VFR INTERCEPTOR 750 front brakes locked up again

VFR INTERCEPTOR 750 front brakes locking up again

Hey guys i took the bike out today after fixing all these eltrical problems, (vfr 750 interceptor)and it was riding great, till i stoped at a store, then i felt the front brakes were locking couldnt move the bike, this happened to me last winter and caused me to go down on the parkway, i walked away with a few scratches got lucky that time, so i got 2 used brake calipers off ebay, they looked like they were in good shape, now the same things happening, could it be the master cylinder? or did i just get another bad set of used calipers? i bled the fluid out of one of the front calipers i got a little squirt, but the other side got nothing, then the bike rolls free again, so they r not rusted, so that would lead me to belive only the left caliper is bad? Also dot 3 or dot 4 does it realy matter? im not sure any help guys? thanks again for all your help, im gonna get this bike running hell and high water its gonna run

Razor

 

Locking brakes

Well, if you replaced the calipers, and it did it again, its probably not calipers. Probably not rotors, you can see them if they're bad.

I vote for a master in need of a rebuild. Sounds like it does not release pressure, clogged up or something.

Larry
VFRrider

 

yeah im with u on that, is there any way to test the master? if i remove the top of the master when the brakes r locked if the pressure releases i guess that would rule out the brake calibers? well im gonna look for a kit on ebay, i never rebuilt one before it cant be that hard any tips?

 

Master cylinder rebuild is easy -

Just remove, inspect and clean the bore if necessary (and it probably will need cleaning).

Rebuild using a kit (new seals) and the hard parts from the bike.

Bleed all old fluid from the calipers and re-fill the whole system with FRESH (new container) brake fluid of DOT4 or higher.

 

so the brake fluid could make this happen? i think the plunger and the master cylinder looks fine, im gonna try to take some of this stuff apart and clean it up

 

there is a very small hole at the bottom of master cylinder (for return of brake fluid) that can clog and cause this problem.......

also can be caused by overfilling fluid reservoir or blocking the small vent on the reservoir cover.

 

I would suggest that you strip down the brake callipers, it sounds like a piston is sticking. I had one on a different bike with this problem, water had entered the piston seal groove, the ensuing corrosion lifted the seal causing the piston to jam.

 

Also check out the brake flex hoses. Sometimes I have seen on cars where these hoses deteriorate, and let fluid/pressure into the caliper, then collapse and will not let the pressure back out. If this is what is happening to yours, it would explain why bleeding the caliper frees it up until you use the brakes again.

 

It's the return port in the bottom of the master cylinder. Take fine tip needle and carefully clean. As the brake fluid heats up, it expands and is supposed to expand back into the MC. If the return port is plugged, the fluid has nowhere to expand, so now it pushes against the caliper pistons, causing the brakes to lock.

This also happens with the Clutch MC (under the silver tang) - the symptom is that as the bike warms, up the clutch will disengage more and more.

For both issues, draining a little fluid from the bleeder valve that fixes it is the clue.

 

thanks everyone for the help, i cleaned the master cylinder and that little pin hole, seems to still be locking up only if i jam on the brakes hard, i drove the bike for the weekend and only slightly used the brakes and it seemed fine, but i just ordered a rebuild kit for the caliper that seems to be locking, i will let u know how it turns out, thanks again to everyone for their help and imput. by the way the tiny hole was gacked up bad, also i might have mixed dot 4 with dot 3 sometime in the past, could that also be a cause for this problem?

 

Probably not drastic problem...DOT 5 would be though as it's totally different stuff. DOT 4 is recommended 'cause the boiling point is higher. Might as well wait til you get your caliper's cleaned and bleed some fresh DOT 4 through.

Masonv45 and Squirrelman were right on. Sounds like you might have a sticky caliper piston also. A quick clean is OK for temp master cylinder improvement, but if you want a really "new" feel for your lever...I'd put the rubber parts in too. I've done this with several older used bikes I bought, and it's easily worth the relatively inexpensive parts.

 

I have viewed this forum many times, but this problem made me register so I could post an answer.

Your problem is the master cylinder. What happens is when the fluid heats up it expands, and the bypass within the master cylinder is not allowing the extra fluid to escape back into the reservoir. The result is the same as you squeezing the lever....the brakes are applied. The more heat in the system the worse the problem is. Your going to need to remove the master cylinder, pull the piston and seals out and flush it thoroughly. Make sure you blow through every passage with compressed air, and don't be afraid to soak it in a bucket of water and a little simple green. Just make sure it is completely clean and dry before re assembly. Look at the bore for any scoring that might cause the piston to hang up. You really need to treat it the same a bore in the engine. The better it is, the better the seal, and the better it works.

When I had my VFR, which I now miss, I had a sticky brake issue, but nothing that caused the wheel to lock. This is a very unsafe condition that you should not take lightly. It won't hurt to rebuld your calipers, because if there is a buildup of sludge from years of use in them, the pistons can also stick, but in the years I worked on bikes, I never saw one stick in the clamped position. The symptom of sticking pistons is irregular pressure being required at the lever to get any notable change in braking force. While you have it apart, it would be a very good idea to fully flush the lines, just in case there is some debris in the system.

Best of luck, and be safe.