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MG MGB Technical - Hood Releasing at Highway Speed

The other discussion on tire balancing reminded me of a problem that developed this summer, my hood pops open at highway speeds (50mph+).

So far the safety catch/latch has kept it from actually opening up into the air, but then I tend to head for the roadside as soon as I notice the hood has popped up out of the fully locked down position.

I've done nothing to the car that I can think of that would cause this this summer.

I've checked the following...
1. Cable at latch has a little play in it so as not to have cable pressure stopping latch from being fully released on to hood locking knob.
2. Cable and handle are fully returning to their position under the dash, and not sticking midway to being in all the way.
3. Latch is lubed and moves freely by hand, so it isn't binding in a release position.
4. I've turned the hood knob (dang I can't think of what one calls the male part that goes into the latch mechanism) a couple turns in (shortening) and a couple turns out (lengthing the knob).

When hood is down it is very securely latched down.

Wiggling the cable handle under the dash doesn't cause it to release.

City driving isn't a problem. Closing hood I just drop it from 1-2 feet and let it latch.

Now that I've balanced the wheels it isn't releasing quite so much as it had been, but it I go over rough roads or too fast it just pops to the safety catch position.

All I can think of is that the front end of the car is flexing too much with road conditions or speed and it flexes the hood latch to a point of releasing hood.

Anyone else have this problem? I cannot see any wear on the male or receptor parts. Latch appears very stron.

Thanks.

BobA
R.W Anderson

Bob,
Its an adjustment issue - try lengthening the probe on the bonnet half a turn.

Good luck.
R Walker

Bob. I had the same problem. Agree with R that it is an adjustment problem. However, in my case, it was adjusted too long, allowing the hood (bonnet) to move up and down at speed and causing it to release itself. My suggestion would be to screw the adjustment mechanism in until the hood will not close securely when pushed downwards, then, adjust downwards until it will just secure itself fully. When John Twist closed the hood on one of my cars, he put his hands about about a foot from the center line and pushed downwards. Told me that was the method he recommended as it was less likely to damage the hood.

Les
Les Bengtson

Bob,

You might also check to see if the spring that pulls the sliding part of the latch is connected properly and is strong enough. I'm not talking about the spring on the hood, but the one on the slam panel that stretches when you pull the cable.

Charley
C R Huff

There is some wear and/or misalignment that causes the latch bar to back off the (top)annular surface of the peckerhead, and/or the bar is not in fact returning all the way to the shaft of same when latched. The last is what happens when it's adjusted too tight; it's still on the radiused edge.
If the underside of the latch bar or the top side of the peckerhead is worn it will do this. If the latch is off laterally, the ph is not bearing against the raised lip of the lower latch plate, which lets it vibrate sideways and unlatch itself. If the pivot point of the latch bar is sloppy, or the bar is twisted, it cants over and presents a non perpendicular surface to the ph. These things are all a result of no lubrication (past or present), accident damage, or bad assembly.
Really makes you appreciate that safety catch and the importance of checking that it is engaged EVERY time you close the bonnet!

FRM
FR Millmore

I have to say, I've never closed my bonnet/hood by dropping it. I always lower gently onto the slam panel they push firmly downwards with both hands, similar to the John Twist method, as described by Les.
Dave O'Neill 2

I've always dropped mine, never pushed. Pushing the early alloy bonnets can dent them I hear, and the steel ones in particular just aren't that flimsy that dropping a short distance will hurt them. Depends how far you drop them of course, 4-5 inches is enough on mine, from just above the safety catch on the ZS which is heavier.

Check the moving part of the latch is coming fully back when the knob is released and isn't hanging up on a stiff cable. Check the adjustment of the bonnet pin by pressing down on the *fastened* bonnet (carefully :o)), you should be able to feel a little bit of free play i.e. fuether movement. After that it is usually down to wear on the bonnet pin, giving it 1/4-turn is usually enough to present a fresh surface to the latch.
P Hunt

I had the hood open at 55 mph on my midget.
$1000 body work later I installed a hidden race pin
I couldn't drive it confidently till I installed this.
The clip to open the hood is well hidden and accesable through the grill


Phil

Dropping the bonnet means you do not check the safety catch every time. Since I work on many cars, I never know how it is adjusted. If it goes on the wrong side of the latch bar one time, it bends and never works again. I hold the safety back, lower the bonnet, release the safety, lift to make certain it has caught. Let the bonnet down and push gently with both hands on the front edge, not the upper surface.

At 16, I had the hood come open at 60mph on my '47 Ford, destroyed it and put a big dent in the roof, but scared me senseful!
I have a Rover 2000TC in my back field that was totaled a week after the guy replaced the screen and bonnet from just this; the total was because he didn't listen to me about the busted seat back catch, just as he did not listen on the bonnet catch.
I have a friend who was driving his freshly painted MGB home the two miles from the paint shop when the bonnet came open - destroyed bonnet, windscreen, and beat him over his head - now he listens!

FRM
FR Millmore

I have a strange way of checking: I always listen for the spring in the mechanism to go "boooiiiing"; it almost sings! If it doesn't do that the latch didn't catch properly.

Willem vd Veer

As others have said, if it keeps popping open, something is out of line. If you slack off the bolts that hold the mechanism on the slam panel you will be able to move it fractionally so that there is more of the latching plate engaged with the probe thing on the lid. If I dropped my lid it wouldn't latch but just spring back up. I push it down with two hands a la John Twist.
Mike Howlett

Seems like we all have our own ways of closing the bonnet / hood.

Mine is to close it gently ensuring the safety catch is engaged properly then use all fingertips & thumbs to press the outer corners down till the catch locks.

Using the palms of your hands on the top surface will dent the bonnet, whether alloy or steel.
Chris at Octarine Services

If it's shut you know the safety catch is engaged! If it has a tendency to go the wrong side of the bar, or baulk on it, then it is way out of adjustment. I also listen to the sound as I drop it, partially shut and hence liable to pop open makes a different sound to fully shut, same with doors. Never had a bonnet pop up in over 40 years.
P Hunt

Paul -
"If it's shut you know the safety catch is engaged!"

Reckon you never worked on customer cars, or cars just back from the body shop, or cars built by amateur restorers!

"If it has a tendency to go the wrong side of the bar, or baulk on it, then it is way out of adjustment."

Or there's some or all of the pieces missing.

All being true but that doesn't straighten the bonnet out, or fix the windscreen or the crash damage. It also does you not much good in court, as they contend that because you changed the spark plugs, you are a professional and "should have known that the latching mechanism was not correct and posed a substantial hazard".

In recent years I've seen more safety catches that do not work than ones that do.

FRM
FR Millmore

I had a friend who was driving at 60 mph on the highway when his hood let loose, clearing the windshield and hitting him and his brother squarely on the head. They were lucky enough to just barely see enough to get the car to the side of the road. When I shut my hood, I close it with a hard push at the front center of the panel. After this, I attempt to lift the hood by placing my fingertips at the outer edges of the hood and lifting up. If it lifts up, I repeat the procedure. Twice I have had the hood unlatch, but both times the backup safety catch has saved me from total failure, allowing the hood to rise only about 1". RAY
rjm RAY

I just reattached all those bonnet latching parts as part of my restoration. The first time I thought I had it right but on starting the car it did pop open. I had to adjust the locking pin so it was longer and was definitely engaging.

As for closing it I also go by the noise. It definitely makes a boiiiing when it goes properly. I then also try lifting it back up just to make sure. I usually close it by pushing down on the very front edge just to the side of the centre where the bump above the badge is.
Simon Jansen

I had this same thing happen to me last summer. I couldn't figure out why it went out of adjustment nor why with just a little bit of tweaking to make the pin longer or shorter the latch would not engage.
Referring to http://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=29049
My thimble is not perfectly round (is is suppose to be?) and the spring was not properly seated into the thimble. Once I firmly seated it into the thimble it was easy to adjust and close firmly.
Thanks to FRM re If it goes on the wrong side of the latch bar one time, it bends and never works again.
This is another problem I had. I guess when trying to get the darn thing latched I pushed too had on the hood in the wrong place and dented it as well as bent the safety latch, also denting the under side of the hood. To fix this I re0bent the safety latch and put a couple of washer on the screw towards the engine. Now it drops from a few inch's and works just fine or close softly and careful push on the outside front edges of the hood.

Hope it helps
MGBV81

Note also that many cars are missing the 4 rectangular rubber blocks (hood buffer by Moss) the bonnet rests on in the wing gutters. If these are missing and the latch is not just right, the bonnet vibrates side to side which can cause the latch to undo. The bonnet should just touch them with little or no pressure when the latch is adjusted correctly.

All very similar to the time the fifth wheel on my big truck unlocked as I made a U turn, and dropped the loaded (22 tons of scrap) trailer crosswise in the middle of the highway at night - on a blind hillcrest/curve! Turned out the DPO had assembled the latch with the springs positioned incorrectly. No lights on the trailer since it unplugged, and hydraulic oil everywhere since it broke the wetline hose off. Rough night!

FRM

FR Millmore

Well thanks for all the recommendations, and of course all the horror stories. I don't need the hood to hit me in the head to learn I have to pay attention to the problem.

But, BOY! That's a lot of responses to my little problem, but by the stories it appears several have experienced this little problem.

Fortunately its winter, usually below 32F/0C and usually a good foot of snow around, so I won't be driving for months.

Here's some additional comment/clarification.

Oh, and of course, being new to owning MG a few years ago, I DID NOT know how easily a hood can go concave when pushing the hood closed. Never did get that pucker out.

So...

When hood is closed it is Very Sound, and secure. Yes I can push gently on the corners of the hood and it does flex down a 1/2" or so, which I assume is the spring on peckerhead compressing. One cannot bounce the car enough or push the hood or the fenders to get the hood to release, only highway speed with a shaking front-end or rough road releases the hood. The car does have the little black rubber bumpers along the side of the hood. Adjusting the peckerhead up or down changes the tension on the hood when closed, but does not make any difference in hood popping open to safety latch.

During a warm spell I'll go out and stare at the latching mechanism to watch the locking arm engage the peckerhead (what a name).

With confidence at a minimum, the locking pin on hood through grill sounds the safest way to go.

Now my 58 Ford would never have this problem, as the hood raised from the back, air kept the hood closed. Now there's Physics being applied properly!

Thanks again for all the good advise. I'll pay attention to at least some of it, promise!
R.W Anderson

This thread was discussed between 16/12/2009 and 24/12/2009

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