Leaving suspension at full drop - problems ?

Leaving suspension at full drop - problems ?

Author
Discussion

GBinUSA

Original Poster:

222 posts

123 months

Monday 22nd August 2016
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Are there any inherent problems that could be caused by leaving both front and rear (trailing arm) suspension at full drop for an extended length of time whilst the car is on axle stands. I'm talking about a few months.

Thanks.

mrzigazaga

18,534 posts

164 months

Monday 22nd August 2016
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Hi mate.

Not 100% but perhaps it could effect the trailing arm mount/Pin in some way...Not sure if it could bend the pin???

calgarytrainnut

44 posts

125 months

Monday 22nd August 2016
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Mine went up on jackstands for most of the winter a couple of years back while waiting for a part. If there are any issues from that, I haven't found them yet.

Cheers!

Michael

mrzigazaga

18,534 posts

164 months

Monday 22nd August 2016
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There you are then...smile

Wedg1e

26,760 posts

264 months

Monday 22nd August 2016
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I wouldn't do it. You may not see any problem but the Metalastiks only have a limited range of torsion distortion before they'll start to tear (which you won't see). I suppose if you slackened all the bolts it'd be less of an issue... but on a trailing-arm car the t/arms would twist in a way that wouldn't do the forward pivot bush any good, IMHO.
All this is why you're not supposed to finally-tighten the suspension bolts until the car is back on its wheels.

I was impressed with my 'new' MOT tester this year who took one look and insisted on jacking the rear of the car at the outboard end of the A-frames so they didn't droop. He also listened when I told him it has an LSD so didn't test the rear brakes independently (the last monkeys never listened).

Mind you he was equally as impressed that the bloody handbrake worked biggrin

GBinUSA

Original Poster:

222 posts

123 months

Monday 22nd August 2016
quotequote all
I suppose I could measure each hub center to the top of the wheel arch with the car on the ground, then put the car on axle stands, and with the wheels off jack up each hub to match the previous measurements, or as close as I can get it without lifting the car off the axle stands. Then place more axle stands under each hub. This would load up the suspension and help minimise any bush distortion or rotation.


Wedg1e

26,760 posts

264 months

Monday 22nd August 2016
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GBinUSA said:
I suppose I could measure each hub center to the top of the wheel arch with the car on the ground, then put the car on axle stands, and with the wheels off jack up each hub to match the previous measurements, or as close as I can get it without lifting the car off the axle stands. Then place more axle stands under each hub. This would load up the suspension and help minimise any bush distortion or rotation.
Could work... how about finding a manky old set of wheels to fit instead (assuming that you just want the wheels off to avoid flat-spotting the tyres)...? There must be some car over your way with similar 5-stud spacing?

GBinUSA

Original Poster:

222 posts

123 months

Tuesday 23rd August 2016
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I want to lift high enough so I can work underneath it during the off season. Just want to be able to leave it up in the air rather than have to lift it and then drop it every session. Granted I will be working on both front and rear suspension, so bushing or pin stress maybe irrelevant.

So, if don't have a lift or a pit how on earth do you torque up the suspension at ride height?. Slightly tighten everything, drive somewhere with a pit or lift and then torque it?.

Edited by GBinUSA on Tuesday 23 August 00:55

Hamish400

274 posts

256 months

Tuesday 23rd August 2016
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To torque up suspension in working position, put axle stand under wheel hub (with or without wheel fitted) and lower car until weight is on axle stand. Torque up with suspension in this position.
Alternatively while chassis is on axle stands, place jack under wheel hub and raise until virtually all weight is on jack, then torque up suspension in this position.
IIf both sides are interconnected in some way eg by a roll bar, put axle stands (or jacks) on both sides and then load up and torque up both sides together as above.

Regards
Hamish

Edited by Hamish400 on Tuesday 23 August 09:45

Wedg1e

26,760 posts

264 months

Tuesday 23rd August 2016
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Drive up onto ramps and tighten one end at a time?

JVaughan

6,025 posts

282 months

Tuesday 23rd August 2016
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Mines currently on axel stands, and will probably remain on them for most of the winter, while I finish rebuilding the brakes.

wouldnt have thought there would be issues.

Wedg1e

26,760 posts

264 months

Tuesday 23rd August 2016
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The design of the suspension bushes is such that you have two tubes, inner and outer. The inner is longer than the outer and in a typical application is the bit that fits between two brackets on the chassis through which a bolt is passed and done up tight, preventing rotation. The outer tube is a press-fit in the suspension arm (being shorter as the arm is narrowed to clear the chassis brackets).
The gap between the tubes is a solid cylinder of rubber which, in a 'fully-bonded' bush is (effectively) glued to the outside of the inner tube and the inside of the outer tube.

As the outer tube can't rotate in the arm and the inner tube can't rotate on the bolt, the only way the arm can move is by twisting the rubber. Once you unload the arm the rubber twists back to its starting point. There's a limit to how far the rubber can distort before it either tears itself or breaks free of either tube, which is why you don't tighten the bolts until the car's on its wheels, because now you have the maximum amount of arm rotation in either direction before the rubber runs out of range.

If the rubber tears free of either tube then it'll appear to be a sound bush other than it can no longer deform and return. In theory the suspension designer takes the 'compliance' of the bush into account when doing the spring and damper calculations... in theory. In practice probably not, which is why even with a torn bush you probably won't notice anything wrong downstairs... until the rubber is so knackered from the 'fretting' action that your MOT man spots that your suspension is slacker than my ex-wife and you end up on the internet grumbling about TVR build quality and the poor quality of Far Eastern suspension bushes.

Some bushes are 'semi-bonded', which means that the rubber is (usually) only glued to the inner tube and is an interference fit in the outer tube. What happens here is that as the rubber is a tight fit in the outer tube it will still act as a normal compliance bush up to the point you exceed the force necessary to unseat it, at which point the outer tube rotates into a new position on the rubber... which is what will happen to these bushes when the suspension goes to full droop. As you put the car back down the rubber twists back the other way, the outer tube breaks free and finds its original position. Ironically semi-bonded bushes are therefore happier to cope with 'drooped' suspension... and in my experience a lot of the bushes you buy now (Far Eastern made?) are semi-bonded, probably as it's simpler/ cheaper to make them that way.

Sorry, here endeth tonight's lecture biggrin
Tomorrow: Rachel Riley. Will she, and if so, when? whistle

tvrmk363

375 posts

128 months

Wednesday 24th August 2016
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I have stored my cars on stands during the winter months for years, November through April and have never seen any issue with them.
Years ago with bias-ply tires you would get flat spots if they sat for an extended period. Radial tires don't do that.
You don't have to store batteries up off the ground either. The wood box's went away long long ago.

adam quantrill

11,535 posts

241 months

Thursday 25th August 2016
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Letting the front droop puts a lot of stress on the ARB drop links that they could do without.


magpies

5,129 posts

181 months

Thursday 25th August 2016
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judging from the comments above - there are some for and against - basically if you are worried then jack up, remove wheels and tyres and then slacken off the suspension fixings. This should only take half an hour. When putting back on the road then jack up each corner suspension before tightening the fixings. If you not worried - and the car off the road for a shortish time - then leave everything alone.

GBinUSA

Original Poster:

222 posts

123 months

Friday 26th August 2016
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Been interning reading all the comments and pretty much confirmed my thinking. Short term, not a problem. Long term not so good. I'll go with wheels off and place a stand under each hub, raising the suspension above full drop.

Cheers for everyone's input.

Gav.