So I decided to drive Katie to work last night and on my way home today I decided I'd let her breath a little the last half mile or so before my exit. The instant we crest 130mph her hood decided it wanted to come unlatched. Anyone else have this happen? It is quite a surprise when it does and very tense until one slows down enough to know that the bonnet won't part ways. What can be done to fix this problem?

 

How did the bonnet unlatch ? Did the lever inside the car drop down allowing it to unlatch ?

Anyway, the bonnet should have a safety catch that won't allow it to come fully open...

Does your car have the safety catch ?

 

Unless you were doing 130mph in reverse then there is not much danger of a front hinged bonnet flying open.

I would suspect that the bonnet was not fully latched closed.

Grease your 2 latches and work the lever, if possible have a friend do this whilst you do a visual check the all is moving as it should.

When you close the bonnet let it drop the last foot or so, to fully engage.

You may have a broken latch mechanism, spring etc but two is highly unlikely.

 

the bonnet came fully unlatched although the handle was still in the latched position. im not quite sure how it happened as everything seems to be functioning properly and smoothly. the safety catch is there but didnt catch as the hood actually opened about 8 inches or so. once i slowed the hood dropped back down and i just reset the latch handle and all was well. now what im unsure of. is there another way i should be closing the hood? i just set it down easily until the safety catch hits then it pulls the rest of the way down via the handle. that would seem to be properly latched correct? thanks chaps

 

Perhaps I am off the wall here, but when you pull the release handle to pop the bonnet, are you able fully return to the rest/closed position? Remember to re-open before attempting to close the bonnet.

So, when you have opened the bonnet, now push the handle back to its normal closed position. Does the mechanism move?

Hope this helps.

NOTE this post has been heavily edited by myself due to the fact that I got the wrong Year.

Sorry about that.

 

Assuming Katie is an old girl (I think I remember 80's vintage from another post) the bonnet does not slam shut like "normal" cars and the bonnet release lever is not on a spring return, it has to be pushed up manually. The XJS only got a "normal" slam shut bonnet from 94 or something. If you return the release lever to it's closed position, then try to close or even worse slam the bonnet shut, you just get a solid thump, the bonnet doesn't close, and things get bent. (I've seen someone do this at a car show)

SERE --> your procedure for closing the bonnet sounds exactly correct, as per the owners manual.

All of this however doesn't get us closer to how the bonnet managed to come open in the first place..... SERE, as your bonnet catch stayed closed (and didn't fall down towards your feet) yet the bonnet came loose.... the only plausible way I could think of would be if the bonnet hooks (one per side) were too far towards the front of the car, and they came out of the catches. I'll take a picture of mine tonight and we can compare (although to be fair, I've never had my XJS up to 130mph.... I think a lot of other things would go wrong before I got there, but anyway)

As for the safety catch, I don't know if this is a common problem on XJSes but mine has a "cunning modification" --> a piece of extra metal pop riveted in place. It looks like without this extra piece the safety catch could easily bend the piece of the scuttle panel it connects to and become inoperative. I'll take a picture of that tonight too and post. In the mean time, try and drive less than 130mph !!

 

SERE and anyone else. Ignore my post no 5 above. At 130 mph I had not realised we were talking about a 20 odd year old car.

A case of finger before brain, I'll edit out the duff bits.

 

Ok SERE, let's see if any of these pics help for comparison to your car.

First of all, bonnet catch with lever in OPEN position under dash



Then bonnet catch with lever in CLOSED position



(actually not a lot of difference)

Now the overlap between the bonnet hooks and the bonnet catches. My bonnet hooks are covered with green heatshrink as they were rattling a bit.



Sorry it's not a great picture, I was trying to hold the bonnet open and focus, etc, etc

This was where I proposed earlier if you didn't have a lot of overlap it may be possible for the hook to slip out, but looking at it now it seems unlikely

Finally here's the pop rivetted on modification to the safety catch which I was blessed with from a previous owner. Looks cheap and nasty, but it works



Let us know how yours all looks in comparison

 

amazing work men. from memory that all looks about right but i'll head to the garage in a bit to confirm. i really do appreciate the work from you all. It also seems that the hood is now higher in the rear than before, like the latches moved perhaps. I'll take a look and let everyone know!
Edit:
Right, so everything seems to be engaging properly, but my hook overhang is almost nothing. I also noticed that i have the pop riveted safety catch thing on my car. Maybe it was a jag fix? thank you for all the help chaps

 

Hi SERE

Glad it helped. There is height adjustment on the catches, but I don't think there is any back and forwards adjustment on the hooks ? Based on your overlap, or lack of it, do you think it's feasible the hooks slipped out? I would suspect that at 130mph once the bonnet slipped the latches there would have been quite a bit of movement going on from left to right. Probably enough for the safety catch to also miss the "extra" pop riveted piece

 

exactly. the latches visibly moved near 1/4 inch or so. i would imagine that there are tremendous amounts of force at those speeds. the right side did appear to let go an instant or so before the left. i may attempt to install a shim to give more overhang, but im sure that just moving the latches back down and making sure they are very secure will cure the problem. (as for the 25 year old car doing 130, Katie is a runner. she may not win alot of beauty contests but she will run. up until the unlatch and near messing of my pants all was smooth and still accelerating. I LOVE THESE CARS

 

Good info from SARC.

SERE, you could look at it another way, you've got Jaguar's Patent Inbuilt Speed Restriction System (P.I.S.R.S.) Above 130 the hood will open and act like an air brake to slow the car down.

Glad that you looked to have cracked it.

 

At least you don't have an XK150. A bonnet catch failure on that causes the bonnet to come up completely (it's hinged at the scuttle) and wrap itself over the roof. If it's a convertible it tend to punch a hole in the roof.

If you've got adjustment on the hooks then you're all set.

Totalle agree about letting them breathe. Mine always runs better and better if I use it continually and on long runs. It will always idle much more smoothly once it's been given a good hard run.