Sponge (bob-square-pants)

Brakepads, discs, handbrake. The brakes are crucial for your Volvo 480. Use this category to learn all you need to know!

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SanPhire
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Sponge (bob-square-pants)

Post by SanPhire » Thu Apr 07, 2005 12:40 am

I have lived a previous life in which the brake pedal in my car gave the impression it, somewhere down the line, caused brake pads to be squeezed onto the discs and caused my vehicle to slow down...

Then one day, after a full set of new pads about, that life was gone... to be only dreamed about.

I have tried full fluid flushes and bedding in the pads on a series of interesting B-road blacktop and nearly 10 thousand mileometers of various other driving - but still, there appears to be a sponge at my foot.
The car still stops effectivly, under stomping conditions wheels lock up and ABS kicks in (although I wish sometimes it wouldn't...) but I have no more of that much-spouted phrase "pedal-feel" :cry:

Various wonderings as to causes of the problem have pottered into my rambling mind - and I would love to recieve comment from others...

Somewhere - possibly over the rainbow, but more likely to be in the braking system - there still be air, or tired old brake fluid. Are there areas of Mk IV ABS system reknowned for hording hydraulic juice and if so how can I get it out of a bleed nipple?

DOT5.1 isn't as good as DOT4 in Ovlov 480s. (just like being five and a bit wasn't as quite much fun as being four becuase compulsorary education got in the way of life) <<side note... why 5.1? why not just 5?>> Our braking systems where obviously not designed for 5.1 because it says to only use DOT3 or 4 on the resevoir cap... is that the problem?

Depsite a large hydraulic pump, I notice the pedal-box still has a master cylinder with vacuum-servo assistance. Could this be where the problem be? I noticed last time my girl was serviced that changing the diddy air filter on the servo wasn't part of the servicing routine and I can't find mention of it anywhere... but if its sucking air, there must be one somewhere...

On the same strand, could the vacuum supplying the VCM (aircon switch-button ventilation thingummy) - which is leaking and hissing all over the place (have you noticed the little orange hose which can sometimes snag your foot and eventually rip away?) be robbing me of full servo assistance?

Comments on above rambling, or on any rambles about spongy braking in a car designed and built by our Volvolian friends would be welcomed

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No really, I'm not on drugs. If I were on drugs I'd get very sensible. I'd be like... "Sooo... Fixed-rate mortgages..."
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:D
Greta - 1994 2.0 480 GT
Herbie - 1972 1.3 VW Beetle Deluxe
Kochanski - 1982 1.7 340 GLE - Gone, but not forgotten

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pol
480 Is my middle name
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Post by pol » Thu Apr 07, 2005 9:05 am

How did you bleed the brakes? I've read funny ways of doing it on these cars due to their 2 diagonal circuits or something but may have just been the shanes book of lies telling me stories.

I've had real bad vacuum leaks at the manifold before and it ran like shit but i never noticed any braking problems. But i dont have vacuum operated air vent things.

Have you no break warning lights on your dash lit up? Its possible the pump could be knackered...

pol

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rpruen
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Post by rpruen » Thu Apr 07, 2005 3:27 pm

Having just asked at loacal Volvo specailist....

If you put 5.1 fluid in your brakes, not only does it attack the seals (if made before 93, after 93 the seals are flurosilicone and won't get hurt), but it also attacks the brake hoses. Pre 93 seals are Viton (maybe, he's not 100% sure)

Possibly what has happened is the inner lining of one hose has gone, and the fluid is leaking into the outer, causing it to baloon, this making the brake pedal go all soft. You should be able to verify this by getting someone to press the pedal while looking at each hose, they shouldn't visably change when the peadal is pressed.

You should change all the hoses as a mater of urgency if you used 5.1 fluid.

It's also possible that the seals have gone in the rear calipers, if you remove the adjuster plug, and fluid drips out, then that's likely to be it. You can get a seal kit, or a new caliper if it's that.

You need to bleed the brakes in the right way to get all the old fluid out, but if you have all the hoses off, it's easy. Just put a bucket under each one, and pump about a liter of fluid through, that will clear everthing out.

To bleed all the air out you need to open the bleed nipple enough, so that the pedal can be pushed to the floor fairly quickly, that way any air is forced allong the tubes rater than rising to the highest point.

Re: Other post.

You have the later type ABS and your rear brakes don't run at 180 bar, since that's the early type. With the ignition off the brakes act like normal brakes.


Hope that helps

Richard
Car Status: Squashed :(
Now have 765 GLE 2.8 V6

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