Saggy offside rear

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RobC
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Saggy offside rear

Post by RobC »

My BX rides 5cm lower on the offside rear than the nearside. Front height is fine both sides. Tyres all good.

What’s causing this then..? Cylinders or spheres? Plenty of softness still in the spheres.
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white exec
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Re: Saggy offside rear

Post by white exec »

Is it still lop-sided when put at maximum height, and at fully down?
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RobC
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Re: Saggy offside rear

Post by RobC »

Good question. Certainly even when fully down and resting on the bump stops.
will try fully up and report back...
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Re: Saggy offside rear

Post by RobC »

Yes it’s still uneven at full height: only 2cm difference rather than the 5 cm at normal height though.
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white exec
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Re: Saggy offside rear

Post by white exec »

Unusual.
So,
fully down - sitting evenly
normal height - one side higher than the other, by 5cm
full height - same side higher, by 2cm

My thoughts...
- Not likely to be tyre/wheel/trailing arm*, as the car sits level when at Lowest
- * possibly a very badly seized/still trailing arm bearing, preventing one side from moving properly
- possibly a rear hydraulic ram has become dislodged from its prooer seating in the subframe; can happen when depressurising and changing spheres.
Last one:
Jack up the car
Let wheel hang clear of ground
Check that the ram is properly seated.

Another possibility is a problem with the rear anti-roll bar. This connects the two trailing arms, and also feeds height position via a mechanical link to the rear hright corrector. But note that height instructions are fed to both rear rams simultaneously, not separately.
Chris

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Re: Saggy offside rear

Post by RobC »

Thanks for the ideas. Will investigate.
What about mismatched spheres?
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Jaba
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Re: Saggy offside rear

Post by Jaba »

Another possibility, an unwelcome one, rust at the mounting point of the front of the rear subframe.
I know you say that the front end is level but something at the front end too, like a very stiff front strut for example would give same symptom.
Any strange noises on speed bumps/ potholes?
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Re: Saggy offside rear

Post by white exec »

RobC wrote:
Sat Apr 24, 2021 7:24 pm
What about mismatched spheres?
Mis-matched spheres - or even correct ones with little/no/too much gas - will affect ride quality, but not running height. Additional (or less) fluid will enter the sphere to compensate.

Can you post a photo or two of car, in its worst state - on flat, level ground, one pic from front square-on, another ditto from the back?
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Re: Saggy offside rear

Post by Kitch »

That's really odd. It can only be a bent suspension component, or so much corrosion that the subframe is collapsing in, but that's far-fetched.

What datum point are you using? Nothing on the bodywork, right?
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RobC
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Re: Saggy offside rear

Post by RobC »

Turns out I was mistaken sorry: there is also sag in the lowest position: 5cm difference again.
There is an approx 1cm difference in tyre height (they’re both 60s, but the offside one is running slightly lower pressure it seems, plus it’s more worn) but that’s not enough to make the rest of the 4cm difference.
@Kitch it’s measured at the wheel arch, and while that’s bodywork it’s also obvious when you look from the rear, as per this pic:
C50177DE-6E23-4845-9E1A-EC738F1C517D.jpeg
Not the best shot due to the shadow soz but you can still tell it’s clearly wonky!

Front struts and spheres are brand new- it’s perfect from the front. No noises from rear suspension, which is soft and smooth as it should be.
I don’t have access to a lift or garage at the moment, just the street, but once I do I’ll be able to make some more accurate measurements.

Weird.
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Re: Saggy offside rear

Post by Dave_16v »

Is it sagging on the o/s or is the n/s too high. It looks pretty high off the ground when you look at the mud flap.
Is that normal height?
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Re: Saggy offside rear

Post by RobC »

Yes that’s “normal” height. Might be running slightly high but even if so both sides should be level!
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Re: Saggy offside rear

Post by Dave_16v »

Yes, should be level, I just wondered if something was making it go higher on the left although I can't imagine what. It's just that the o/s looks about right. I don't have flaps and perhaps the angle is deceiving. I suppose there is more chance of something keeping the right down than lifting the left in isolation but you never know.
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Re: Saggy offside rear

Post by white exec »

Rob,
Can you post some pics from each side, and the front - at Normal height ?
This will help.
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Re: Saggy offside rear

Post by Kitch »

That's weird. Been over any huge bumps recently? Only thing I can think of would be body corrosion as mentioned, or a bent trailing arm or anti-roll bar. Never seen that before on a BX. Activas, yes (often!) But never a BX.

The anti-roll bar hasn't disconnected at one side, has it? Or the cylinder popped out of its socket?
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