ABS assist please

SS2115 · Post by **SS2115** » 03 Feb 2016, 23:30

I tried a search for anything ABS but the search kept telling me I had too many words????

Had a sway under brakes on the 850.
Two out of four rear pistons seized - overhauled with new pistons, machined rotors and new pads.

Sway still there. Cutting out a lot of suspension investigation, it turned out one front calipher was slow to move compared to the other. I put it in suspecting internally swollen brake hoses but it ended up being a sticky caliper. Both calipers overhauled, both brake hoses replaced anyway, both rotors replaced and new pads later and the car brakes straight. Hurray.

However, the ABS is obviously not working. The brake pedal feels terrific but the car doesn't want to stop as well as it should in a panic stop. It won't lock up the wheels in the wet and the ABS doesn't chatter when I try.
I admit the front brakes need to bed in a bit more but the ABS should still have worked on the rear brakes at least.

Can someone talk me through the diagnosis of the ABS system please:
How do I tell which unit I have - Bosch, TME etc? Its difficult to see tucked under the ECU.
Is it electronic and the electronics fail and can be replaced (like on my BMW)?
Is there a fuse to check first or any other obvious thing like that?
Does it have any sort of mechanical reset? (In the old days we had to reset the tandom master cylinders after a bleed by unscrewing a small spigot bolt, it clicked, and then re-fasten it).

The ABS unit has had heaps of new fluid bled through it now, but it could still be hydraulically failed/seized in some way. Can they be repaired/overhauled? The brake specialist didn't think so. A new module from the Volvo dealer is actually as much as the car is insured for!

Any advice would be appreciated.

Post by **rspi** » 04 Feb 2016, 03:26

What year is the vehicle? Does the warning light in the dash cluster work?

Post by **Matty Moo** » 04 Feb 2016, 03:28

What year is the car?

SS2115 · Post by **SS2115** » 04 Feb 2016, 04:12

Its a 1995 2.5 SE sedan.
Plain standard model.

Yes - the globe works when the dash powers up for its system check when the ignition is turned on, but the globe doesn't light while driving or braking.

Post by **Matty Moo** » 04 Feb 2016, 16:05

This is what I have.

You replaced a handful of parts, some calipers, rotors and pads. Now the brakes won't lock up when you really get on the brakes.

The ABS system is fine, if there were an issue it would turn that light on to tell you. What's going on is that your brakes aren't "biting" . It's either your choice of pads, oily rotors or both.

Since I had a set of brake pads awhile ago that really didn't like to bite, I'm going to go with brake pads.

SS2115 · Post by **SS2115** » 04 Feb 2016, 16:34

I admitted I haven't bedded the front brakes in properly yet - probably only about 20 klms on them at most.
But at the same time, it was a wet road in rain and they still wouldn't lock or start the ABS chattering.
And the rears were done over a 200klms ago, so they should have tried to lock up even if the fronts wouldn't. They were new pads but on a machined rotor which would have no glazing or shinyness at all.
I'm not saying your wrong and in fact hope your right, but with all my driving years and experience, they don't feel right. Your correct in that they don't bite past a certain point of pedal pressure - ie: light braking feels normal but pushing harder does not increase the braking effect at all. It just pulls up in its own time.

Post by **Matty Moo** » 04 Feb 2016, 19:27

It's your pads.

The ABS won't kick in until a wheel locks up. It won't stop a wheel locking up until it actually comes to that point, which your car isn't getting to that point...if that makes sense. When the ABS kicks in you will know it by the noise and pedal feel, but until then it's up to your brakes to get you to that point.

I bought a set of ceramic pads for my other s70 that wouldn't lock up unless I was on snow, ice or a rainy stretch of road.

Post by **abscate** » 06 Feb 2016, 06:20

The whole point of ABS is that your wheels never lock. Matty has sailed it with pads or rotor combo not being right.

In some markets you can turn ABS off with a switch to test your brake function. You should be able to lock with ABS off.

Do you hear a burp at about 10-15 mph when you first accelerate after starting?