[Runnin'Rich]

I recently picked up a cheap e83 X3 that i thought would be good beater to keep the miles off my e91
It turned out I much prefer the steering on the X3 compared to my e91!
This maybe due to the X3 having a steering ratio of 16:1 vs 18:1 on the xdrive e9x.

The design of the x3 rack is totally different but the e46 xi rack looks very similar to the e9x xdrive rack. Although Ive been unable to find the steering ratio of the e46 Xi online

Is there anyone that could take a measurement from an e46 xi rack?
I would like to know how many mm the rack moves per one rotation of the steering wheel.

E90 Xdrive


E46 Xi

[Runnin'Rich]

Just gonna document what I found out today.

I measured the e90 xdrive rack(18:1 ratio) and one full steering wheel turn yields 47mm of rack movement.
I’ll have to measure an e46 xi in a pick a part yard for comparison, hopefully someone can measure theirs for me.

As for the mounting it looks possible at this stage.
The e46 rack mounting holes are centred and 340mm wide. The e90 is 380mm but offset.
It looks like some of the e90 awd front subframes have an elongated pressing which has been specifically designed to enable the fitting of the e46 rack! I’ll just have to drill a hole and move the top bracket slightly.

if there’s anything I’m missing please tell me!

[bshambam]

member here in Vancouver BC with an e91 xdrive.

any progress w/ this?

I need to replace my rack. looking for options but the internet can be a scarce place

[Runnin'Rich]

Thanks for checking in.
Waiting for an opportunity to measure an e46 xi rack.
Will hopefully be in the next few months when I have to go to the city picknpull (4 hour drive for me)

Here are my latest findings:

I measured my X3 rack at 46mm of movement per one turn of the steering wheel so the rack is slightly slower ratio than the e90 xi.
X3 steering wheel turns lock to lock are ~3.4 turns compared to e90 ~3.2 turns.

So not sure why the steering ratio of the x3 is stated at 16:1 than the e90 xi 18:1 When the steering is slower on e83 x3. Maybe it’s more feedback I’m feeling from the x3? It definitely feels like the wheel straightens up nicer after a turn on the x3 like a feeling of greater castor.

The other difference from the e46/e83 x3 Generation vs e90 and newer is the length of the steering arms from the front spindle(hub or knuckle). They are a lot longer on the older cars, which I think would give more feedback to the driver. Longer arms would maybe have a greater leverage of force feedback to the steering rack.
This maybe BMW moving their focus from a drivers car in the e46 generation to more of a luxury car in the e90 generation. Maybe customers complained that the car follows undulations in the road (too much feedback)

[Runnin'Rich]

Got to the yard today and the e46 xi rack moves 51mm for one revolution of the steering wheel.
Etched a line on the plastic cap against the rack body and measured the movement with a ruler

I managed to get it off the car without dropping the subframe. Luckily someone had already removed everything in front of the engine

So 4mm more than the e90 xdrive per rev.

That would be a great improvement in response.

Next step will be removing my e90 rack and putting them side by side for comparison

[Runnin'Rich]

Ok I removed the rack from my e91 to compare with the junk yard e46 awd rack.

I measured the rack movement with one rotation of the pinion again.
E46 AWD 51mm per rev
E90 AWD 47mm per rev
This should be a good improvement in steering response.

The mounting blocks are different thickness so both mounting tabs on the subframe will need to be modified. The blocks on the e46 rack are more centred, whereas the e90s sit lower.
E46 AWD 40mm
E90 AWD 31.5mm

The maximum travel of each rack is roughly:
E46 AWD 175mm
E90 AWD 155mm

Length of the pinion shafts are roughly the same.

[rothwem]

Whoa, cool find.

I also owned an E83 X3, and yep, the steering is better than the E90 xi cars, way more steering feel and self centering. I got a RWD E90 instead of messing with the steering rack, but I do think the difference between the E83 and the E9x is in the damping setup of the rack, ie, how much drag is engineered into the rack to isolate the driver from road feedback. The E83 feels a lot more like an E46 than an E90 despite having a very similar front suspension design (double ball joints) to the E90.

[Runnin'Rich]

How do you mean ‘drag’ in the rack?
Are you referring to the thickness of the torsion bar?

[Runnin'Rich]

I’m hoping to preserve the steering geometry of the original rack. Even a minor difference could cause bump steer or a change in Ackerman. If possible I would like to have more steering centring but I think this comes from an increase in castor angle.

So Good news, the left hand mounting position of both racks is exactly 70mm from the centre of each rack.

To match the e90 awd rack the e46 rack rod will need be shortened by 7mm(3.5mm from each end)
This could be done by a machine shop using a lathe.

Bolting the e46 awd rack into the e90 awd subframe left mounting hole will result in the rack centreline being 7mm forward and 1mm lower than the original.

I can raise the rack height easily by using a 1mm shim.
To move the rack back 7mm is trickier.
It’s not enough difference to to make an adaptor of sorts.
So I could ovalise the hole 7mm rearward which would be possible but I don’t want to compromise the strength of the mounting position.
For the right hand mounting position I would simply drill my new hole in the subframe.
If anyone has any advice for slightly moving a mounting position please reply.

[rothwem]

Originally Posted by Runnin'Rich

How do you mean ‘drag’ in the rack?
Are you referring to the thickness of the torsion bar?

Maybe I'm using the wrong term. Basically, sit in the E83 with the car idling. Turn the steering wheel just enough that you feel the tire flex, but not so much that the tires actually change position on the pavement. It might be just a half inch or so. Now let go. The steering wheel snaps back pretty quick. Do the same thing with your E9x car, it'll return slower.

There's flex in the whole system, but the rack has some degree of damping engineered in, just like a shock absorber on your suspension.

[rothwem]

I think that since the subframe is steel, I'd cut and weld in new mounting locations.

[Runnin'Rich]

I think When the tire returns the steering wheel to centre you’re feeling the tires leverage force back into the steering wheel. The further the tie rod end connecting point is from the lower ball joint the larger this force will be. The tire has more leverage over steering wheel so you feel more through the steering wheel and there is less power steering assistance force to turn the wheels. The downside is more kick back when hitting pot holes in corners and more tram lining due to grooves in the road.

The e90 geometry has shortened steering arms compared to the e46 so it’s more ‘comfortable’ but gives less feedback back to the driver.
The shorter steering arms also mean more power steering assistance force is needed. The power steering system is doing a greater amount of the steering for the driver becuase so much force is required.

Try steering both cars stationary with the engine off. I imagine the e90 would require move force compared to any e46 generation car

[Runnin'Rich]

Back to the project.

With the mounting blocks being a little taller on the e46 rack, I deformed the left side bracket on the subframe for a trial fit with the left mounting hole.

The underside nut of the rack interfered with the subframe. I filed off the corner for clearance. The e90 rack doesn’t have this cap with the large nut covering the pinion nut.

Once in position I could see that the splined part that connects to the column was too close to the axle.
The e90 awd rack has a steeper angle pointing more upwards to clear the axle. This wasn’t obvious with both racks on the bench.
To clear the axle I would need to move the rack forward. This is not ideal as I already needed to move the rack back 7mm to maintain geometry.

Unless I could rotate the mounting blocks somehow, I’m declaring that using the e46 rack body is a dead end.
Instead I’m going to persue changing the intervals of the e90 Awd rack

[Runnin'Rich]

Ok so I dissembled both racks and started measuring for comparison

The teeth on the rack rod appear to be of the same spacing although e90 awd has a slight angle to the teeth.
The straight teeth on the e46 awd rod also has the teeth cut deeper into the rod. The rods are both the same diameter except the e46 is 1mm thinner where the teeth are cut for some reason!

The pinions are of the same outer diameter therefore it must be that the e46 rack body orientates the pinion a bit closer to the center of the rack rod, hence the gears being cut deeper in the rack rod.

Even though the pinion outer diameter is the same, the e46 pinion has 9 teeth over the e90 having 8. Looking closely you can see that the e90 pinion teeth have flat tops as they are more widely spaced. I don’t know how they would have crammed in 10 or maybe 11 teeth on the m3 rack!!

The rack rods are not interchangeable due to the piston size being ~2mm larger on the e90. Plus the teeth are cut too deep on the e46 rack rod

It wasn’t possible for me to insert the e46 pinion gear into the e90 body with the e90 rack rod inside. The angled cut on the e90 rack rod means they are incompatable

[Runnin'Rich]

So to use the e46 9 tooth pinion with the e90 rack body I’ll need a rack rod that has the larger e90 piston diameter but also has straight cut teeth.

Looking at the e90 RWD racks on eBay, I think they have straight cut teeth and I would assume the thread pitch and diameter is pretty standard across all the rack rods. The girth of the rack body looks similar to the awd e90 rack so piston size should match fingers crossed.

With a good feeling about a suitable rack rod being available at the junk yard, my next task is to get the e46 9 tooth pinion to work with the e90 rack body.

I hammered out the pins and took apart the pinions to reveal the torsion bars

[Runnin'Rich]

It’s getting difficult to describe what I’m doing as I don’t know what all these parts are called and there’s not much info out there.

I’m proposing to use the e46 pinion/torsion bar part mated with the e90 spline/collar part.

Unfortunately this is not a direct swap as the male / female parts are opposite style!

I will have to get lots of machining made to the e46 pinion, firstly to reduce the pinion gears length and remove the threaded end to match the e90s. This could easily be done on a lathe.
I’d then need to get the e90 splined part machined to make two tabs that slot into the e46 pinion part

I’d then need to special order a bearing and oil seal of specific sizes to be able to put it back together

[Runnin'Rich]

I received the RWD e90 rack.

Bad news, the RWD e90 gear pitch is different to the e46 awd pinion.
Although they are the same orientation.

e90 RWD is 53mm rack movement per 1 revolution of the steering wheel.
So slightly faster than the e46 awd rack

The rack teeth are not a standardised pitch, I guess they can fine tune the rack ratio by varying the pitch. With coarse adjustment being done with the pinion tooth count.

My next idea is to try and swap the larger diameter rack piston from e90 Awd rack to the e46 rack rod.
I’ve no how idea how they fit the piston. Maybe they heat it up then slide it into position?
There is no circlip to remove. People in the Mazda Miata world cut them off with an angle grinder!

[ptpending]

this all modifications are not worth effort because there is an M3 E92 rack which does same
and also there is and active steering rack which adjust number of rotation depending on speed and IS a factory option which can be retrofitted

[rothwem]

Originally Posted by ptpending

this all modifications are not worth effort because there is an M3 E92 rack which does same
and also there is and active steering rack which adjust number of rotation depending on speed and IS a factory option which can be retrofitted

That's only for the RWD cars. The AWD front end is different--the M3 rack doesn't swap in, and active steering was never an option on the AWD cars.

Runnin'Rich - keep it up! I don't own an AWD BMW anymore, but I've always been curious what is going on in the steering racks of the BMW's I've owned. If I'd had more time and money when I owned my Xi wagon, I'dve definitely liked to take it apart like you're doing to see what's going on in there and why its so different from other BMWs I've driven.

[Runnin'Rich]

I took the pinion out of the RWD e90 rack and it’s 10 teeth!
Removing the bolts and then sliding off the pinion top cover. I held the splined end in a vice and used a mallet to tap the rack down and away using gravity’s help

The helical teeth on the pinion are cut only at the very end. Therefore shortening it for use in the AwD application is not possible.

Also the angle at which the body holds the pinion is different. Putting the RWD parts inside the AWD is not going to be possible.

The the pinion angle on the e46 awd visually matches the e90 awd rack.

[ptpending]

Originally Posted by rothwem

That's only for the RWD cars. The AWD front end is different--the M3 rack doesn't swap in, and active steering was never an option on the AWD cars.

Runnin'Rich - keep it up! I don't own an AWD BMW anymore, but I've always been curious what is going on in the steering racks of the BMW's I've owned. If I'd had more time and money when I owned my Xi wagon, I'dve definitely liked to take it apart like you're doing to see what's going on in there and why its so different from other BMWs I've driven.

here is picture of the both racks, the upper is from m3
if TS is trying to adapt e46 rack why do not try to adapt m3 rack from same body generation (E90)

[Runnin'Rich]

I was hoping to simply swap internals to make this work, or do very minimal modifications to parts.

The e46 awd pinion(9 teeth) is very close in length to the e90 awd(8 teeth) version. So could be easily modified to work in the e90 rack body using a lathe.
There doesn’t seem to be any other BMW rack with a short pinion and a greater number of teeth. So the best short pinion I’m aware of is the e46 awd one with 9 teeth.

I purchased the RWD e90 rack rod to see if it would marry up with the e46 awd pinion, but the gear pitch does not match.

My options are now to
A) machine a helical gear of what ever tooth count / pitch onto a shortened e90 RWD pinion
B) keep buying racks until the rack rod gear pitch matches the e46 awd pinion.

M3 racks are more than 3 times the price of the non-M cars. The pinion is too long and would need to have the helical gear cut further up the pinion and then shortened by a couple of inches, to fit in the e90 awd rack body.
I would also need to then add servotronic which is would add further cost.

For such a fast steering ratio the pinion must be 11 or 12 teeth and of a larger size. You can see from the image below that maybe the rack rod is thinned out compared to where the inner tie rod connects, to make room for the larger size pinion - possibly?