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Old 12-22-2011, 02:31 AM   #1
bastianshaw
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bumpsteer and e36 rack spacer location

Sooooo I think I MAY have put the spacers under the rack and read on e30tech that thjis can lead to bumpsteer

What is bumpsteer?
if I need to change the spacer location can I get away with moving the spacers and keeping my alignment?
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Old 12-22-2011, 04:53 AM   #2
Sagaris
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It is when the suspension and steering follow different arcs during suspension travel which will cause your car to turn just a bit when you hit a bump.

Good:
http://www.miracerros.com/mustang/t_...umpsteer_0.gif

Bump steer:
http://www.miracerros.com/mustang/t_...umpsteer_1.gif

Last edited by Sagaris; 12-22-2011 at 06:25 AM..
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Old 12-22-2011, 05:16 AM   #3
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Quote:
Originally Posted by Sagaris View Post
It is when the suspension and steering follow different arcs during suspension travel which will cause your car to turn just a bit when you hit a bump.
Not quite. Bumpsteer is a change in tow as the suspension compresses and decompresses. It doesn't make your car turn right or left, but it can make it feel "twitchy" and less stable in certain circumstances. On the street, I don't think most people would notice a difference. It is caused by the tie rod and the control arm having different pivot points (following different arcs as Sagaris put it). Ideally, they should be the same, but pretty much every car ever made has some bumpsteer in it. It's kind of hard to get rid of from a design standpoint.

This website has some good info:

http://acceleratingperformance.blogs...ump-stops.html
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Old 12-22-2011, 04:34 PM   #4
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Quote:
Originally Posted by bastianshaw View Post
Sooooo I think I MAY have put the spacers under the rack and read on e30tech that thjis can lead to bumpsteer
You need to take up some slack in the fitment, and under the rack is the best place for spacers. The geometry is best when the rack is close to the oilpan. (this has nothing to do with the oilpan, but you can't go higher because it's in the way)


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What is bumpsteer?
if I need to change the spacer location can I get away with moving the spacers and keeping my alignment?
Probably not. Just moving spacers from one side to the other tweaks the to-in enough that you should recheck it. DO NOT PAY ANYBODY TO CHECK IT.

Buy a set of "toe-plates" and do it yourself.

http://www.amazon.com/Longacre-Toe-P.../dp/B000VAOHB2
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Old 12-25-2011, 05:45 AM   #5
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Everything I have read says to put the rack spacers on top, but taking a look at the geometry yesterday, the tie-rods would be more parallel to the control arms (on my car at least) if the spacers were put on bottom. I am going to change it up and put my rack spacers on bottom and see what happens.
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Old 12-25-2011, 08:10 AM   #6
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Bump steer can definitely steer your car by itself on the street. All you need to do is hit a good bump with one wheel or one wheel first like a set of train tracks at an angle. A friend had a '59 bugeye sprite with bumpsteer issues we were fixing and it was all you could do to stay in your lane in those situations.

bastianshaw, do like hellabad suggested and get some toe boards, it's really easy to do and if you take your front springs out you can check your own bumpsteer by raising and lowering the chassis through its normal travel and measuring the toe change.
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Old 12-25-2011, 10:43 PM   #7
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Quote:
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Bump steer can definitely steer your car by itself on the street. All you need to do is hit a good bump with one wheel or one wheel first like a set of train tracks at an angle. A friend had a '59 bugeye sprite with bumpsteer issues we were fixing and it was all you could do to stay in your lane in those situations.

bastianshaw, do like hellabad suggested and get some toe boards, it's really easy to do and if you take your front springs out you can check your own bumpsteer by raising and lowering the chassis through its normal travel and measuring the toe change.
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Old 12-26-2011, 04:56 PM   #8
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Hellabad is correct, everything I have read about e36/z3 rack swaps is wrong.

Here is the tie-rod angle with the spacers above the rack


Here it is after moving the spacers below the rack


My car drives normal now after putting the spacers below the rack and has a normal/basically undetectable amount of bumpsteer

Last edited by Sagaris; 12-26-2011 at 05:07 PM..
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Old 12-26-2011, 05:06 PM   #9
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Good to know, I am doing an e36 rack right now and I was wondering about the orientation myself.
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Old 12-26-2011, 05:10 PM   #10
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If you run power steering it would be great to see how you route/bend the power steering lines to get them to work, I have mine working but there has got to be a better way to do it than how I did.
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Old 12-26-2011, 05:12 PM   #11
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Quote:
Originally Posted by Sagaris View Post
If you run power steering it would be great to see how you route/bend the power steering lines to get them to work, I have mine working but there has got to be a better way to do it than how I did.
I just bent my E30 line a little bit and it worked fine.
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Old 12-26-2011, 05:16 PM   #12
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Good to know. About a month passed between the start and finish of my rack swap and I didn't quite remember how the lines were routed when it came time to put it together. Everyone seems to say it is just a small bend in the HP but I wasn't seeing it. I will have to take a look at someone else's e30 and see how the stock lines are routed again (its just that coiled portion of the HP hose that threw me off, it wasn't fitting nicely anywhere)
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Old 12-26-2011, 05:18 PM   #13
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I'll try to take a pic of mine and post it here.
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Old 12-26-2011, 08:38 PM   #14
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I did a rack swap yesterday and wrapped it up today. There was no way to get the spacers underneath the rack as the hard pipes hit the pan. I wasn't too concerned as my 84 318i rack did not look at all like the e36 rack and its center line (rack plane) would have been higher than the original with the spacers underneath. I also have Eibach Prokits and Bilstein Sports.

The steering is more stable and just enough quicker to make me smile. I'm wondering if its possible that the revised geometry could have eliminated the bit of bump steer I had ?
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Old 12-26-2011, 09:06 PM   #15
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wow, so i messed up good huh lol sweet
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