Brake Pulsation and Steering Shudder

[artbuc]

Re 2007 Subaru 2.5 OB wagon. I do maintenance on this car every 6 months for a friend. For the last year I noticed steering wheel shimmy when applying brakes, especially when applying brakes lightly on an uneven surface. Feels like a classic warped rotor problem. Today I replaced the PS fluid. I had the car jacked-up and expelled the old fluid by turning the steering wheel lock-to-lock with the return line disconnected and directed into a waste container. Engine was off. Topped-up with Subaru HP ATF as the reservoir level dictated. When I got done and reconnected return line, I started engine (car still jacked to keep load off front wheels)and slowly turned steering lock-to-lock to bleed off any air which may have gotten into the system. I noticed that if I turned the steering wheel too fast I got a shudder. Felt like the rack was hanging up or maybe a strut bearing was sticking. I have replaced PS fluid many times on Lexus, Toyota and Honda cars and never felt this shudder. I could always turn the wheel as fast or as slowly as I wanted and the steering action was smooth. Maybe this is what normally happens for this car when you have no load on the front wheels?

Have any of you experienced this type of steering shudder? The car seems to steer fine out on the road. Do you think there is any connection between the brake pulsation and the steering shudder? Thanks for any and all help.

 

[jdmstr22]

May be a strut bearing but sounds like uneven pad wear or warped rotors.

 

[Donald]

The brake pulsation is called "warped rotors" but in reality the rotors no longer have a uniform thickness. They need to be turned or replaced. The hubs should be checked for lateral runout. The pulsation will only get worse.

 

[artbuc]

Thanks. Your replies addressed the braking issue but what about the steering wheel shudder with the car jacked-up? Do you think I still have some air in the PS? I just read where you sometimes have to go lock-to-lock 20 times to expel all air. I didn't do nearly that many but I do not see any bubbles in the fluid reservoir.

 

[brandini]

Could be air, strut bearing (top), ball joint (bottom), or possibly a tie rod end.

check em all

 

[artbuc]

Thanks to all. Looks like I did have residual air in the PS system. Did another dozen lock-to-locks and all seems well. OTOH, I could not stand driving a car with that much brake pulsation but the owner says she doesn't even notice it.

 

[JHZR2]

Steering wheel shake or a brake pedal pulsation?

Im starting to notice just a steering wheel shake on braking, but nothing in the pedal. Will let you know what I find out, please share the same if this is your situation...

 

[threeputtpar]

I see that you solved the steering shudder issue, as I was going to mention that air in the system will cause the steering to bind as you turn from lock to lock.

With the brake shuddering problem, I've had the problem before where light application of the brakes would produce a steering wheel shimmy but pressing the brakes harder would make it go away. Is this what you have experienced?

If so, check the front wheels for a bent rim on the inside bead. I found two of my rims were bent and one happened to be on the front and one on the back, so rotations would not isolate the problem. My winters have the same issues, so when I changed twice a year, the problem persisted. I spent $$$ and time replacing all of the suspension, steering, and brake parts in an effort to find the problem, with no success. Even new tires on both sets of rims didn't eliminate the problem.

 

[artbuc]

Originally Posted By: threeputtpar
With the brake shuddering problem, I've had the problem before where light application of the brakes would produce a steering wheel shimmy but pressing the brakes harder would make it go away. Is this what you have experienced?


Yes, much more noticeable with light braking, especially on an uneven surface. Wow, what are the odds of two bent rims with one on back and one on front?

 

[artbuc]

Originally Posted By: artbuc
Thanks to all. Looks like I did have residual air in the PS system. Did another dozen lock-to-locks and all seems well. OTOH, I could not stand driving a car with that much brake pulsation but the owner says she doesn't even notice it.


Well, I did not completely eliminate the "notchy" steering. I think the system may be sucking in air somewhere. Apparently this is a well known issue with Subaru's. With the car jacked-up and engine off, when the wheel is turned as far as it will go, when I very slowly start turning the wheel back, I hear a little gurgling noise. This happens in both directions. I need to get a helper to turn the wheel so I can observe the reservoir. I have never heard this on any other car although I have not carefully listened for it. Have any of you heard this gurgle right at the point where you start reversing the wheel? Any thoughts about what this is and if it is a problem? Thanks.

 

[SHOZ]

Whenever I've had "warped rotors" it was from brake pad material transferred onto the rotor. A couple good hard stops to heat up the brakes would cure it. But the cause is cheap brake pads, like Motorcraft. The Ford OEMs are really good pads, the Motorcrafts are junk.

 

[artbuc]

Originally Posted By: SHOZ
Whenever I've had "warped rotors" it was from brake pad material transferred onto the rotor. A couple good hard stops to heat up the brakes would cure it. But the cause is cheap brake pads, like Motorcraft. The Ford OEMs are really good pads, the Motorcrafts are junk.


These are Subaru pads and rotors. From what I have read, most experts say pulsation is almost always caused by pad deposits, not warped rotors. I have tried the hard stop solution on this and several other cars and never had success until I replaced the rotors.

 

[SHOZ]

Originally Posted By: artbuc
Originally Posted By: SHOZ
Whenever I've had "warped rotors" it was from brake pad material transferred onto the rotor. A couple good hard stops to heat up the brakes would cure it. But the cause is cheap brake pads, like Motorcraft. The Ford OEMs are really good pads, the Motorcrafts are junk.


These are Subaru pads and rotors. From what I have read, most experts say pulsation is almost always caused by pad deposits, not warped rotors. I have tried the hard stop solution on this and several other cars and never had success until I replaced the rotors.


Put more effort into the hard stops. Street driving will seldom do it. A day at the track will clean those rotors up.

The only time I ever replaced a rotor as warped was when I had a rear caliper seize and it turn the rotor blue.

If you are getting pad deposits it say a lot about your driving style and pad choice IMHO.

 

[artbuc]

Originally Posted By: artbuc
Originally Posted By: artbuc
Thanks to all. Looks like I did have residual air in the PS system. Did another dozen lock-to-locks and all seems well. OTOH, I could not stand driving a car with that much brake pulsation but the owner says she doesn't even notice it.


Well, I did not completely eliminate the "notchy" steering. I think the system may be sucking in air somewhere. Apparently this is a well known issue with Subaru's. With the car jacked-up and engine off, when the wheel is turned as far as it will go, when I very slowly start turning the wheel back, I hear a little gurgling noise. This happens in both directions. I need to get a helper to turn the wheel so I can observe the reservoir. I have never heard this on any other car although I have not carefully listened for it. Have any of you heard this gurgle right at the point where you start reversing the wheel? Any thoughts about what this is and if it is a problem? Thanks.


Ok, the gurgling noise is coming from the rack. I think it is the sound of air being sucked in if/when you reverse steering wheel direction too fast. Since the car is not running, there isn't any internal hydraulic pressure and a quick direction change causes a momentary vacuum. Does this make sense?

 

[stephen9666]

Originally Posted By: artbuc


These are Subaru pads and rotors. From what I have read, most experts say pulsation is almost always caused by pad deposits, not warped rotors. I have tried the hard stop solution on this and several other cars and never had success until I replaced the rotors.


Pad deposits could be a cause, but it could also be caused by runout in the hub or rotor, rust between the hub and rotor or other things. Trying to do a re-bed can't hurt and might help you determine if you're dealing with pad deposits or something else.

 

[artbuc]

Originally Posted By: stephen9666
Originally Posted By: artbuc


These are Subaru pads and rotors. From what I have read, most experts say pulsation is almost always caused by pad deposits, not warped rotors. I have tried the hard stop solution on this and several other cars and never had success until I replaced the rotors.


Pad deposits could be a cause, but it could also be caused by runout in the hub or rotor, rust between the hub and rotor or other things. Trying to do a re-bed can't hurt and might help you determine if you're dealing with pad deposits or something else.


New rotors solved the brake pulsation problem. Installed Centric Premiums. However, still have an unresolved issue with the PS. Definitely feels a little notchy at times.