MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - STILL BUSTED

We are still off the road. Frontal impct due to a twit doing a U Turn - $8000 worth of damage. Panel damage now repaired bu when they wenrt to doa wheel alilgnment found that I had collapsed the steering column. All very interesting - now explains the damaged elbow - But is it normal for this to happen without the airbag going off?

David
DAVID RICHARDS

I thought that the air bag should deploy if you are doing more than 30 mph and come to a very sudden stop.
Steve Ratledge

The airbag only deploys when the ECU tells it to. There are a number of factors involved in triggering the ECU, decelration of the car being the main one (i believe there is a mercury switch inside the ECU, might be wrong in this) - it has nothing to do with impacts on the steering wheel (decelaration of the occupants), so it is conceivable that the steering collumn could collapse and the airbag not be deployed. Particularly as the 2 systems are completely independant, the SRS set up being electronically controlled and the collapsable steering collumn being an entirely passive, mechanical solution.

The steering collumn is a telescopic tube, with the outer tube being secured with bolts through rectangular 'washers'. They are about 10mm thick and have grooves in the sides. These washers sit within U shaped brackets (with the U facing away from you) and there are 4 small plastic lugs per washer that secure them into the U brackets.

What happens in an impact is that the 8 plastic lugs (4 per bracket, 2 brackets) break, allowing the washer to slide forwards out of the U bracket, the collumn then telescopes forwards, and because the collumn is now free of the brackets, it also drops away into the footwell. It's all rather ingenious really, a good bit of engineering.

But as i said, it is entirely mechanical and reactive to impacts on the steering wheel only. It is therefore a completely separate mechanism to the airbag / pretensioner system.

SF
Scarlet Fever

> (i believe there is a mercury switch inside the ECU, might be wrong in this)

Close, it's an accelerometer which is really a 3D weighing device. The ECU will use this to work out where the impact is, and it will NOT deploy the airbag if you have anything other than a straight front impact as it doesn't know where you're sitting.

How did you hit the stearing wheel so hard? were you not strapped in properly?
Will Munns

<$8000 worth of damage>
was the F on the road in the US???
Blue Max

just saw the e-mail address address...nz!
doh!
Blue Max

Well and truly strapped in - doing about 25km at the time of impact. hit the brakes so hard tha i destroyed the brake light switch.
I simply pushed the steering wheel down its shaft. Other than a sore elbow which should up a day or so later not a scratch on me. - car rather messy. To top it all off the tow truck operator used the rear tie rod to hold the car down and this had to be replaced - insurance complained initially so had to do some hard talking

Car will now be off the road for another three weeks awaiting new column from UK.

Sorry about the USA confusion on my log in - have fixed that

David
David

This thread was discussed between 18/08/2004 and 19/08/2004

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.