Twisting

Dave-R · Post by **Dave-R** » Tue Nov 18, 08 9:24 pm

Oh. And as for the rubber mounted bit.

You should ALWAYS use poly bushings. Not just on the sway bars but also in the leaf spring eyes.

They do wonders.

NaughtyAlan · Post by **NaughtyAlan** » Tue Nov 18, 08 9:30 pm

Polly bushed leaf spring eyes. Bobs got a rear sway bar on the runner could try it

Still seems weird that the car sort of quivers to the right on launch?
Stock heavy duty RT bar on front.

Ivor · Post by **Ivor** » Wed Nov 19, 08 9:31 am

Alan, I've got a nice pair of these on the shelf you can have for nowt!

Dave999 · Post by **Dave999** » Wed Nov 19, 08 10:09 am

axle shafts load up and twist.
the wheel that tries to lift looses traction fora split second
its axle shaft unloads and twists back past where it should be. the wheel gets traction again loads it up again, twists, it wheel loose traction
repeat..............every second

each time it unloads it sends a shock down the axle shaft to the centre
the shock is absorbed by the locker and the relentless power against it from the ring gear driving it the other way.
some gets through to the other axle shaft but not enough to cause it to loose traction because it is the favoured wheel.

i.e you set up perfectly circumstances for a harmonic vibration in the axle shaft of the wheel that tries to lift until its speed of rotation and hence the loading and unloading or indeed traction becomse less of an issue.

i think its the same issue that smashes spider gears in an open diff or loose LSD centre and if that doesn't get them that way, galling the cross shafts and then incorrect mesh with side gears does.

its a microscopic wheel hop issue affecting one side only

the weight length twistyness of axle shaft
the type of centre
the power and torque applied and the weight of the car and its distribution as you leave the line will all affect how bad or not this is.

you may find something simple like a different tyre makes a difference or a lighter or heavier wheel...anything that changes traction and the weight of the rotating mass on the ends of the axle.... as alternatives to suspension mods.

the same affect can be observed by driving a rear wheel drive transit van up a very steep cobbled hill in the wet....you can get the wheel hop to combine exactly with the rocking of the back of the van and have it lurching up and down about a foot side to side..... fun until you hear ya telly slide into the wheel tub and smash or you start sliding backwards.

as per usual i have applied what i know (half baked theories) about other stuff to this situation so it might all be Bananarama!

i.e if this was a crank with a harmonic vibration caused by using heavier con rods a lighter flyhweel i'd be putting a different damper on. same princepal a rotating shaft with a centre of balance that has forces applied in a cyclic manner. you don't want it to go spinning top mental

Dave

Anonymous · Post by **Anonymous** » Wed Nov 19, 08 10:37 am

No to a heavier wheel Dave, thats unsprung mass and that will effect the stifness component and the damping component.

I think, if Al's damping rate is too high, its overcoming the stiffness of the spring (he has already said the dampers are wound right up). Dampers are velocity dependent and non-linear. Springs are linear. If you have too much damping the spring becomes almost pointless. I think Dave R is closer to the point with an anti roll bar etc. etc. I would go towards a stiffer spring with a matched damping rate, on both sides of the car first and then go from there. From a physics point of view, winding dampers tight up is never going to work.

Dave-R · Post by **Dave-R** » Wed Nov 19, 08 10:54 am

Clivey wrote:No to a heavier wheel Dave, thats unsprung mass and that will effect the stifness component and the damping component.

I think, if Al's damping rate is too high, its overcoming the stiffness of the spring (he has already said the dampers are wound right up). Dampers are velocity dependent and non-linear. Springs are linear. If you have too much damping the spring becomes almost pointless. I think Dave R is closer to the point with an anti roll bar etc. etc. I would go towards a stiffer spring with a matched damping rate, on both sides of the car first and then go from there. From a physics point of view, winding dampers tight up is never going to work.

I would agree with that to a point. But to control the forces applied to the axle by engine torque in the two planes at 90 degrees to each other you need to apply opposing forces to control them. The pinion snubber (or slapper bars) control the rotation in one direction. A higher spring rate or offset mounting position on the right side is needed to control it in the other plane.

Dave999 · Post by **Dave999** » Wed Nov 19, 08 11:21 am

i agree

not a heavier wheel if the issue is suspension related.
harder to control more unsprung mass. A bad thing on a rough road.....?

but the fix will be as suggested a change in suspension

but the busted lockers and quivering are going to be down to shock loads through the axle shaft on the side that has the issue

Alan asked why the quivering?
and got
suspension needs sortin to fix it and based on what you have said do xyz
Alan asked again but why why why the quivering
and i could have said Its quivering because..... you haven't fixed yer suspension

but that seemed a little churlish

Dave

NaughtyAlan · Post by **NaughtyAlan** » Wed Nov 19, 08 5:18 pm

Well took it for an MOT today with Adam and while it was up on the ramp i noticed that the axle has twisted that much under load the axle beam has dented the shocks

There seems to be a lot of clearance between the snubber and the box section i welded on the tunnel, with is now dented.
More issues up front that i don't need with the drivers lower control arm being longer than the other side thus camber kicking out at the lower.
Anyway got it through the MOT and Adams van passed as well after A grand spent on it.
Think I'm parking it up for a bit and see how work goes in the new year and maybe sort a new control arm and call tracks, frustrating as it is i cant spend dollar on the car at these present times.
I am very grateful for all your input to this subject and have learnt from it. Ivor might take you up on that offer thanks mate if work doesn't pick up

Cannonball · Post by **Cannonball** » Wed Nov 19, 08 5:23 pm

NaughtyAlan wrote:Well took it for an MOT today with Adam and while it was up on the ramp i noticed that the axle has twisted that much under load the axle beam has dented the shocks
There seems to be a lot of clearance between the snubber and the box section i welded on the tunnel, with is now dented.
More issues up front that i don't need with the drivers lower control arm being longer than the other side thus camber kicking out at the lower.
Anyway got it through the MOT and Adams van passed as well after A grand spent on it.
Think I'm parking it up for a bit and see how work goes in the new year and maybe sort a new control arm and call tracks, frustrating as it is i cant spend dollar on the car at these present times.
I am very grateful for all your input to this subject and have learnt from it. Ivor might take you up on that offer thanks mate if work doesn't pick up

what is your line off work alan ????

NaughtyAlan · Post by **NaughtyAlan** » Wed Nov 19, 08 5:34 pm

Self employed mechanic with a small garage and a two poster. Repair anything from a van to a Bentley, a lot of it is done on my scanner.
Had an 05 VW Passat in the other day with electronic handbrake and had the same problem as the Bentley with rear pads, so going to have to invest in the resetting tool i think as no other garage has one apart from main dealer.

Cannonball · Post by **Cannonball** » Wed Nov 19, 08 5:42 pm

NaughtyAlan wrote:Self employed mechanic with a small garage and a two poster. Repair anything from a van to a Bentley, a lot of it is done on my scanner.
Had an 05 VW Passat in the other day with electronic handbrake and had the same problem as the Bentley with rear pads, so going to have to invest in the resetting tool i think as no other garage has one apart from main dealer.

shame your not closer al my mate has the scanner that winds the pistons back, also be ready for the calipers rear ones bein knackered if the pads have worn to low,

Pete · Post by **Pete** » Wed Nov 19, 08 5:44 pm

Hope you get it sorted, buddy - plenty of time to plan and prepare for the next season.

I have some spare LCA's but with no provision for ASB...drag cars don't need these either

Ivor · Post by **Ivor** » Wed Nov 19, 08 5:45 pm

I tell you what Alan the smaller mechanics are doing a roaring trade around here servicing and repairing cars that would otherwise cost a fortune at the main dealer...re-setting tool for an electronic Passat handbrake, what's all that about?

I was given a new one by our local car hire company, I couldn't get it started because you had to press the brakes and clutch or something and when it did eventually, it had engine like an old tractor, then came the hill start with that poxy handbrake, what's more it was damned uncomfortable, so I gave it straight back to them..it is without doubt the worst car I've ever driven.

Anyway, if you want those traction bars just to tide you over just say mate and I'll drop 'em in.

Anonymous · Post by **Anonymous** » Wed Nov 19, 08 6:18 pm

Leave my road runner alone there will be nufink left on it soon

Blue · Post by **Blue** » Wed Nov 19, 08 7:01 pm

I had the same problem with the back brace denting the shocks. I had several failed attempts at spacing them back out of the way, in the end I welded in a new cross member and mounted them in front of the axle out of the way. Same thing with the snubber, run it too close to the floor on the street, and it will hit when you go over bumps. Actually smashed a hole in the floor on one of my cars....

Mopar Muscle Association UK

Twisting

RR