Manky Monkey Motors

Right,pay attention at the back please............All ideas/thoughts appreciated........
   I have Golf rear brakes and gsxr twin front discs,all powered from one 3/4" bore (I think) mastercyclinder.Originally the brake pedal travel was fine,but of late ,(ie after about 1500 miles max,I have driven the trike) the pedal has developed a lot of travel . It will just about stop the trike on one push of the pedal,but ideally needs to be released and pushed again,to give much better braking. Now,ordinarily I would put this symptom down to the brakes needing adjustment,but of course,being discs and pads ,there is no adjustment.I suppose they could need bleeding,but they dont feel spongy,just low. I havent looked at the pads,but Im guessing that they cant have worn down that far in 1500 or so miles? If they had worn down,or 'bedded in' would they increase the pedal travel that much? How do cars with discs all round compensate pedal travel for the pads getting thinner? I could lengthen the pedal to m/cyl shaft???? I dont see any leaks anywhere else in the system.
  Also...I have problem with leakage (oo er) from the cap of the m/cyl. At first I thought it was leaking from a split in the screw top,but Ive sealed that up,and the fluid appears to be coming out of the tiny pinhole in the centre of the cap. There should be a disc of plastic in the cap that acts as a baffle to,I presume ,allow air in,but prevent the fluid escaping as it sloshes around.I doubt if this problem is associated with the low brake problem.The fluid does need a small top up occasionaly,but has never got so low that air could get in the system through the m/cyl.

The pads are pushed away from the disc by a very minute amount. A disc that is warped or out of true can cause a very small amount of excess travel but I think you would notice that.
Is the master cylinder a good make. Some cheaper ones have very soft bores and are prone to very fast wear, but 1500 miles seems low even for that. Unless the pushrod is not pushing in line with the bore which will wear the seals and bore quicker.
Is the pedal return spring good,  pulling the piston fully back. only when the piston is back or very nearly so, does fluid from the reservoir enter the cylinder to replace any that has leaked back past the seals, or to make up for wear.
It may be that the brakes just need bleeding.
Bikes and trikes tend to bounce around a lot more than cars. Bike reservoirs have a rubber bellows to allow for level drop without risk of leakage.
Might be worth looking to see if you can find one that will fit, or be modified to do so,  if you are worried about it.
Hope you can sort this one out.

Bit of an update........
 A thought Ive just had...Maybe when I first fitted the m/cyl it was already on the limit in bore size to push the caliper cylinders? and a small amount of pad wear has shown up the lack of cylinder bore size? Not sure what the next size up is. Im pretty sure mine is .6-- something or other
 
 Extremely  good points there ON! Just checked my pedal,and it snaps open when released,so thats ok. I seem to remember some old cars had a taller than usual m/cyl body extension,so maybe I'll make an extension on the m/cyl body to prevent fluid sloshing out.If I only top up the fluid to the existing level,that may do the trick to prevent the fluid loss.(I often wondered why bike cylinders were sealed top! ) Gonna have a go at bleeding the system tamara.

If yours is .6 something then its .625" next size up is .750" (3/4")
I use .625" just for the rear drums and I think I could operate those + one front disc from it.
Not sure how much fluid movement the golf discs require.
Rather than a reservoir extension, you could possibly fit a breather tube.

youre calipers ,,should,, auto-adjust, if set up correctly ,if the h/brake cable is set up wrong they won,t adjust , ::)

do you have residual pressure valves fitted

Or it could be that old chestnut.....volume vs pressure.

I think you hit it on the nose with it being on the limit rod,
Slight pad wear things loosen up,
Rod if you have flexi front brake pipes clamp on off,
And see if the pressure comes back,if so you may want to fit a 7/8 Master.

I do have a balance valve on the rear brakes,which I have recently slackened off a bit. I didnt mention that in my orig post as I was still getting the symptoms ,although to a lesser degree,before I altered the balance pressure. Cant clamp off the fronts easy,as they are stainless hoses.
  Ive already been rummaging through my boxes to find bits to make up a breather for the top of the cylinder. I found some stainless brake hose fittings,and I figure I will make up a elbow from a couple of fittings welded at 90 degrees,bolted through the centre of the cap,then run a piece of ,stainless flexy about 6 inches long upwards. that should stop the leaks from the sloshing about.
  I'll look in to the self adjustment of the rear calipers.
   I used the pads that came with the front calipers,and I dont know how thick brand  new ones are,so cant compare pad wear yet.
 I'll also get hold of a larger diam bore cylinder this week,as it cant hurt to push more pressure.

larger bore will give less pressure,,,,, but,,, more volume,,,

Got my volume/pressure mixed up there! ::) Meant more volume,and more pressure to push the pedal  (I think!) Getting confused,its been a long day !
 
 Oh ,and hello T bone,long time no speak!  ;D

This maybe what is required. Is the master cylinder mounted lower than the callipers? Fluid can run back into the master cylinder. The vaccuum can cause the calliper pistons to be drawn back a small amount creating the problem you have. The 1500 miles may be just that everything is moving freely now.

 
 Hmmm...Ive just read that res valves should not be put in a disc brake system ,as they hold the pads onto the discs?

2 lb valves for disc brakes.
10 lb valves for drum brakes, (fitted to my truck -discs on the front & drums on the back).

Yep,I understand now! The lower poundage ones are for discs. Can I just get away with putting one into the line from m/cyl to all the brakes,or do I need one in each line? (ie lots of pipework changes)

If you've got both discs & drums I'd say one to front & one to back.

are you using a dual brake circut system.

No ,one m/cyl powering all 4 brakes

I assume it's a Girling style integral reservoir master cylinder.
One 2psi rpv in the line before it splits to front and back should be ok.

so its one pipe out off m/cyl to a two way splitter to the front and rear. ???

Yes thats correct Terry.
 Today I experimented........ shut the balance valve to the rear brakes,then depressed the pedal,appears to need less travel to operate the front brakes.I then opened it about 3/4 of the way. This caused the nose to dive and lock up,but I still had to double pump the pedal to do this. My thoughts are that the bal valve should be fully open to allow the rears to brake first,or at very least all brakes come on together.But with valve fully open I still have to double pump to get a bit better pedal. You can actually see that the second pump doesnt allow the rod operating the cylinder to go in as much,so I think it needs a larger (7/8"?) bore m/cyl,a good bleed out,and then if prob persists I will get the residual valve in line as per ON's post.Would I benefit from a higher (remote) mounted reservoir to maintain a 'head' of fluid,or does it only matter that the height of the actual m/cyl bore should ideally be higher?

so is the hand brake easy to get at when riding

 ;D  Are you trying to tell me summat Terry?  ;D

Try bleeding first as that costs near nowt. Bleed with valve fully open.
A remote reservoir will help but I believe it should be as high as the highest pipework(not sure)
I would have thought that on a trike, if you are going to fit a balance valve it would be in the front line to prevent front end lock up.
Locking up the rears can be very entertaining while locking up the front can be very frightening.
I rarely use the front brakes,  (twin Z1000 discs) but its good to know they are there when I need to stop a bit fast.

no Rod just curious. if you could reach the hand brake if the main brake failed  :)

Yes not a problem to reach,very accessible!
 
 O N ...yes,good idea, I will try bleeding them tamara. If that fails,apparently theres a Land Rover place a few miles away who does all the cylinders,so will run over there to get a 7/8 bore one.

Ive now bled the brakes,but still have the same" double pump to get good brakes ",symptom. Ive looked at adjusting the Golf calipers to allow the pads to be closer to the disc,but they seem ok. Ive tried pulling the handbrake on one notch ,thinking it would take up the wear in the pads,but it still needs a double pump.The larger bore m/cylinders dont appear to come in the integral reservoir type (remote only) . Wheres the best place to get residual pressure valves?

http://www.cbsonline.co.uk/
They do integral master cylinders in 0.625"  0.7" & 0.75"
or separate reservoir kits in 0.625" 0.750" 0.875" & 1.0"
& 2lb residual pressure relief valves
Probably not the cheapest place. Their catalogue is worth having just to show what's available and for ideas.
If the problem exists with the handbrake on it suggests that the trouble might be with the front. The brake line probably goes up from the master to a splitter near the headstock before going back down to the callipers. This can be really difficult to bleed fully. Ideally you should get the brake line as near to level as possible, or take the callipers off, and bleed with them higher than the splitter, as any air will try to go to the highest point.

Thanks ON ,all the things Id thought of too! CBS are very cheap for the cylinders.Im going there tomorrow to pickup a residual valve. I'll fit it immediately after the m/cyl and see what happens then. Rally Design in Kent have a good article on their site about all this. I rang them with the problem and explained that the splitter on the headstock was the highest of all the pipework, and they didnt think a larger m/cyl would help much. They suggested a R.V. as a start.Their article suggests that if you put the reservoir high it will help,but he said that even if this was done on my system,it still wouldnt give enough 'head' of fluid to push the fluid up to the highest points. OK in a car where all the lines are more or less on a horizontal with the m/cyl.
  Roughly speaking the dimensions,using the floor as a baseline are..
 m/cyl to floor 6"
 caliper tops to floor 15"
  Headstock splitter to floor 24"
 
 I have a bleed nipple at the headstock,actually on the splitter,but it didnt seem to be releasing any air when I bled the system.
 
 I'll keep you posted!
 

Today I received the RPV from car Builder Solutions,great! Took pipe off trike(brake fluid discovered on frame ..see other post in Gen Section.) Dug out my pipe flaring tool..bu**er!.. A part is missing for the tool! It was only a cheapo one,and didnt work succesfully previously,but I thought I might get away with making 2 flares,especially as Im doing it on the bench ..had to order a new tool from amazon,different design this time..so more waiting! At least Im a bit nearer solving the problem.

Getting there Rod, getting there.  ;)

RPV is fitted and definitely improves the brakes! ..BUT.........before the RPV was fitted and now,after its fitted I still have fluid spluttering out of the breather hole in the cap cos the plastic disc,valve thing in the cap broke off,so I fitted a union and a plastic pipe about 12" long mounted vertically of f the union. Im still getting fluid going up the pipe after about half hours run(ie various times applying the brakes) I'm not convinced that the vent valve that broke would stop the amount of pressure needed to push the fluid up the plastic pipe Ive fitted.I have the fluid at the correct level in the m/cyl . The union I fitted in the cap sticks down around 4 or 5 mm into the cap,and I suppose fluid could touch this as it is washed around inside the m/cyl.(I suppose it must do ,as how else would the fluid get in the pipe? )There seems to be gaps of air/fluid/air etc in the pipe,so could it be that the fluid is going up as mentioned,then being sucked down as the level in the m/cyl rises and lowers as the brakes are applied?I ve looked at other caps,and some dont have a valve,just a hole. Im also told that some more modern caps dont have a hole at all.Surely this wont allow air in ,therefore causing a vacuum on top of the fluid in the m/cyl,which would hold the fluid back when braking? Im going to have to buy a complete new m/cylinder and cap with a vent valve in it,as I cant seem to buy a cap with the plastic vent in it on its own.