Brake failure after changing pads

[yeoblade]

So after putting new front a pads in my Vivaro Van, 2012, they don't work.

There is a loud hissing inside the cab when pedal is pressed , engine on, and pedal will slowly drop to the floor.
(ABS is fitted)
Engine off and the pedal stays firm OK.
Just wondered what I have messed up, having changed pads many times before on vauxhall, nissan , Porche, .... never had an issue before.
Must be the servo hissing but what do I do to fix it?
ALL was absolutely fine BEFORE I worked on it.
Yes I did push the pistons back in without opening any bleed valve etc.

Edited by yeoblade on Sunday 18th December 18:38

[Ian Geary]

Evening,

The law of sod says it's probably something you've done, or disturbed. I once caused poor braking by fitted new pads to lipped discs, but that's not relevant here.

I would recommend going back to the principles.

A servo is a vacumn chamber with the engine on. It helps suck the pedal (well, master cylinder linkage) down when pressed, by opening one side to atmosphere and getting the remaining vacumn to do the work.

I would inspect the pipework and connections around the servo first.

Could you have introduced air into the fluid? Which is also a common cause of soft pedals.

Sorry if you know the above already.

Ian

[Bdevo3]

Sounds like you've twisted the seals in the brake master cylinder. Probably forgot to open the cap on the reservoir

[yeoblade]

Bdevo3 said:

Sounds like you've twisted the seals in the brake master cylinder. Probably forgot to open the cap on the reservoir

Ok thanks for that posibility, but I did loosen the cap prior to any work, fluid level was never low, efore or after work.

[anonymous-user]

Engine on open brake fluid reservoir so cap is completely off and push pedal up and down 10 times..

Air in the system I reckon.

[jamieduff1981]

I reckon you've stuffed the master cylinder seals too.

Open a bleed nipple and see if you can pump fluid out.

Actually, feel around the master cylinder and check the calipers for hydraulic leaks first. If the pedal is going to the floor then either the master cylinder seals are passing or it's losing fluid. It must be one or the other.

[Bdevo3]

Try removing the pads and sanding the the friction surface and the face of the discs. Re fit them and give the brakes a quick bleed all around. If it improves and goes back to being a bad pedal I'd put my money on the master cylinder. If I remember correctly a servo failure will result in a a rock solid feel to the pedal rather than a soft one

[yeoblade]

[quote=Ian Geary]Evening,

The law of sod says it's probably something you've done, or disturbed. I once caused poor braking by fitted new pads to lipped discs, but that's not relevant here.

I would recommend going back to the principles.

A servo is a vacumn,................/snip

Thanks Ian,any ideas are appreciated, as I didn't touch the servo at all I couldn't have damaged it, well externally anyway.
I have heard, now, that often people clamp the brake hose and open bleed valve before pushing pistons back in to avoid any reverse pressure messing things up . I'll do that next time. But as it's my work van I need to fix this now.

[kev b]

Have you driven it yet? If not then give it a short run if safe to do so, using the hand brake to slow, sometimes the abs plays up until the wheels have rotated a few times.

[yeoblade]

kev b said:

Have you driven it yet? If not then give it a short run if safe to do so, using the hand brake to slow, sometimes the abs plays up until the wheels have rotated a few times.

Yes, took it round the block, no improvement.

It don't think it can be losing fluid as pedal is working fine, (as normal)can't see any leaks and level in res is OK. It all goes wrong when I start the engine.

As has been said above I'm leaning towards master cylinder seals, as I pushed the fluid back up that way. Though I don't understand how this would make the servo hiss when brakes are applied, can any one explain that.

[shake n bake]

It's worth pointing out this generation of Trafic van have an adjustive servo (or called something similar)
We get an occasional customer who is concerned that the pedal goes to the floor if you keep your foot on the pedal. Don't assume the hissing sound is a fault as they always make this sound when you press/hold the pedal down.
Are you sure the pads are located correctly, locator pins in correctly ect?

[E30M3SE]

Are you sure the pads are fitted correctly?



On a serious not are you sure the pads don't just need to bed in and you are not just experiencing 'diesel creep' given that the pedal pumps up and remains firm with the engine off and there are no fluid leaks. I'm assuming your Vivaro is a diesel?

[yeoblade]

shake n bake said:

It's worth pointing out this generation of Trafic van have an adjustive servo (or called something similar)
We get an occasional customer who is concerned that the pedal goes to the floor if you keep your foot on the pedal. Don't assume the hissing sound is a fault as they always make this sound when you press/hold the pedal down.
Are you sure the pads are located correctly, locator pins in correctly ect?

Ah didn't know that, yes I had noticed that prior to me working on it, pedal slowly sinks to floor, and did wonder why.!
I have had the van from new and this is the first change of pads.

Definitely hissing really loudly now. After I had changed one side I had to turn the van around to get to the other side and immediately noticed the noise and V poor brakes.

I will check they're fitted correctly tomorrow.

Having done this job numerous times on various cars I'm really peed off this time

[mickthemechanic]

As above the pedal dropping when held is not always a sign of a problem. Mercedes vans are bad for this hold the pedal and they will go all the way to the floor. Jamieduff maybe onto something if you push the caliper pistons in to quick the master cylinder seals flip round. I have never seen this so can only guess but I would have thought engine on or off would make no difference if the seals were flipped but maybe worth checking.

[yeoblade]

E30M3SE said:

Are you sure the pads are fitted correctly?



On a serious not are you sure the pads don't just need to bed in and you are not just experiencing 'diesel creep' given that the pedal pumps up and remains firm with the engine off and there are no fluid leaks. I'm assuming your Vivaro is a diesel?

Yeap,
Those in your pic look the same as the ones on my Boxster, I fitted yellowstuff. And had NO problems

[shake n bake]

yeoblade said:

Ah didn't know that, yes I had noticed that prior to me working on it, pedal slowly sinks to floor, and did wonder why.!
I have had the van from new and this is the first change of pads.

Definitely hissing really loudly now. After I had changed one side I had to turn the van around to get to the other side and immediately noticed the noise and V poor brakes.

I will check they're fitted correctly tomorrow.

Having done this job numerous times on various cars I'm really peed off this time

Then you know what side to start with first then, I think a pad is incorrectly located and the servo is trying to adjust for it.
Stop stamping on the pedal until you've stripped it down again, it's not going to help it.

[Josho]

So are there any brakes?

I had similar on a Crafter last month. Caliper slider was seized so the pistols were going back between each brake pedal press.

[yeoblade]

Josho said:

So are there any brakes?

I had similar on a Crafter last month. Caliper slider was seized so the pistols were going back between each brake pedal press.

Yes brakes work, but pedal falls slowly to the floor with loud hissing.

I didn't strip the caliper slider mec. as they were sliding quite freely and it all felt good.

[V8 FOU]

Clamp off the front hoses to isolate the calipers. If the pedal is ok, then the problem lays with the calipers. If it still drops, then it is the master cylinder.
Off you go from there.

[yeoblade]

Got out this morning and took off the first side I did and took out pads, not sure that they were in straight or not,but all back together and

Working OK now

I did notice the hissing in the cab still but of course when they're working OK there is less pedal travel and noise.

thanks for all the help / suggestions, must check my work better next time . Doh