Brake Wierdness - 84 VF500

So this morning I had the BabyCeptor out and I wasn't happy with the front brake. Very squishy - steel lines and a new master cylinder assembly complete are inbound, and I plan to rebuild the front calipers using the rebuild kits offered at V4Marked, so figured I'd push the envelope on what I've got.

During a series of hard stops - basically coming onto the brake lever at 9/10ths, the front would dive down, then suddenly the forks would feel nearly "locked". Only happened when braking hard, but it would feel like the steering head locked or at least became very very stiff, resistant to being moved either way without some deliberate force. A bit disconcerting at first.

Never had this happen on any bike in the past 20 years, on my CBX 550, FZ-6000, ZX-7, my 98 VFR or my BMWR1200GS - a first for me. Anyone had this happen or have an explanation? Does the anti-dive system have something to do with this?

BTW after about 15 hard stops, front disks were very hot (heat radiating off them) and darkened, but the grip did improve. During a ride later in the evening, brake feel was improved.

Interesting.

CdnPz

 

Lots of variables. What's the tire pressure in your front tire? When was the last time the steering stem bearings were inspected or replaced?

 

Good point, Captain. Unless the headset bearings were replace some time, they're probably shot if the bike has lots of miles.

According to the symptoms, changing out the brake fluid would be the first thing to try.

 

Always liked the FZ-600... would love to ride 6000cc version.

 

Let me tell you, the 600 to 6000-conversion was a hella big Wiseco kit!

Ref the last, tire pressure was a bit low, but steering stem bearings UNK - no obvious play in them, no drifting side to side when the front tire's lifted off the ground (while on the centrestand), no binding, no gravelly feeling, no wandering to them.

Just got my steel lines in today, so a line change and fluid swap is in the works once I get my front caliper rebuild kits from V4 market. Not sure when (if ever) the front calipers were really disassembled and cleaned, so when I've got all the bits and pieces apart, I may as well take care of everything at once.

 

Check. The brake pads and rotor for contamination sounds like maybe some oil or grease contaminantnation. Spray them off with bbrake cleaner and go for a ride. Could be fork oil dripping on them from the fork seals. Just a thought

 

I'd cleaned them with brake cleaner before the ride, but will try again. Interesting, they are now a very dark colour, with some scoring, although there was some light scoring before. They're not warped, though, no vibration. I'm wondering if I'll have to replace the rotors or pads. Pads were new last summer from the PO (exact age UNK) and I have a new set of EBC pads. I'm hesitant, though, to put a new set of pads on and risk messing them up on dodgy rotors for no good reason. Wondering if maybe before the pads were not bedded in at all, or maybe pads were contaminated but not necessarily the rotors. The colour change is puzzling, though.

Cdn Pz