Flexing calipers = soft lever?

[Guest]

About a week ago I flushed and bled my brakes and replaced the pads. I THOUGHT I always had a hard time getting air bubbles out but now I know it's something else.

I bled by taking the calipers and splitter off the bike with the system closed. I pushed the pistons back in fully and held them with C clamps and then bled the master, the splitter and each caliper and ended up with a rock hard lever!

Woohoo!!! Finally good brakes! Or not. When I put them back on the bike the lever was as spongy as ever and now that I've put a couple of hundred miles on the pads I can clearly see that they are only hitting on the outer 2/3 of the rotors. I'm thinking this is due to either slop on the axle bores in the caliper carriers or flex in the actual caliper itself.

I've been looking for a thread on re-bushing the carriers, I've seen it referenced in other threads but never found the main thread. Any links? Any ideas other than new/rebushed carriers? I want to do the twinpot upgrade but not until I replace my wheels.

/\/\ac

[Calvin Blackmore]

doubt it caliper flex


mosty likely its normal run in on a very worn disc combined with fork flex

[Macmatic]

So if there a thread on re-bushing the caliper carriers? I've searched but I can only find a few threads that talk about reading about it but none that have any detail.

Would bronze/oilite be good enough material for a few thousand miles? I guess it would be as durable as the aluminum or near enough. I know I can get bronze or oilite bushings at a farm supply shop near me in a range of sizes and I could drill out the carrier to accept the bushing but I don't have a good example to know what size to make the ID. I don't want to go too big and just re-create sloppy fit or too tight and maybe bind them up or something.

/\/\ac

[Nessism]

Bushing sounds like a good idea. The early round puck calipers were bushed in a similar way so I can't think of any reasons why you shouldn't be able to do similar.

Regarding size, not sure. I do know you should ream the hole, not just drill out the bushing since the hole won't be round.

[kingofvenus]

You should put a 600 katana front end and rear wheel on it. It is a very easy swap, i can tell you exactly what to do. And the parts are cheap and easy to find. The brakes are way better than your stockers could ever be and you'll be able to run radial tires. Trust me, it's the best thing you could ever do to your bike.

[Macmatic]

You should put a 600 katana front end and rear wheel on it. It is a very easy swap, i can tell you exactly what to do. And the parts are cheap and easy to find. The brakes are way better than your stockers could ever be and you'll be able to run radial tires. Trust me, it's the best thing you could ever do to your bike.

Oh I know its a great upgrade and I'd planned on it but I've changed directions with this bike. At some point I decided I want to keep this bike close to stock looking... kind of.. so I'm only worried about these brakes for the next five months or so. i say "kind of" because I'm planning to change the fairing to a Pichler I got off fleabay a couple of years ago. It looks pretty much the same but is a little wider with a little more windscreen. basically I have an eye towards making this my 2-up and touring bike instead of my only bike. I have another project in the works that will be a solo blaster for day rides and the like.

Over the next year I want to rebuild the stock forks with a set of inners with the screw in cap, add cartridge emulators, cut the Progressives or add RT springs and blank off the already disconnected anti-dive units.
At the same time I'm going to put on rims from an '86 GSXR-1100 so I can run radials. These are the same style but 18" F/R although I may get a 17" front because rubber is easier to find and closer to stock, just 1" up front and rear. I may also use the Kat 600 swinger since its a little wider and has a clevis shock mount and should open up the shock swap options.
While all this is going on I'm also going to do the "twinpot" upgrade or something like it but in the meantime, you know, stopping is good.

/\/\ac


P.s. The solo project is using Kat 600 forks and a GS1100 swinger with Kat 600 wheels.

[Macmatic]

Regarding size, not sure. I do know you should ream the hole, not just drill out the bushing since the hole won't be round.

Thanks, I wouldn't have thought about reaming. I may take them down to a friends machine shop in New Milford, CT and have him to the ID. Especially if I can't come up with good numbers for the size although it's probably and even, half or maybe quarter MM size. I'd trust his experience to choose a working clearance if need be. I'll check the manual too, just thought of that, maybe it has a spec.

/\/\ac

[kingofvenus]

Sounds like a plan. Just thought i'd throw it out there. So many have asked me about it, but i have yet to see anyone do it. Most people would see mine and not notice, due to it not looking too much differant from stock. Got my 850 last year so i'd have a two-up bike.

[SqDancerLynn1]

Make sure you are using the correct type of bolts!!

[Macmatic]

Make sure you are using the correct type of bolts!!

Good thought, what mark should be on them? I'm using the ones that have always been in there since I got the bike but I never checked specifically to make sure they were the right spec. [Edit: My carrier bolts are 7's and the caliper axle bolts are not marked. Same on the '87 GS450 I'm working on right now with the same setup]

/\/\ac

[koolaid_kid]

The marking indicates the grade (hardness) of the bolt. If they are unmarked, they are low grade (soft) bolts. Basically, it relates to the tensile strength of the bolt. If it is under a lot of stress, you want a higher grade bolt. When I built my turbocharged engine last year, some bolts I used were grade 9, which has a pretty high tensile strenth. But it was also an 800 hp. engine, so it needed them.

[Runningdog]

My '80 GS850 front calipers are experiencing the same symptoms.....spongey, and the calipers actually move when brake pressure is applied.
I split the calipers on the bike, and noticed that the pins seemed sloppy in the slider bores. The inside brake pads looked like they have never been used. When I put it all back together, the bottom pin bolt would tighten right up, but the top bolt seemed to not reach the end of turning...no stripped threads, I checked that.
The master has a new kit, new fluid throughout, installed with a pressure bleeder, and no air in system.
Haven't checked the pistons, yet, but the sloppy pin issue has me scratching my bald head......stumped.

[Macmatic]

My '80 GS850 front calipers are experiencing the same symptoms.....spongey, and the calipers actually move when brake pressure is applied.
I split the calipers on the bike, and noticed that the pins seemed sloppy in the slider bores. The inside brake pads looked like they have never been used. When I put it all back together, the bottom pin bolt would tighten right up, but the top bolt seemed to not reach the end of turning...no stripped threads, I checked that.
The master has a new kit, new fluid throughout, installed with a pressure bleeder, and no air in system.
Haven't checked the pistons, yet, but the sloppy pin issue has me scratching my bald head......stumped.

I think I'm getting a new to me set of caliper hangers from a member here, I'll post back when I get them on and see if that is the fix.

I have an '85 GS450 here with the same brake setup on one side and the lever is much firmer than my bike. When I wiggle the 450 caliper it has play but significantly less than my 750. I'd just go ahead and do the twinpot upgrade now but I'll be switching wheels over the winter and I don't want to waste the tires I just mounted up. Oh, that and money is an issue!

/\/\ac

[TheCafeKid]

Flexing BRAKE HOSE = mushy lever. If you're not running stainless lines, start there. IIRC your bike also has anti-dive, remove it and clean all the orifices inside. The first pull if the lever arms this system, then the brakes kick in. I fought and fought with these systems, both in trying to disarm the antidive (which while it helped brake feel SOME, make the bike feel less predictable than with the unpredictable antidive system installed) and found that stainless lines with a completely CLEANED and freshly lubed system made a HUGE difference. Whether it's been sitting or on the road, after 20 plus years if you haven't rehabbed the brakes, it's long past time. If you haven't in four or five years, it's probably a good idea.

[TheCafeKid]

Another thought too... You haven't by chance replaced your master cylinder have you? Your 450 may have the same caliper, but the MC is different. On the single disc bikes they used a 14mm diameter bore in the MC, on the twin binder bikes they used 5/8" bore. If you've replaced the MC with another stock GS unit and used 14mm, your stroke and bore will be too short/narrow to push the volume of fluid required for a good brake lever feel. It will still actuate the brakes, but it runs out of travel before it feels stiff. I've experimented with different aftermarket MCs and still haven't found one that feels acceptable for twin disc bikes, even if the bore is the same size, the stroke is too short, and the lever feels like crap. I need to find out what the stroke length on the stock MCs with 5/8s bore was, if anyone knows off the top of their head. I'd imagine i can find something acceptable from a Gixxer of some year as they still use 5/8 bores, or did for a while anyway, but I dunno if the stroke was close to comparable.