanks

 

You have to get to the heart of the matter.
Bleeding a System that needs new Master Cylinder Hydraulic Seals is a waste of time, fluid and money.

If the Master Cylinder isn't supplying Hydraulic Pressure ... ( ... and I'm pretty sure that's what's wrong ...) ... all the New Fluid and Bleeding you do with the Vacuum Tool won't fix it.

Rebuild the Master.
Clean the Caliper Seal Channels.

Once the Calipers are "Un-stuck" ... and, ...
The NEW Seals are in place in the Master Cylinder, ...
You won't need the Vacuum Tool to bleed the Brakes.

But, it will make it easier than Old School Pumping and Bleeding.

 

Hey guys, I just read up on Bill... I didn't know till now. Terrible thing. So sorry that I won't ever hear from him again... Sorry if I was a little harsh on my last post.

I sent Chacal an email on parts already.

*humbled*

 

If I were to try and describe what spongy brakes feel like it would be feeling resistance on the brake lever (and some braking efficiency) when braking, but still being able to draw it in more without much (if any) increase in braking power.
This is caused by the fact you are compressing the air buble(s) in the brake line, so the lever continues to draw in, but the pistons in the caliper do not continue applying pressure to the rotors at the same rate.
The reason is that air compresses easily, hydrolic fluid does not.
Pretty basic, but that is the idea..
I'll leave weak or bulging lines for another post.

 

for repair purposes if it don't leak it aint broke, does anything leak?
if you rebuild it the most you could hope for is it works the same
YOUR BRAKE LINES ARE SHOT
replace them and you'll be happy, broke but happy
preventive maintenance is another story

 

It can also be related to Master Cylinder Hydraulic Seals which are leaking by.

Real simple test:
Level the Master Cylinder
Remove the Cover.
Add or remove fluid to have reservoir 3/4's full.
Pull Brake Lever.
Fluid in Reservoir "Fountains-up" like mini-Old Faithful?
If YES >> Replace Master Cylinder Hydraulic Seals (New Kit)

 

Ordered new stainless steel lines from Chacal. When they get in stock I'll be ordering a piston kit for the calipers, the MC, the crush washers and banjo bolts, bleed screws, and the little pins and bellows for the calipers.

... it's a bunch of money, but I guess it will pretty much be redoing the whole system.

 

Completely rebuilt brakes with SS lines will astound you with the improvement over stock. It's well worth it, trust me.