Forum:
hi all i got a problem with 1990 sportrak brakes, if i clamp all flexis off the brake is spot on take the clamps off the front and brakes a crap i changed rear wheel cylinder and adjusted them which didnt help the problem is obviously with the front theres no leaks and no air in the system its got me baffled forgot to say if i keep my foot on pedal it slowly goes to the floor as if there is a leak cheers
brakes
if you have adjusted the rear shoes and changed the cylinders.
check for split hoses if not id think it would be the master cylinder.
brakes
yeah i thought it was master cylinder at first but when i clamp off all 3 flexies the pedal is rock hard, i took this to inicate the master cylinder's fine, is this the case, or am i wrong (again)
Could be the master cylinder
Could be the master cylinder is dammaged inside. If so the break fluid will pass around the plunger seal, alowing the peddle to head carpetwards. However if the damage is not at the top of the stroke, then you may well get a rock hard break when the flexi's are clamped off.
Any veiws expresed in this thread by me are purely from my own experience, and (sometimes) falible memory. Hope my comments help, but please don't take them as gospel.
brakes
hi, i have replaced the master cylinder and the servo but the brakes are still crap, the only options left open are callipers and flexies, the front pads are very worn, could the brake pistons be reaching the end of their travel befoer they bite? would that give a spongey feel? or could it simply be crap flexies? i have checked them and the dont seem to be flexing overly much, thanks cheesed off chappie
Brakes
You may find that if your pads are worn very low the calipers may not be behaving as they should, sometimes pistons can stick / jam up when they are near to the end of they're travel.
Brakes
You say pedal goes hard when you clamp off front hoses, are your front wheel bearings ok ?, Had similar symptoms on a transit van, the guy was recommended to change master cylinder, which we did, problem was still there! Turns out he had a totally shot front wheel bearing which was allowing the disc / hub to tilt over, which inturn pushed the caliper pistons futher in, so, each time the pedal was pushed the pistons had further to travel out whilst straightening the disc up before the pads could actually grip correctly, rebuilt the hub etc, problem solved, in his case!
Had you not already replace the master cyl I would also have suggested this could be the fault, however as you say the fault goes when you clamp the hoses this would suggest the problem is elsewhere.
Are both your front callipers working correctly, not partially siezed?
Could be two things, as previ
Could be two things, as previously said it could be the master cylinder. What you describe does point me to that conclusion but I've been known to be wrong. If you're sure there's no leaks and when you isolate the front brakes it's ok, it could be the brake hoses are passed it.
Rubber hoses tend to break down from the inside which means they look fine but when you press down on the pedal they bulge.
Other than that I've no idea as when I had brake problems it was different symptoms.
http://www.mobtour.uk.btinternet.co.uk/mobtour/dirty_swine_4x4.html
Dirtyswine4x4.co.uk
Bleeding
If pedal under pressure is slowly travelling to the floor I would expect a master cylinder problem. However the fault could be air is trapped in the brake pipes. There is a pressure value at the rear union of the pipes and any bleeding of the system must be done in the correct order or air remains trapped at this valve.
Did you bleed the system in correct sequence? First from the longest brake and lastly at the shortest brake? If you fail to follow the sequence your brakes will be very spongy. I assume you are employing the method of bleeding correctly!
brakes
could the p & b valve be bypassed? i was told its common for these to fail (mounted on bulkhead under the master cylinder) just thinking of all the options, what are your thoughts? chhers
Brakes
My money is on the flexies. Don't pay more than about £15 for rubber ones though, you can get stainless ones custom made for about this much each. Firmer feel and longer lasting.
Let us know.
brakes
just been out to check the flexies, had the wife sit pumping the brake pedal (engine running)while i held the pipes, there is a small amount of flex however i dont know how much flex is acceptable, if any, i have discovered the pedal does pump up with the engine off, hold the pedal down while starting the engine makes it fall, pumping doesnt work then, any ideas?
Check these.
1. Flex pipes do flex! The diameter should not increase.
2. Vacuum servo will reduce the brake pedal height when engine is started.
3. With engine off and pump brake - pedal should go solid but sporty is known to remain soft/spongy. If depressed pedal goes slowly towards the floor the master cylinder is faulty -- possibly the piston seal leaking.
My thought are:
1. You failed to adjust the rear brakes - there is an adjuster on each back plate. The initial set-up must be done using the snail cam. The front brakes are discs and are fully auto adjusting.
2. Have you adjusted the handbrake? Should lock rear wheels on 3rd to 4th click.
3. Fit a new set of bleed nipples. Get them from a motor shop - not diahatsu. Take a used one to the shop and match it with new. They are standard bleed nipples and very cheap.
4. Did you read my earlier post about sequence of bleeding the brakes? Did you use new and unopened 'dot fluid of the correct grade? If proceedure is not followed to the letter, you brake pipes will have air inside.
I still reckon its the flexies !!
The rubber flexy hoses degrade from the inside and even though they may look and feel perfectly good on the outside they may be all but blocked on the inside. This may not be apparent under the full pressure of braking but when trying to bleed the brakes this can cause problems.
My 3 year old motorbike had a similar problem of spongy and slightly binding brakes which only started after removing and re-fitting the calipers. I suspected the master cylinder (even though the problem had started immediately after the system had been disturbed) and stripped and cleaned it but to no avail. After much bleeding of the brakes and swearing a lot it was still no better. Only after removing one of the flexy hoses and trying to blow through it did I realize they were at fault. They would let fluid pass down the pipe when pressurized by the master cylinder, but would not let fluid pass back up, therefore not fully relieving pressure on the pistons and causing slight binding of the pads and discs. When I cut the flexy open (after buying some nice Goodridge stainless ones) I could see the state of the inside. To the eye it appeared totally blocked.
If the brake fluid cannot return under the much lower pressure of the pistons/cylinders retracting then it stands to reason that air may be trapped as well.
Try taking off a flexy and blowing down it. You can easily blow through a new one !! If you can't blow through yours, I reckon you've found your problem.
One last thought, is there a load compensator valve in the pipework to the rear, and does it have a bleed nipple on it? Have you bled there too?
brakes
is the load compensator valve the same thing as the "proportioning and by-pass valve" or p&b valve? (thats what the manual calls it) if its the same, its on the bulkhead under the master cylinder and allas no bleed nipple