'99 S70 FWD, Base, Auto -- Front end vibration on braking

Post by **E Showell** » 29 Jul 2017, 13:33

So I'm getting an intermittent front end judder when braking from moderate speeds -- say 50 plus. And I'm not talking panic stops here. Even with nice smooth application of the brakes, I'm getting the steering wheel vibrating back and forth. Alignment is good. Tire pressure and wear good. Wheel balance believed to be good. Local independent said brakes looked "fine." Not getting any ABS light but I am wonder whether at c. 139K miles my ABS brain could be going. I did have an instance recently at a stop light where I was slowing down for a car stopped in front of me and it felt like the brakes momentarily gave out before grabbing immediately -- just the ever so slight hiccup. That's what has me thinking it could be the ABS brain. None of the other usual symptoms with funky tachometer/speedometer readouts and that kind of thing, though and no ABS light. Also, I don't know that I've ever been conscious of this car doing that low speed ABS self-test.

Maybe Matty Moo will wander by?

Any thoughts?

Post by **kahl** » 29 Jul 2017, 18:16

To me it sounds like warped rotors. I have run into this issue many times. It doesn't take much warpage to feel the pulsating. Most shops and NAPAs have a disc turning machine to get them back to specks. I took a set into my NAPA and had them turned for $20.00 each. There is a minimum thickness regarding how much material can be removed.

Post by **abscate** » 30 Jul 2017, 04:23

The ABs modules fail safe. You could just unplug the power for the pump motor, and see if that stops the shudder. I'll guarantee it won't.

I think I remember you have a good scanner and can clear ABS faults, as disconnecting this will cause a light.

The self test is a light " chirp" sound at about 15 mph on mine. I theorize it has to happen at speed so that the wheels are spinning fast enough to give the ABS module a clean signal from the reluctors or toothed wheel on each wheel. It tests all four sensors

Post by **abscate** » 21 Sep 2020, 02:24

Old thread alert. This car eventually joined my fleet and the problem returned. The root cause was the caliper pins on the rebuilt calipers were mild steel instead of stainless and corrode, causing non-smooth caliper sliding and grabbing. Cleaning them with sandpaper worked to address this

Thread if bookmarked in my Maintenance reference for “Lady Evita“ , link Below to that forum

Post by **abscate** » 17 Nov 2020, 05:17

Add on to this thread

I’ve found in my area NAPA no longer turns rotors, but Oreillys does. That being said, they refused to turn the last set I offered citing too far out of round.

It looks like FCP fir life is the way to go on these for a car in long service

Post by **scot850** » 17 Nov 2020, 12:09

I find the same here in Calgary. Fewer repair shops have the equipment to turn rotors. It is easier and quicker to just swap the rotors in most cases.

Strangely the last set I had turned were at the dealer as they still had the equipment last time I needed this done.

The issue of the caliper slider pins it truly an issue with re-man'd calipers. Some of the sliders were such poor quality they looked like pot metal. They were so soft I could not turn them out when brand new!! Returned them as the same calipers had re-used rusty pistons that had been badly filed to try to make the contact area flat'ish. Totally un-acceptable!

Neil.