5-10 Grand Master
on the e39 the 6 cylinder has a rack but the v8 has a reculating ball including the mighty m5
all america wants is cold beer warm cat and a place to take a poop with a door on it
George,
You make an interesting point about the turning radius. I think you are correct in that my tuner was conservative in max wheel angle. No rubbing, but my turning circle is larger by a couple feet, I would say. Not horrendous, but noticeable. When I get an opportunity to get the car in the air, I will try to portray the layout. I havent checked turns lock to lock yet, but I will.
Thanks for the feedback, Colin
Originally Posted by George M
The only E34 with R&P from the factory was the AWD 525ix. I looked into swapping in that setup but too complex. All others are RB.
Thanks for all the feedback. I will fill you in on what I know.
The pump used was from an m50 e36, so it will fit directly on an m50 525i. The stock E34 RB pump operates at way too much pressure for any factory rack to handle (around 1700psi). The upper steering linkage was cut and the lower one custom made. As the angle from the shaft to the rack was too tight for standard u-joints, racing units (by Torgesen) were used which can accomodate a 70% angle.
I will try to get some photos in the by and by and post them up. Custom welding was needed for the subframe rack mounts and bearing support flange also.
Cost was about $2800, but my mechanic burried himself in hours, so the next job might cost a bit more (his first time on an e34). he charged me the price because that was what he quoted me. he is a good guy to work with.
Grand Master
Colin,
Increase in turning radius can be due to a couple of things. Most likely there aren't any rack travel restricters on that particular rack, but what you can do is pull up the bellows on each side and take a look. Removing the bellows isn't easy if you have Oetiker clamps, which many do...but since you may have custom outer tie rods to connect with your steering knuckles, you may have serviceable clamps on your bellows. If there is a wafer like part..generally made from a glass filled nylon, that looks like a poker chip with a hole in the middle where the rack end goes through between the undercut of the rack end adjacent to the thread where the tie rod ball joint threads on...you could try removing them, threading back on the tie rod (with loctite 242)...and seeing if you have restored your turning radius without rubbing. Again, possible that your tuner is savy to this...but maybe not. If no restrictors on the end of the rack, then you are internally limited to rack travel relative to knuckle arm length which not only affects overall steering ratio (over and above rack specific gear ratio) but turning radius relative to rack travel.
Do post up some pics Colin when you get a chance.
George
Major Contributor
One of the stated benefits of recirculating ball steering systems as originally advocated by BMW (and Mercedes for that matter) was the non-linear steering response possible in the RB unit. As the wheel is turned farther from center, the faster the ratio becomes.
Rack and pionion steering is great for on-center feel but is restricted to linear ratios.
My $0.02 (Canadian)
Anthony
Grand Master
even if BMW and Mercedes espoused that particular benefit of a RB box over rack & pinion...it is an unworthy tradeoff as you spend very little time off center when you drive your car. Any give up to the RB box in this regard can easily be compensated for with a R&P gear by changing the pinion/rack ratio which is historically much faster than RB boxes anyway and also compensated by revising torsion bar spring rate which can more precisely calibrate pressure versus angle onset of assist. There is no comparison in terms of steering precision between a RB box and R&P....why virtually all cars have evolved to it..including BMW's foray into electric steering which is a motorized screw nut mounted on a steering rack in replacement of conventional hydraulic assist.
George
Rack and pinion is not limited to linear ratios. For example, most years of the e36 M3 have a variable ratio rack (14.x to 19.x) that speeds the ratio up further from center.
Thanks for the info George. Ill look into that and see how it looks.
Right now it is livable, but a tighter circle would be nice (though I dont think it will compare to the ole Volvo 740)
I emailed my mechanic for photos as I know he snapped a few. Ill get them up as soon as possible.
Colin
Grand Master
you are right Colin about variable ratio R&P as well...sounds like you know a bit about steering...explains why you went to the effort you did to transform your car. The book on variable ratio R&P is...on center you want a numerically higher ratio for good on center feel thereby reducing the car's nervousness, and conversely you want a quicker ratio off center for lively overall steering transient response, also helping for example in parking manevers. This is accomplished with a fixed involute/helix angle pinion with variable rack tooth/involute spacing. For those interested, the reason this will work...not unlike a variable ratio RB steering box, is on center where you spend most of your time, you have the highest rack forces/gear tooth stresses....therefore you want rack to pinion engagement to be its fullest...which is called optimizing the contact ratio and crunched by a computer program based upon twenty or so gear tooth geometry inputs. Off center the rack tooth spacing is increased which in effect compromises gear engagement and reduces contact ratio but is tolerated because maximum hydraulic assist off center diminishes rack stresses.
George
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