chassis patch and suspension geometry

[johne]

Hi,

I've just been looking at the nice shiny painted chassis of the MKIV Spitfire that I bought as a collection of boxes a few weeks ago and have found that one of the main rails has been patched from just in front of the front outrigger up to the bracket for the suspension tower. All 4 sides of the chassis rail have been patched so the lower wishbone rear bracket will be on the outside face of the patch and will be sitting 2 or 3 mm outboard of where it should be and that's if the patch is flat against the original rail. I'm thinking that this will twist the lower wishbone and try to pivot the trunnion forwards and it would take an unfeasible number of shims behind the front bracket to even the wishbone out and if I did that the trunnion would then be too far out and ruin the suspension geometry that way.

I'd like your comments and suggestions, do you think it's as serious a problem as I do and what could be done to correct it.?

 

Thanks, John.

[Pete Lewis]

Is the front pivot not ontop of the repair aswell ? So castor remains ok but camber will need adjustment

I would think adding removing shims to the top mount would correct any camber errors 

Is the patch to a good standard or needs further examination,   sounds more like accident repair than rot.

Pete

 

[johne]

Hi Pete,

The patch on the outside of the rail only extends as far forward as the rearmost two hole bracket - the one which holds a narrow plate with two threaded holes - for the suspension tower, though the patches on the other 3 sides are a little longer as they don't run into the two hole bracket. 

On closer examination the plate on the inside of the rail is bowed so I'm not sure that the nut holding the wishbone bracket would sit flat and so end up bending the threaded stud, but otherwise the weld quality looks good (as far as I can tell without destroying it to check!)

I recall reading somewhere in the dim and distant past that there is a reinforcing bulkhead inside the main rail in the area, the other rail inner face has a small change in section just in front of the wishbone bracket which would seem to support this thought. Again, of course, I've no way of checking what the repaired side is like without taking it apart.

Thanks for the quick reply, John.

[Pete Lewis]

its also worth checking the through studs on these brackets  can be very prone to rust  ive found some rusted inside the rails down to about 6mm dia  with a good chance of shearing off......  and  hedges and ditches become a reality 

still think any solutin is to re shim cambers easy to check with a square and spirit level or Johns plumb line and card idea

castor needs the wheels turned in and turned out 20 deg so chalk lines on the floor for the turn in  but measuring the angle is not so easy

if theres a way to measure the angle of the upright copy the opposite side 

Pete

[thescrapman]

We need a photo, photos are nice... ?

 

[johne]

I'm away from the car for a few days but I should be able to get a photo  next week. 

[johne]

Here are a couple of photos. The first one hopefully shows the increased width of the chassis due to the plate welded on the outside and the second shows the bowed inner repair.

I guess the best   solution is another  chassis.

[Pete Lewis]

the chassis were built to an open tolerance  thats why there are shims all over to correct geometry.

   i would, if the repair is sound just re shim to correct the brackets and  add  the turret top shims to adjust the camber 

Pete

[JohnD]

Johne,

2-3mm is nothing!     In pursuit of negative camber that no road user would need, I've made up spacers from 6mm alloy sheet (equiv. to 4-5 shims).   You can add more shims under the bracket on the unpatched part and expect perfect camber settings.

There are expensive camber gauges,or DiY ones (do a search, or I can send you a design)

Good luck!

John

[johne]

Thanks for the encouraging replies, but I think I'll see if I can find a better chassis which has not been so obviously repaired, that way hopefully I'll avoid any possible questions and subsequent strip downs when I get to the re-registration inspection - I had a similar experience when I imported my Stag, there were obviously some repairs, which had passed an MoT in the UK and continue to pass the equivalent WoF in NZ, but the stricter initial inspection meant that the paint on the underside had to be removed and the welding inspected.

John.

[johne]

Is it really that long ago I posted about this?

Anyway I got around to doing a bit more paint removal on my second chassis and found these cracks around the rear lower wishbone mounting hole, from 12 o'clock to 2 and 5o'clock to 7.

 

So, I thought I'd cut out the corresponding area on the original chassis to use as a replacement section and - as the other two pics show - the inside shows evidence of a dent, but the outside seems flattish apart from the imprint of the shim and the roughness in the bottom left, I assume it's been filled with weld.

Maybe I've not been very observant, but is this a common problem area (I know, it's a 50 year old car), or is it maybe related to the quality of the roads in NZ - more unsealed roads and potholes - so far that's 3 damaged areas at the rear lower wishbone mount on 2 chassis.

My latest plan is to cut out a repair section from the middle of the spare chassis and fit that.

John.

[Clive]

Yes, a common area to crack, though often undetected unless the wishbone mounts are removed.

I have welded a couple, and made bigger repairs on one. The wiggly reinforcer means the failure is not obvious when driving.

[johne]

Might have been a bit stronger if the wiggly reinforcer was somehow welded to the vertical face as well as the top and bottom.