tony pashley Posted August 29, 2001 Share Posted August 29, 2001 Quick rack (''+22%''); standard track; just a touch of toe-in; Above about 50 or 55 mph a very small ''rotational shimmy'' or vibration' of steering wheel is exhibited at the straight-ahead position on decent roads. It doesn't seem to affect directional stability and the weight of both hands resting on wheel is enough to stop it without making hands vibrate. (Will have to check if it goes away at much higher speed). UJ and clamp all appear to be done up properly. Steering wheel has no slop on the (QR) splines, but a tiny, tiny bit fore and aft. Does anyone know what might be going on here? Is it going to wear the rack in the straight ahead position? Do I, perhaps, have far more toe-in or (-out) than I think I have? Anyone recognise the symptoms? Although there is no discernible (or measurable) slack in the steering, the wheel is noticeably ''lighter'' for a smidgeon either side of straight ahead. Link to comment Share on other sites More sharing options...
Gary Furst Posted August 29, 2001 Share Posted August 29, 2001 Stupid Question but have you had the wheels/tyres balanced. Maybe a wheel weight has fallen off? Link to comment Share on other sites More sharing options...
Graham Sewell Posted August 29, 2001 Share Posted August 29, 2001 Tony, It sounds like the age old problem of a wheel out of balance. Unfortunately, you have to run the gauntlet of the tyre fitters to get it checked. Cheers, Graham Link to comment Share on other sites More sharing options...
tony pashley Posted August 29, 2001 Author Share Posted August 29, 2001 Not so stupid - but I'll check again to make sure I haven't missed one on the inside. Suppose I should swap the wheels around too and then try my other set as well. Thanks for quick response... Link to comment Share on other sites More sharing options...
V7 SLR Posted August 29, 2001 Share Posted August 29, 2001 I've got a 80 - 100mph wheel wobble. Took the front wheels to BMTR in Perry Barr, B'ham and on their computerised piece of kit it said 0.0g out of balance. Nothing..! On refitting the wheels I find I've still got quite a serious wobble, and no weights on the inside of the wheel. BMTR say they only fit weights to the offside rims so as to adequately clear brake calipers. They fit a lot of race cars see. this isn't a problem, even on the SLR with the big fron brakes, so I'll take the weights off myself and get them rebalanced, and ask them to use the inner rim too. Link to comment Share on other sites More sharing options...
ashaughnessy Posted August 29, 2001 Share Posted August 29, 2001 This is a bit spooky. I have a similar store. I've just had a quick rack fitted (I asked for 8%, but the invoice says 22%, so I don't know which) and I've now got a 70-80 mph wheel wobble. Symptom is steering wheel vibrations at about that speed, though not all the time. I can be driving along and suddenly it will start to vibrate even though I haven't speeded up, or I'll speed up to 70 and get the vibration, then after a while it will suddenly stop even though I haven't slowed down. My wheels should be well balanced. Firstly, I had new tyres fitted earlier in the year and the wheels were balanced then (and it looks like the weights are all still there). Secondly, I didn't have the wobble before I had the quick rack fitted. Can incorrect tracking cause a wobble? What about worn bushes? Link to comment Share on other sites More sharing options...
R2D2 Posted August 29, 2001 Share Posted August 29, 2001 Has anyone measured the backlash between the gears in the rack unit? If there is some free play it must allow some float and instability. I seem to remember a thread where some people discovered that their brand new racks weren't well set up. Link to comment Share on other sites More sharing options...
Gary Furst Posted August 30, 2001 Share Posted August 30, 2001 It might be that the 22% rack being much more direct amplifies any very slight out of balance of the wheels, so that for the same o.o.b you get higher levels of steering shimmy. Link to comment Share on other sites More sharing options...
jonhill Posted August 30, 2001 Share Posted August 30, 2001 ashaughnessy, The 8% rack is just over 2 turns lock-to-lock, the 22% is under (around 1.8 ISTR). Jon Link to comment Share on other sites More sharing options...
ashaughnessy Posted August 30, 2001 Share Posted August 30, 2001 Thanks Jon, I'll try twirling the wheel tonight to see what I've got. Chris Flavell, I've tried searching previous topics for threads about this, but the search always times out. Can you remember off the top of your head what the result of the thread was? Which backlash are you talking about and can it be measured by a mechanical incompetent (i.e. me)? Anthony Link to comment Share on other sites More sharing options...
R2D2 Posted August 30, 2001 Share Posted August 30, 2001 There are a couple of threads on Techtalk that may be interesting: "Steering Rack Play" dated 30th Dec. 2000 Talks about how to adjust a rack. "Quick Steering rack" dated 15th Feb 2000 There are some useful comments about Bump Steer by Mike Bees. I have an article about rcaks at home. Will try to mail it to you later. Link to comment Share on other sites More sharing options...
tony pashley Posted August 30, 2001 Author Share Posted August 30, 2001 Anthony - AFAIR the 22% rack has a bare metal casting (ie silvery coloured) while 8% has a black finish (or I think maybe green, yellow or something for widetrack without the extenders) The turning circle is noticeably poorer with the very quick rack - so I suspect the percentages reflect some measure of amount of twirl needed lock to lock (rather than the actual ratio) which would exaggerate the percieved change over standard. The difference between the 8 and 22 didn't seem so vast as the figures led me to believe. But I'm just making this up - has anyone measured or taken one apart? Haven't touched car again - will report ''as and when'' ... Link to comment Share on other sites More sharing options...
ashaughnessy Posted September 3, 2001 Share Posted September 3, 2001 Well, I seem to have an oddity. I'm struggling to search back through previous threads (again, keeps timing out on me) but from this thread and things I read on Friday, the 8% rack should have a black casing and be about 2 turns lock to lock. The 22% rack has a silver casing and be 1.8 turns LTL. My rack has a black casing and is 1.8 turns LTL. So, what type of rack is it? I'll try and search through the old threads again, but 9 times out of ten the search times out :-( I know there were articles there that described different racks for different cars. Anthony Link to comment Share on other sites More sharing options...
Graham Perry Posted September 3, 2001 Share Posted September 3, 2001 I have just had something similar on my road car. I had the wheels balanced and they were exactly right. I then re-did them on my 'old-fashioned' mechanical wheel balancer and they were still okay. However, when I put the wheels back on my road car, I spun them in situ, and discovered that one of the front ones had a 3mm distortion around its circumference. It was really easy to see when spun slowly but at the speed a wheel balancer works it was invisable. I swapped the tyre and all is now well. Check to see that the tyre isn't distorted when spun by hand. Link to comment Share on other sites More sharing options...
old captain slow Posted September 4, 2001 Share Posted September 4, 2001 If you have been doing a lot of hard cornering the wheels may have gone out of balance because of shoulder wear on the outside of the tyres. It puts the balance along the axis of the wheel out. Just had to re-balance mine for that very reason. Link to comment Share on other sites More sharing options...
EFA Posted September 4, 2001 Share Posted September 4, 2001 Tony, Quick rack 22% wide track turning circle is about 15ft with engine running, 40ft without....... I suppose I should come clean that I put lead inserts in your dustcaps........ Fat Arn See another FAT ARNIE here See a meaty Vauxhall car here See the Le Mans Trip Website here See the Lotus Seven Club North Kent Website here Link to comment Share on other sites More sharing options...
tony pashley Posted September 4, 2001 Author Share Posted September 4, 2001 Arnie - I thought your turning circle was zero with the engine running, regardless of rack... Without - sounds like too much hard work! Link to comment Share on other sites More sharing options...
EFA Posted September 4, 2001 Share Posted September 4, 2001 Tony, Its just the "power steering" is more difficult to operate with the engine switched off..... Does take about a cars length to turn it around though.... Fat Arn See another FAT ARNIE here See a meaty Vauxhall car here See the Le Mans Trip Website here See the Lotus Seven Club North Kent Website here Link to comment Share on other sites More sharing options...
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