740 Antilock Brake Problem
 

Hello,

I am new to the forum but have always had a Volvo. The car I am writing about is a 1988 740 GLE with 240,000 miles on it. I am the second owner and have had the car since it had 71,000 miles. I know enough about mechanics to do all the maintenance and can even do a fair amount of major repairs if I have the time and I know what I am doing. The newer cars are getting so electronic that they are very difficult to work on. Anyway...I need some help with a brake question. I tried searching the site but could not find any posts that addressed my exact problem. I notice several months ago that the ABS light would go on when I started the car and stay on for several minutes and then go out. I know that the brakes were replaced 23,000 miles ago and the pads are OK. I checked the fluid and it was OK. Since the brakes seemed to work fine, I ignored the problem (I know - not really smart). Anyway, more recently, the brakes have started pulsating like when the ABS activates. It usually does this when I am coming to a slow stop. The brakes still work fine but the problem seems to be getting worse. When I was searching this site, I came across a post that mentioned the "ABS Sensor". Could this be my problem? If so, where is the sensor and what does it look like? Does anyone know what the symptoms of a bad sensor are? Please help.

Thanks,
Frodo

PS: I forgot to mention that the brake pedal is no longer coming all the way back up. Is this signs of the booster going out too?

RE: 740 Antilock Brake Problem
 

Try removing the sensors and cleaning all of them. Most likely that will fix it.

RE: 740 Antilock Brake Problem
 

Bare with me on this one. I know next to nothing about the ABS. On the passenger side of the car under the hood, there is a hydraulic octopus looking thing that has brake lines going in and out of it and several electrical relays. Are the relays the "sensors" you are referring to? Or is there a hydraulic fluid pressure sensor somewhere that I need to find? Also, What do you think about the pedal not returning. Is this the power booster?

Thanks for your help,
Frodo

RE: 740 Antilock Brake Problem
 

The sensors I am refering to are at each wheel.
Look at the back of the wheel on the inside of the car.
You will see the brake lines going to the Caliper. Then you will see electrical wires going into the backing plate. The sensor should come out with a 10mm screw. Remove and clean them. Over time they collect metal shavings from the Brakes because they are magnetic. Then when you hit the brakes they think the wheel is locked up. That is why it activates the ABS pump.

RE: 740 Antilock Brake Problem
 

Thanks Tech!

I know what you are talking about now and will try this next weekend. I'll let you know if it works.

Frodo

RE: 740 Antilock Brake Problem
 

Hey Tech,

I thought I would let you know that I finally had a chance to clean out the antilock brake sensors last weekend and they were filthy! After cleaning them, the brakes worked fine and no more antilock brake lights.

Thanks for you help!

Frodo

:)