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SHOCK ABSORBERS

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Post by robbymax Fri Jul 29, 2022 4:13 pm

Shock absorbers Do they have to be renewed at a cetain milage, or if and when they are judged to be knackered,and if so who is the judge. My mercedes Devon feels as though it has got square wheels sometimes i know people say it is british roads but traveling in a car is a hell of a lot better so now i have got to look at shocks and tyre pressures, and hopefully improve things, any advice would be very helpfull.
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Post by Caraman Fri Jul 29, 2022 4:32 pm

Someone will correct me if I'm wrong, but I believe shock absorbers are checked at the MOT.  They certainly should be as they have a profound affect on handling.

There is more written on tyre pressures on this Forum than anything else which I have contributed to.  It is possible that your cold tyre pressures are too high.  The best way of checking this is using Tyresafe's on-line calculator:

[You must be registered and logged in to see this link.]

don't be misled by what is written on your tyre pressure label which may relate to much higher axle masses than you have or different tyres

don't drop your pressures just to achieve comfort as that may compromise safety


Last edited by Caraman on Fri Jul 29, 2022 4:41 pm; edited 5 times in total
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Post by Paulmold Fri Jul 29, 2022 4:35 pm

If you're running rear tyres at 80psi as recommended then you'll feel every tiny imperfection of the road surface. If leaking , MOT will tell, then they need replacing.

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Post by IanH Fri Jul 29, 2022 4:51 pm

If leaking, or too rusty as Paul says, they'll fail on MOT.
However that does not mean they're actually working. You'd know from wooly handling and someone following may see wheels bouncing after a bump.
Any doubt, new ones will be infinitely better, your's are almost certainly 12 yrs old and you have some symptoms, so, I'd go for a change. Garage job though.....
They have no defined total life, like tyres for example.....
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Post by Caraman Fri Jul 29, 2022 4:57 pm

Paul is correct.  If you have Camping Pneu (CP) tyres (80 psi on the rear), they are much stronger than equivalent Commercial (C) tyres.  This allows them to be run at higher pressures than C tyres.  This is to compensate for the extra demands placed on motorhomes' tyres compared to commercial vehicles' tyres.  The downside is that CP tyres give a firm ride.  If you were to drop a CP tyre's pressures to those of an equivalent C tyre, you would be compromising safety in the interest of comfort and there would be no point in having the CP tyre.
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Post by robbymax Fri Jul 29, 2022 5:40 pm

Paulmold wrote:If you're running rear tyres at 80psi as recommended then you'll feel every tiny imperfection of the road surface. If leaking , MOT will tell, then they need replacing.
on a MOT test they don't actually run the vehicle down the road so how the hell would they know, as long they are showing signs of damping that is it, so I don't count the value of that, so I am sure KONI would think that laughable, and I ride along thinking it is the British roads and no doubt they don't help , now i don't like to spend money if i don't have to
and Trevor at KONI says they don't fit the shocks at A S they are already fitted on the chassis so do A S specify what they want on, or can they be improved on by someone like KONI.
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Post by Paulmold Fri Jul 29, 2022 5:47 pm

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Last edited by Paulmold on Fri Jul 29, 2022 6:04 pm; edited 1 time in total

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Post by Roopert Fri Jul 29, 2022 5:52 pm

robbymax wrote:on a MOT test they don't actually run the vehicle down the road so how the hell would they know

I don't know how, but my local test station seems to know, somehow. I took my AS Flair there when it was about 10 years old and it failed on rear shocks. I was sceptical because they looked perfect (no leaks or rust) and the van's handling was not particularly bad, for a van. But when I got the old ones off, they were found to be almost completely ineffective!

Most stations seem to have hydraulic shakers on their ramps these days, so it may be that they can see the reaction at the back of the van when these are in use.
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Post by BobK Sat Jul 30, 2022 11:26 am

If the vehicle is up on the ramp, the tester can give the ramp operating lever a quick flip up or down.   If you watch the vehicle closely, it will either briefly rise or settle once.   Any more that once is a good sign of worn shocks.
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Post by Roopert Sat Jul 30, 2022 11:52 am

BobK wrote:If the vehicle is up on the ramp, the tester can give the ramp operating lever a quick flip up or down. 

Ah yes - that must be how they do it. I'm glad they did, because I had no idea that they were completely worn out. They are an MOT-test-only garage - they do no other work, so there was no financial interest to them in failing it without good reason.
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Post by robbymax Wed Aug 03, 2022 8:29 pm

just spoken to Trevor at KONI and he has convinced me that a proper pair of shocks on the back will make a big difference so i have bought them, should be here tomorrow and i think i will fit them myself, will let you know how i get on.
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Post by Minormatt Thu Aug 04, 2022 11:00 am

The MOT test was changed about 4 years ago...

The only official checks on the dampers now is whether there is any visual indication of failure (e.g. leaking oil, or its bent etc).

A shiny new MOT is not evidence that anything on the vehicle is working correctly tbh (except maybe the exterior lights?), just a confirmation that the vehicle meets the bare minimum standards

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Post by robbymax Thu Aug 04, 2022 11:40 am

robbymax wrote:just spoken to Trevor at KONI and he has convinced me that a proper pair of shocks on the back will make a big difference so i have bought them, should be here tomorrow and i think i will fit them myself, will let you know how i get on.
i mentioned KONI because it is the only company i know not because i am on commission
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Post by robbymax Thu Aug 04, 2022 12:27 pm

robbymax wrote:just spoken to Trevor at KONI and he has convinced me that a proper pair of shocks on the back will make a big difference so i have bought them, should be here tomorrow and i think i will fit them myself, will let you know how i get on.
i mentioned KONI because it is the only company i know not because i am on commission
hi [You must be registered and logged in to see this link.] sounds like you have experience I just wanted to know if changing the shocks could improve the ride, so in the end I thought do it and see, my KONI active suspension units have arrived and I am putting them on so I can see how they go on my trip to Deepdale and because I have spent £300, nobody is going to believe me when I say they are fantastic [I HOPE] because I do not want to look a fool I have just had my 80th birthday and I am not going start telling porkies now
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Post by Minormatt Mon Aug 08, 2022 10:49 am

No direct experience, but I do a lot of work with Transits as a second job, and MOT 10-20 vehicles a year so keep up to date with any changes.  I also spent 2 years as a Chassis Engineering Lead at JLR Gaydon (that was a good job!) so have some idea about vehicle dynamics (although that was learning by listening to others rather than direct experience)

If your dampers are worn out, there are several different handling experiences... every so often I see a vehicle on the motorway and a wheel is bouncing rapidly up and down - this would be a dead damper and could be what your describing as "square wheels".  More often though it feels like the car is less stable/attached to the road than it should be (and is often worse in one direction or the other) or can get bounced around by pot holes or road imperfections.

So changing worn dampers can massively improve the feel of a vehicle!

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Post by robbymax Tue Aug 09, 2022 10:59 am

My KONI's are on looking forward to our trip to Deepdale, hope it makes a difference, now changing them was a small problem drivers side the bottom bracket was bent and must have effected the old shock, but a big hammer put it right no problem. The new KONI's look good pity no one will see them I just hope I have not wasted my money but the old shocks were judged to be soft but still working. Now just got to change a roof vent for an extractor fan my son had it spare after fitting aircon, I can pick up 12 volts from a ceiling light only 9 in away so now just waiting for SGB to do the scaffold and we are getting up there. Well Deepdale on Monday can't wait, wonder what we forget  I will let you know
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Post by Roopert Tue Aug 09, 2022 11:18 am

robbymax wrote:Now just got to change a roof vent for an extractor fan my son had it spare after fitting aircon, I can pick up 12 volts from a ceiling light

I would check the power consumption of the fan, as the one that I had in my last A/S van took a ~lot~ of current at startup on max setting. You may find that the ceiling light circuit will not supply enough current (when the ceiling lights are on).
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Post by robbymax Tue Aug 09, 2022 1:45 pm

Roopert wrote:
robbymax wrote:Now just got to change a roof vent for an extractor fan my son had it spare after fitting aircon, I can pick up 12 volts from a ceiling light

I would check the power consumption of the fan, as the one that I had in my last A/S van took a ~lot~ of current at startup on max setting. You may find that the ceiling light circuit will not supply enough current (when the ceiling lights are on).
roopert checked the power consumption of the fan 0.5 /2.5 do you think the lighting circuit will carry that because i am screwed if not.
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Post by Roopert Tue Aug 09, 2022 2:09 pm

The thing that caused me a problem wasn't the full-time power consumption, but the startup surge - but that does of course depend on the size of fan. Mine was a factory-fitted option, but it was still on the edge and blew the fuse occasionally. You can check the wire rating by stripping back the outer insulation to measure the core size. I would expect that it would be Ok, but of course you have to add up all of the lamps running at once and then compare with the fuse rating on that circuit to see if there is any spare. From memory I think each Labcraft-type dual bulb fluorescent takes ~1 Amp.

In reality I don't think I ever had all of the lamps on in my van - but from a safety point of view it's probably wise to include them all in the calculation.
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Post by Caraman Tue Aug 09, 2022 2:55 pm

This might be an excuse to change to LED bulbs if you don't already have them.
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Post by robbymax Tue Aug 09, 2022 7:55 pm

Caraman wrote:This might be an excuse to change to LED bulbs if you don't already have them.
Hi took me all afternoon to get the opening cleaned up so before i fit the the fan, i stuck a clamp meter on, soft start on low at 0.5 rising to 3.0amp on fast but that was too fast and noisey but 1/2 speed was good the lights 2 prong fluorescent and there are 4 of them so i think i will take your advice and change to leds but i shall to have to change the inside fitting and get rid of the choke, but can i get a ied to fit the little tube fitting ?
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Post by HairyFool Wed Aug 10, 2022 4:24 pm

The basic shock absorber test is the rebound test. On a CAR if you lean on a wing to push the wing down and then release it it should rise back up to the resting position and stop. If it rises above the rest position and then drops back to the rest point then the shock absorbers have failed. 

The heavier the vehicle the less practical this is but it should be possible by standing on the door sill and then step of to get some idea as to how effective they are. The name "shock absorber" is a bit of a misnomer as that is really the job of the springs, the proper name is a "damper" in that it restricts the oscillations of the springs and stops resonation and rebound.
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Post by Dave 418 Thu Aug 11, 2022 7:50 am

When I was working on the buses we had an issue with shock absorbers. We changed front shock absorbers because one was leaking. Very soon after this the same bus had vibrations through the steering on rough roads. 
We went through everything we could think of but found no fault but our boss said we should try changing the shock absorbers again. 
We could find nothing wrong with the ones we took off but the fault was cured. Obviously faulty new parts.
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