Front brake help

[93max]

Ok it does work BUT when I pull lever in it goes fine the seems to bind or stick then it seems to get past it with more pressure the front will dive under hard braking.
What should I look for? A piston maybe sticking in the caliper or maybe something in the MC ?
Any help would be appreciated ?

 

[Fire-medic]

First thing I would try is pulling the master cyl lever pivot pin, cleaning everything, lubing it, and reassembly. I wouldn't ride this until it's decisively-fixed, completely. If that doesn't completely do it, then the below:

I would disassemble completely the entire system, and look for sticking points, partial blockages, delaminating hoses, stuck caliper pistons, worn master cyl piston, rusted caliper brake pad pins, whatever.

What does the fluid look like?

Sludge forms in the brake system from not changing the fluid, deterioration of the interior lines, absorption of water past the seals, pad dust, etc. Sludge can obstruct your lines, partially or completely.

A failing brake line can separate and become like a 1-way valve, building pressure but not releasing it. It could restrict normal flow in both directions, in another instance.

Stuck pads likely will cause abnormal drag on the rotor, overheating it if it's bad enough. The rotor could become overheated so that it no-longer provides uniform braking. Pads will glaze, reducing the coefficient of friction. Stuck caliper pistons are more-likely than stuck pads. Both can cause abnormal drag on the rotor.

Usually a worn master cyl piston will leak internally, losing effective lever travel used for braking. This is similar to having air in the system, no resistance in the lever, where the lever comes back towards the handlebar with no resistance commonly felt in a correctly-operating front brake. Leaking externally, brake fluid will bypass the piston seal and leak down the lever, making it moist, and dripping-off the bulb end of the lever.

Perhaps my recent 'how-to' on caliper repair will assist your efforts: http://www.vmaxforum.net/showthread.php?t=47304 It has info on removing stubborn frozen pistons which won't co-operate in removal efforts, and 'reverse-bleeding' to quickly-restore a firm brake lever, also useful for hydraulic clutch work.

 

[93max]

Thanks for the tips.
I kinda think it's in the lever or pivot point. I do have new braided lines that the PO gave me when I bought the bike so would be a good time to do that too!

 

[Fire-medic]

Thanks for the tips.
I kinda think it's in the lever or pivot point. I do have new braided lines that the PO gave me when I bought the bike so would be a good time to do that too!

Are they aftermarket levers? People have had problems with the brake piston-pin to lever distance being incorrect.

If you've never done the reverse-bleed, this would be a good time to try it, much-quicker than the traditional method. More-effective too, as you are using the physics principle of, 'bubbles rise,' to flush any residual air out.

 

[93max]

Are they aftermarket levers? People have had problems with the brake piston-pin to lever distance being incorrect.

If you've never done the reverse-bleed, this would be a good time to try it, much-quicker than the traditional method. More-effective too, as you are using the physics principle of, 'bubbles rise,' to flush any residual air out.

Yup! I've done that to my EXC 400 several times to get a good feel on the lever.
I'll have to look at the levers to see if they are aftermarket....but I doubt they are as this bike was completely stock when I bought it.

 

[MaxMidnight]

I would be very surprised if it was as simple as a lever issue causing the symptoms you describe.

I suspect a full overhaul of the calipers would not go amiss.

Unless you know it has been done within living memory then while you are doing the lines pull the calipers, remove the pads and clean the years of crud that has (probably) built up around the pistons.

Look for any signs of corrosion on the pistons and if significant pull the pistons to enable a full inspection.
Helpful hint: Using Stiltons or a mole wrench is a BAD way to get the pistons out.
Note the bore that each piston came from.

When re-assembling use rubber grease on the seals and make sure that the pistons move freely in their bore.

 

[Fire-medic]

I had to look this English term up to discover what in-the-Whitworth this tool was- it's a Vise-Grips pliers set.

Helpful hint: Using Stiltons or a mole wrench is a BAD way to get the pistons out.

Here's an internally-expanding wrench which may also be useful for piston removal, once the caliper is split: https://www.homedepot.com/p/Ridgid-1-in-to-2-in-Model-342-Internal-Wrench-31405/202826782

 

[MaxMidnight]

Also do a search on 'Caliper piston removal pliers' (no translation necessary! :ummm

 

[Fire-medic]

This is the "mole" with which I've been familiar with since childhood.

 

[93max]

Thanks guys!

 

[[email protected]]

This is the "mole" with which I've been familiar with since childhood.

I had that book as a child

 

[93max]

Ok, upon further investigation, I found a slight ridge in the piston face that the adjustment screw from the lever rides on.
I knocked it down with a dremel tool, applied dab of wheel bearing grease and it works fine now.

 

[[email protected]]

I wouldn't have that of that one.
Thanks for reporting the fix

 

[Fire-medic]

A tip for your brake master cylinder overhaul.

I had an old SOHC 750 Honda front brake master cyl I was trying to rebuild. It was fighting me at every step.

The piston was frozen.

The external circlip holding the piston broke one of the holes at its ends, making it difficult to remove.

The banjo bolt was frozen, and it broke when the air impact was used to try to break it loose after a socket wrench wouldn't work.

The small hole in the floor of the master cyl was clogged, and I couldn't get it cleared with a small wire I usually use on the small brass pilot jet in the jet block.

A sewing kit to the rescue!

Using a hand sewing needle in a pin-vise the small master cyl hole was cleared-out. My friend at the shop volunteered to show me how to do it. He used the pin vise with the sewing needle in it, spinning it between his thumb and forefinger. He would stop that, leaving the pin vise/needle in-position, and he would use a light object to tap-tap-tap on the end of the pin vise/sewing needle. You aren't driving 16d sinkers (3-1/2" long common nails), you're just trying to punch the needle tip through the accumulation of whatever is blocking the small, tiny master cylinder hole.

It took him less-than 5 minutes, and he was careful to ensure that he didn't break-off the needle in the hole. I used a small flashlight to see that the hole was cleared. I shined the LED light (one of those Harbor Freight freebies) into the open bore from the lever attachment side, adjusting the angle of the light pointing down the master cylinder bore until it showed the best deflection of light where the small hole just-cleared was. It's a really small hole, and there isn't much light going to come-through, but if you're viewing the area of the small hole from about two feet away, and you change the angle of the LED light down the bore, all of a sudden you're going to see the light through the hole. That shows it's clear. Then view the bore where the small hole is, to ensure there's not any debris or a burr sticking-down into the bore, where it might tear the rubber pieces of the piston.

A bolt-removal tool removed the broken banjo bolt with the use of some gas axe time. A tap cleaned-up the threads.

A long punch drove-out the piston. Before that, a pick dislodged the one 'good end' of the circlip, so the piston could be removed.

Now it's time for cleaning the bore, and installation of the new piston.

 

[93max]

What a pleasure it is having full control of the front brakes!

 

[Fire-medic]

Here's a pic of removing the piston from the caliper of the SOHC Honda 750 I'm working-on. I used my manual lever-action grease gun to free the piston, when my air hose and rubber-tipped airgun wouldn't budge it. Works every time.

 

[Fire-medic]

This is more on the CB750 front master cylinder, though the VMax is virtually the same, just a different piston bore size:
I was waiting to clean the lower part of the front brake master cylinder bore, I had used a brass cone brush and a dremel-type tool, as-far as it would reach, but it wouldn't go far-enough to reach the bottom, it actually only needs to clean-up wherever the front rubber seal (the one closest-to the banjo bolt) is, the one on the end of the piston spring rather than the rubber seal on the piston. So, maybe a bit over an inch from the banjo bolt, if the spring is fully compressed.

I had used a tear-off round sanding disc, rolled-up and with a round driftpin inside, trying to get a close fit to the bore. It worked ok, doing it by hand. When I was at my friend's shop, he said, "why don't you use that sanding disc, and just chuck the end into a cordless drill?" I had another front master cyl. to do, so I gave that to him, and in no-time, the bore was good to-go.

Watching him, I thought of a couple ways to make this work even-better:
Using a wood dowel w/a nut-sert in it, and then a bolt fitting the nut-sert, w/the head cut-off, to place into the drill chuck. Wrap the round sanding disc around the dowel, size the dowel maybe 1/8" narrower than the cylinder bore. Sand-away w/a cordless drill.

Or you could use one of those bolts having wood screw threads on one half, and machine screw threads on the other side/half. The machine screws would chuck into the drill, the wood screw side would go into the end of the wood dowel. Just make-sure that you wind the sandpaper around the dowel clockwise, so you aren't using the drill rotation to cause the screw to back-out of the dowel. You can buy several dowels to fit whatever your powersports master cylinders use. Just buy the dowels slightly-smaller than the bore so you can wrap the sandpaper and have a snug fit in the bore.

Of course, you want to thoroughly-clean the bore and ensure the holes didn't get plugged. My friend uses a bit of Vaseline on the piston rubbers for reassembly. I usually just use a bit of brake fluid, but I tried his method, and it worked fine.