Bonnet Opens on Bumpy Roads

[ianc]

I am afraid that Paul Harvey is incorrect.  The safety catch, which is basically the same for TR4/4A/5/250/6, is there solely to stop the bonnet lifting when the car is in motion should the bonnet catch be released.  If the bonnet catch were to be released at, say, 100 mph, the safety catch would limit the back of the bonnet lifting by much more than an inch or so - the driver would still be able to see where s/he is going!

If you look at the TR's safety catch you will note that it is a comparatively flimsy device which cannot possibly be strong enough to cater for a frontal collision.

This matter was raised recently in a PQI, and Neil Revington provided a very comprehensive response which states what I have said in my first paragraph (above), and then cites his personal experience of two serious frontal crashes in TRs.  Unfortunately, I have mislaid the email, but I expect Ian Brown &/or Roger Hogarth will see this and be able to insert Neil's response.

Ian Cornish

[Bleednipple]

My 4's bonnet automagically pops open the moment I get onto rough gravel and onto the power, and hence venting excess under-bonnet heat. It's a feature, not a bug. And a lot cheaper than installing those wing vent thingies. 

Seriously though I'm planning to put in a pair of bonnet pins/clips to circumvent the whole stuck bonnet 'mare (sounds like a line from Tam O'Shanter)... although I've not noticed them on too many rallied TR4s so maybe carefully fettling of the mechanism is all that's needed. Decisions decisions.

Nigel

[cvtrian]

11 hours ago, ianc said:

I am afraid that Paul Harvey is incorrect.  The safety catch, which is basically the same for TR4/4A/5/250/6, is there solely to stop the bonnet lifting when the car is in motion should the bonnet catch be released.  

This matter was raised recently in a PQI, and Neil Revington provided a very comprehensive response which states what I have said in my first paragraph (above), and then cites his personal experience of two serious frontal crashes in TRs.  Unfortunately, I have mislaid the email, but I expect Ian Brown &/or Roger Hogarth will see this and be able to insert Neil's response.

Ian Cornish

Ian Cornish is correct, Waldi raised a PQI report regarding this very item, and below is the relevant edited feedback from Neil Revington regarding the purpose and use of the catch:-
 

"Whilst the hook part of the catch is called a safety hook, it is not a safety hook in the manner you describe. I have seen many cars which have had front end collisions and the catch assembly and hook is in no way strong enough to arrest a flying bonnet.  It simply twists and mangles and the bonnet flies up with its back edge above the windscreen. I have experienced this twice myself when w*nkers have pulled out in front of me.  What it does do is stop the bonnet becoming a wing and lining itself up with the top the windscreen as the air passing over it will create lift, obscuring the drivers view should the bonnet not be secured properly and want to open of its own accord.

Most failures of the safety hook are owner induced. I cannot count how many times we have seen catches bent away from the loop it is intended to engage with. This results in repeated bending back to the right place which will inevitably weaken the pivot point. It follows then that if the peening is anything other than super robust, it can fall apart. Bear in mind that the catch should never actually do anything so the pivot should never be under stress. What happens is that insensitive owners who are not fully in tune with their classic car seem to be under the impression that they can simply drop the bonnet as they can with their modern car. This in not the case with a TR and as you both will know the bonnet should be lowered gently, with the safety catch pulled out of the way, checking it is engaged properly with its loop then the bonnet can be fastened by pushing the bonnet down directly above the catch.We have seen them bent side way, doubled over, bent forwards, in fact in any position other than where they should be, no wonder the peening gives out. I accept there are probably some really poor ones out there that have fallen apart with the gentlest of owners who care and pay attention but I bet the majority have failed after a spell of misuse."

This thread originated several years ago (2013) and has come around again. Earlier this year a thread about "bonnet stuck" was as a result of an incorrectly fitted secondary release mechanism which morphed into the design of the original catch and perceived shortcomings, which Waldi followed up with a PQI submission, and the above formed part of the feedback provided directly to Waldi.

Ian