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Caution with your bonnet catch
Malcolm Venables reported a dangerous experience with his bonnet catch failing which allowed the bonnet to blow up onto his screen. Here he describes how it happened and recommends the bonnet catch is checked carefully as a service item. (Sep 11)

Malcolm Venables' posting on the V8 Bulletin Board was - having finally got my Factory MGBGTV8 back on the road last year, I have been gradually ironing out all the wrinkles. A couple of months ago whilst driving home from picking up a new computer monitor I had the bonnet fly open. Now I know this is not an unheard of experience, but it did take me by surprise particularly as I make a point of listening for the catch to click home when I shut it. Fortunately it happened as I was leaving a 40 mph limit and on a straight road with little traffic, so I was able to stop the car safely. However the bonnet was now bent back over the windscreen and the roof.

Careful examination revealed that the primary locking mechanism had started to work loose, that is the spigot that screws into a threaded hole in the bonnet and had a certain amount of play, sufficient I suspect to become disengaged with the latch, however I was surprised the safety catch didn't hold it.

I have on rare occasions in the past known the bonnet to pop at low speed if not completely shut, this would always happen very shortly after starting off and would always be contained by the safety catch. However on reflection the MGB bonnet has an aerofoil shape and I suspect that once 40mph or so is reached there is sufficient lift to overcome the safety catch, certainly it is much more flimsy than the one on my C class Mercedes for example.

So the moral of the story is make a careful check of the condition of all the bonnet securing devices and as, with everything else on the car, significant wear is likely after 30 years. I was very fortunate in obtaining an unused heritage bonnet on eBay for under £100 which I thought was a bargain, I have also now fitted a bonnet strap just to be sure!

Editor's footnote: the MGB Workshop Manual AKD3529 covers removing and refitting the bonnet lock in Section
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3
AHA5543
Cup-lock locating
4
HZA4551
Plate-catch
SF604041
Screw-catch plate
LWZ204
Washer-spring
5
14G2444
Pin-bonnet lock
6
4G3676
Thimble-bonnet lock
7
HZA563
Spring-bonnet lock
8
4G2494
Spring-catch plate return
9
HZA332
Catch-safety
PMZ308
Screw-safety catch
10
BHA4338
Nut-anchor
11
AHA5617
Bracket-safety catch
PMZ308
Screw-bracket
PMZ203
Washer-plain
LWZ203
Washer-spring
Source: MGB/V8 Parts Catalogue AKM0039, Section - Bonnet and control details, page 108-K1

R: The Body (on page R2 issue 10 in the 15th edition) and notes that when refitting the lock "ensure that the bonnet lock, safety catch and the bonnet are correctly aligned before finally tightening the securing screws. After assembly adjust the latch pin to obtain ease of closing, lubricate the lock, catch, hinges and check them for correct operation." Malcolm's note is a very useful cautionary tale.
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