Hola chicos!

Car is almost totally stripped and I'm not feeling quite as far out of my depth as I probably ought to ;-)

I'm really keen to crack on with the suspension rebuild. Having wheels back on would assuage my unease about having 2 very inert tonnes of parts in someone else's building.

Front and rear subframes are both fully stripped. I'm planning to wire wheel, phsophoric acid and POR 15 them; money that I save on sand-blasting and powder-coating could go on other things instead. Happy to hear you slate my idiocy on that point, it's not too late to change my mind.

The rear cage is as close to rust-free as dammit. The front is not toooo bad. The spring towers are the worst, but I think they'll scrub up and pass MOT, and if I get five years before I have to do more work then I'm happy.

But.

I can just about see through the drainage hole that surface rust does exist on the inside of the subframe.

It feels like the right thing to do would be cut the flat bottom panel off the subframe, treat the inner surfaces, and weld a new panel back on. My welding is poor but I'll do plenty of practice joints first.

It looks much harder the longer I look at it, though. I'm getting jittery. And I can't seem to find anyone else who has done the same thing and written about it. What's the approach?

The edge seams are some form of plug weld that's really turned the seam to molten slurry. The panels are visible at the edge, but I reckon it's a fools errand to try to slice between the panels.

That leaves me slitting around the panel just inside the seam. I'll have to drill out the plug welds from the bottom panel to the ribbing with a die grinder and carbide burr. Then transfer the holes onto a new panel. I'll have to use new steel for the bottom panel, as I'll lose a few mm all round. And I'm not sure how well I'll be able to recreate the curve where the bottom panel folds up to meet the springs, so I'll just slit around the flat bottom section.

How's my plan so far? Will I be able to get into the curved-up section if I only cut out the flat section?

<pics to follow>

 

'94 Jaguar XJS front subframe

'94 Jaguar XJS front subframe

'94 Jaguar XJS front subframe

'94 Jaguar XJS front subframe

 

Thing is, the outside of the bottom panel is pretty mint. Am I overthinking this? Maybe I should pour in some phosphoric acid, slosh it around, then pump in a gallon of waxoyl and call it good.

Bear in mind, I don't need the subframe to last for ever. I want to get the body and paint good and not touch those again - but I don't mind if I have to come back to the subframe in a few years. I've pulled a V12 and 4L80 out now - dropping a subframe is a walk in the park. Especially now I've broken 27 years of rust on the bolts.

 

Hello Fred

To me - you are overthinking it a bit. Maybe if you are concerned with loss of material - you can get a small ultrasonic thickness tester to see if you do have loss of material issues. (I have one of these - but it used to be what I did for a living).

A gallon of waxoyl done today and again in the future at all those other suspect spots is what I would do. Just forms part of the service roster

Cheers
Steve

 

I would not advise cutting open the subframe, particularly as your looks from here as being OK. I would look VERY carefully at the spring towers and the top wishbone fulcrum attachment points. If they are solid, no rust holes, and no flakey rust anywhere (you can poke your finger into the tower quite easily to check) the subframe is fine.
I would certainly slosh the phospheric acid into it; then slosh in this stuff AquaSteel
https://aquasteel.co.uk/rust-treatment/
Just pour it into the holes and slosh it about, do it the normal way up and let it dry then do it thebother way up and leave it towers-downwards to dry. This will protect the s/f forever nearly, and forever and a day if, after you have let the stuff dry, you spray in Dinitrol:
https://www.dinitroldirect.com/produ...on-protection/

The subframes are welded on a jig at the factory, and if you cut it open, you absolutely must have the suspension points jigged, which is a great deal of effort when not necessary.

 

I am with Greg @ 100%.

Over thinking, waste of drinking time

Cutting that open would destroy the structural strength of it. The rust, for what there MAY be, is only surface with a few flakes.

Down here, old engine oil is used, and then the odd oil leak does the balance as the "Automatic Rust Preventive Feature" as Elinor in the Series section has said so well.

Look around and get a replacement front cradle. Word has it they are HARD TO FIND, and in 5+ years, good bloody luck. Store the thing, sort out any ailments, ready for the day.

 

In the UK, 100%, if I buy another subframe it's not going to be better. They come up on ebay at around the £500 mark, but the ones that come up are from cars that are being parted out. Most likely, because of rust, and that won't get better while they're sitting in a junk yard in soggy Surrey.

Thanks for the tips re Aquasteel/dinitrol/etc, and especially about the need for the jig. Yuhhh... that didn't occur to me...

Consider me advised!

 

I'm absolutely with the mighty G's and others in saying I wouldn't bother if I was you. I've seen loads of XJ front subframes over the years. Yours seems very good indeed for a UK one!

Sort the outside, pay particular attention to the spring seats and towers, slush the inside then wax it. You'll be fine for years!

Good luck

Paul

 

I blush, PTJS!!
Also, I am not worthy to be commended in the same breath as the Mighty XJS Prophet of the Southern Cross!

 

If you use any kind of acid treatment, be sure to neutralize it before drying and applying waxoil. I would just use waxoil spray, using a wand through all the holes. I believe it will be as effective and less likely to create problems.

 

Don't be silly.

 

One further reason not to cut open the subframe - after you clean it, you cannot treat it with anything flammable before welding. And after welding, you will have bare, untreated metal inside around the welds.

 

Y'all IS toooooo damn smart...
Not that I was gunna do any cut'n
But I'm taking ALL of this advise....!
Deep bow,,, Thank You!