Brake Pedal Travel. Mot Fail.

[anr]

Hi, Just had brakes fail mot on. Pedal travel to much, no reserve travel.

1.9tdi x reg, Always been like it. Seen a few ideas on here about this.

Story goes like this check over ready for MOT. Rear calipers seized on handbrake linkage, fitted exchange units also rear flexi hoses (inner and outer) and brake pipes. Was told that servo and master cylinder was changed for mot last year by previous owner and it does look like they have. Bleed all calipers no air in system. ABS working fine had pump running when bleeding. Pedal just like before. Pedal has a little travel with no engine servo, start engine pedal drops away and keeps slowy going to floor. road test brakes work fine. Effort on brake tester fine at MOT. Drive home brakes like they always have been.

1. All rear brakes new and checked so no fault there. So poss front brake fault.

2. Remove front wheels and check, replaced pads because close to wear limit, clean caliper,caplier carrier, slide bolts and discs both sides. Refit all parts.

3. Test brake pedal travel before fitting wheels. Same travel as before.

4. Clamp both front flexi pipes close to calpier, test again. Pedal travel now about 20mm after servo help then solid. So now is it a caliper piston fault.

5. Remove both calipers and fit a solid piece of metal the same thickness as pads and disc between piston and lugs to stop piston from coming out. pump brakes to get solid pedal.

6. Test brake travel solid pedal, start engine about 20mm drop with servo help. Pistons ok. no leaks dry behind bust seal.

7. Refitted capilers, Had my son press the pedal and then start engine when i looked to see what was happening, found that when servo help starts the caliper twists on slide bolts rubber mountings trying to push caliper outwards. Rubber gives a bit and piston moves more pedal travels. Tried with each caliper in turn and with each clamped off so one at a time.

8. Now for the question is this normal because the servo effort is to much, had same sort of caliper set up on my old fiesta many years ago but not this fault (smaller car less effort from servo).

Any info would be good.

[Bigjeeze]

Hi, Just had brakes fail mot on. Pedal travel to much, no reserve travel.

1.9tdi x reg, Always been like it. Seen a few ideas on here about this.

Story goes like this check over ready for MOT. Rear calipers seized on handbrake linkage, fitted exchange units also rear flexi hoses (inner and outer) and brake pipes. Was told that servo and master cylinder was changed for mot last year by previous owner and it does look like they have. Bleed all calipers no air in system. ABS working fine had pump running when bleeding. Pedal just like before. Pedal has a little travel with no engine servo, start engine pedal drops away and keeps slowy going to floor. road test brakes work fine. Effort on brake tester fine at MOT. Drive home brakes like they always have been.

1. All rear brakes new and checked so no fault there. So poss front brake fault.

2. Remove front wheels and check, replaced pads because close to wear limit, clean caliper,caplier carrier, slide bolts and discs both sides. Refit all parts.

3. Test brake pedal travel before fitting wheels. Same travel as before.

4. Clamp both front flexi pipes close to calpier, test again. Pedal travel now about 20mm after servo help then solid. So now is it a caliper piston fault.

5. Remove both calipers and fit a solid piece of metal the same thickness as pads and disc between piston and lugs to stop piston from coming out. pump brakes to get solid pedal.

6. Test brake travel solid pedal, start engine about 20mm drop with servo help. Pistons ok. no leaks dry behind bust seal.

7. Refitted capilers, Had my son press the pedal and then start engine when i looked to see what was happening, found that when servo help starts the caliper twists on slide bolts rubber mountings trying to push caliper outwards. Rubber gives a bit and piston moves more pedal travels. Tried with each caliper in turn and with each clamped off so one at a time.

8. Now for the question is this normal because the servo effort is to much, had same sort of caliper set up on my old fiesta many years ago but not this fault (smaller car less effort from servo).

Any info would be good.

 

Not sure but it does sound like there may be excesive wear on the caliper mountings - it may be that you will have to replace the caliper - or at least the mountings.

[sparky Paul]

Yes, sounds to me like the sliders and/or caliper slide bushes are worn too. Edited April 26, 2012 by sparky Paul

[daddyfixit]

i would expect that any caliper can move a little bit on its slide ?

 

but they would have to move quite a bit to allow the caliper piston to move out further when the pressure is on and cause brake pedal to travel so far?

 

if you pump up the pedal a few times and keep pressure on it, does it stay in same place or creep down?

 

if it creeps down then i would say the primary piston seal has gone and allowing brake fluid back into the reservoir while the piston carries on moving forwards. if its doing this, you may also see the brake fluid level raise while pressing the pedal and keeping it pressurised, possibly seeing tiny little bubbles coming to the surface of the brake fluid in the reservoir.

[anr]

Hi. Update on brakes.

When both front pipes are clamped off close to caliper the pedal is solid and does not creep down even with servo help.This must rule out any faults with rest of system?

Undo one clamp and press brake with out engine running pedal travels a little then solid, hold brakes on start engine servo kicks in pedal travel drops about 20mm but then keeps creeping to just before floor. Repeated test on other side and same thing happens.

Got my oldest son (heavy left foot) to press pedal when i had another look. Could not beleave what i saw. Under no servo help piston takes up slack clamps pads etc solid brake. Hold brake on start engine pedal creeps again but you can see the caliper now flex against itself (piston pushing that hard) trying to open up gap between piston and outer lug ears where outer pad sits against.

You can see the caliper flex on back edge letting piston travel a little more (pedal creep), when you let go of the pedal the flex is released so piston return correctly. Then clamped off one caliper pedal creeps to just before floor again.

Removed both calipers and blocked with metal spacers again, this time with heavy left footed son you can get calipers to flex outwards, release pedal and piston returns. If you could release pedal and pump again fast enough i would guess that it would flex more, just like a bottle jack on pump stroke.

Now is this problem a one off or we all driving around with calipers that will get weak after so many cycles on off stops.

[octo0072000]

well on T4 vw transporter you can do this as normal the servo over powers the master cylinder

not sure on the gal but gal has a big servo have a word with another test station or vosa about it

 

heres a link scroll down says galaxy does it as well as vw T4 and skodas

known as diesel creep

 

http://www.briskoda.net/forums/topic/91416-vrs-brake-pedal-going-down/

Edited April 26, 2012 by octo0072000

[gd autos]

hi your master cylinder is faulty .get a new one only 20 quid saves all that messing about BRY