Problems with rear brake vibrating front wheel.

Hello all, I'm looking for a linked brakes expert or advice. I live outside Sydney and ride a 5th Generation (1998) VFR800. I've got two problems that i think are related:   1) When i use the rear brake without any front, i get a "violent" shudder through the front. This was minor at first, but is now bad enough to push the bike wide if trying a slow speed round about or hairpin. Braking with the just the front or front and rear together is no problem. Lever is firm and good braking pressure.   2) Today on a ride it felt like the rear was grabbing (that might have been my imagination after all the reading i've done), i was coming off the freeway and had no where to stop. A couple of km up the road when i stopped at the lights i had no rear brake at all. No pressure in the foot lever and the rear wouldn't even hold the bike on the slight slope of the traffic lights. I pulled over and decided to make it to a mates house 20km up the road with just the front brakes. By the time i got to his house the rear was back. The problem didn't occur again for the next 150km to make it home. Problem 1) is still there and probably worse. Is this an issue with the Secondary Master Cylinder (SMC)? The bike is new to me (2500km) but had a brake bleed (or so they say) before i bought it.   To make it worse when i arrived home on the driveway the vibrating front wheel is gone now and the brakes feel like they should.   Confused and concerned.   Thanks for any tips or advice.

46 minutes ago, Drtmonster Hello all, I'm looking for a linked brakes expert or advice. I live outside Sydney and ride a 5th Generation (1998) VFR800. I've got two problems that i think are related:   1) When i use the rear brake without any front, i get a "violent" shudder through the front. This was minor at first, but is now bad enough to push the bike wide if trying a slow speed round about or hairpin. Braking with the just the front or front and rear together is no problem. Lever is firm and good braking pressure.   2) Today on a ride it felt like the rear was grabbing (that might have been my imagination after all the reading i've done), i was coming off the freeway and had no where to stop. A couple of km up the road when i stopped at the lights i had no rear brake at all. No pressure in the foot lever and the rear wouldn't even hold the bike on the slight slope of the traffic lights. I pulled over and decided to make it to a mates house 20km up the road with just the front brakes. By the time i got to his house the rear was back. The problem didn't occur again for the next 150km to make it home. Problem 1) is still there and probably worse. Is this an issue with the Secondary Master Cylinder (SMC)? The bike is new to me (2500km) but had a brake bleed (or so they say) before i bought it.   To make it worse when i arrived home on the driveway the vibrating front wheel is gone now and the brakes feel like they should.   Confused and concerned.   Thanks for any tips or advice.

 Hi.

Sounds like you've got a few things going on there bro?

A few things to check:

SMC & caliper mount's where I'd be checking, SMC should be fairly solidly mounted, if slopping around, summat's worn, whole assembly should pivot smoothly on the lower allen bolt, upper clevis should be free moving, stick bike on centre stand, get someone to spin rear wheel while you swing the SMC/caliper assembly upwards, this operates rear brake, let SMC go to release rear brake, if brake sticks on or has excess drag, green return valve will be blocked with crap & SMC likely needs a rebuild kit, same deal as doing a front master or clutch master cyl rebuild, (Tourmax) are only brake parts I use, OEM quality, way cheaper than Honda prices, there's a green plastic return valve hidden under the bolt off banjo mount on the rear of the SMC,  if blocked with crap, it totally screws the braking up, rear brake grabs, can lock up enough to leave you stranded  or spit you off,  a good blow down SMC bore will pop the green valve out,  carefully prise it apart & surgically clean the tiny ports & both mesh screens don't lose the tiny spring & ball inside or ya Fooked, can't buy em, no mention of valve in manual.

SMC bore's are prone to collect crap in the bottom, needs to be spotless or green valve gets blocked & problem starts all over again.

Proportional valve under rubber heat shield near tank hinge can get crap stuck in it too, can be stripped for cleaning, no service parts are available, seen a few partially blocked, never known one fail or wear out yet.

Left front caliper pad mounts are known to wear out where pads reside, pad come adrift under braking, check stainless thrust shim is present, seen loads of slide pins corroded, rubber bush/boots that pins slide in can be torn/worn out, only ever use silicon grease, copper & petroleum grease swells em & ruins rubbers.

Regular Fluid changes are vital to keep a linked system in good order, obviously check discs are running true, corrosion under disc mounts can lift em enough to cause judder. 👍