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+--- Thread: Is it possible to reverse in a rush? (/showthread.php?tid=1215)
Is it possible to reverse in a rush? - DavidL - 21-05-2018
My special will tramp like mad if I try and reverse in a rush - for example against the clock at a driving test. From the thread on a recently purchased 1936 Ulster it seems I'm not alone with this. Rather than add to that thread (I was going a bit cross eyed there) I thought I'd ask the question here.
Has anyone got to the bottom of the cause and fixed it?
With my car the prop is the late type and rebuilt so no slop. Short damper arms and done up tight. Flat springs. Boxed chassis but the body adds nothing to the rigidity which comes out at about "normal level of not very stiffness". Engine is soft mounted.
If I'm gentle with it then its fine...
RE: Is it possible to reverse in a rush? - AustinWood - 21-05-2018
Is this possibly caused by the front brakes dragging slightly. In reverse this causes the axle to move forward and apply the brakes harder. this results in lots of shuddering and clattering. Possibly aggravated bu a loose radius rods anchorage.
RE: Is it possible to reverse in a rush? - DavidL - 21-05-2018
Good thought... I've got a "floating cross shaft" to balance the brakes front and rear and I could imagine that flapping about. Am sure they'll be a queue of people saying "nothing wrong with the standard setup if in good repair and properly adjusted" and in time it might go back to standard.
In terms of isolating it does anyone running hydraulics get the same tramping action? Its roughly a cycle per second and the wheels up and down in turn perhaps as much as a couple of inches if really wanting to provoke it.
RE: Is it possible to reverse in a rush? - Alan - 21-05-2018
Have you thought about the difference in static and sliding friction in the dampers? It might be what you need is not two disc dampers done up tight, but 4 or more discs done up not quite so tight.
RE: Is it possible to reverse in a rush? - Rogerfrench - 21-05-2018
It's a normal thing with 1/4 elliptics. As you reverse they try to dig in, raising the rear of the car. Then the tyres let go and the cycle starts over again. Even flattened springs won't totally cure it, but I found that slightly reversed springs did. I accomplished that by turning the main leaf upside-down.
RE: Is it possible to reverse in a rush? - Chris KC - 21-05-2018
I think Roger's right - it always was thus. Some cars are more or less prone according to a mix of factors.
RE: Is it possible to reverse in a rush? - DavidL - 21-05-2018
I like that thought with dampers...worth the tiny bit of extra weight...
Have looked back at the "thoughts on roll oversteer" thread and there's a suggestion that a bit lower at the back than the front works well. If that improved performance in reverse that's another reason to do the work. If I was also to soften the rear at the same time what other problems might that bring?
http://www.austinsevenfriends.co.uk/forum/showthread.php?tid=821&page=5
Lots on that thread regarding front end patter. I've half a memory of another thread discussing it but am struggling...all I remember is a recent "ah-ha" moment, then forgetting what the answer was 8((
RE: Is it possible to reverse in a rush? - Alan - 22-05-2018
I think Roger is right about the cause. I suggested damper modification as an attempt to control the movement.
RE: Is it possible to reverse in a rush? - Bill Sheehan - 24-05-2018
(22-05-2018, 09:46 AM)Alan Wrote: I think Roger is right about the cause. I suggested damper modification as an attempt to control the movement.
Of course, if you really wish to make your Seven go faster in reverse, do what many have done unintentionally in the past - fit the crown wheel the wrong side of the pinion! (I remember a friend getting trapped against the rear wall of his garage when his son tried starting the car). Makes the Seven rather slow going forwards of course. Cheers, Bill in Oz