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MG MGB GT V8 Factory Originals Technical - Sloppy handling: too little yaw control
|I am puzzled over the so-so handling of my GTV8 conversion. |
What I don't get is why the car seems to have little yaw resistance. That is, driving along at 40 mph or so, if you oscillate the steering wheel quickly left/right through 20 degress or so, the car doesn't follow, it just kind of slobs along without reacting. Sort of like you'd expect in a huge American land yacht from the '70s. Not at all what you'd expect in this case, which on paper looks light a very tight system:
The car is a '73 GT, ride height exactly 15" front and rear (center of hub to bottom of chrome moulding). This seems just a tad high -- visually I'd say it is just about exactly what the factory V8s had.
Front: X-member is stock CB; front springs are stock CB and front shocks are stock and in fine shape. V8 lower bushings; Prothane trunnion bushings. Hopkinson 7/8" sway bar. Steering rack is in the stock CB location.
Rear: Doug Jackson composite leaf springs (this set is 139 lb-in), Spax, Hopkinson sway bar. Shackle plates at rear of leafs are the adjustable type sold by Doug Jackson (gorgeous product, BTW); the leaf springs are mounted in the center position of those plates (+1/2"). The end links on the Hopkinson rear bar were left very loose, as per many gurus' suggestion, so that the bar does not come into play at all until there is a fair amount of body roll.
15x6J wheels, 22mm offset, with 195/60R15 tires, inflated 28 front, 30 rear. Wire wheel axle with bolt-on hubs added.
Would a Panhard bar or traction bars help the yaw/sloppy handling? Is the ride height simply too high? ... if so, why might this be, given the stock nature of the front susp. components? Any ideas _much_ appreciated!
|Bill, you are going to get a lot of advice about the rear end - a couple of thoughts about the front; first off the kingpins - the MGB is fairly forgiving of worn kingpins until you get to a certain point - you know when you have got there because ruts in the road seem to lead the car and you get an uneasy vague feeling. Often overlooked are the front shockers, sometime they damp as they should but fail to give the lateral support needed at the top end of the suspension which wanders in consequence (basically the shocker arm moves sideways as well as up and down). The last point concerns your choice of tyres - 195/60 is increasingly popular - they are cheap, look good and drive well on the highway but the MG goes round european corners best on 175s - the car will feel a lot more responsive with skinny originals.|
..and my son's 1800 roadster is also too high - fat tyres, has rear sway bar and doesn't go round corners. Your problem will probably turn out to be a combination of height and rear suspension but the front is easily overlooked.
A Panhard rod would improve lateral location of the rear axle and could sharpen steering response somewhat, but if you've got 20 degrees of slop in the steering wheel in either direction, something's wrong! You might want to check internals of the rack and pinion for slop. The pinion gear could be moving on the shaft. If this is in fact the cause, the car is unsafe to drive. Don't drive it again until you have checked for this possibility. Roger is correct to bring up the possibility of the kingpins and their bushings being worn. He is also correct in directing your attention to the possibility of lateral motion in the damper units. However, there is yet another outside possibility: the tires that you have selected may be el cheapo family sedan tires with flimsy sidewalls. This would readily explain sluggish steering response, but not 20 degrees of play in the steering wheel. If you want razor-sharp steering response, I would suggest mounting a set of Michelin XGTV4s.
|I'm running stock (rebuilt) front '67 gt suspension and 114 lbs plastic springs, stock shocks all new bushings etc and 195 55 15 tires with 15 x 6 wheels. The car changes lanes on the freeway with an imperceptible nudge of the steering wheel. Turn the wheel and it feels like a direct connection to the road. Sometimes the back end under braking or acceleration or pushing it in a bumpy corner moves a little unpredictably (probably a panhard bar would help) but yaw? Are all your bushings new, your rack tight, tie rod ends tight, rear shackle bolts tight, rear ubolts (the ones that hold the axle to the spring tight)? With the thin plastic springs sometimes the u bolts are too long and you run out of threads and don't actually have the rear axle tight even though the nuts feel tight. I had to put several washers as spacers to get the rear u bolts tight. Also check the rear spring shackles. I found that after a few miles the bushings seated in and the rear shackle bolts needed further tightening.|
One of the reasons people bought these cars was because they handle well. A good stock system with modern tires is a responsive car with little or no apparent yaw.
This thread was discussed between 14/05/2001 and 16/05/2001
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