Bonnet support frame brazing in situ?

Rafa · Post by **Rafa** » Sat Jul 05, 2014 4:11 pm

Sadly just failed an MOT due cracking in brazing of tubes at the point they connect with their brackets on bonnet support frame (Part no. C32395). Hopefully the photos illustrate this.

My question is has anyone experience of re-brazing here with everything else (bonnet, radiator, pipes and hoses) in situ, which would obviously be a much simpler job than stripping everything out? The joints are readily accessible from underneath.

I have no experience of brazing/welding, and the garage who raised this issue are worried about damage to surrounding components due to the temperatures involved. They are not E type/classic car specialists and lack the confidence of tackling it. May be there is no easy answer but I would be very grateful for any information or tips to make the job as easy as possible.

Many thanks

https://www.dropbox.com/s/8jusarcoy40qa ... 282%29.JPG
https://www.dropbox.com/s/o6jxwolnnoj6s ... 283%29.JPG

Moeregaard · Post by **Moeregaard** » Sat Jul 05, 2014 4:34 pm

For reasons unknown I was unable to view your photos, but I'm curious about whether the joint failure is from over-stress (impact), or from internal corrosion. As we all know, Jaguar has emphasized for many years that the subframe components are not to be welded under any circumstances.

Since the bonnet frame isn't subjected to the forces the rest of the subframe experiences, the failed joint could probably be re-brazed if there isn't a lot of internal corrosion. I would remove any surrounding components to avoid thermal damage and to make things easier for the guy doing the brazing.

Since all original E-Type subframes are now between 40 and 53 years old, it wouldn't surprise me if the failure yours has experienced is due to internal corrosion having compromised the joint, and all that was required to complete the failure was a bump on the nose. The wall thickness of the Reynolds tubing used by Jaguar is surprisingly thin when new. If you do find significant corrosion, I suggest having a good look at the rest of the subframe. While expensive, the replacement subframes made by E-Type Fabs are absolutely superb and better than the originals.

christopher storey · Post by **christopher storey** » Sat Jul 05, 2014 6:23 pm

I had cracks on the underside of the left hand bonnet frame on my S2 about 3 inches forward of the picture frame . I brazed it perhaps 10 or 12 years ago and have never had any more trouble. There is nothing in the vicinity to hurt with the brazing torch ( except the tube itself ! ) , since the picture frame is of course welded pressings rather than Renold tube

Post by **1954Etype** » Sat Jul 05, 2014 6:48 pm

Should be simple enough. I'd remove the bonnet though.

Rafa · Post by **Rafa** » Sat Jul 05, 2014 8:54 pm

Thanks for the tips, I will feed it back and try find someone local and willing on Monday. Bath/Bristol area if any recommendations are forthcoming?

Rafa · Post by **Rafa** » Sat Jul 05, 2014 8:59 pm

Thanks Mark, no known bumps as far as I'm concerned. Underneath is in very good condition, and almost all of the frame has corrosion free paintwork in good nic. I guess therefore some internal corrosion has happened. Everything seems and looks sound to me but I'm no expert and have to take the advice of the MOT inspector!

It's a pity there is know modern alternative to brazing.

Moeregaard · Post by **Moeregaard** » Sat Jul 05, 2014 11:46 pm

Rafa, Jaguar employed brazing because welding milder steels will result in a phenomenon called hydrogen-embrittlement, due to the higher temperatures needed for welding. Brazing uses brass-alloyed (usually silicon-bronze) filler material that has a lower melting point, thereby avoiding the embrittlement problem.

If you look closely at the failure of your bonnet frame, you'll see that the steel tube has failed, while the filler material has remained intact. Lotus brazed their formula car chassis for many years, and I believe Caterham still use it for the Super Seven.

PeterCrespin · Post by **PeterCrespin** » Sun Jul 06, 2014 2:39 am

[quote="Rafa"] the garage who raised this issue are worried about damage to surrounding components due to the temperatures involved.

From the look of it the repair itself is feasible but brazing requires significant heat over time to get everything up to temp, unlike elctric welding whicg gets hotter but is instantaneous and can be confined to short bursts with cooling bimmediately between. Your garage is probably worried about toasting the rubber suspension bush, as well they might be. I thought I saw the bonnet plug cable in one pic but that ould be moved out of the way.

A good shop will have all manner of welding putty and heatsink/shielding materials, but they will still be nervous with the big 'soft' flame you need for brazing compared to welding.

Pete

Moeregaard · Post by **Moeregaard** » Sun Jul 06, 2014 4:28 am

After a nice Islay single-malt and some more thought, if this were my car I would remove the bonnet subframe and make the repair on the bench. As Peter correctly points out, brazing will require more comprehensive heating of the entire area.

Rafa · Post by **Rafa** » Sun Jul 06, 2014 7:55 am

Great info Mark and Pete, thanks indeed.

christopher storey · Post by **christopher storey** » Sun Jul 06, 2014 7:59 am

Now having seen the pictures, my opinion is that this is mechanical damage, probably the result of someone trying to lift the car with the bonnet frame, and I would be very surprised if it did not repair satisfactorily i.e. it does not look to me as though it is the result of corrosion. I agree that repair in situ of that joint might be difficult . It's not in fact a very long job to remove the bonnet and take the frame off . BTW, I use Mapp gas for brazing which quickly brings everything up to temperature

Post by **1954Etype** » Sun Jul 06, 2014 8:03 am

So as this frame isn't load bearing, can it be welded?

PeterCrespin · Post by **PeterCrespin** » Sun Jul 06, 2014 12:24 pm

It IS load bearing. Bonnets are effing heavy! :-)

It's under compression normally so brazing is plenty strong enough. You don't want to start welding where braze exists - it screws up the process - plus it's thin high tensile tubing so there's little to weld even though the bracket is mild steel (much thicker, so there's another challenge weldi g dissimilar section). Brazing is the perfect technique and provides a nice stress-reducing fillet with altering the tube's metallurgy. Do what Jag did wherever they used various techniques.

Pete

PeterCrespin · Post by **PeterCrespin** » Sun Jul 06, 2014 12:29 pm

'Without' altering metallurgy of course. Damn fat-fingered iPhone typing.

Pete, in a Dunkin Donut in rural Maryland with my Triumph, waiting for e-typers Doug Wolfire and David Lowenstein to appear so we can teR up a few roads and annoy the guards around Camp David . Wonder if these leathers are bullet-proof?

Shimmer1 · Post by **Shimmer1** » Thu Feb 19, 2015 11:49 am

Having found rust in the bonnet sub frame assembly I have decided to replace it with a spare (stored for 40 years).
With the bonnet and radiator removed I have weighed the job up and it looks far from simple. My main concern is with the weight of the engine there will be differential movement of the engine frame/picture frame (although not all the bolts need to come out) leading to a very difficult reassembly.
My plan, the next fine day, is to position the car under an I girder in the garage and take most of the weight of the engine with a block and tackle. SNG Barrett do a fixing kit which I have, so another plan is to reverse all the bolts that can be turned so the bolt heads are engine side.
So gents any tips please.

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Bonnet support frame brazing in situ?

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