[onebluemcm]

Also firmly in the not-a-fan camp of the xdrive steering ratio.

I recently had been thinking about acquiring both E9x M3 and xdrive racks to see about swapping internals, but yeah, they are pricey for some experimentation. And from what you are saying here, it's a no-go. So I'm glad I saw this.

I'm beginning to wonder if a subframe modification - mainly thinking about a weld-on, possibly bolt-on, bracket to make a M3 rack fit is the best option. I'd have to get under mine to see if there was room though. And if the M3 pinion is that much longer, sounds like there would be a steering column modification needed as well. Sheesh.

[Runnin'Rich]

It’s the left CV shaft that is really in the way. The angle of the pinion is 9 degrees further to the left and much shorter on the awd car.

I’m looking into getting a RWD pinion cut with the 9 degree difference further up the pinion shaft so it’s shorter. Unfortunately the gear teeth size is totally unusual so it’s probably going to be a struggle to find a machine shop which would do it. Let alone at a reasonable price.
I might be better just get a fully custom matching rack and pinion made from scratch using standardised gear teeth sizes.
Although I’m concerned there will be backlash and therefore some steering ‘play’ felt at the steering wheel.
Maybe the compression spring and the helical teeth eliminates that problem?

[Tambohamilton]

I'd be going fully custom here. The chances of a shop being able to accurately match or reverse-engineer an unknown rack tooth profile are low, so much better chance of success if they make both from scratch.

Have you offered up a rwd rack to see how close it is to fitting? Obviously this would be the simplest way by far, if it's possible. I'd fancy my chances much more of being able to alter a mounting point or something rather than somehow getting mismatched or custom internals to marry up perfectly.

[Runnin'Rich]

Thanks for the reply Tam
Yes that is last resort to have a fully custom set up like what quaife are offering for the Old Ford escorts and Honda Civics.
I just was hoping to at least modify a pinion to reduce some of the machining costs. The rwd ones are so long there is a long enough ‘blank’ section that could be used.

[onebluemcm]

I would think modifying the RWD pinion in this situation would be CNC work for the most precision. Maybe the best way would be a 3D scan of it and CNC machining. And if it's hardened, that may be a factor.

It's starting to sound like a xdrive to RWD conversion would be needed to get a quicker ratio!

Joking aside, I do think the only realistic, however impractical, option is changing the rack and pinion in the AWD system because of the mounting and geometry of the housing.

[Runnin'Rich]

Yeah I’d rather modify the existing pinion and rack so i don’t need to worry about material choice. You can figure out the module (pitch) of the pinion from the counting the teeth on the rack

[Runnin'Rich]

So I finally got to a machine shop to see if something could be manufactured.
Firstly modifying any of the parts is out of the question. The parts are hardened and cannot be machined after the hardening process as it would damage any tooling.

This throws out the idea of modifying a RWD pinion, a new pinion will need to be manurfactured from a piece of stock material bar and then hardened.

The RWD pinion was confirmed as a non-common gear size. The machinist measured it to be very close to an imperial size 15 Diametral Pitch but not exact. The closest nominal size in metric would be a metric size 17 module. He didn't have a 17 module tool or size guide to be able to confirm it as 17.

17 Module gear pitch is a non-standard size so I would need to have a gear hob made to be able to cut a new pinion. Or he suggested maybe I could order one from europe because they use more metric sizing there.

A gear hob could cost a $2000+
And then the cost to manufacturer one pinion would be $1500+

Another option would be to skip buying the hob and have new matching rack and pinion cut with a generic gear pitch that the machine shop already has a hob for. However I was told this would be in the ball park of $5k! due to the polished finish on the rack!

So at this point, it's looking pretty unrealistic to follow through with the project.

[Tambohamilton]

Shame, but as I expected for trying to match the existing rack. I wonder if it would be different for a matching set if you approached a shop who already do custom racks?

[onebluemcm]

Originally Posted by Runnin'Rich

So I finally got to a machine shop to see if something could be manufactured.
Firstly modifying any of the parts is out of the question. The parts are hardened and cannot be machined after the hardening process as it would damage any tooling.

This throws out the idea of modifying a RWD pinion, a new pinion will need to be manurfactured from a piece of stock material bar and then hardened.

The RWD pinion was confirmed as a non-common gear size. The machinist measured it to be very close to an imperial size 15 Diametral Pitch but not exact. The closest nominal size in metric would be a metric size 17 module. He didn't have a 17 module tool or size guide to be able to confirm it as 17.

17 Module gear pitch is a non-standard size so I would need to have a gear hob made to be able to cut a new pinion. Or he suggested maybe I could order one from europe because they use more metric sizing there.

A gear hob could cost a $2000+
And then the cost to manufacturer one pinion would be $1500+

Another option would be to skip buying the hob and have new matching rack and pinion cut with a generic gear pitch that the machine shop already has a hob for. However I was told this would be in the ball park of $5k! due to the polished finish on the rack!

So at this point, it's looking pretty unrealistic to follow through with the project.

Well dangit it, unfortunate, but not surprising. I wondered about the machining prospects because of the hardening. This stuff has to be hardened to give it the longevity.

May have to live with limbering up and moving the wheel more I guess.

Thanks for the time taken to look into this.

[Runnin'Rich]

I won’t give up. This is the perfect platform for me except for the rack ratio designed for an icy autobahn at 200kph.

New ideas:
1) Check an M3 rack tooth pitch to see if it’s a normal regular tooth size and therefore cheaper to get a pinion made.

2) Find another short pinion steering rack that has the same rack to pinion angle. Then shorten the m3/rwd pinion without gear cutting. Maybe e83 X3
Going to be a pain to fit a different rack body into the subframe though.


So, CAN SOMEONE PLEASE MEASURE AN M3 rack pitch!
Turn the rack all the way to the left and then tell me the distance in mm for a specific number of teeth.

I’ve bought 3 racks already for this development. I can’t justify an m3 rack!

[tteg33]

Originally Posted by Runnin'Rich

I won’t give up. This is the perfect platform for me except for the rack ratio designed for an icy autobahn at 200kph.

New ideas:
1) Check an M3 rack tooth pitch to see if it’s a normal regular tooth size and therefore cheaper to get a pinion made.

2) Find another short pinion steering rack that has the same rack to pinion angle. Then shorten the m3/rwd pinion without gear cutting. Maybe e83 X3
Going to be a pain to fit a different rack body into the subframe though.


So, CAN SOMEONE PLEASE MEASURE AN M3 rack pitch!
Turn the rack all the way to the left and then tell me the distance in mm for a specific number of teeth.

I’ve bought 3 racks already for this development. I can’t justify an m3 rack!

I am pursuring a similar project, however for a different car, will update here if I ended up going all in. Just a reminder that the M3 is a servotronic so comes with a very different valve body and possible the internals, not sure if that's relevant to your plan though. By the way if you can share the diameter of the rack rod/main rod and diameter of the rod pistons it might be helpful to future modders.

[Ricthewrench]

Professional machinist here. Hardened steel is 100% able to be machined
. Happens a lot in my job. Most any shop could do it, they do not want to do the job. I make make many of my own parts. You need a gearhead/ machinist that understands the thrill of making the unmakeable part! Good luck, we are rare. Ric

[Runnin'Rich]

Well that’s amazing to hear Ric thank you for the reply.
If I sent you the parts do you think you could cut the RWD gear profile at a slightly different angle on to the ‘blank’ section of the RWD pinion.

I would be using the AWD housing, the RWD rack and then your custom angled pinion. This custom pinion would have the gear pitch of the RWD rack but cut at a different angle to match the AWD housing.

[onebluemcm]

Originally Posted by Runnin'Rich

Well that’s amazing to hear Ric thank you for the reply.
If I sent you the parts do you think you could cut the RWD gear profile at a slightly different angle on to the ‘blank’ section of the RWD pinion.

I would be using the AWD housing, the RWD rack and then your custom angled pinion. This custom pinion would have the gear pitch of the RWD rack but cut at a different angle to match the AWD housing.

I think there is a good chance once you find a guy willing to do this, he will have other interested parties. I for sure would be one of those. This slow rack is the final thing keeping the car from being fully amazing.

[Runnin'Rich]

TLDR:

The potential easiest/cheapest way to make a part would be:
1) anneal (remove the hardening) the original RWD pinion
2) Shorten the pinion length by cutting off the original gear form to the same length as AWD pinion.
3) Cut a new gear form at a slightly increased angle to match AWD housing angle
4) Harden the pinion once again.

The unknowns that an expert could answer:
a) is the meshing depth of the RWD and the AWD gear sets the same? is the centreline of the rack and the centreline of the pinion the same offset for both the RWD & AWD housings. I've done some basic measurements and they appear to match, but would need to confirm.
b) can annealing allow a used pinion to be re-machined and then hardened for a second time?
c) What size gear hob do we need to cut the gear. Does it need to be custom made? The machine shop I spoke to thought is was metric 17 Module. Having measured the rack yesterday I calculated it to 1.7Module using a formula I found. Whichever is correct, they are both non-typical sizes that would potentially need a custom gear hob specially manufactured. Big $$$.
d) Is the change in gear cut angle a nominal size? As in the AWD is 18 degrees and the RWD is 15 degrees. The difference needs to be accurately measured.
e) How do you polish the fresh cut gear before hardening?

The M3 rack could be advantageous if the gear module is more normal and we could buy an off the shelf gear hob. Will definitely need to retrofit Servotronic when using such a fast ratio.

[onebluemcm]

Thanks, got the DM too.

Yeah, I'd have to ask/read more about annealing and rehardening to see if that is possible with similar strength characteristics.

The hardening issue aside, machining an already made part might not be too tough, but there are still some unknowns. I'll start keeping my eye out for an M3 rack. Maybe we can find a busted one for cheap.

Going back to earlier stages of this thread, with the subframe being steel and easy to fabricate on, I wonder if we should reconsider the E46 rack option with some modified mounting points on the subframe? Re-reading, it sounds like it needs a slight rotation, to make the pinion/input side miss the axle and not have to move it forward too much, to preserve geometry, as you said, if I have that right.

Ideally, I'd get my hands on a D9x xdrive front subframe, E91 rack and the E46 rack (exactly which one was it that you picked up again?) and then see about some fabrication work. I wonder if the result could be some custom brackets that would bolt or weld in to hold the E46 rack in the proper orientation and location for the needs of the E91 chassis.

[Tambohamilton]

Regarding the M3 rack/servotronic - I have an M3 rack on my RWD e91 330d, and no servotronic. It's certainly heavy for parking, but really not the end of the world. Maybe with wide and sticky tyres it would be bad, but factory size eagle F1 as6 are fine for me. Once you're moving it's all good, providing you're ok with feeling the road and camber changes through your hands.

Apparently servotronic can be retrofitted, but it seemed like a pretty solid project in itself!

[rothwem]

Originally Posted by Runnin'Rich

TLDR:

The potential easiest/cheapest way to make a part would be:
1) anneal (remove the hardening) the original RWD pinion
2) Shorten the pinion length by cutting off the original gear form to the same length as AWD pinion.
3) Cut a new gear form at a slightly increased angle to match AWD housing angle
4) Harden the pinion once again.

The unknowns that an expert could answer:
a) is the meshing depth of the RWD and the AWD gear sets the same? is the centreline of the rack and the centreline of the pinion the same offset for both the RWD & AWD housings. I've done some basic measurements and they appear to match, but would need to confirm.
b) can annealing allow a used pinion to be re-machined and then hardened for a second time?
c) What size gear hob do we need to cut the gear. Does it need to be custom made? The machine shop I spoke to thought is was metric 17 Module. Having measured the rack yesterday I calculated it to 1.7Module using a formula I found. Whichever is correct, they are both non-typical sizes that would potentially need a custom gear hob specially manufactured. Big $$$.
d) Is the change in gear cut angle a nominal size? As in the AWD is 18 degrees and the RWD is 15 degrees. The difference needs to be accurately measured.
e) How do you polish the fresh cut gear before hardening?

The M3 rack could be advantageous if the gear module is more normal and we could buy an off the shelf gear hob. Will definitely need to retrofit Servotronic when using such a fast ratio.

I'm a metallurgist actually, so I can answer the heat treating questions. The answer is, "it depends" . Really, the particular alloy and the current heat treatment are going to dictate whether you can anneal and re-harden the parts. My guess is that this is a fairly "normal" steel like a 1045 though, so I'd venture to guess that you'll be okay. With that said, one thing I'd be a little concerned about would be distortion. When you anneal a hardened part, you're taking it from martensite to austenite when its at temperature, and then back down to ferrite/pearlite at room temp. Martensite/austenite/ferrite/pearlite are all just different ways that the atoms can be arranged; temperature and temp changes alter the way that the atoms want to sit next to each other. So with all the atoms moving around, there are slight volume changes that can occur and with a non-uniform part the result can be distortion.

At the axle plant I worked at, we would do a rough turn, finish turn, heat treat, THEN grind the bearing diameters and thread the ends of the fixed joints. I suspect that some kind of finish grind might be required on your pinion gear and I'm not super familiar with the equipment that would be used to do that. We had specialized grinding wheels made for each family of part numbers but there's got to be an easier way to do it for small volume production.