99 V70 T5 - Steering pulls on braking

Post by **j-dawg** » 18 Jul 2016, 21:25

My car darts slightly to the left upon initial application of the brakes and then straightens itself out, with the steering wheel shifting to the right. This is especially noticeable under light braking. If I hold the wheel as firmly as I can, the car curves gently to the left until I let go of the brakes. Driving straight on the highway, the car simply does not feel as stable as it used to - the steering feels numb and prone to being pulled, requiring frequent correction. The symptoms are textbook ball joint or tie rod, yet I can't locate the failing component.

Things I have done to try to fix this, in order:
- Alignment
- Replaced both front calipers and hoses, bled system
- Inner and outer tie rods
- Another alignment at a different shop
- Rotated tires front-to-back
- (Separately, I replaced the left control arm before these issues began, for a failing ball joint.)

If I lift the left wheel and wiggle at 9 and 3, I can hear something bonking against something else, but I can't see it. The bushings and ball joints all seem fine, the left control arm being just a few thousand miles old. Tie rods are new (after these symptoms appeared) and I couldn't detect any play in the steering rack when I was swapping the tie rods.

There is a slightly loose sway bar endlink, but that shouldn't cause these issues.

I'd suspect a wheel bearing except that there's no play at 12 and 6, just 9 and 3. I have a broken exhaust so I wouldn't be able to hear a busted bearing. Someday I'll fix it, but the safety issues are more important.

Any suggestions? Is there a good way anyone can think of to test for play in the rack itself? I'm going nuts here - probably $500 now thrown at parts and labor, with no improvement. I feel like I can't really drive the car, but there's no clear path to fixing it.

Post by **E Showell** » 19 Jul 2016, 19:40

Check your front wheels for a thrown wheel weight. Out of balance wheels can produce the symptoms you describe.

Post by **j-dawg** » 19 Jul 2016, 20:20

I'll take a look, but after swapping wheels front to back it'd surprise me if two wheels had the exact same problem. How does an imbalanced wheel result in the car pulling under braking?

Post by **E Showell** » 20 Jul 2016, 20:35

Don't know the whys and wherefores, only that it can happen since I experienced it. More probable is a sticking caliper or perhaps a collapsing front brake hose. What shape are the brake hoses in?

Post by **scot850** » 20 Jul 2016, 21:30

Evan has a good point. All problems affecting steering are not always caused by the front end. Check flexi hoses for bulges at front and rear, check all calipers and brake pads are free to move. Rear calipers are more prone to sticking than the fronts.

Neil.

Post by **j-dawg** » 21 Jul 2016, 21:48

New front hoses and calipers after this thing started, did not help. Rear hard lines are fine. The pathology of a nonfunctional rear caliper causing a steering wheel wiggle is not quite clear to me...

Post by **scot850** » 21 Jul 2016, 22:38

You have 4 wheels and 4 brakes. If one side of the car has less brakes than the other, then when you brake the car will brake harder on one side over the other and cause a wiggle, if there is an issue with the rear brakes.

Neil.

Post by **tryingbe** » 23 Jul 2016, 04:36

What are your alignment specs?
How are rest of the suspension parts? How old are the spring seats?

Post by **j-dawg** » 23 Jul 2016, 11:48

I've always been under the impression that stuck-caliper wiggly-wiggles are a result of suspension geometry. The brake caliper and disc are not necessarily aligned with the contact patch of the tire. When the pads clamp down on the brake disc, it creates a moment about an axis between the brake pads and the center of the contact patch.

If you have two functional calipers, this effect balances between the two wheels, via the tie rods, and the steering wheel does not move. If you have one sticky caliper, the effect does not balance and both wheels turn in the direction of the moment on the wheel with the good caliper, causing the steering wheel to turn. If you have a loose suspension component, the wheels rotate until the play in the system is completely taken up, causing a brief steering wheel wiggle, like I'm experiencing.

If a rear caliper is seized, there's no means of the effect getting to the steering wheel. The moment on each wheel is always reacted out independently in each side of the rear suspension, because the rear wheels aren't coupled by a steering linkage. If one caliper is stuck, the front wheels will only experience a negligible lateral load, the entire 105" wheelbase reacting the ~0-2" of moment arm between the disc and contact patch. With the steering wheel held straight, one should be able to apply braking force to just the left rear or right rear tire and stop the car in a straight line. In fact, I'll generalize that a step further: any vehicle with multiple non-collinear axles can be accelerated or decelerated by any combination of those wheels without turning, as long as those wheels don't swivel and the tires retain traction. In the case of a car, a steering wheel held straight - if the suspension is not loose - is a good approximation of wheels that don't swivel.

All of the above is my understanding of the forces involved, which would rule out a rear caliper. I present a case study as an application of the above: a motorcycle with a sidecar. Power and braking are delivered entirely on the left side of the vehicle, yet its tendency is not to rotate right upon acceleration and left upon deceleration. Likewise, a stuck rear caliper would not cause my car to want to steer in any given direction.

Finally, a thought experiment. Picture a rigid platform with four non-swiveling, rubber-tired casters bolted to it, all aligned with each other. Sitting on this device, apply power to just one wheel. Which way does the platform go? A car isn't far from this ideal.

Whoo! I gotta go dust off my statics books. Took me a while to convince myself.

Post by **j-dawg** » 23 Jul 2016, 11:49

tryingbe wrote:What are your alignment specs?
How are rest of the suspension parts? How old are the spring seats?

All in spec, according to the sheet I got from the alignment shop. Spring seats are ~3 years old, IPD HD units.