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Bonnet Opens on Bumpy Roads


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Does anyone know why my bonnet springs open if I hit bumps in the road? The spring on the bonnet looks OK as does the retainer in the latch. Could it be that the rubber 'bump stops' that support the two rear corners of the bonnet when shut need adjusting? They seem tight and the bonnet is flush with the surrounding bodywork.

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Dont mess with this before getting some foolproof way of opening the bonnet if it gets jammed.

 

I'd guess that the tapered "arrow-head" does not go right past the lock-arm that is moved by the release cable.

Tts just being gripped by the sideways spring pressure.

 

Needs adjusting so its longer. Make sure its in the middle of the hole.

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Paul

I'd try winding the two corner bump stops down a couple of revolutions and try again.

 

Check that the " screw " end doesn't foul anything in the engine bay.From memory...failing slowly at my age.. I seem to recall chopping a bit of the windscreen wiper side to adjust clearance.

 

This may be just enough to allow the bonnet pin to fully engage i.e with the latch closing, fully above the base of the cone shaped pin.

At the moment It seems as though the cone is being pinched/partially trapped by the latch and the first speed bump / pot hole does for it.

 

At word of caution before proceeding.Check the condition of the release cable and how secure the screw,holding the cable, is.If you don't have a secondary bonnet release cable/ system fitted...I suggest fitting one NOW !!

Any TR owner who has been unable to get their bonnet open, will recount the hours of endless fun that can be had getting it open.

 

If the shut lines look horrible, as you adjust the bump stops,you can adjust the length of the bonnet pin.It's a fiddle but measure the start length first, release the lock nut inside the spring and use a stout screwdriver to wind the pin either in or out.

 

I found it easier to remove the pin assembly from the car, having marked it's position on the bonnet itself.I used a valve spring compressor to squeeze the spring clear of the lock nut.Wear safety goggles, the spring packs a punch !

Reassemble with plenty of grease and refit.

 

Bob

Edited by bob-menhennett
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Hi Paul,

mine has started doing this recently. It did it once a few years ago and I found the centre pin in the bonnet springy thing had unscrewed - easy to sort.

However my recent bout of happenings (or openings) are caused by the lever, that holds the centre pin in place, not closing fully after an opening event.

I have a secondary release that if used tends to not return fully.

 

Clean the whole mechanism then re-lubricate.

Make sure any secondary opening mechanisms are working as well as could be expected.

 

Roger

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Paul,

 

Don't adjust the bonnet buffers/bump stops if the bonnet sits correctly when closed.

The spring mounted bonnet pin can be adjusted for length by untightening the lock nut up against the bonnet panel and screwing the pin in or out. You may need a screwdriver to wedge open the spring to fit a spanner over the lock nut.

(As Guy's link suggests:) In your case I would first put masking tape or similar over the hole where the pin engages and lower the bonnet to mark the tape. Adjust the whole plate that mounts the pin to the bonnet until this is central over the hole. Make sure the release cable works and fit a back-up as suggested.

In your case keep unscrewing the pin until you get a satisfactory 'click' when the bonnet is fully closed.

 

Despite all of the above, I managed to get the bonnet stuck shut and both release cables worked but failed to release the bonnet. You will only ever make this mistake once. IMHO it is better to be too loose than too tight.

 

Nb. the safety 'hook' as fitted to TR6 and replacements is not there to stop the bonnet flying open on the move. It is there (and recommended) to stop the bonnet releasing in a head-on crash and being forced through the windscreen with obvious potential consequences to occupants.

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Hi,

 

Just a question of adjustment, OR the arrowhead is tapered. If the bonnet has no free move or is not protruding, the bump stops are OK.

Happened to me last year, due to a misaligned and 50 years-old arrowhead.

Do the adjustment by very small increments AND with a safety opening device installed.

 

Badfrog

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Hi Paul,

I had exactly the same problem ever since completeing the Resto (see my previous postings)....2 miles and Pop, 2 more Miles Pop, 300 Yards Pop....of all the problems, engine rebuilds, fuel lines, etc etc etc, this was the hardest to rectify. I tried everything, even a new catch and it still didnt solve it.

 

In the end the bonnet springy thing needed an amount of packing under the bonnet springy thing as it was not locating paralel to the catch. I'll take some pics of it and post later or tomorrow. It is now sorted and doesnt pop anymore! Also make sure you have the rubber wedges fitted to the sides to stop sideways movement of the bonnet

 

One word of warning as everybody has said....make sure you have a secondary method of release, I suffered the bonnet stuck down phenomenom, and it aint pretty!!

 

Cheers for now,

Simon

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The ideal time to sort this is before you have fiited the engine.

You climb in and shut down the lid. Now you can see what happens and adjust as required.

 

Have a socket with you just in case it jams.

 

Of course you need to take the lid off to put the engine in.

I put 1/8in jig pins through mine so as to get the hinges back in the same place.

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There is a lot of adjustment of the bracket which bolts to the bulkhead and holds the entire release mechanism.

This needs to be reasonably correct up/down before fine tuning the plunger/mushroom.

Alan's suggestion is ideal but probably not an option for most of us.

If you have any doubt about the pain of a truly stuck bonnet you can relive my nightmare here:

 

http://www.tr-register.co.uk/forums/index.php?/topic/39654-providence-tempted-bonnet-jammed/&do=findComment&comment=312275

 

It is easy to see why rally cars replace the bump stops with quick release fasteners to avoid the whole scenario!

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Mine are LHD, but my driver's got stuck due to a bad repro cable sheath. Had it open in 10 minutes with a long screwdriver through the bulkhead opening where choke and heater cables go. With someone pressing down on the bonnet directly over the latch it was easily released with the screwdriver. It happened at a show 125 miles away, and I had to do it again when I got it home, daughter helping that time.

 

So at least in the LHD world, no need to do any body piercing for the sake of a backup release mechanism ^_^

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Hi Paul,

 

Your car was specified with the engine diagnostics & maintenance system, the mechanical brain has obviously decided its time for an oilchange or other maintenance and is automatically opening the bonnet to signal to you that it's time to get your hands dirty.

 

Does anyone know why my bonnet springs open if I hit bumps in the road?

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Dont mess with this before getting some foolproof way of opening the bonnet if it gets jammed.

 

 

A quick and easy emergency bonnet release can be made using a cord. I used a piece of woven nylon, when fiddling with the same problem. Tie it round the release arm and route it round the brake master cylinder and then thread it down through a convenient hole into foot well. A good tug should pop the bonnet. On my list of things to do for some years now is to replace this with something slightly more spiffy.

 

Mike

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It's crucial to get the alignment of the arrowhead correct or you can have the bonnet jam and even if you have an emergency release it won't necessarily work. Happened to me when the locknut wasn't fully tight and it moved.

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Interesting that the answers are more about the thing sticking*, rather than popping open when not requested to do so.

 

Looks like you have discovered another way to unstick the bonnet when jammed. Find a bumpy road.

Think Roger, paul, BF and Alfietom have given you enough info to sort it out.

 

* my answer was a 2" hole in the metal directly under it inside the cab. One of the big Moss plastic plugs fits it nicely. You can also inspect the alignment through it, if so inclined.

During the reconstruction, bonnet adjustment phase, I grew to love it.

latch.jpg

Edited by littlejim
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Nick,

 

That's the steering column with its clamp.

The hole in the release mechanism for the bonnet pin is to the left of the hole partially obscured by a heater hose.

As Jim says you can reach the bottom of the bonnet pin with a long screwdriver and force it free if it is stuck, or you can release the mechanism if the cable(s) don't work.

I guess this is the ultimate safety access hole.
As Jim says, it also allows you to see if the bonnet pin is actually in the centre of the hole as you close the bonnet.

Edited by Paul Harvey
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Thanks Paul, you've answered it for me.

Crummy camera angle didn't get the bottom of the bonnet catch.

Haven't had to use it since the rebuild, but paid for itself while I was setting the bonnet catch up during the rebuild.

Having the seats out made it easier and quicker. Think the photo was after the seats went in which makes it a bit more back cricking.

Edited by littlejim
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  • 3 years later...

I tried for a long time to cure this problem on my TR6. Tried bonnet realignment, new guillotine catch etc. but the problem kept recurring. I might have finally fixed it by totally degreasing the mushroom head on the spring loaded striker, then filing the flat top that engages the guillotined catch perfectly flat. It seems use over the past 47 years has worn the flat mushroom head top into a more rounded shape. Just tried it over my local speed humps, that normally spring the bonnet, and it holds fine.

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I tried for a long time to cure this problem on my TR6. Tried bonnet realignment, new guillotine catch etc. but the problem kept recurring. I might have finally fixed it by totally degreasing the mushroom head on the spring loaded striker, then filing the flat top that engages the guillotined catch perfectly flat. It seems use over the past 47 years has worn the flat mushroom head top into a more rounded shape. Just tried it over my local speed humps, that normally spring the bonnet, and it holds fine.

Yes but can you get it open again now ;)

Stuart.

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I can Stuart , but it's definitely a lot harder to do than it was when everything was generously greased.

 

John bonnet straps did cross my mind, it might come to that if necessary.

 

I had a bit of excitement when I floored the throttle during new seasons testing on a local freeway The throttle jammed against a heater hose moved to install a battery tray over winter. The car wouldn't slow down ( I never suspected the arm would be jammed) so I pushed in the clutch in and braked. The unrestrained bonnet flew up while braking and the tacho went off the scale before I cut the engine. That gave me a few jobs to do when I got home.

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  • 3 years later...
On 10/31/2013 at 2:11 AM, Paul Harvey said:

Nb. the safety 'hook' as fitted to TR6 and replacements is not there to stop the bonnet flying open on the move. It is there (and recommended) to stop the bonnet releasing in a head-on crash and being forced through the windscreen with obvious potential consequences to occupants.

All these years I have been thinking "why have a safety catch?  If the bonnet ever releases, the forward motion of the vehicle will stop it from flying up and obscuring your view" Now it all makes sense. Thank you

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