spongy brakes on VW LT van

[iainbo]

Hi everybody,

I've recently bought a VW LT van and have brake problems. The pedal is very spongy. It will firm up a bit with pumping, but will slowly creep to the floor when pressed. Thought this may be the master cylinder, but I've changed that and the problem is still there. There are no obvious leaks in the system and I've also used a gunson eezibleed kit on it and there appears to be no air in the system. Anybody got any ideas?, could it be one of the wheel cylinders passing, but would the brakes not still be ok if one was a bit dodgy? could I clamp off the hoses before the wheel cylinder to check if that is a problem?

Any help much appreciated.

Iain.

 

[Stivino]

Just had the same thing with Merc sprinter, the rear discs and pads were knackered.

 

[^neo^]

Has it got rear discs or drums?

 

[iainbo]

Neo - It has got discs on the back, have you any ideas? (the back brakes also seize solid after it's been left for a week or so - even with the handbrake left off - the van will hardly move to start with, but after about a mile of burning brakes they free off fully). Handbrake works fine.

Stivino - thanks for info - didn't think the pads or discs would have caused this problem - will take wheels off and check them, did you have similar probs as above with back brakes siezing if van was left a while?

Thanks guys.

 

[Stivino]

This van is used daily. Sounds like your brakes need attention anyway if you need to do that with them.

 

[^neo^]

If it's discs, try taking the calipers off of the carriers and then bleed the brake with the nipple facing upwards.
Stick a piece of wood in the caliper to stop the piston popping out when you do it.
For some reason VW thought it a good idea to put the bleed nipple on the side of the caliper, causing air to get trapped above it.

 

[TicklyT]

Got me thinking along the lines of a seized caliper- eventually getting hot enough to free itself off, but boiling the brake fluid in the process.

I once had a seal fail in a remote brake servo. The car had a very healthy appetite for brake fluid, but no evidence of any external leaks. Eventually the servo filled completely with brake fluid, and the engine started cutting out as it got a big gulp of brake fluid into the cylinders through the vacuum line whenever the brakes were applied.

 

[hi1]

If this is a diesel it may well have a separate vacuum pump to assist the master cylinder, follow any pipes leading from the cylinder, if theres a pot stuck on the side of the engine block this may well be such a thing. There is a diaphram inside these which can split and effect the braking. regards

 

[iainbo]

Thanks for all the info guys - going to have a further go at the brakes over the weekend!

 

[iainbo]

Hi all,

Took the back brakes apart - the pads have got some life in them, 6 - 7mm thick but the calipers were a bit stuck. Got everything freed up and working smoothly - pistons also moving in and out freely. Put them back on and bled again - STILL GOT PROBLEMS. When I bleed the system everything seems fine, even loosened the nuts at the master cylinder a touch and bled there. Everything tightened up and you can stand on the pedal and it won't move. As soon as the engine is started the pedal goes soft and you can hear a wooshing noise as if it's drawing air somewhere. Pump the pedal a bit and it will firm up but will slowly creep down if you hold your foot on the pedal. The master cylinder is brand new.

Can the servo cause problems like this? - I don't see any evidence of a separate vacuum pump on to the master cylinder. - I thought the servo only 'helped' the brake pedal.

Can there be anything wrong with the fluid resevoir? Don't see any leaks at the seals where it's mounted on to the master cylinder. And the fluid doesn't drop at all during this whole process.

Any further help much appreciated - or the name of someone who could fix it in the Glasgow / Ayrshire area.

Thanks,

Iain.

 

[andyandy2]

Is it a diesel ?

If so switch off engine, pump pedal a few times to exhaust vacuum,
Press pedal, does it stay hard ?

If so start engine and press pedal, does it then creep to floor ?

If it creeps to floor with engine running (diesel with vacuum pump) it is not unusual, some vehicles do this, (read my old posts there is a thread about an astra i think with similar) Do the brakes work ok in normal use ? (I'll explain more later if needed)

 

[iainbo]

Andy,

It is a diesel.

Engine off, pump pedal and it stays hard. Start engine and the pedal will creep to floor. The brakes were very poor in normal use but I don't know if this was because the calipers were a bit stuck. I've freed off the rear ones, but haven't checked the fronts yet. What makes the pedal go to the floor with the servo going - I thought the pedal should stay hard with or without the servo as long as all the air was expelled from the system.

I think it's also got ABS - could this be causing any problems?

Thanks,

Iain.

 

[andyandy2]

I think you need to check the front brakes and make sure they are ok, sometimes pads can get very hard and affect brake efficiency, might be worth a new set of pads

I think you've established that there is no air in the system, you can get a hard pedal without the servo, If there was air in the system the pedal would be spongy

With a seperate vacuum pump the pedal can creep slowly to the floor (doesn't always happen, doesn't happen on all vehicles) the pump is constantly creating a vacuum, the more you push the pedal the more the pump assists you're effort and the pedal goes a bit further down. Some vehicles use vacuum for other purposes, heater valves etc, so this situation doesn't always happen

Check out the front brakes first, then find a quiet stretch of road and try an emergency stop, see how the brakes perform and where the pedal ends up

If you still feel brakes are poor you could get a brake test done at your local mot centre

I think you might be trying to fix something that isn't broken.

 

[iainbo]

Andy,

Thanks for the info on the servo - I had no idea that could happen - will have a go at the front brakes tomorrow.

Cheers,

Iain.

 

[iainbo]

Thanks Andy, Stivino and all who gave advice.

Checked front brakes, seemed fine, gave van a run and can gome to very quick stop - locking wheels until ABS kicks in from 45mph in wet. Pedal still has a wee bit of extra travel for my liking, but I reckon if I renew the back pads, run it and give it a final bleed it will be OK.

Cheers all,

Iain