Suspension strut - best practice - technical

[Kojac]

Neighbours car: 

Auris 1.6 VVTi T3 5d - 2008/57 - Petrol

Pre Mot check done: Front pass side suspension strut is leaking oil.

Question: When replacing a leaking suspension strut - what is best practice (why).

Is it correct, that technically - both sides should be changed at the same time? Even if one is undamaged?

Why/Why not. 

The neighbour will be keeping the car for the foreseeable future.

(Anti-rollbar knocking too - work needed there).

[forkingabout]

Ideally they should be replaced in pairs - but its down to the person paying the repair bill.

If one has failed / leaking oil, the other with the same amount of age / wear wont be long behind it. 

Also sometimes manufacturers modify the shock absorber design as was the case with my current vehicle - both front shocks changed under warranty but only one had failed.

 

[flash22]

Best practice change them as an axel pair - if one side has failed it puts extra stress on the other side, this can lead to premature failure, it's the same with the springs - If you change one side only you risk the other failing over time - you end up in a circle

 

If the anti roll bar bushes have gone, it will take out the drop links

[Kojac]

So the thinking is twofold?

A) Replacing just one is likely to create an imbalance in the way the suspension geometry will be affected & unbalanced - under dynamic loads.

 

B) If the design has been modified or changed - then you effectively have two different products - responding out of sync / unison - and so can start impacting the rest of the worn joints / coupling's  and bushes. This imbalance will be transmitted to other joints in the damping/steering assembly causing premature failure.

C) Could affect braking performance? 
 

Are there any other considerations that i've missed?

 

[Stivino]

8 minutes ago, Kojac said:

Are there any other considerations that i've missed?

Although it's best to replace both at the same time, for one reason or another, that doesn't always happen. 

So, It's possible that the other side has already been changed. I would look at it before making your mind up how you are going to proceed. 

[Mooly]

I think I would be just looking to replace the leaking one. Talk of 'matching dynamics' by replacing both is all well and good except for the fact that it would only matter if the left and right wheels encountered similar road defects and road rolling characteristics at identical times... which they don't. Each wheel is constantly doing its own thing all the time. 

The last time I had shock replaced (also front passenger side) was on my Corolla TSport when it was around four years old. I kept it another four and never had any issues at all.  

  

[TonyHSD]

You can only replace the faulty one with using the same oem shock absorber if the other one is still the original, when the car is old like in your case, if you find a used one from same make and model you can just buy it as a set and replace it and match the old but good one from the other side, or perhaps change both sides with new. For the stabiliser bar bushes change both sides together with the links. 👍

[Kojac]

Honing in on the technical angle:

As each wheel has independent damping through its own strut, why oh why do some recommend changing both at the same time.

As Mooly mentioned above - the wheels will not be encountering the same realtime damping when in use (other than speed humps perhaps). They work as independent units.

So here it is -

Assuming that the replacement is the same product as the undamaged one - why is it still considered 'best practice' to change the pair at the same time.
 

What is the technical reasoning behind this?

 

 

 

[TonyHSD]

27 minutes ago, Kojac said:

Honing in on the technical angle:

As each wheel has independent damping through its own strut, why oh why do some recommend changing both at the same time.

As Mooly mentioned above - the wheels will not be encountering the same realtime damping when in use (other than speed humps perhaps). They work as independent units.

So here it is -

Assuming that the replacement is the same product as the undamaged one - why is it still considered 'best practice' to change the pair at the same time.
 

What is the technical reasoning behind this?

 

 

 

While Mooly is right about that each corner has its own things to do when braking and accelerating most of the times both sides will experience same or similar dynamic forces, because the wheels on both sides are the only points of the car that made contact with the road and they are directly connected to the suspension (shocks) if one or the other is unequally worn out will create imbalance between both sides and car may loose straight directions especially on hard braking or hard acceleration. If you ever seen a car with bad shocks driving near you and you noticed how the bad side jumps off the ground constantly and loosing traction and the whole car is jumping, in extreme situation or at higher speeds you may easily loose control and crash. The advice is same as for the tyres, both sides always with some exceptions. I had done change with oem used one successfully and it’s something that I recommend for old cars , but if you able to source a good used genuine part., for me was easy job and the part was good., picture below. 
If not just get new both sides. Original Toyota shocks are not expensive, check online and with dealers, eBay too. 

[Kojac]

So basically it comes down to this:

Replacing both at the same time, is good engineering practice. 

Upon hard acceleration or breaking - it help keep the steering true, as the struts ultimately transfer the load of the car through to the tyres. 

I think that, if the car is to be kept for considerable time, it makes sense to change them both simultaneously. 

I would ask the community:

A) What additional parts would need to be ordered (in addition to the struts themselves) - to complete each swap.

B) Where can I find the relevant torques required so that the jobs a goodun' '?

 

Edited October 19, 2021 by Kojac
Michael Myers

[Matty.g92]

I would only ever change the one that's failed, chances are the other one could go on for years. I've not had a car come back for a second strut after changing one side. 🙂

[Gerg]

I had some Toyota warranty work done on our Mk2 Auris (for a suspension noise), this was replacing the strut top  bearings, as per a TSB.  Even though the car was low mileage and about 4 years old, the main dealer cut the anti-roll bar drop links off with a gas torch, as they couldn't get the nuts off (or maybe they couldn't get them off easily enough?).  So new drop links had to be sourced (from another dealer) before the job was finished.

If you can get some penetrating oil on these fasteners a few days beforehand, then this may not be such a problem for you. Getting the old drop links off, especially if intending to reuse them, could take time and a bit of patience.

The dealer missed off a part (a weather-sealing washer) on reassembly.  I noticed this just as I politely asked to see the old, replaced parts - the washer was still attached to one of them!  It was easier to do the job again myself, rather than go through all the faff of booking, waiting, courtesy cars etc.  It was quite easy, but all the 'difficult' fasteners had recently been undone once by them, so that wasn't any surprise.