Brakes... or not to much of !!!

[tj2]

This is becoming a super puzzle

Starting from first principles: If the lever is going back to the bar it can only be caused by two things.

1. The caliper pistons are retracting to far and thus need more fluid to bring them back to the pad. Except pumping the lever does not firm up the action.

2. If not 1. above there still has to be air in the system (somewhere).

Did you ever have normal lever response before refurbishing everything ?

Cheers Geoff

Geoff it was a box of bits and a very loosely assembled engine frame and wheels.

When applying the brake the pads contact the discs and apply enough pressure to lock the wheel fairly quickly, however the calipers appear to twist away from the disc and the mounts by a small amount (visibly) giving the extra travel in the lever.
Just cant figure out why.
There is no air in the system and there are no leaks.
Starting to get a touch miffed by it now....................

Terry

[tz375]

That makes perfect sense. I have yet to see it on a GT but it's a common problem on old yamahas.

The issue is that either the calipers themselves (the bracket part) or the bosses on the fork legs are worn/damaged/tweaked.

Loosen the two caliper bolts on each side and apply the front brake. Hold the lever on with a strap or bungee cord so you can see the gaps between the brackets and the bosses.

Two things to look for. First: the bracket should be parallel to the bosses and should be stiff but able to move side to side. If it does not move the pads or pins are binding and the caliper needs to be stripped again to fix whatever is binding. Second: if that is fine, look to see if the gap between the brackets and fork bosses are the same front and rear. It is quite common for the gaps to be uneven. Withe the brackets touching one boss, find a washer to take up the gap on the other boss.

Reassemble with the chosen washers/shims in place and all should be well

[Zunspec4]

Hi Terry,

Thinks..... When a caliper applies pressure to the pads they should grip the disc from both sides. When they do this there should not be any side force involved (equal pressure on both sides)...... Unless the caliper is not sliding on it's mount correctly and if fact only one pad is making contact. I can't think of any other explanation for the caliper moving.

A conundrum.

Cheers Geoff

[tz375]

Geoff,

It's really common on old bikes. I have had a few RD/TR/TD/TZ that have the same flexy calipers and always because they are not square to the disk so the caliper flexes as more pressure is applied as you surmised.

The right answer is to re-machine the fork legs, but a selection of washers of different thicknesses is usually good enough. In this case, it's also possible that the central part of the caliper that bolts to the fork may be tweaked in one or two planes.

[tj2]

Now there's a thing.

I cant remember if the calipers were together or in pieces when I got the bike.......

Could it be I have the brackets bolted to the wrong legs?

As the sliding pads fit either way......

That's a job for the weekend.

(In between returning grandchild and going to weddings..)

Thanks for that insight, may just be the cause....

Terry

[tj2]

Small update.....

The bike is now uk registered First small test ride last night out on the road where things can be better assessed.

The brakes actually feel fine, lever travel yes, but work smoothly.

Starting issue appears to have been due to ignition timing being set wrong or slipped (maybe not fully tightened at last fiddle)

Fuel tap appears to have a leak on the vac valve o ring and possibly leaking fuel through the carbs. Anyway the tank was empty again

Fresh fuel fully charged battery and away it went, needs a few bits looking at now but actually useable.

If it plays nicely on sat morning, it will be in Stafford town centre, with Oxleathers MCC Stafford Poppy Appeal !

(Failing that I suppose the Honda will have to do)

Thanks for your help and advice on the current problem (brakes) when I think I have it sorted I will let you all know.

Still think it may be parts interchanged on the calipers now.

Terry

[tj2]

Well it didn't make any difference by swapping the centre parts of the calipers: same same same.......

It started perfectly and ran really well on Saturday, did not miss a beat. Now has a whole 19 miles since the rebuild.

Now it wont start, not just struggle a bit, will NOT start.

I have rechecked timing, rechecked points, rechecked compression. I have a good spark and new plugs, all plugs are wet but not dripping.

Just does not want to start.

Please not crank seals now

[Alan H]

If the plugs are wet the crankcase(s) are flooded. Take the plugs out and put an old towel over the head. Spin the engine and open the throttle wide. When nothing comes out of the plug holes and you've cleaned up the mess, put some fresh plugs in and try it.
Please don't ask how I know to fo this, the memories are too painful.
Get an in line fuel tap fitted.

[Suzsmokeyallan]

Just touching back to the master cylinder situation sometimes things are contrary to what you think should or should not work. Suzuki used a 5/8 bore ft cylinder on Vstrom 1000s for many years, then recently switched to 14mm bore cylinders and changed nothing else on the braking system. It still seems to work as before,so maybe they were looking for more modulation at the lever.

[tj2]

If the plugs are wet the crankcase(s) are flooded. Take the plugs out and put an old towel over the head. Spin the engine and open the throttle wide. When nothing comes out of the plug holes and you've cleaned up the mess, put some fresh plugs in and try it.
Please don't ask how I know to fo this, the memories are too painful.
Get an in line fuel tap fitted.

Mess........yes !!!!

Need a new fuel tap, fitted one in line for now with a filter.
Carbs stripped and everything replaceable replaced float heights checked.... r/h 5mm out l/h 3mm out centre bang on.

Lots of fuel out of r/h cyl, fair amount from l/h, none from centre...............

So hopefully a fix for now, just need to spend on a new tap

Or do I buy some higgspeeds??

Thanks for all help

Terry

[Alan H]

Depends on the look you want. I've got original Gibson spannies on my Kettle (bought 1979) but they are like rocking horse poo now. Delkevic do 'standard' exhausts at about £1500 ish.


Does the bike run now?

Taps available from Bluesmokebaz on kettleclinic (or ebay) at just over £100.

[tj2]

Yes starting up no problem.... just got to make sure everything set up right now days are just not long (or warm) enough to spend much meaningful time at my lock up especially as the neighbours don't like my generator !

Brakes are getting better with some use tho.... maybe they will firm up as the new pads bed in

Cheers Terry

[sportston]

No wonder it flooded if your floats were up to 5mm out. That was waaaaaay far from correct. Glad you got to the bottom of the problem.

[tj2]

No wonder it flooded if your floats were up to 5mm out. That was waaaaaay far from correct. Glad you got to the bottom of the problem.

Never thought to check as it ran well with no problems......................



On the remote fuel tank.

[Alan H]

Using the tank with a vacuum tap actually pumps fuel into the carbs, it doesn't just dribble in, so the float valves must work properly and seal when they should.