[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.