kevfromwales
Posted a lot
the conrod's REALLY out the block now!
Posts: 3,909
|
|
May 31, 2016 21:08:11 GMT
|
|
BEFORE I START THIS IS NOT A THREAD ABOUT A FRAMES NOT BEING LEGAL ETC ETC ETC
I want to know the mechanical reason why today, after a framing alsorts of shonky cars and vans over the years, I had an epic fail.
The car I towed was an m reg bmw e34 525i, and I used my bmw e36 tds. Now, I *know* the e36 isnt man enough for the job, id have used the tathauler but its done a front wheelbearing.
The thing is, even while driving across a tarmac carpark at less than walking pace, as soon as I put ANY right hand lock on, the e34s wheels went to full LEFT hand lock?!?!?
Ive had a few people mention its because they have alloy front arms, but tbh I cant see how that would affect it? And I don't think its because it has a steering box, as I framed an ldv pilot several miles of lanes a few weeks ago, no probs.
I fitted the a frame to the front of the arms, double wrapped the chains, and it was all tightened up.
Anybody got any ideas?
|
| |
Almost on the road: b11 sunny breadvan, e36 tds, 325i skidcar,
nearly there: ford f250 tathauler, suzuki alto, u11 bluey
not for a while: ford pop, 32 rails,
not in this lifetime: ruby, '29 hillman
''unfortanatly I'm quite old and scruffy and in need of some loving. my drive shaft needs a new boot....''
|
|
|
|
scimjim
Club Retro Rides Member
Posts: 1,503
Club RR Member Number: 8
|
|
May 31, 2016 21:11:43 GMT
|
|
assuming it was a solomatic type, did you definitely have the cross-plate fitted? leaving that off can give strange movements (don't ask!)
|
| |
|
|
|
|
|
|
|
|
Hi, I was reading the other thread on this earlier today and have been thinking about it whilst doing other mind numbing jobs. The only thing I could think of that would effect the steering like that is the thing that has the most effect on steering normally, castor angle. Some cars have lots notably German like BMW and Mercs when on full lock the wheel has a pronounced lean towards the back of the car because of high castor angle. High castor angles give strong self centreing.
If you think of a shopping trolley with their castors, when you push them the castor always turns round so the wheel is behind the swivel axis. If you tip them back at a shallow angle and try to push them forward the wheel kicks over sideways, you have to tip them right back to stop it doing it and even then they're not happy about it. I think a similar thing is happening.
I'm not sure I've explained that very well.
Colin
|
| |
|
|
steveg
Posted a lot
Posts: 1,565
|
|
|
|
|
Does it have anything to do with the amount of overhang behind the back wheels of the tow vehicle ?
Another thing I have noticed is that BMW's seem to have a lot of castor or at least the top of the struts are set back from the wheel centre a lot.
I wonder if the sideways motion of the tow ball, which is opposite the way you are turning to begin with just has too much effect on certain cars. Would using a Land Rover with a short overhang have as much bad effect ?
I took so long writing that Colin said most of what I was thinking already !
|
| |
Last Edit: Jun 1, 2016 0:20:49 GMT by steveg
|
|
|
|
|
|
|
|
Pretty sure the E34 uses a very similar front suspension setup to my E39.. in that it has double lower arms rather than a conventional lower wishbone to control the side/side and front/back motion of the wheel, which work together with the track rods to create a "virtual" steering axis with better geometry that is further out into the wheel than would otherwise be possible with a normal lower ball joint. It might be that this means the forces on the front wheels act in a different way to what your used to.
|
| |
|
|
hario
Part of things
S202 C300STD
Posts: 421 
|
|
|
|
|
Something something something steering rack on the other side of the axle?...
If an A-frame thing turns the wheels for you, then you have to mount it differently if the rack is infront or behind the axle right?
No A-frame experience just thinking out loud..
|
| |
*S202 C300TD Wagon*
Installed:
OM606 & 722.6, Evo6 IC, S600AMG callipers & 345mm rotors. No catz. Leatherish seats.. Rust..
Future:
DIY manifolds & turbo compound build.
Built IP, & some kind of software. Less rust..
|
|
bortaf
Posted a lot
Posts: 4,549
|
|
|
|
Something something something steering rack on the other side of the axle?... If an A-frame thing turns the wheels for you, then you have to mount it differently if the rack is infront or behind the axle right? No A-frame experience just thinking out loud.. It doen't turn the wheels for you it just pulls the car from the lower wishbones, if the rack is in front of the wishbones (ala e30) then you cant bolt it on, simples (squeek). Usually a car will track straight when moving and there is no load on the steering, (IE take your hands off the wheel and a vehical will go stright when moving) a lot of FWD cars have issues with the diff dragging when there is a lot of lock on and causing the sterring to stay on full lock but thats not the case with a RWD (diff is at the back) so there is another reason for the bad steering and thats what we/OP is trying to figure out. IMHO it's the castor, when you accel using the engine the lower wishbones are pushed back due to the drag of the tyres, when you A frame they are pulled forward (the lower WB bushes are well know for play on later BMWs) even new they have loads of slop in them, pulling the WB forward changes the castor and impacts on the steering, just a guess  To test drive the vehical in reverse and see how the steering feels then, i bet it's all over the place it's how i test how bad the WB bushes are on later BMs rather than jack it up and wobble the front wheels. |
| |
Last Edit: Jun 2, 2016 15:08:29 GMT by bortaf
R.I.P photobucket
|
|
|
|
|
|
|
|
You don't have to attach them in theory to the wishbones. You could attach them behind the bumper, it would still steer.
|
| |
|
|
|
|
|
|
|
Pretty sure this has got to do with certain "newer" cars suspension geometry IE no Ackerman angle,coupled to strange steering axis inclination. Strange to me,that is  |
| |
Last Edit: Jun 3, 2016 19:25:39 GMT by Deleted
|
|
Bracey
Part of things
Posts: 208
|
|
|
|
|
When I sold my E34 520 to a Polish fella, he brought a VW T5 and an A-frame. He couldn't get more than a couple of metres without the front wheels turning.
I couldn't offer any advice then either but it must be the setup of the E34 suspension.
|
| |
|
|
|
|
|
Jun 10, 2016 16:08:51 GMT
|
|
I think Steve g has got it right. If you have a large over hang on the tow car when you turn right slowly the tow ball will go left the pivot point being the rear axle. At higher speed you would not notice as the pivot point is changing lessoning the effect.
|
| |
|
|
|
|
|
|
|
|
Kev, I've done a fair amount of A framing, often from distant climes,& have suffered this on a wide range of vehicles, old and new(ish).
The two that spring to mind was my 68 Moskvich 408 and 53 Renault Prairie, that both did exactly that. I think, having looked carefully, that it's Ackerman at fault, and a bloody nuisance. I've yet to find a way around it, other than a tow dolly.
In an emergency , as I was both times, needing to tow back from the continent , the answer is either a passenger short term, steering the towed car until you hit the straight, or simply strap the steering wheel straight.
It's then simply horrible on any sort of corner, & the car will try to force a jacknife whilst the tyres scream in protest, but- assuming the towcar is grunty enough, you will get home.
It will be fine on the straights, but you'll dread corners/ roundabouts!
|
| |
|
|
