Topic: Front brake engages when turning left

[theoctopus]

Took the new (to me) 750F out for a little spin today.  When turning the wheel full lock to the left, the brakes engage.  This does not occur when turning the wheel (in its full range of motion) to the right.  Needless to say it has me a little uncomfortable in the turns.

Any thoughts?

Any suggestions on where to buy a brake rebuild kit for a '76 CB750F Super Sport (front and rear)?  Both brakes need some work aside from this strange turning issue.

[Frostyboy]

Well this is certainly a strange one.
Do you still have rubber brake hoses on this machine?
If so & if they have some years on them, perhaps a hose is getting kinked on left lock and displacing enough fluid to apply the brake?
Might pay to check the routing & condition of the hoses.
It surely can't be related to the m/cyl, because that's just sitting on the bars.

[fasturd]

+1!
 Check the routing. Before putting in kits just rebuild the calipers and master. It is easy (if a little messy) and you will most likely get the result you are looking for. Poor aftermarket kits cause more problems than they solve. I would NOT ride it until you get that sorted out. Bad enough the cagers are always trying to kill us no need to do it to our selves.

Getting everything CLEAN is the trick. The seal groove for the caliper seals is critical. On the master BOTH holes you can see in the bottom of the fluid cup MUST be clear. Flush the brake lines with mineral oil or clean brake fluid. I replace lines quite often but I re-use the factory caliper and master seals unless they are cut or nicked.

Good luck.
Might want to post your project over on the project side of the forum there is plenty of support threre.

[RatBikeRandy]

I had the exact same problem with my 500.  I thought that I had cleaned the caliper well enough, but you need to remove the piston and install a new seal (like a square edged o-ring).  Make sure to get it clean behind the piston, just enough gunk back there to cause a problem.  Honda still carries the o-ring and it was fairly inexpensive.

[MCRider]

Besides all the very likely concerns about the brake gear itself, I'll throw in a potential outlier.

YOu could have a wheel bearing issue that is allowing the disc to tilt, wouldn't take much, and bind in the caliper when the wheel is turned.

This is a very remote item, but all the obvious ones were already taken.   

[HondaMan]

I have also seen deteriorated rubber lines that are delaminating inside, which lets them twist and "apply" some hydraulic pressure when turning, cause this problem. It's usually the bottom hose.

If the Honda hoses are too expensive for your taste, contact Z1 Enterprises' "Tech support" people (I do it by e-mail from their site) to have them figure out the right hoses and banjos that they sell: these newer-technology parts are slightly smaller in diameter and stiffer, which improves the braking forces. They even sell the right grommets to fit them into the Honda brackets. In the future, they will not crack or delaminate inside, so they make a good long-term investment.

[brett_bike]

I had the same problem on my '73 CB500.  I rebuilt my master cylinder, caliper and installed SS lines all at the same time.  I really can't say which one solved the problem, but doing the whole enchilada is worth it.  It's easy and you will have better braking and piece of mind.

[MCRider]

I have also seen deteriorated rubber lines that are delaminating inside, which lets them twist and "apply" some hydraulic pressure when turning, cause this problem. It's usually the bottom hose.

If the Honda hoses are too expensive for your taste, contact Z1 Enterprises' "Tech support" people (I do it by e-mail from their site) to have them figure out the right hoses and banjos that they sell: these newer-technology parts are slightly smaller in diameter and stiffer, which improves the braking forces. They even sell the right grommets to fit them into the Honda brackets. In the future, they will not crack or delaminate inside, so they make a good long-term investment.

Yeah, that makes sense. The lines can deteriorate just sitting there, plus replacing them is an improvement even over brand new stockers.

[theoctopus]

Thanks so much everyone.  I'm going to be installing new wheel bearings, and I'm considering putting in a whole new master cylinder/lever from a modern Honda.  Either way the brakes will be overhauled before I put it out on the road again.

[HondaMan]

I have also seen deteriorated rubber lines that are delaminating inside, which lets them twist and "apply" some hydraulic pressure when turning, cause this problem. It's usually the bottom hose.

If the Honda hoses are too expensive for your taste, contact Z1 Enterprises' "Tech support" people (I do it by e-mail from their site) to have them figure out the right hoses and banjos that they sell: these newer-technology parts are slightly smaller in diameter and stiffer, which improves the braking forces. They even sell the right grommets to fit them into the Honda brackets. In the future, they will not crack or delaminate inside, so they make a good long-term investment.

Yeah, that makes sense. The lines can deteriorate just sitting there, plus replacing them is an improvement even over brand new stockers.

Your post about the wheel bearings reminded me: I have seen that, too, but not in a long time! The disc would rub against the inner puck and drag from worn bearings, when tilted over.

[BeSeeingYou]

I got OEM parts from www.Babbittsonline for my brake rebuild on my 76F.  Don't get the slightly cheaper ebay generic stuff.  Get the caliper seals as well as the kits for the MC's.  I think it came to around $100.  The rear caliper is a twin piston design and a bit trickier to get apart.  I came up with a way to do it without splitting the caliper like it shows in the manual.  I hooked it up to my rebuilt front MC and used a long reach c clamp to hold one piston down while forcing out the other.  Clean it up and install the new seal, install the piston , do a quick bleed.  Clamp the other one and repeat. I did the upstream one first as not to force any junk into the rebuilt side when doing the second one.  I did not see any way to get the pistons out if you split the caliper as per the manual.