E34 Rack and Pinion conversion completed...

[MBXB]

What was your bottom line for the conversion? Parts cost, Man Hours etc.?

MBXB

[Cacatfish]

I was charGed $2800 because we areed upon that price ahead of time.
It ended up takin him a lot lonGer than he estimated, so the next one may
be sinificantly more.
hours: many, but it was a first for him on an e34
Parts: Im not sure. With fab work (some outsourced), at least $1500

[black_bird_blue]

:P I know... that's why I was asking what the advantages of the stock box are over the simpler R&P. :P hehehe I enjoy reading all the stuff people do to their E34s... at the same time, I'd also like to know the advantages of the stock setup, over the mods... BMW engineers are far from stupid, so I just enjoy knowing the reasons for certain stock component choices over aftermarket upgrades.

Steering boxes have some different characteristics that may be thought of as advantages or disadvantages depending on context. The big difference is that they have a very poor reverse efficiency, which translates as superb isolation from road disturbances. Or very poor steering feel, depending on how you view it. Personally, I've never found the feel on my E34 lacking; as soon as the back of the car moves the steering tells me where it is well enough. That's all I want, the rest is noise.

Steering boxes also have a great package flexibility, you can pop them more or less anywhere, whereas a rack has to be in just the right position, which is one of the reasons why BMW stayed away from it. However, as crash legislation has got more and more stringent, there is more and more space being forced under cars and so it's getting (comparatively) easier to fit a rack in.

The other difference a steering box has is an increasing ratio as you come off-centre, which naturally gives lighter parking efforts for a given level of assistance. To make a rack offer the same level of ratio compensation you end up needing Active Steering or some other fancy tomfoolery in the rack cutting, both of which are expensive - see, for example http://www.bishopsteering.com/steer_tec_rack.htm.

Another advantage is the ability to dial in different levels of friction in different parts of the travel - firm for on-centre disturbance rejection and looser for good feedback in corners, as our E34 boxes are.

Yet another advantage is the ability to get very large levels of rack bar travel without some of the rack-based difficulties associated with that - in particular the position of the valving has to move inboard the more rack travel you have, and inboard is exactly where you don't want to go - back to that package advantage again.

There is also some sort of detail design advantage inside the unit. The high precision components are balls, which are cheap because they are made in volume. Everything else is more or less "industrial", whereas a power rack is quite an expensive piece of machinery gram-for-gram. However, so much effort has been put into power racks now that this one is not really true any more.

If you look around at very maintainable vehicles with a tight turning circle - London Taxis and most delivery vehicles - then they almost all use recirculating ball. It used to be the norm until racks started to become cheap enough. Then for cars the level of feedback (the primary technical difference) was allegedly an advantage, and so racks started to take over. I say allegedly because there is a lot of friction and other stuff going on in the steering that significantly reduce levels of steering feel, and most people don't know what they're feeling anyway, so it's all a waste!

Damian

[Cacatfish]

Double post

[Cacatfish]

London Taxis are back in SFO again. Anyone seen em?

[black_bird_blue]

oops, sorry - finger trouble...

[jplacson]

Steering boxes have some different characteristics that may be thought of as advantages or disadvantages depending on context. The big difference is that they have a very poor reverse efficiency, which translates as superb isolation from road disturbances.

Damian

THAT'S what I was looking for. Thanks! I figured BMW engineers are far from stupid. Having been given the task to design an executive car, I'm sure they were told to make it as comfy as possible... I don't think they expected suits to do slalom turns home at break-neck speeds... or do a 180 driving their kids to school! Although it would make the 'fetch the kids from school' a fun-drive everytime! hehehehe

It makes sense why they placed a RB instead of a RP in the 5. Thanks!!! Learn something new everyday!

[flash635]

I've been thinking of doing this conversion on my E28 based E24.
I'm in Australia so my car is right hand drive.
This conversion would free up a lot of space for a turbo installation.

My question is- can I use the same pump for the rack and pinion as is used for the brakes?
How do you get around this?

[grave77]

your project sounds awesome, I really wish to have that feeling on the steering, but one thing I tried was when I drove my dads car 735i it has a softer steering and it has no gap too, I asked about it and they told me that the hydrolic pump it uses is differant. but it seems to work on the 535i too.. this sounds like a cheep upgrade and easy one too.
I also like to ask about the popular vibration 5 series suffer from when anything fails in the steering system, any effects happenend with ur upgrade ?

[winfred]

one thing that most e32s have that i've yet to see on a e34 is servotronic, it varys the steering effort in relationship to speed

I tried was when I drove my dads car 735i it has a softer steering