Bad braking in my dippy

[mycav]

When the pads/discs were new the brakes were ok but got progressively harder to operate over a couple of years. I thought this'd be a simple problem but all the points I checked seem ok.
The brake pedal goes down a couple of inches and then feels very hard when the brakes start to work...but they don't have any bite and don't slow the car down quickly.
The servo's working, tested by turning the engine off and pumping the pedal which then hisses 2 or 3 times.
The front pad material is 7mm thick, and all pads have balanced wear side to side and left to right. The ventilated discs are clean and smooth with just a small amount of undercutting and there are no leaks.
With the calipers still connected to the car I can push back the pistons using a valve spring compressor and push them out again using the pedal with the engine off. I assume this means the master brake cylinder's working normally. The caliper guides look fine.
How much pressure should you need on the brake pedal to move the piston when the pads are out and the engine off? Hand pressure?
How hard should it be to press a piston back with fluid in the system?
Help!

[Cavalier342]

Only thing I can say there is if my calipers are off and I'm replacing pads, to push the piston back manually in the caliper is hard. I use a jack handle as a lever.

[thegriffin]

Clean the pads on a flat surface with coarse sandpaper .
If no better fit new quality pads.
You should clamp pipe and loosten nipple before pushing piston back .

[Envoy CDX]

Could be a few things really.
What are you driving? 1.401.8 or a 2 litre?
If a 1.4-1.8 and you still have drums on the back, check the rear drums for signs of a leaky slave cylinder.

Then I would be trying is the cheap things.

Change fluid / bleed brakes
Clean up the carriers and calipers to ensure they are free of dust
Rough up the pads if they require it
Knock off and "lip" on the disc surface.
check the flexi's for any cracking - get someone to press the pedal and see if there is any excessive buldging from the flexi - they maybe breaking down (especially if they are original)

Then onto the slightly more expensive side of things.

Rebuild or replace the master cylinder
Replace discs and pads

[mycav]

Thanks for all the suggestions.
The car's a standard C20NE Cavalier Diplomat with disks all round.
The pipes, metal and flexible, are all original so I take the point about bulging...particularly after 160,000 miles.
I'm just recuperating after replacing a noisy drive shaft yesterday and when I've replaced a leaking lower suspension arm swivel joint I'll get back to the braking problem!

[mycav]

The long drive shaft replacement gave no improvement to a wheel rotation scraping noise that was bugging me. So I replaced the passenger side drive shaft, and the driver's side lower suspension arm with damaged joint, and that's taken a lot of time. At least the scraping's gone now.
I'll refurbish the master cylinder shortly because everything else listed as possibilities have been done.
Thanks for the suggestions.

[humbucker]

As a footnote, you can fully retract caliper pistons by using a Tech 1 (ABS-equipped models). This is recommended by the manufacturer when changing brake fluid.

[Robsey]

No-one has mentioned about ensuring that the callipers slide freely on their carriers.

I had this issue on my car.
Press the brake pedal and the calliper tried to pivot instead of slide on it's carrier.
A quick clean of the sliding faces and a lube with pencil graphite sorted my woes.

[Envoy CDX]

No-one has mentioned about ensuring that the callipers slide freely on their carriers.

I had this issue on my car.
Press the brake pedal and the calliper tried to pivot instead of slide on it's carrier.
A quick clean of the sliding faces and a lube with pencil graphite sorted my woes.

[James McGrath]

Cavalier brakes are a bit spongy compared to modern cars and the pedal does have allot of travel.

It may be something as simple as cheep brake pads. If you go to somewhere like quick fit or Halfords they are guaranteed to put on the cheapest pads they can find which will be allot worse than the genuine ones.

Another common problem is the calliper slider pins rust and stop one side of the calliper making contact with the brake disc. I had this issue with my CD manual.

Unless you know that you have got some decent pads on there already, I'd suggest getting yourself a nice set of EBC ultimax brake pads. They are not too expensive, made in the UK and they are even better than the genuine Vauxhall pads.
Then just take the wheels off and have a good look for any wear or rust on the callipers while you're fitting them. It's an afternoons work if you've never done them yourself before but it's well worth it and you'll save yourself a fortune over getting someone else to change them for you. Even if it doesn't solve the problem completely it can't do any harm and is a worth while upgrade.

[planetc]

As a footnote, you can fully retract caliper pistons by using a Tech 1 (ABS-equipped models). This is recommended by the manufacturer when changing brake fluid.

Twoddle..... You can operate the abs solenoids, to facilitate bleeding the pump and valve body, but you cannot retract caliper pistons.

[humbucker]

As a footnote, you can fully retract caliper pistons by using a Tech 1 (ABS-equipped models). This is recommended by the manufacturer when changing brake fluid.

Twoddle..... You can operate the abs solenoids, to facilitate bleeding the pump and valve body, but you cannot retract caliper pistons.

Ah yes, that's what I meant

[mycav]

The pads are Jurid. They do seem a little harder than any previous ones I've fitted...but they didn't seem noticeably hard when they were new...and the calipers work fine if the balanced pad wear is any guide.
When this cold weather ends I'll get a master cylinder replacement but until then I'll call it a day.
Thanks to everyone for their suggestions.

[mycav]

The braking problem's taken a turn for the worse. When driving it this morning the pedal was really hard near the top of its travel. Apart from the free play, where you can move the pedal by hand, I don't think there was more than a few millimetres before it felt really hard. At this point the brakes were pretty much ineffective.
By really, really, pushing hard the pedal dropped quickly a few centimetres and then the brake pedal felt "normal"... very slightly soft underfoot. However, because of the pressure I had to apply, the ABS kicked in. The car pulled a bit towards the kerb but it wouldn't skid however much I tried and the car stopped quickly.
The front wheel hubs were quite warm after this (but no hotter than they have been when there was no problem) and both smelled of hot pads to the same extent (this was something I haven't noticed before when there was no problem).
When the engine's off, pressing the brake pedal makes a hiss, and this can happen 3 or 4 times before the hissing stops.
When the engine's started, with my foot on the hard brake pedal, it'll drop a few centimetres and feel "normal".
This "normal" feel can stay for a few minutes when driving but then the pedal reverts to being very hard after the brakes have been used a few times.
So, the servo feels like it's working when idling, the ABS works under the conditions I mention, the pistons and calipers move ok and the pads don't bind when the wheels are removed and the brake fluid reservoir level hasn't dropped.
Can a defective ABS unit stop the effect of the servo and give the results I've got?
Is there anything I've overlooked?
Can anyone throw some light on what's wrong with the car, please?

[mycav]

I have just driven the same route with the ABS fuse out.
The result was a hard pedal throughout the drive and a pull to the left when pushing the brake pedal really hard.
The difference was that there was no dropping of the pedal just before the ABS kicked in on hard braking. Obviously there was no ABS this time but why did the ABS originally allow the pedal to drop and soften?

[planetc]

Have you eliminated the possibility that something is getting hot and giving you brake fade. I've seen cases where some bright spark has adjusted out pedal free play in the quest for a firmer pedal, which has led to everything getting tight when warm and fade causing the reduced response.

[mycav]

That's a good point and I hadn't thought of that. It does seem like it develops when the car's been driven several miles so I'll check into that possibility.
I got vacuum into the servo by starting the car and checked the number of pedal presses needed to get rid of the vacuum with the engine off. Then I started the engine again and turned it off, leaving it off for 5 minutes. It took the same number of presses to get rid of the vacuum. So there seems to be no leak in the valve between the servo and manifold or the servo itself.
I'm getting some original GM pads next week as they'll be what the car had when I got it, and that'll give me a point of reference. Until they arrive I'm loathe to drive the car.

[planetc]

Reading between the lines, it really does sound like fade.

[mycav]

I'm almost back to square one after replacing the nearly new hard pads with original softer Cavalier ones.
Five miles into a test drive with lots of braking (and no traffic) the brakes were performing really well...balanced, softer underfoot and with quite a bit of bite...taking into account they weren't run in. Just like they used to be!
The next test braking saw the return of the hardness underfoot and, when braking really forcefully, ABS operation on the driver's side wheel coupled with a real pull to the left.
These problems were still there 6 miles later during the drive home. Then the passenger's side front hub area felt cool and the driver's side felt very hot.
So looks like pads weren't the answer.
Even though it wasn't apparent when I forced the calipers open to fit the pads to the disks, I'm now suspecting a sticking driver's side brake piston.

[mycav]

Some success!
I did the now normal test drive from cold and the brakes were really good. I thought the problem had gone away until I realised I'd not yet got the ABS to operate, even though the braking had been very heavy-footed. So, up to 40, on with the anchors, on came the ABS, the car veered to the left and the pedal went hard.
Every use of the brakes after that was hard and veering left. The ABS didn't cut in as the braking wasn't fierce enough for a skid.
I stopped the engine and restarted it. The brakes were back to normal, working perfectly with good bite and dead straight operation.
I removed the ABS fuse and did the tests again under otherwise the same conditions. The braking was perfect and, even though I was very fierce with the brakes, it skidded straight.
The osf wheel had got hot again after the problem happened so it looks like its piston was locked on. Something's possibly wrong inside the ABS, since under "normal" braking the piston must be retracting as the hub stays cool.
The next move will be another complete fluid change to see if it's something reversible in the ABS valves. I say "another" complete fluid change as that's what I did 2 years ago when I fitted new pads and discs. If it's crud-related maybe that initial change wasn't the best thing as I may have stirred stuff up.
I initially posted about decreasing brake efficiency and pedal hardness which may well have been down to the original pads. I can't remember the ABS coming on in the years I've had the car, so I probably had two problems...one of which I wasn't even aware of.
Has anyone else had similar problems?

[jimzzr]

Some success!
I did the now normal test drive from cold and the brakes were really good. I thought the problem had gone away until I realised I'd not yet got the ABS to operate, even though the braking had been very heavy-footed. So, up to 40, on with the anchors, on came the ABS, the car veered to the left and the pedal went hard.
Every use of the brakes after that was hard and veering left. The ABS didn't cut in as the braking wasn't fierce enough for a skid.
I stopped the engine and restarted it. The brakes were back to normal, working perfectly with good bite and dead straight operation.
I removed the ABS fuse and did the tests again under otherwise the same conditions. The braking was perfect and, even though I was very fierce with the brakes, it skidded straight.
The osf wheel had got hot again after the problem happened so it looks like its piston was locked on. Something's possibly wrong inside the ABS, since under "normal" braking the piston must be retracting as the hub stays cool.
The next move will be another complete fluid change to see if it's something reversible in the ABS valves. I say "another" complete fluid change as that's what I did 2 years ago when I fitted new pads and discs. If it's crud-related maybe that initial change wasn't the best thing as I may have stirred stuff up.
I initially posted about decreasing brake efficiency and pedal hardness which may well have been down to the original pads. I can't remember the ABS coming on in the years I've had the car, so I probably had two problems...one of which I wasn't even aware of.
Has anyone else had similar problems?

I've had problems with brakes intermittently locking partially on, on a motorcycle before due to the flexi hose breaking down internally. Hard to explain, but there was actually an inner and outer hose - if the inner hose splits it can collapse inside the outer hose and become a one way valve. If the piston isn't seized I think this would be my next suspect. These hoses are usually quite cheap anyway.

[mycav]

My overriding thought now is the near consistency of what happens and when.
Yesterday I swapped over the two relays in the ABS box and did the test run again. The car had good, balanced braking every time.
Then I tried harsh braking that operated the ABS. It brought the car to a halt, straight. That was an inconsistency as "normally" the car swerved with a hard pedal as soon as the ABS operated, so I though I might have cracked it with the relays.
But, braking to get the ABS on the next time, it swerved left with a hard pedal, and that's the way the braking stayed until I took the ABS fuse out.
Then it would stop straight with normal brake feel every time.

So the ABS has to have operated for the hard pedal and swerving to occur on subsequent braking.
That hard pedal feel is different from the feel when you have the engine off and push the brake really forcefully. It feels like something solid is under the pedal.

Until I Googled this problem I hadn't appreciated that so many people had had similar experiences.The general conclusion was that it was caused by ABS valves sticking,
a situation that would not necessarily turn the ABS warning light on.
I'm going to eliminate the common factor here and replace the ABS unit next week.

[Robsey]

The fact that it can work perfectly when the ABS module is reset rules out all other brake components.

I think that you are correct to point the finger of accusation at a possibly faulty module.
That would be a logical conclusion.

[mycav]

I finally got around to fitting a secondhand ABS unit today... and now the braking is completely normal. The ABS operates when you try to skid the car and, under normal and ABS braking conditions, the brakes have feel and balanced action.
Even bleeding the brakes was easy, just like with a non-ABS Cav.
Now it's fit for the MOT!
Thanks for everyone's input.