Problems after front disc and pad change

[Japtastic]

My brake pedal now travels far further than it used to and feels a bit spongy, it still brakes fine but doesn't feel right at all, I have changed lots of discs and pads on several different cars and never had a problem, can any one suggest what might be wrong, I have tried bleeding just in case some air had entered the system but with no luck, really need to use the car tomorrow!

Cheers

Stewart

 

[Will]

Definately sounds like air in the system, caused by the caliper pistons being wound back in.

I'd try bleeding again. Was it front or rear discs that you've fitted?

Try bleeding starting from the furthest caliper (Ie, rear (N/S?) ) working towards the front one nearest the resevoir (brake cylinder)

What method for bleeding were you using BTW?

Will

 

[television]

Hi Stewart, I have heard it said that that when you just push the pistons back, rather than clamping and undoing the bleed nipple that damage can be done to the master cylinder rubbers, these as you know are tandem devices, the section for the rear rubbers can sometimes invert themselves.

I would just bleed them once more, starting from the rear furthest away.

 

[Bazzle]

Do they feel the same after they have cooled down from the initial problem? Sometimes new pads get an excess of plasma gas when burning in and hot .
If still the same then as stated has to sometning else.

Bazzle

 

[Dieselman]

I'd say it's just he new pads bedding in.
Have a drive wilst pressing the brakes pretty hard with your left foot to bed the pads.

 

[Japtastic]

Thanks for all the feedback, I'm pretty sure it's not just new pads, I'm going to try and bleed again now, it was just the fronts I changed, I used one of those 1 man bleed kits from halfords, used it before and it seems to work well.

Just realised I've some how lost between last night and this morning my locking wheel nut adapter

When bleeding do I have to do the back ones as well or just the front as those are the ones I've changed? Edit: just noticed some one mentioned to the back as well...

Knowing my luck it's the master brake cylinder...

Thanks for all the help.

P.S

 

[television]

Thanks for all the feedback, I'm pretty sure it's not just new pads, I'm going to try and bleed again now, it was just the fronts I changed, I used one of those 1 man bleed kits from halfords, used it before and it seems to work well.

Just realised I've some how lost between last night and this morning my locking wheel nut adapter

When bleeding do I have to do the back ones as well or just the front as those are the ones I've changed? Edit: just noticed some one mentioned to the back as well...

Knowing my luck it's the master brake cylinder...

Thanks for all the help.

P.S

No your fronts are on a separate circuit,I do not think that the pedal is ever spongy due to bedding in

 

[c240yaz]

When bleeding do I have to do the back ones as well or just the front as those are the ones I've changed? Edit: just noticed some one mentioned to the back as well...

Knowing my luck it's the master brake cylinder...

Thanks for all the help.

P.S

I done my fronts a few months back and had a similar problem. Bled mine the old fashioned way, pumping the pedal to the floor, master cylinder seals did not invert. But it was necessarry for me to bleed the rears also., then everything was ok.Try bleeding again.

 

[television]

I done my fronts a few months back and had a similar problem. Bled mine the old fashioned way, pumping the pedal to the floor, master cylinder seals did not invert. But it was necessarry for me to bleed the rears also., then everything was ok.Try bleeding again.

This is an interest point, does pushing the fluid back up upset the dual master cylinders

 

[bolide]

I'd check the pads are seated properly first. Caredfully brush out any dust and make sure they're not catching in the caliper

Then I'd re-bleed the brakes but I'd gravity bleed them - just open the nipple with a length of hose on it and keep topping up the reservoir. It'll bleed naturally

I've had the best results with this method

Nick Froome
www.w124.co.uk

 

[Will]

Gravity bleeding never seemed to work well for me - my logic against it was that air naturally wants to rise when trapped in brake fluid, and the very slow rate at which it is being bled through by gravity means it's less likely to be expelled from the system.

Two people, start to depress the pedal, open the nipple, stop a fraction before the pedal is on the floor and close the nipple, repeat.

I'd bleed about a litre through starting from the furthest caliper from the master cylinder and finishing with the nearest. At least you'll not have to replace the brake fluid for about another year or so

As has also been said, double check that the pads are seated properly although I doubt this is the problem.

Good luck,

Will

 

[Dieselman]

This is an interest point, does pushing the fluid back up upset the dual master cylinders

It shouldn't as the master cylinder seals should be clear of the inlet ports so fluid will just vent back into the reservoir.
If the seals are not clear then there will be constant pressure in the braking system and the brakes will bind.

 

[television]

It shouldn't as the master cylinder seals should be clear of the inlet ports so fluid will just vent back into the reservoir.
If the seals are not clear then there will be constant pressure in the braking system and the brakes will bind.

Yes I understand that bit thanks, its just that sometimes the master cylinder does fail shortly after, I know the the piston travels further when bleeding than ever it does in the normal working life.

 

[eurico]

You're right Telly. It travels to "unknowned territory" and sometimes gets the seals scratched resulting in the obvious. I once replaced the fluid in a perfectly healthy brake system of a Renault 5 and ruined the master cylinder just by making the piston travel further than it usually did.

 

[c240yaz]

This may be irrelevent, but my mate who is a Vauxhall tech says, it has been known for some cars, dependent on the condition of the caliper, to draw air back in past the caliper piston seals, when your pushing the caliper pistons home, when fitting the pads. (as the pistons seals are going back to "old" territory)

Personally I have never encountered this, but he insists that this has happened with him in the past.

 

[miro]

This is an interest point, does pushing the fluid back up upset the dual master cylinders

Yes it does. The moving parts in the pistons deposit metallic debris into the braking system when the piston moves backwards. Bleeding is not a science but when it is done with a pressurized feed the results are always excellent.

 

[miro]

Two people, start to depress the pedal, open the nipple, stop a fraction before the pedal is on the floor and close the nipple, repeat.

Too bad that it doesn't work on the W211 or any other car with SBC. The braking system is not connected to the pedal and the fluid needs to be run out with Star Diagnose.

 

[Will]

Too bad that it doesn't work on the W211 or any other car with SBC. The braking system is not connected to the pedal and the fluid needs to be run out with Star Diagnose.

Yes, a good thing that he has a W208 CLK

Will

 

[Dieselman]

Too bad that it doesn't work on the W211 or any other car with SBC. The braking system is not connected to the pedal and the fluid needs to be run out with Star Diagnose.

Not strictly true. The unassisted feed is connected to the pedal master cylinder just as normal. Only the high pressure application is carried out by the booster motor instead of a servo.

 

[Japtastic]

Thanks for all the replys guys, I still can't find my locking wheel nut key! Can't believe it. Going to Merc today to get a new one, then will try bleeding again, will let you know the outcome.

Stewart