My S70 is Eating Calipers

[WhatAmIDoing]

I see three suggestions - Mr Parker's suspicion of the ABS module is very viable.
You've been through everything else and there are moving parts in there that may seize.
You might consider contacting Matty Moo at Midwest ABS and running this concept past him.

I was just thinking about sending Matt an email right before I saw your post.

[WhatAmIDoing]

Here is an update. I am still getting intermittent sticking calipers. They seem to be slow to release. They seem to lock up after many successive braking events (curvy roads, stop & go). After a while they will fully release with the engine running. If I shutoff the engine and park they will barely release (still difficult to turn the tyre by hand).

I emailed Matty Moo, and this was his reply:

From my understanding, nothing will activate without the pump also activating or else it would trigger a code, turn on the light and shut the system down.

I know of no way to test the abs pump assembly as far as internal operation goes on a 96-98.

Disconnect the harness going to the pump motor, that will disable the electronic part of the system and see what happens.

Sounds like I should be getting ABS codes if this is the case.

I have been driving with TRACS off. I seem to be having less problems, but I cannot confirm scientifically. Last night when driving in heavy rain (lots of water on the roads), I had to drive with TRACS off or else traction control was freaking out. Could there be a wiring issue or bad wheel speed sensor causing the TRACS system to apply the brakes for phantom wheel slip (without setting a code)?

What I know so far: It only appears to be affecting the front calipers, the right more than the left. The slides are smooth and properly greased, and the calipers slide freely. The rotors are not warped.

What I have yet to try: I have not opened the bleeder when the caliper sticks to see if it will release (in the past it has not, but those calipers were already permanently seized). I have not tried disconnecting power to the ABS pump or module. I really don't want to replace the mechanical components of the ABS system.

[E Showell]

Collapsed front brake lines can cause a host of problems. They degrade internally. Fluid flows in on brake application but the internally collapsed line chokes off the return flow through the systems causing calipers to stick. The lines will have no outwardly visible signs of being compromised. If the soft front brake lines are original to the car, might be time for a refresh.

I would seriously consider this if you've ruled out everything else.

Good luck and be sure to report back when the problem is solved.

[WhatAmIDoing]

Collapsed front brake lines can cause a host of problems. They degrade internally. Fluid flows in on brake application but the internally collapsed line chokes off the return flow through the systems causing calipers to stick. The lines will have no outwardly visible signs of being compromised. If the soft front brake lines are original to the car, might be time for a refresh.

I would seriously consider this if you've ruled out everything else.

Good luck and be sure to report back when the problem is solved.

Sorry, forgot to reiterate. Both flex lines were replaced this summer after another set of calipers died.

[E Showell]

My bad. Should have re-read original post before replying. That's a puzzler. I too have to replace calipers frequently -- but on the order of every two years for rebuilts, not every 300 miles. ABS module sound like a viable theory.

[WhatAmIDoing]

Everything seems fine now, but then again the last set of calipers suddenly failed without warning. I want to install new Volvo calipers because I'm tired of junky rebuilds, but not if something else really is the problem.