Steering oscillates under moderate braking

[conez0]

When going faster than 60 Mph if I apply the brakes soft or moderately (normal driving) I get a nasty oscillation in my steering system. If I brake hard or very hard I don't get this.

I've been in the process of rebuilding my whole cars suspension so in the front so far I've replaced the sway bar links, control arms, thrust arms, tie rod ends, and tie rod idler. I also have newly installed/balanced tires on the OEM bottlecap wheels. I had an alignment done after replacing the tierod ends. I also did a 4 wheel brake job around the same time.

I'm not sure when this developed as I usually don't drive over 55mph except on the freeway where I don't really brake much. I first noticed it when I took a trip and had to use the brakes going down hills.

The only source of front end issues under braking that I'm aware of is worn control/thrust arm bushings. Since its been less than 5k miles since I replaced them I don't think that would be the cause. I feel that it may be alignment/steering related since I never noticed it until after I replaced all the steering stuff in december of last year.

I don't want to take it to a specialty shop if I don't have to but I don't really do steering stuff and I already got it aligned.

[Bert Poliakoff]

`Warped rotors?? For sure will cause oscillation when brakes are applied whether easily or hard.

[1986series6]

If the control arms were not loaded when tightened, the bushing could easily wear out in 5000 miles.

[conez0]

I replaced the rotors when I did the brakes, I think they should be fine however I can get a gauge and check them for warping.


I did torque the control arms with the suspension loaded (i.e. car on the ground) when I replaced them. I know sometimes the passenger side can also prematurely die from exhaust heat but I made sure when I replaced them that the heatshield was solidly in place.

[1986series6]

Looks like you got all that covered so I'm at a loss as well.

[FernandoBunster]

Did you spray cold water on hot brakes? Do this a few times and you can easily warp rotors.

[ldk]

A long shot, but are lug bolts torqued uniformly to 82 ft-lbs?

[mauryc]

Center link (aka center tie rod)? Steering mount repair?

Swap rims front to back just to rule them out too.

[conez0]

`Warped rotors?? For sure will cause oscillation when brakes are applied whether easily or hard.

Well I got my hands on a dial indicator and measured the lateral runout for both sides. Measured 0.015" on the left side and 0.005" on the right side. According to the Bentley manual the upper limit is 0.008" so I took both rotors to be resurfaced. Re-installed and the steering feels nice and solid under light/moderate braking now.

Did you spray cold water on hot brakes? Do this a few times and you can easily warp rotors.

I talked to the machinist and we think this is something to the effect of what happened. I first noticed the oscillating while driving the I-70 mountain pass between Grand Junction and Denver in Colorado. It was pretty cold (0-10F) and I suspect that I may have hit a puddle or something while coming down a longer hill which could have had the effect of rapidly cooling.

Thanks for all the input everyone. Too bad my A/C decided this was a good time to go....

[RSheiman]

There is a way to work in rotors. I have had them warp quite quickly, especially when in storage and regardless of manufacturer.

[tschultz]

Sounds to me more like incorrectly preloaded control arm/thrust arm bushings. Warped rotors, out of balance wheels/tires are also common causes.