Odd ABS problem after brake job (2002 volvo s40)

Maintenance/Repairs
1

The car is a 2002 Volvo s40, automatic, and 150k miles.

The car needed new front brake pads and a wheel bearing. I broke the wheel speed sensor while trying to remove it, so I ordered a new one. Got the car all buttoned up. We just drove the car with out the speed sensor (no abs or speedo) for a few days until the new sensor came in the mail. Everything worked just fine apart from the ABS and speed0. Braking was fine.

New sensor arrived, installed in 10 minutes. Took it for a drive and now when you do a normal braking to a stop, just before you stop, say 5 mph the pedel drops a bit, vibrated like abs is kicking in, and you loose a bit of braking power. If you get up to 25mph, do a hard (slam) stop, no problem. Slow stop = weird funkyness at the end of the stop. Feels very wrong and odd since it seems to loose braking power there.

I pulled the ABS fuse and drove it to see what would happen, brakes just fine (sans the lack of ABS). No weird vibrations or odd pulling or diving. Just “normal”

So whats the dealo? I am going to try bleeding the brake lines tomorrow to see if that has anything to do with anything. But really, its a shot in the dark.

2

Some of these wheels speed sensors simply bolt on. Others require adjustment of the air gap upon replacement. Dunno about Volvo, but you need to check.

3

Also, some modules need to be sync’d or calibrated to the new sensors. I don’t know why, but a learning routine is sometimes required.

4

The sensor was a bolt in, no adjustment that I could see.

The ABS light was not coming for the 20 miles or so I drove it after replacement, and there were a few “stops” in there too.

Any ideas on if it needs this syncing or calibrating? Mainly how?

Maybe I’ll call the service shop tomorrow.

Silly volvo annoying me. Anyone want to buy it?

5

Well at least you have narrowed it down to the ABS kicking in inadvertently, are the ABS and speed sensor the same?

6

I bleed the brakes on Saturday and it made quite the difference. Its has done the funny thing once since then, but no longer on every stop.

Maybe a bit more bleeding and call it good.