Technical Sticking brakes

[hastingsmum]

I've just come back from a journey, on my way there I had to stop as there was some noise from the front and eventually hot smell, both front discs were very hot and on the way back at one point the brakes slowed the car down but didn't stop it.

I've had sticking calipers before but it seems strange that they should both start sticking at the same time.

What else could cause this?

 

[portland_bill]

Now then young lady, if you don't stop breaking things, you'll be made to stand in the corner.

With both front brakes on, this would suggest a hydraulic or pedal fault. Bit late now, but I would expect the rears to be a bit warm too. With all the clutch bleeding, might be a good idea to check the brake pedal pivot, see if it is free to move, as they share the same pivot shaft I think and they might just be objecting to all the extra movement recently.

While under there, upside down under the pedals, check that the brake light switch is not holding the brakes on. This seems to be a common issue on Stilo, search the Stilo thread for details. I think all the switches are same/similar.

Also while under there, see if you can see/feel the brake pedal free travel, to ensure it is letting go properly.

If the pedal area appears ok, another possibility could be a dead servo. When the pedal is pressed, it allows atmospheric pressure to the pedal side of the diaphragm, and with vacuum on the other side, the diaphragm helps apply the brakes. If vacuum is being applied when the pedal is at rest, it will apply the brakes.

There are various threads with a similar problem, on different vehicles. Have a wee search and see what you can find. I'm off out now, so can't do it myself.

For diagnosis, you could detach the vac pump hose from the servo and see if it then allows the brakes off. be careful where you drive though, as it will require a lot (a hell of a lot!) of pedal pressure to stop without the servo.

Edit: Why not grab a servo and master cylinder form the guy breaking one.

 

[hastingsmum]

Now then young lady, if you don't stop breaking things, you'll be made to stand in the corner.

With both front brakes on, this would suggest a hydraulic or pedal fault. Bit late now, but I would expect the rears to be a bit warm too. With all the clutch bleeding, might be a good idea to check the brake pedal pivot, see if it is free to move, as they share the same pivot shaft I think and they might just be objecting to all the extra movement recently.

While under there, upside down under the pedals, check that the brake light switch is not holding the brakes on. This seems to be a common issue on Stilo, search the Stilo thread for details. I think all the switches are same/similar.

Also while under there, see if you can see/feel the brake pedal free travel, to ensure it is letting go properly.

If the pedal area appears ok, another possibility could be a dead servo. When the pedal is pressed, it allows atmospheric pressure to the pedal side of the diaphragm, and with vacuum on the other side, the diaphragm helps apply the brakes. If vacuum is being applied when the pedal is at rest, it will apply the brakes.

There are various threads with a similar problem, on different vehicles. Have a wee search and see what you can find. I'm off out now, so can't do it myself.

For diagnosis, you could detach the vac pump hose from the servo and see if it then allows the brakes off. be careful where you drive though, as it will require a lot (a hell of a lot!) of pedal pressure to stop without the servo.

Edit: Why not grab a servo and master cylinder form the guy breaking one.

Ok great thanks! a lot to take in will have a look later on or in the morning as it's pitch black out anyway so not much I can do now

 

[hastingsmum]

So far I've established that the pedal area seems fine, the brake lights don't come on unless I depress the brake pedal.

And yes the rear drums do also get a bit hot, so that seems that rules out a quick and easy fix

 

[portland_bill]

So either the servo is sticking, or the master cylinder is sticking. Hopefully master cyl, as it will be cheaper and more readily available. When pressing the pedal, does it seem to have a lot of travel before doing anything, suggesting that the master cylinder may not have returned fully?

Might have to remove master cyl from servo to check operation of both.

More bleeding! Sorry.

 

[hastingsmum]

So either the servo is sticking, or the master cylinder is sticking. Hopefully master cyl, as it will be cheaper and more readily available. When pressing the pedal, does it seem to have a lot of travel before doing anything, suggesting that the master cylinder may not have returned fully?

Might have to remove master cyl from servo to check operation of both.

More bleeding! Sorry.

I know, when you posted about the servo and master this morning/last night (?) my first thought was NOOOOO I', sure I swore I would never go there again, lol


Not the bleeding that worries me so much as if I have to re attach that flippin pipe :bang:

I don't think there is any travel, I haven't felt anything unusual at all, apart from that there is no roll back when doing hillstarts... that should have given me a clue really before I lost the brakes shouldn't it?

Today one time only after brakes had been applied the pedal went down a bit further for no apparent reason, it hasnb't ever happened before or after that give you any clues

 

[portland_bill]

Sorry for late reply, I'm not getting the notifications. Is it just me?

The pipes will be easier (hopefully) as they will be all screwed in. The clutch system works only because it uses a low pressure. The brakes use higher pressure, so need a firmer fixing.

If the master cylinder is not returning fully, the servo should return, so no excessive pedal free play, but there would be some extra movement before you get pressure as the servo pushrod has to travel to meet the master cylinder piston. (Does this make sense?) Will need careful pushing and feeling to determine if this is the case. It is less likely to be the ABS unit causing this.

 

[hastingsmum]

Sorry for late reply, I'm not getting the notifications. Is it just me?

The pipes will be easier (hopefully) as they will be all screwed in. The clutch system works only because it uses a low pressure. The brakes use higher pressure, so need a firmer fixing.

If the master cylinder is not returning fully, the servo should return, so no excessive pedal free play, but there would be some extra movement before you get pressure as the servo pushrod has to travel to meet the master cylinder piston. (Does this make sense?) Will need careful pushing and feeling to determine if this is the case. It is less likely to be the ABS unit causing this.

I don't get notifications either but I never have on this forum, only when people quote me but that's always massively delayed...

Anyway, yes I think it makes sense, I tried to determine earlier today if there was any extra free play at all but I'm pretty sure it's as it's always been not that that proves anything one way or the other...

 

[portland_bill]

Just had another thought. On some vehicles the pushrod through the servo is adjustable. They can come loose, and then usually extend themselves, holding the brakes on. Only way to tell is to remove the master cylinder from the servo and look. (ePER does not show enough detail) If it is adjustable, the procedure should be in the workshop manual. Have you downloaded yours?

 

[hastingsmum]

Just had another thought. On some vehicles the pushrod through the servo is adjustable. They can come loose, and then usually extend themselves, holding the brakes on. Only way to tell is to remove the master cylinder from the servo and look. (ePER does not show enough detail) If it is adjustable, the procedure should be in the workshop manual. Have you downloaded yours?

I have the elearn cd, nothing else

 

[portland_bill]

I have the elearn cd, nothing else

That's the "workshop manual".

Some more thoughts while out today.
If the servo is causing the problem, it might try to apply the brakes before you do. The master cylinder however, will just hold them on once applied.

Free them all off.
Start engine and see if brakes apply. If not, hopefully servo is ok.
Stop engine and pump pedal until all assistance has gone. Pedal will become very firm.
Make sure brakes are free. Do not restart engine as we need servo to be empty of vacuum.
Gently apply brakes, then release and see if they stay on. If they do, fault will almost certainly be with the master cylinder.

If it needs a new cylinder, Fiat do not list a repair kit, and a new cylinder is pots of money. If you look at breakers, try to get a fresh one as brake fluid absorbs water and one that's been sitting for more than a few weeks will be starting to corrode inside.

Good luck.

 

[hastingsmum]

That's the "workshop manual".

Some more thoughts while out today.
If the servo is causing the problem, it might try to apply the brakes before you do. The master cylinder however, will just hold them on once applied.

Free them all off.
Start engine and see if brakes apply. If not, hopefully servo is ok.
Stop engine and pump pedal until all assistance has gone. Pedal will become very firm.
Make sure brakes are free. Do not restart engine as we need servo to be empty of vacuum.
Gently apply brakes, then release and see if they stay on. If they do, fault will almost certainly be with the master cylinder.

If it needs a new cylinder, Fiat do not list a repair kit, and a new cylinder is pots of money. If you look at breakers, try to get a fresh one as brake fluid absorbs water and one that's been sitting for more than a few weeks will be starting to corrode inside.

Good luck.

Sounds great thanks! I will come back to this whenever I get the other, now slightly more urgent, issue sorted. :bang:

 

[portland_bill]

The other issue, as you've been advised, remove the belt, see what's not rotating as it should.

Been searching for m/cyl. Fiat 77364498. Also TRW PMH669 (Good brand) and Pagid is a good brand.
Best I've found is this: http://www.ebay.co.uk/itm/FIAT-MULT...rts_SM&fits=Car+Make:Fiat&hash=item43c4ad1118
Or this:http://www.mister-auto.co.uk/en/brake-master-cylinder/trw-pmh669_g258_a161PMH669.html

Or PM Sturgess, see the traders section. See what he can quote for a genuine one. If you need one of course.

 

[hastingsmum]

The other issue, as you've been advised, remove the belt, see what's not rotating as it should.

Been searching for m/cyl. Fiat 77364498. Also TRW PMH669 (Good brand) and Pagid is a good brand.
Best I've found is this: http://www.ebay.co.uk/itm/FIAT-MULT...rts_SM&fits=Car+Make:Fiat&hash=item43c4ad1118
Or this:http://www.mister-auto.co.uk/en/brake-master-cylinder/trw-pmh669_g258_a161PMH669.html

Or PM Sturgess, see the traders section. See what he can quote for a genuine one. If you need one of course.

thank you!

 

[hastingsmum]

For diagnosis, you could detach the vac pump hose from the servo and see if it then allows the brakes off. be careful where you drive though, as it will require a lot (a hell of a lot!) of pedal pressure to stop without the servo.

Brakes still on when I did this

 

[portland_bill]

Sadly, I think a new master cylinder is on the cards. Piston seems to be sticking.

When you press the brake pedal, this pushes the pushrod through the servo, which then connects to the master cylinder piston. Can you feel this moving further than normal before it contacts the master cylinder piston? Once the brakes are on, does the pedal travel feel different, longer before pushing? This might confirm the master cylinder as the issue.

Otherwise, master cyl needs to be removed, then piston pushed and see if it returns properly. Seals could be worn/swollen, or internal spring broken.

At the wheels, caliper pistons seize, and wheel cylinders at the rear can seize, but all at once is unlikely.

 

[hastingsmum]

Sadly, I think a new master cylinder is on the cards. Piston seems to be sticking.

When you press the brake pedal, this pushes the pushrod through the servo, which then connects to the master cylinder piston. Can you feel this moving further than normal before it contacts the master cylinder piston? Once the brakes are on, does the pedal travel feel different, longer before pushing? This might confirm the master cylinder as the issue.

Otherwise, master cyl needs to be removed, then piston pushed and see if it returns properly. Seals could be worn/swollen, or internal spring broken.

At the wheels, caliper pistons seize, and wheel cylinders at the rear can seize, but all at once is unlikely.

it's a tricky one tbh, I can't feel that they feel any different to what they used to, but I'm also assuming it happened gradually maybe over time...?

They feel maybe a little spongy and actually very noisy (air)

 

[portland_bill]

They feel maybe a little spongy and actually very noisy (air)

Spongy could be air in the system, or the seals being lazy as they apply pressure.

The "air" noise I assume is the air operating the servo. If servo travel is greater than normal, air noise will be more. Being diesel, you have an air pump to create the vacuum to operate the servo,so this may be noisier than a petrol.

(Petrol engine creates vacuum in inlet manifold, which is used to power servo. Diesel creates almost no vacuum, so a mechanical air pump is used. Turbo petrol engines often use an air pump too. Just info, not related to problem.)