Locking bushings incorrectly

[Tony]

Bushings form a connection point that needs to be dampened, these areas are wishbones, tie rods, trailing arms and so on. The bushings absorb energy removing road perturbation's from the cabin.

 

Bushings are a high wear and tear item on any car so it's inevitable your car will experience the need to replace one or more during you ownership of the car.

 

But we have a problem. All bushing replacements require the wheels to be off the ground so that the wishbone or tie rod or whatever can be replaced, this in it's self is obvious but what's overlooked is the method of reinstalling the replacement.

 

For the purpose of this thread i'm going to use an example of lowering coils we fitted to a Mazda MX5. The lowering coils offer a -30mm drop.

 

With the vehicle raised the suspension and satellite running gear are in a position we call "droop".

 

 

To install the lowering coils we need to remove the upper wishbone

 

To the point

This is where it all goes wrong, it seems natural even logical to lock/ tighten the wishbone on re-installation, at the end of the day everything need to be tight, right?..... wrong!!

 

The bushing positions are still at "droop", if the retaining bolts are locked now the bushings will "preload" as they adopted the natural loaded position when the wheels hit the ground.

 

Results

We locked the upper wishbone bushings on droop and now the car is on the Geometry rig. The -30mm drop with preloaded bushings actually displays a -15mm drop

 

Here are the uncalibrated positions with preloaded bushings

 

With the wheels on the ground we released the lock nuts on the wishbones allowing the bushings to unload the preload

 

An additional -15mm drop is observed as is a change in the Geometry statues

 

The moral

Bushings must be locked is their relaxed state, from there any preload negative or positive is by design, locking the bushing on droop is not only dangerous but will destroy the bushing prematurely.

 

Tony@ wim

[Rich]

Great explanation Tony

 

What about the home mechanic though like me...I can't access the bolts to the wishbone once the car is on the ground?

[hms]

Ramps or raise the car and drop the wheel onto blocks to give you extra room underneath.

I've also heard of someone jacking on the hub or wishbone to put the suspension under load. Don't know if that is an approved method tho'.

 

I've heard Tony release bushes that have been tighten'd whilst under droop, there is a hell of a bang as the bush is released!

 

h

[Tony]

Great explanation Tony

 

What about the home mechanic though like me...I can't access the bolts to the wishbone once the car is on the ground?

 

I can't offer a solution for the home mechanic in this situation, only a heads up if you don't follow the procedure.

[Rich]

So in the case of the mondeo (mk1 and 2) do you think this will make the bushes last longer? I personally can't see it happening as they designed them to be vertical...most other cars see to have them horizontally. This is proved with the ST200 as it uses different wishbones to all of the other mondeos and they last for a very long time.

[Tony]

Actual longevity i cannot comment on, what this thread displays is how to install the bushings in a relaxed state and how the industry can easily lock the bushings on droop and preload them.

 

The example MX5 held the front +15mm after lowering, that's a mighty fine load on the bushings at a relaxed state.

[e4tnu]

Great write up Tony.

Now this may seem like a daft question but does this method also apply for installing Polyurethane bushes as well?

[Tony]

Great write up Tony.

Now this may seem like a daft question but does this method also apply for installing Polyurethane bushes as well?

 

Although polly's float to some extent i would still say yes.

[phipck]

great information, i learnt this the hard way when changing the lower arm on my girlfriends mk1 clio, i tightened the bushings while jacked and the car held its height when put back to the ground. thankfuly being so obviously high i reaslied what was needed, but on the mx5 with only 15mm i doubt i would have spotted it!

[Rich]

The height issue, is this only with bushes mounted horizontally?

[jon.l]

This is very interesting, I'd be willing to bet 90% (or at least a high percentage of people out there) do this when reinstalling suspension items.

 

Tony - would you object me posting this on a forum I am a member of?

[phipck]

i had the same issue with my girlfriends clio, when changing the lower arms and locking the bushings in while jacked.

 

it looked like an off-roader when lowered back to the ground. simply dropping onto blocks was enough to get access to the bolts and get it right.

 

its simple things like this that make a huge difference in the safety and road holding of a vehical, great advice!

[Tony]

This is very interesting, I'd be willing to bet 90% (or at least a high percentage of people out there) do this when reinstalling suspension items.

 

Tony - would you object me posting this on a forum I am a member of?

 

Not at all..... Go for it.