XK-140 bonnet latch adjustment (coming loose while driving)

Have noticed after the last few drives that the bonnet latch has “unlatched” while driving. Secondary safety hook has taken care of the issue so there’s no catastrophic problem resulted yet, but clearly something is wrong.
When I close the hood (bonnet) pre-drive it feels secure, the latch mechanism seems to be OK, but perhaps there is some fine adjustment I’m missing?

It shouldn’t be doing that, obviously. I’d suggest watching the bonnet catch spring loaded pin carefully as you lower it and it makes contact with the latching plate. If it is sitting centrally (side to side - I don’t think there is any adjustment fore and aft), you are OK, otherwise loosen the three bolts holding the top plate and centralize it. Check that the sliding catch in the latch mechanism is fully returning to its closed position when the bonnet cable is released.
If the bonnet is popping up whilst driving, the most likely cause is that the bonnet pin is not going down far enough to engage fully. Try lowering it a couple of turns by undoing the locknut and turning the pin downwards so it engages more fully with the catch.

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Hi Brandon. I think the male part (whatever it’s called) on the bonnet is not engaging fully. Make sure the spring on the receiver piece is connected and moving freely. You should be able to screw-out the male piece so it engages fully. If you screw it out too much you will be able to move the bonnet up and down slightly.

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slight adjustment as others described…however–note the many cars of the day, and now, with bonnet leather straps–it was / is obviously a problem. I use a 3/8 strip of Velcro tape…thru the lowest part of the grille…(one vane), and around the chin. Risk solved…unobtrusively. You can even color the velcro strip…car body color.
Nick

Thanks for the responses, that’s pretty much what I was thinking but wanted to make sure I’m going down the right track. Didn’t realize anything could be adjusted left to right so that’s good to know as well.

IIRC, XK-120’s didn’t have the secondary catch, thus the leather straps, or more creative solution like yours, were sort of a “must have”. For the 140 Jaguar added a secondary safety catch so the leather straps should be unnecessary, and most 140 or 150 with them are just done for aesthetic reason.

I may look at the velcro method as a 3rd safety solution that is less obtrusive/expensive than the leather straps.

Nick,
I’m sure you have confidence in the Velcro tape, but I would be hard pressed to think that at speed Velcro tape would secure the bonnet.
Alan

IMG_2635

The most common method is a cat (or small dog) collar with a lever type catch. I keep a picture of an aluminum XK150 bonnet neatly folded over the wind screen to remind me to use it.

Brandon:

Not sure about the early cars, but my '53 120 has a safety catch. As Rob pointed out some time ago, “bonnet flyaway” it appears to be a problem more associated with 150s than 120s.

Chris.

Velcro and the 120: .i am no engineer…but I use 1 3/4 inch wide velcro tape…overlap it about 2.5 inches…and I can not pull it apart in a shear direction–hands in the loop. It would be easy enough to put a lbs test on it…You may be right…maybe I will add a second strip…the force to separate in shear is based on square inches…and a note;;hook and loop degrades of multiple uses…so a new strap after 6 or so separations is a good plan. Probably would not hold at 100 mph…I wonder how much upward wind pressure in on the bonnet, when fully closed position at 60 80 100 mph. Maybe nylon rock climbing web tape for quick draws—would be the way to go–I have some…the trick is how to fasten the ends–hmmn…headed to my rock climbing gear for quick draw webbing.
Nick
Nick

Here is a picture from the bottom with the latching pin engaged and captured by the lever.
IMG_20211105_163114804

Here is the latching pin nut for adjustments.

All XK120s had the same catch, hook and striker assembly with the safety hook.
I haven’t had it come loose ever at up to 90mph.

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I think Rob’s photo shows pretty clearly that if the latch is adjusted properly, there shouldn’t be any problem.

but–begs the question…on the 120, why so many leather bonnet straps…? (back in the day–when not done just for a “look”.

Nick

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I’m really wondering now where I got the impression XK-120s didn’t have the secondary safety catch… I was certain I’d read that was why so many had the leather straps.

Me too - are the 120 and 140 latches different?

Here is what I believe is the standard catch hook on my Nov '51 car.

There is no separate part number for the hook, it was all part of the BD.2951 Hook and Striker Assy., and this is the only part number shown for all 120 including the alloy cars.
As this was the first Jaguar model to have or need such a thing, it is possible that the first few alloy cars that hit the race tracks may have had some inferior version, which the racers felt was inadequate or simply didn’t trust it, and they added the bonnet strap?
Later it may have been improved and retrofitted to them. The details of the previous version (if it ever existed) are lost to history.
A bonnet catch on a very early alloy with the starting crank hole is shown on Plate A12 of the manual. The instructions say to pull it forward. I wonder if it didn’t have the wing shaped handle that you push up like on mine?
The alloy cars did have an inferior bonnet hinge, which was improved for the steel cars.

A bonnet strap is not listed among the Optional Extras in the SPC.
I scrolled through some old race photos and it looks like the Silverstone entries and Jabbeke runners did not have it but NUB120 and the LeMans entries did.
I would imagine that anyone who adds one today does so because the racers had it, or it looks cooler than a cat collar. :wink:

OK, well I tried adjusting this, but when the plunger is sufficiently long to comfortably engage the latch, there are no threads left to engage with the jamb nut…
Something seems amiss, but I’m not sure what.




My car’s a 140, so I think there are some differences.
I had a problem here when painting, which turned out to be failed spot welds on the upper nut, shown in the photo from above. Once I had that sussed and redid the welds, it worked OK. Yours looks to have some rather ropey welds around this nut, so I wonder if it’s been off and someone’s attempted to reweld it? Certainly on the 140 these should be invisible spot welds holding the top nut to the bracket.
The other photo shows mine side-on. In this position, everything works fine, so you should have similar amounts of thread showing. I can’t imagine why anyone would shorten your pin - I’d check assembly carefully. The barbed head of the pin has to be fully beneath the sliding plate in the closed position, with the plate firmly locking it in position.


edit - sorry, just re-read this and realize that your car is a 140. The hook of the safety catch should be in a similar relationship to the end of the pin as mine is, i.e. pretty much level with the rim of the cup. I’m wondering if that evidence of welding around the pin mount has something to do with this. Remember that the spring should be in compression when the bonnet is closed.

So on yours the top nut is fixed? Is the bottom nut loose, as a jamb nut?
Mine is the reverse of that, top nut is jamb nut, bottom is fixed…

Your hook looks different than mine as well…
Any chance you can check the length of your pin from the bracket?

The top nut is spot welded to the top of the bracket. The locknut is accessed through the coils of the spring, as is usual with a lot of 50s and 60s British cars. In the photo, with the spring relaxed, the spring is loose in its mounts and can be rotated by hand.

Length of pin and cup in the relaxed position:

The car is a June 1955 140DHC, and the latch mechanism is the original.