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Front Wheel Misalignment Issue - Concentrcity

  • 31-07-2020 11:47am
    #1
    Registered Users Posts: 158 ✭✭ Exodus 1811


    Hello all,

    I have a BMW E21 320/6. Recently I have come across an issue with its front wheels coming out of concentricity. Mainly, my driver side wheel is too far forward. A problem that has existed since I got some front end work done to the car by a mechanic, which was then discovered myself during some work I was doing.

    When I received the car, no issue was noted regarding wheel position in the arch. BBS spoiler was fitted which decreases arch clearance in the problem area, so for sure it was not a problem. Front end needed new springs and shocks, rear had been done by previous owner (odd?). I should note that from the offset, no peculiar chassis misalignment is noted and the car appears to be true in terms of alignment.

    First Maintenance interval:
    - top mount bearings
    - front springs and shocks (only new back units was installed when I bought the car),
    - reconditioned rack, Powerflex poly bushes installed.
    - Work was carried out by a local mechanic

    Post maintenance: Car drove fine, no problems with arch strike (I think). I didn't have the car on the road for that long, so it could have been an issue that wasn't solved and I just didn't notice.

    Second maintenance interval:
    NCT was carried out, found some worn track rod ends. I decided to change the wishbones also to the standard ones so I could get a retest quickly and not have any other questions asked of the assembly. Upon disassembly, I noticed the following as noted below (picture 1). An extra washer on the passenger side had been cut (green) and slid behind one of the washers on the front side only. Odd I thought! Wishbones were changed out and standard bushings left in (I was going to change them back to the Powerflex at a later stage)
    Ym7h1Wf.jpg

    Upon lowering the car, the arch striking issue began, passenger wheel was way too far forward, and was striking the arch. Bugger. By calculation, the thickness of the yellow and blue and green section above equals about 12-13mm (if anyone could verify this, it would be great). So a piece of stock was cut and flattened. This came to about 11mm and was inserted as below.
    sPvHxOd.jpg
    Comparison to driverside:
    B0uQtzq.jpg

    Current Standing

    I am now getting struck on both sides of arches (PS + DS). PS is worse than DS, driveable but not liveable. Steering is loose enough, far looser than poly bushed wishbones (expected?).

    Driver Side
    KzNasRn.jpg

    Questions
    - Is this due to the fact I don't have any washers present on the front side of the wishbone? If the wish bone gives slight flexibility, how does sandwiching it between two metal washers allow the movement to occur in driving?
    lLcK49s.jpg
    - The wheels seem to find their own alignment after driving, reversing, turning etc. Is this due to the lack of washers on front end of wishbones also?

    Apologies for the long post, but I figure this might give people a better idea of what's going on.


Comments

  • Moderators, Motoring & Transport Moderators Posts: 2,941 Mod ✭✭✭✭ macplaxton



    Questions
    - Is this due to the fact I don't have any washers present on the front side of the wishbone?

    There should be washers either side of the bush in the wishbone, otherwise the wishbone can move around (move fore and aft pivoting around the axis of the bottom arm inner bush.

    IMG_0926-X2.jpg

    diag_2p5.png


  • Moderators, Motoring & Transport Moderators Posts: 2,941 Mod ✭✭✭✭ macplaxton


    How a McPherson strut is located.

    main-qimg-64d07e84f5e3ea6b00e5a5896c61d126.webp

    Note: Anti-roll bar is integral to lower control arm location.


  • Registered Users Posts: 158 ✭✭ Exodus 1811


    macplaxton wrote: »
    How a McPherson strut is located.

    Note: Anti-roll bar is integral to lower control arm location.

    Thanks for your response macplaxton.

    That explains the new found driver side wheel issue. I reckon once I put the washer in on that side, it'll resolve that issue. I should have copped that.

    Still up for debate is the passenger side. It seems to be a good 10mm off when identically set up to the drivers side. We had the sway bar off, and it didn't seem bent? Is it possible that the clamps have lost their rigidity around the sway bar bushings?


  • Moderators, Motoring & Transport Moderators Posts: 2,941 Mod ✭✭✭✭ macplaxton


    Disclaimer - I've never knowingly been close up to an E21 front suspension. This is based on my general suspension knowledge.

    521772.jpg

    521773.jpg

    In the third diagram of the first picture, I've put four round blobs to highlight the four location points of the front suspension. All bushes would have some movement in various directions, with worn bushes allowing more movement in various directions.

    The inner control arm to front subframe / crossmember pivot point which principally allows the wheel to rise and fall vertically. Depending on the slop in the bush, this arm would also be able to move backwards and forwards under acceleration, braking and steering.

    The backwards and forwards movement is limited by the contol arm to anti-roll (sway) bar bushes and the anti-roll bar bushes. Washers only on the ends would limit backwards movement, but not forwards movement. Washers either side would limit both. When the wheel rises twist in the bar would be resisted by the other side of the suspension.

    The top mounting of the strut, so in this case you've found places where it can move around.

    For a wheel to sit forward in the arch then something has to be amiss somewhere. As listed, the bottom/control arm could be bent, the subframe to which it attaches (or the body to which the subframe is attached), or the strut itself.

    Perhaps find some place that can measure the suspension alignment and get a starting set of figures to work from and compare them with what the manufacturer recommends in the service manual.


  • Registered Users Posts: 158 ✭✭ Exodus 1811


    macplaxton wrote: »
    Disclaimer - I've never knowingly been close up to an E21 front suspension. This is based on my general suspension knowledge.

    In the third diagram of the first picture, I've put four round blobs to highlight the four location points of the front suspension. All bushes would have some movement in various directions, with worn bushes allowing more movement in various directions.

    The inner control arm to front subframe / crossmember pivot point which principally allows the wheel to rise and fall vertically. Depending on the slop in the bush, this arm would also be able to move backwards and forwards under acceleration, braking and steering.

    The backwards and forwards movement is limited by the contol arm to anti-roll (sway) bar bushes and the anti-roll bar bushes. Washers only on the ends would limit backwards movement, but not forwards movement. Washers either side would limit both. When the wheel rises twist in the bar would be resisted by the other side of the suspension.

    The top mounting of the strut, so in this case you've found places where it can move around.

    For a wheel to sit forward in the arch then something has to be amiss somewhere. As listed, the bottom/control arm could be bent, the subframe to which it attaches (or the body to which the subframe is attached), or the strut itself.

    Perhaps find some place that can measure the suspension alignment and get a starting set of figures to work from and compare them with what the manufacturer recommends in the service manual.

    Macplaxton, thank you for the comprehensive explanation. That is great.

    I dropped the car into a classic mechanics for their opinion. I went down for a chat and we had a discussion about the next course of action.

    As far as we can tell, the subframe, chassis etc are not bent or distorted in any way. I recognise the that there is no washer on the front end side of the sway bar to the wishbone, but I am also confused by the fact that this will not touch the wish bone, albeit being a diameter that suggests it would. This is slightly confusing to me, is it to limit movement in the bushing?

    We have the following course of action
    - Remove sway bar, check between both sides if it is bent
    - install Powerflex polyurethane bushings and spacers. (1x extra on the passenger side
    - Reassess.

    Do powerflex bushing normally have one small side and one large side? As pictured?

    MOKr952.jpg


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  • Registered Users Posts: 12,554 ✭✭✭✭ galwaytt


    Can i suggest as a simple check - if not done aleady - is to measure the wheelbase on each side.

    That is, measure from wheel centre to wheel centre, front to back, on each side.

    The forces involved on bushes is such they should be very tight statically, certainly no discernible movement by hand anywhere, and only some with a good lever bar.

    1.5t of car moving at 60mph won't be long compressing & moving parts around.

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  • Registered Users Posts: 158 ✭✭ Exodus 1811


    I did a rough measurement of this at the beginning, we found about 10mm difference, although hard to accurately measure.

    I am planning on getting a little laser set up to get to the bottom of this.

    The current remedy is polybushes on both sides, thicker washers for clearance, now both sides line up with reference to expose threads on the end of the ARB. which i find strange!


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