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  #16  
Old June 4th 2009, 11:47
IMPI IMPI is offline
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When I bought my super it had a Golf rack in almost the same position The previous owner took it of the road as it was lethal to drive horrible bumpsteer. I am slowly replacing the rack with one from an early Passat which in turn is almost identical to the rack from a late 1303.
I also lowered the frame head in the rack position to approximate that of the late 1303I really love the work that you have put in so far especially that rear apron
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  #17  
Old June 4th 2009, 17:39
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Thanks for bringing the bumpsteer issue up. I havn't tried driving with the rack since I havn't gotten far enough to put an engine in the with rack in place. I'm not exactly sure how to measure bumpsteer, and I know the wheels accually turn farther then the normal steering set up. I have come to grips with the fact that I may need to modify the setup before I'm done, but any suggestions would be welcome.

Last edited by panic; April 16th 2013 at 22:17.
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  #18  
Old June 4th 2009, 20:18
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Since I've become more and more knowledgable about suspension systems (I still have LOTS to learn) it has become more and more surprising when people just start bolting stuff together. The geometry of a suspension system is sooo complex, if it was easy every Chevy would handle like an M3! So, just because it might look cool or be different doesn't necessarily translate into any performance improvements, in fact in the suspension department it often leads to a failure, as I can attest.

Jason
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  #19  
Old June 4th 2009, 22:34
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http://en.wikipedia.org/wiki/Bump_Steer

If what I read is true, I could probably modify the rack to work. Im not really to afraid to do some more hacking to get it right.
But then again, you take the cake here, as your car is a source of insperation for me, and the idea to fit the rack was a spur of the moment ordeal.
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  #20  
Old June 5th 2009, 05:26
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I see that you have standard track control arms that must use the standard inner pivot positions. The general princples behind getting zero bumpsteer is for the rack track rod to describe the same arc as the suspension so that the axle does not need to pivot as it goes through the suspension movement - if it does then that is bump steer. With a simple geometry like the 1302/1303 super if the pivot for the trackrod is at the same distance from the axle as the track control arm AND it is parallel to the track control arm in the mid turn position then I would expect minimal (if any) bumpsteer.
The rack you are using has the pivots well outboard of the inner suspension pivot so that the track control arm and the trackrod will describe different arcs thus pulling the outer steering arm in as you pass the static pisition on both bump and droop.
The best VW racks are the Polo and early Passat that have central style pivots for the trackrod that make it very adaptable for different inner pivot positions.
The other thing to be aware of when locating a rack is the effect of the fore and aft position of the rack on the ackermann steering. You ought to be aware that the inner front wheel describes a tighter radius than the outer wheel in a turn (ackermann steering). This is effected by the position of the rack and the steering arm angle at the axle end. IIRC moving the rack forward of the parallel position locates the instantaneous centre forward of the rear axle and behind the parallel position puts that centre behind the axle. For true ackermann steering the instantaneous centre should be in the centre of the rear axle. I realise that most circuit racing designers are not overly bothered about ackermann steering and the current trend in F1 is for parallel steering but it ought to be recognised that circuit racing demands small steering angles and front end scrub can be desireable to put heat into lightly loaded front tyres. That is not the case for a road car or one that is used for autotesting/autosolo/slalom.

Clive
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  #21  
Old June 6th 2009, 15:44
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Hmmm looks like I should have done some more researching first!
Thanks for your knowledge EvilC!

What if I where to fab up new lower control arms with inner pivot points closer to the racks pivot points? I have always thought I would like to make the lower arm into an A arm. Would the shorter arms bung up with the struts positioning?

I am an autobody apprentice at the moment, but I always end up doing the mechanical stuff around the shop too. I have also worked in the restoration business for a few years. I'v poked around quite a few vehicles of all sorts (pre ww1 all the way till now) so I think I have some good info up in my head, I just havnt done all the theory and research to fully understand suspention setups.
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  #22  
Old June 6th 2009, 18:17
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that dash looks incredible
cant wait to see the finished product
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  #23  
Old June 8th 2009, 07:53
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Quote:
Originally Posted by panic View Post
Hmmm looks like I should have done some more researching first!
Thanks for your knowledge EvilC!

What if I where to fab up new lower control arms with inner pivot points closer to the racks pivot points? I have always thought I would like to make the lower arm into an A arm. Would the shorter arms bung up with the struts positioning?

....................
The bugs inner pivot point is an advantage so don't screw it by matching the rack. Its the rack thats wrong not the bugs suspension. Having such long TCAs (Track Control Arms) means that the potential for unwanted camber change at the wheel end is reduced so any suspension modification should enhance that provision.
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  #24  
Old June 10th 2009, 22:43
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After assembling the rear brakes, I found I still have play with the hub. Any ideas?

Also, the front pads are touching the rotors at all times...
I wonder if I got a mixed matched bunch of parts shipped to me when I purchased the lot.

From what I know, I am using early 944 spindles/hubs etc. The rear assembly is from the same car. The axles are the original vw ones.

Last edited by panic; April 16th 2013 at 22:19.
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  #25  
Old June 11th 2009, 03:52
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Hi

You can get up & down play from flogged out trailing arms.

Steve
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  #26  
Old June 11th 2009, 07:55
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The front pads in the standard 944 single pot caliper do touch the discs at all times. Its probably because the non-return spring that is on one side only exerting a sideways force on the sliding piston body giving a twisting action that means one part of the pads is in constant contact. This eventually manifests itself in the tapered wear on the pads (equal but opposite on the two pads). Its not a great design IMO but I suppose it was cheap! There is nothing to worry about but I have purposely left the pads out for the time being so as to be able to push the car around with ease and no drag. I doubt whether there is any noticeable effect on performance. One point that concerns me though is that the pads mould themselves to the disc thickness. As the discs wear down the pad shape changes. That's OK until you come to change just the pads or the disc - the shapes are then unmatched and you will be braking on the edge of the pads until they have corrected themselves. The solution is to change pads and discs always at the same time.

Clive
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  #27  
Old June 13th 2009, 19:21
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What I ment was at the end of the shaft where the rotor and the hub sits for the rear, I can move the hub/rotor in and out on the shaft, even if the nut is tight on the end. Im kind of worried about this, and Im wondering if anyone else has had this problem. Can I put washers in? That would be nice...

Thanks for this info on the fronts Clive, good peice of mind.

Have a good day fellas, its really nice out here in southern ontario.
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  #28  
Old June 14th 2009, 11:18
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Very nice build! It shows your a bodywork guy professionally, very nicely done rear apron.
The cage is very close to the pillars, which I can appreciate very much as well!
Hope it stays aircooled...
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  #29  
Old June 14th 2009, 19:01
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Hi

With your in & out play, are you using stock bug trailing arms? Is the caliper mounting bracket thicker than the stock backing plate?

Steve
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  #30  
Old June 15th 2009, 05:24
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Quote:
Originally Posted by panic View Post
What I ment was at the end of the shaft where the rotor and the hub sits for the rear, I can move the hub/rotor in and out on the shaft, even if the nut is tight on the end. Im kind of worried about this, and Im wondering if anyone else has had this problem. Can I put washers in? That would be nice...

Thanks for this info on the fronts Clive, good peice of mind.

Have a good day fellas, its really nice out here in southern ontario.
Hi,

Moving the hub and rotor inn and out is endfloat and should be almost zero on the rear. That endfoat is free play within the bearings between the balls and the races given that everythng else is correct. You should be only able to measure that endfloat with a dial gauge and not be able to 'feel' it at all.
If you are using the 944 stub axles are you sure about the compatability with the trailing arms. IIRC the bug bearing is significantly shorter than the 944 one, which is a double ball and race thing, so the 944 stub axle may be too long for the bug bearing. Please don't quote me on that as I haven't carried out an extensive comparison check but that would be my first port of call to check all the fitted sizes to make sure they are compatible.

Clive
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