LS430 and NCT suspension test - air suspension

kevpants

Just back from first nct with my 04 ls430. They failed it on the front axles suspension imbalance test. I was warned the air suspension on these is almost incompatible with the test but I'm wondering the best course of action.

Details were 32mm nearside and 54mm offside. Both pretty soft but its the difference between them they measure and bigger than 30% differential is a fail.

Rashly replacing suspension in one of these is not gonna be my first option here because its bloody expensive and probably doesn't guarantee a pass.

A limo driver who i was chatting to once about these cars mentioned he had multiple fails with the suspension on these and he just asked them to do it again before he left and it invariably passed.

There was damage to a tyre and a loose handbrake to be addressed also so i needed to go back regardless so would chancing my arm and seeing if the suspension passes in the retest be wise? Any recommendations on people who could look at the suspension on an ls and know what theyre doing? Dublin based.

What a racket this is. Ironically they don't test suspension quality, just even-ness. Two busted shocks will pass the test!

Chippy01

IIRC, although the LS430 has air suspension, it also has shock absorbers. The air suspension just replaces the suspension springs that are fitted to other vehicles.
I would think that the imbalance recorded is for your shocks, not the air system.

Sabre Man

I recently replaced air suspension on one side on my 04 LS430 after a pre-NCT indicated imbalance in my front air suspension. The garage said it was possible that I would have to replace on both sides, but we decided to change only on one side at first, which was enough to reduce the imbalance to 28% and pass the NCT.

I wonder if raising the suspension to the high position would make a difference to the test result.

kevpants

Sabre Man wrote: »

I wonder if raising the suspension to the high position would make a difference to the test result.

That's exactly what I was thinking. Even putting it in sport.

I get the feeling if you ran the test 3 times you'd get 3 different results. There's a local mechanic just a few doors up so I'll get him to look at the handbrake/tyre and ask his opinion on the suspension.

I wonder how accurate these pre-nct tests garages offer are? Like can they replicate the suspension test?

Chimaera

Unless the garage has the same test rig as the NCT for the suspension test then they can't replicate it.

The reason for testing imbalance only to my mind comes down to two things:

1. Imbalance between two sides of the car will lead to inconsistent behaviour, especially when cornering. Damper rates control how fast the spring extends/compresses during wheel movement and if this is uneven side to side it'll cause weird behaviour.

2. Measuring outright performance would demand that they have details of every variation of every make and model on file, and have easy access to information on what variation was fitted to an individual car. Quite the task. Plus they then need information on what level of performance is acceptable for that vehicle. It's not that hard for a mechanic to determine if the dampers on a car are on their way out - the tester might still fail the car if (s)he believes the dampers are past it.