maestro van brake problems

[maestro vans]

I have a maestro 500 van with spongy brakes. Right here we go. The brake pedal travels a fair way before operation, it feels spongy, it takes a while to raise back up after applying brakes, ie slowly returns, sometimes it stays stuck down, the brakes applied
First thing I did was replace the master cylinder, and put a new set of pads on the front. i also checked the rear shoe auto adjusters were working correctly too. It appears to be the same, now after a run there was smoke coming from the wheels. I assumed that because the disks are worn the pads were bedding in to match the profile of the disk, any how I swapped the old pads back. The master cylinder was replaced and all the system refilled and bled using a gunsons easibleed.
Does anyone know why the pedal should return so slowly sometimes?
I don't know wether to suspect the vacuum servo (booster ) unit.
Does anyone know how I can test this.
Anyway to top it all of today the clutch has given up the ghost, its having a
new one fitted. Maybe the smoke was from the clutch rather than the pads?
The wheel rims feel quite hot thou, I've checked that the pistons and calipers are sliding easy enough.
Iam now at a loose end, any help appreciated.

[dutch-van-driver]

Hi,

I'm not an expert but what I was wondering is if the brake assistence (vacuum system) is OK. Does the vacuum pomp work?

Lots of suc6 with finding the cause.

Marc

[tony]

i wonder if your flexy hoses that go to the wheels have collapsed internally, acting a bit like a one way valve?,they are not too dear to replace as thats the only way i know to check it,.do they bulge at all when the brake peadle is pressed? :)

[maestro vans]

Thanks for the replies guys. I've checked the rubber hoses and they seem
ok. Does anyone know the definitive way to check if the servo is working correctly. I noticed that if I pump the break pedal a lot when the engine is ticking over I can get it to stop.
Any suggestions appreciated.

[tony]

servo check , press brakes start engine, peddle should go down a bit

[maestro vans]

Thanks tony it does this OK, I'm still at a loose end, I did notice however that one of the small vacuum pipes had a split the one that comes from the inlet manifold where the vacuum unit gets its supply from. Do you think this could have anything to do with a peddle that returns slowly?

[tony]

i dont think so , i still favour them flexys tho .what about lifting a wheel up (then putting a axle stand under) spinning the wheel, pressing the brakes on ,the letting go of the brakes and seeing if the wheel still spins free? do it to all 4 wheels .u can tell if its one wheel or not .ie a wheel fault or a system fault? :)

[maestro vans]

Initially I did check that the wheels were spinning freely. When I jacked the van up to change the pads, I spun the wheel it span reasonably freely ie no real binding so still I don't know why the pedal should raise backup slowly
I'm still no nearer to finding out. Do you think I should replace the servo unit would this account for the slow release of the pedal?

[tony]

:giveup: i dont think that the sevro affects the peddle in that way , but must admit i am at a lost too :giveup:
anybody any ideas ?

[e692wtt]

I would expect there to be a spring attached to the top of the brake pedal, to make it return quickly to the top of its travel when released.

If this is broken (or missing), the pedal would 'return' slowly because there are springs in the brake master cylinder and also the rear brakes to force fluid back, but this would only be a small force and the pedal would only 'return' slowly.

I think 'spongy brakes problem' may be something else, but if the brake fluid is old (ie 'boils' easily due to water content and then the brakes feel, politely, 'no good' after this has happened) and the brakes are overheating because of redidual pressure in the brake lines because the brake pedal isn't 'returning' properly then changing the brake fluid along with the brake pedal spring will sort it out...

I would say to check the brake master cylinder, but this has already been done... d'oh! :laugh: And on my Monty (1.6 petrol) if I pump the brake pedal a lot and very quickly I can stall the engine, so I would say that is normal...


Hope this helps, or at least doesn't muddy the waters further... :)

[maestro vans]

Thanks for the reply, I have checked the pedal return spring was intact and working. The fluid was renewed when I swapped the master cylinder,so I don't think that would be a problem.
I'm still open to suggestions!

[e692wtt]

D'oh! :laugh:

Ah well...

[E_T_V]

I would suspect a duff master cylinder but as you've just changed it I'm confused too. Are you sure the old one was dead?

Are you useing the correct brake fluid? (the wrong type would make the seals in the system swell and stick) It should be normal brake fluid not the more uncommon type used.

Does the brake pedel return quickly when the engine is off? I'm fairly sure the brake problems are associated with the fact the pedle isn';t returning meaning that you are overheating the brakes.

Also check that none of the brake lines (metal and rubber) aren't kinked or squashed flat as that may stop pressure being released.

[G Force]

Hi there, your problem sounds to me to be a faulty vacuum servo. Probably the valve sticking or an air leak. You could test for this in two ways, either disconnect and block the vacuum pipe to the servo, then drive the car and see if the brakes still stick on. The brakes will still operate but much more pressure will need to be applied to the brake pedal. If this sounds too risky, then with the brakes connected as normal, drive the car until the brakes are sticking on, then with the engine still running jack up the front wheels and confirm that they are binding, then disconnect the servo vacuum hose and see if that releases the brakes. If so fit a new servo unit.

Cheers Gary :)