Steering problems, questions, swaps and more.

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I drive a 1991 318i airbag model car. I have a bad steering shake, and my steering rack leaks. I think it is time for an e36 steering rack setup. A few questions:
1. Should I replace the steering coupler or solid mount it?
2. Do I need to modify the steering coupler on an airbag car for this swap?
3. Do I need to modify my firewall where the steering column passes through?
4. Where can I get a replacement coupler for cheaper than $90?

Thanks! And I am searching for answers, not only asking.

[TurboJake]

replace
yes
no

http://www.fcpeuro.com/products/bmw-steering-flex-disc-e30-lemforder-32311153993l

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That link is great, that price is much better than $100+ to replace the entire thing altogether. Thanks, and so I do still need to grind off the rivets and space it out for the e36 rack is what you are saying?