Front right brake locking up

TheGlue · Post by **TheGlue** » 26 Apr 2016, 21:39

My son's S60 front right brake locked up and we're not sure why. I replaced the caliper (the old pins were dry. 200k miles on rig, so i replaced it...why not) and the flex line (cracked). I flushed out that line with good DOT4 fluid ran out all the air. So after all that it's still locking up, just that wheel. Fluid is making it to the caliper but not returning. I checked the lines all the way back and they look good (not crimped/damaged). I doesn't seem like the behavior of a bad master cylinder or failed booster so I've come to believe it's the ABS module or pump. I've seen the video of removing the ABS electronics and understand I can drive with this still hooked up but slid off the solenoids.
So questions:
1) could it be/how do I test the ABS module. Is it likely that one of the coils have failed hot and is keeping the solenoid closed? Or could it be that a solenoid failed (is this common?)
2) God forbid it's the hydraulic module (holy shizzle that's expensive) but is there a remedy or a test that I can perform before committing to that nightmare. Can this be fixed by me?

Basically I'm just trying to figure this out and how to do it on the cheap since he's not exactly loaded (good life lesson on why to get a good job and thinking realistically about owning things that will quickly own you...). I'm tired so forgive any obvious things I've said (car died, washer died, an uninvited winter guest chewed the bejesus out of my house wires, first day off in 25 days...), any help will be greatly appreciated. Becoming a Volvo expert (S60) by default one piece at a time....

Post by **abscate** » 27 Apr 2016, 04:59

Does the caliper slide easily on the caliper mount? Clean and grease the contact points on the mount and , with the pads out, the caliper should slide easily by hand.

ABS hydraulic failure is really rare.

MarcM · Post by **MarcM** » 27 Apr 2016, 05:33

Just a note.
Abscate's suggestion would really nail it down.
Generally a (internally) collapsed flex line would cause issues like this such as dragging pads and/or "spongey" feeling.
A collapsed flex line yields to the incoming fluid pressure when brake applied (~1000-2000+ psi depending on veracity of application), but collapses and pinches when the pedal is released and holds pressure at whatever the line's break point is for overcoming the collapsed area ... but you replaced the flex line. Often these collapsed areas are from bending the line when performing brake work and hanging the caliper (or letting it dangle) incorrectly.
2 cent chime-in.

Post by **oragex** » 27 Apr 2016, 05:42

You meant, the wheel locks up upon hard braking? What year the car? The ABS module is known to fail depending on the year.

On the other side, I read somewhere about a Volvo owner having an issue with a wheel locking during driving without touching the brake pedal. If I remember it was related to the DSC receiving wrong information and trying to lock the wheel. Try reading the codes. While there, look at the reluctor rings both on front and rear wheels, these rust and even crack giving the ABS system false information.

Don't forget to check the flex line at the other front wheel, they crack both at same rate;)

Post by **chrism** » 27 Apr 2016, 11:00

Firmly apply the brake (and I assume the problem wheel remains applied after letting up on the pedal), then crack the brake line loose at various upstream locations until you you find a place that loosening it releases the pressure and the wheel spins freely. You should then be able to determine which component is not allowing any backflow.

TheGlue · Post by **TheGlue** » 27 Apr 2016, 13:39

Sorry guys, thought the car year was listed...newbie. It's a 2003 S60 base model. The caliper/bracket/pads are brand new and slide easily. The wheel is locked up currently. pressure can be released at the bleeder valve at which point the wheel turns freely until the pedal is depressed again. The flex line on the drivers side (non-issue side) does need to be replaced (thought I remembered it okay but I was wrong). I'm not sure at the moment whether I have the DTSC or not, but I'm assuming that since it's a base model I do not. I am wondering if it could be a wheel sensor though, not sure how to test this. Chrism, good idea. I'm actually going to drop the ABS (BCM) today off the solenoids to see if the issue goes away, then maybe off to xemodex for rebuild....maybe. Too much thrown at this thing in the recent past.

Post by **oragex** » 27 Apr 2016, 19:02

Base models have DSC if I'm not wrong it has a button on the lower center console.

I would guess-saying it's a valve inside the brake system. Read once it happened when a mechanic force-pushed back the caliper piston to make place for new brake pads without releasing the bleeder.

TheGlue · Post by **TheGlue** » 28 Apr 2016, 00:41

Yeah, I didn't have to do that with this caliper, it came all the way in. That said the pads look almost brand new so maybe junior replaced the pads this way. I didn't get to pulling the ABS unit today due to too much running around and then eventual laziness (it was dark after all). Tomorrow should bring another opportunity

Thank you all for commenting!

TheGlue · Post by **TheGlue** » 28 Apr 2016, 08:00

Clarification: the pads I took out of the old caliper looked new. I decided to use new pads because the "old" pads had a tab that was part of the back plate that was rolled over into the groove that the pad rides on on the brake bracket. These tabs were damaged/missing and the bracket had specific worn spots that had depth, so out the bracket and pads came.

Post by **abscate** » 28 Apr 2016, 09:44

There is a chance your brand new caliper is bad. I would actually rank this as more probable than a brake fluid return problem, especially if it wasnt happening with the old caliper. Have you sent your cores back yet?