My expensive journey with bumpsteer and a tribute to Albert Fang - WP Auto

[tropos_net]

yes the bush on the pic looks like a hat so the thickness of the bigger diam end will stop the tie rod end from contacting the rack housing. so its best to balance it up by having it fitted left and right. the thicker the base the more radius you loose. btw, originally was there any bush of any kind in that place?

 

[astroboy]

The bumpsteer I experience is a bit excessive that I can see the steering wheel turning on its own 5-10 degrees when driving straight slowly on uneven road. It is not just feel.

So from what I gathered here, this so called excessive bumpsteer is an unwanted result for the car, which means some mechanical component in the car is not functioning the way it should. Pardon me for my naiveness as I want to understand more about the "problem", is it the car designer's fault in designing such a car with excessive bumpsteer, or some part faulty/looseness due to wear and tear?

My E90 ran on RFT when it was new, also suffered excessive bumpsteer, I suspect the RFT side wall too stiff. Hence transmitting the bumpsteer effect. Now my bumpsteer not so serious because I use non RFT tyres. Yet, 5-10 degree is common still because it react to the contour of the road surface. Am I suppose to "fix" it? or reduce it's sensitivity?

 

[wutty]

Yet, 5-10 degree is common still because it react to the contour of the road surface. Am I suppose to "fix" it? or reduce it's sensitivity?

While driving just now and recalling how it was before, I think I understated the angle of the wheel rotation - more like 30-45 degrees. 5-10degrees would still be OK to me.

 

[advocates]

tropos,

In the original rack, there is no existing bush in that place. If I am not mistaken volvo's rack has it though. Hence, although the bush will help to reduce the bumpsteer to amost non-existent, I am still pursuing other alternatives to resolve the issue. Do you think the power steering pump could be the culprit. If the power steering pump is no longer as efficient, although yet to kaput totally, is it possible it may not be sending enough fluid to the rack thereby causing the bumpsteer?

Wutty,

Yes, the turning radious should be less by 3 to 45 % degree depending on the length of the bush.

 

[tropos_net]

bro, the power steering pump has to work or else you would not be able to turn it all that easy. however the pinion valve will try and equate the pressure on both L and R side circuits when the power assist is not required ie straight line. this is the part whch should provide resistance to the upwards going force (bumpsteer). if the pressure is not equal then bumpsteer towards one side will be further amplified.

btw, i have been playing around with the york adjust nut (size 17mm socket) on the rack. it seems to add in more feel to the steering if done right and also some bumpsteer can be simulated if its loose.

 

[advocates]

Tx Tropos. Yes, I have played around with the york adjust nut as well and do agree that it will add more feel to the steering and add bumpsteer if it is loose. Tried it before.

Checked with two mechanics and both of them informed me that the pinion valve cannot be replaced as an isolated item. I have to recond the whole rack! Is that true?

 

[tropos_net]

yes bro even realoem does not have part number for the items inside the pinion valve. check with the mscope or advanced recon guys as the get the items from ZF malaysia directly just like the parts inside the autobox.

 

[advocates]

Just an update. I checked my caster measurement and was surpised to discover the reading was as follows:-

Left 7.3 degree Right - 3.4 degree.

If I am not mistaken, the specified range should be 5.1 degree to 6.1 degree.

My trusted mechanic took a pair of original bmw control arm together with the control arm bush and installed it. The new reading is as follows:-

Left 5.4 degree Right 4.7 Degree

This was the reading even after having installed the control arm bush at the 290.9 mm location as recommended by BMW AG. The result is the bumpsteer was reduced by more than half. The left caster seems ok but somehow the right caster is still a bit off...trying to bring it within the specified range and hopefully, will solve the bumpsteer issue without having to use the hat bush in the rack.

The 290.9 mm between the location of the control arm bush and the centre of ball joint must be adhered to strictly. My mechanic and I notice that even a change of 1 mm will change the caster by 1 degree. So if any of you were to change the control arm bush next time, please ensure the mechanic knows how to install it properly.

 

[advocates]

My mechanic managed to get a new steering rack (remanufactured from ZF) for me to try it. Will do it besok and update all.

 

[advocates]

An update...

I installed the remanufactured rack from ZF. There is no improvement at all to the bumpsteer issue. Conclusion : it is not the rack

I bought a pair of original control arm bush from bavarian auto just to try it out. Costs me a bomb but after installing it, it appears my caster is adjusted to the acceptable range. I also have flushed the steering fluid and replaced the PS filter....Amazingly the bumpsteer reduced substantially...it is the same as if the nylon bush was inserted.

The question is why does changing of the PS fluid and filter has such a remarkable effect on the bumpsteer issue? anyone?

 

[xcrave]

Ive asked my mech and he said that... its the same as engine oil... in time its not doing it's job.

By changing the filter and oil, the system will function much better (as doing oil service) as the flow of fluid in the system is increased and friction reduced

But i think those who change the master pump/power steering pump actually might just need to do the above, unless the pump is really broken.

Im going to do all this at the end of the month as the mech can better zero in the problem with my bump steer too, he said better not install the "hat shape bush" as it will collect all the bump force elsewhere and it might cost more in the end.

BTW anyone had a reliable Alignment Values for a lowered E46 320i 6 potter?

As ive tried a few and it was said that this will also reduce bump steer...

 

[wingzee]

@xcrave, any updates on your issue? Been experiencing more than normal bump steer lately & decided to gather more feedback. From my survey, looks like it's pointing to the control arms? Have not changed mine as mechs claimed that it still in good condition (ball joints looks ok) & only changed the control arm bushes.

My caster adjustment might be out though.