Hi
I'm stuck and would appreciate some advice before I get into deeper water . Defender 90 300tdi. I've taken the rear tub off to fit a replacement A frame crossmember. Doors, seat box and everything forward has not been touched. rear axle sits on stands, Shocks are off but springs still in. The top of the chasis rail below the old crossmember was toast as was a couple of inches of the chassis walls either side - the bits behind where the crossmember side plates weld on. I cut these out ( 30cm or so of rail tops and 6cm or so down either side) and welded in new 3mm steel. I also replaced the chassis wall behind the shock absorber brackets as thsi too was not great. I got the A frame crossmember lined up and tacked in place with just a few small tacks. Before fully welding up I decided to test fit the tub and to my horror it would no longer fit between the rear crossmember brackets and the seat box!!! If lined up at the seat box the tub sits on top of the rear brackets and overhangs them very slightly. No way will it drop in behind. I decided to cut the rear crossmember brackets off to let the tub sit on its six chassis mounts and it overhangs the rear crossmember by a few mil. What I then discovered is that the door gaps at the top of the tub have practically dissapeared. If the upper side panel is put in place no way will the door shut as it overlaps. I can't see that the tub could have changed as it has just been sat upright at the back of the house so I can only conclude that the tub is tilted, being now higher at the back than it was. This in turn implies the rear crossmember is higher which, since the tub sits flat on all six mounts, implies the whole rear part of the chassis has twisted upwards. I've seen Mr Crokers chassis antics but his repairs are way more extensive. Is it likley that my rear chassis could have moved so much or am I missing something. I can't see any way of measuring it as I have no reference points. If the conclusion is it has, then is the fix to take off the A frame crossmember and to cut through the top and sides of the chassis below it to bring the rear of the chassis down? Now I'm sure some will reccomend a new galved chassis but I neither have the time or resources to go down that route.
Any advice gladly received - thanks

Sounds like something has moved when you cut stuff out and welded in.
Got pics?

Is this any help.

J

I watched this a while ago Britannic restorations. Just shows that when you buy new replacement chassis bits the don't always fit! It may well be something wrong with your new part?!? Skip to 12 mins in for the interesting bit! . May help you, may keep you sane!! ;-)

Sounds like the rear part of the chassis has bent upwards while you cut out and welded up...but as @marjon said pics would help...

Not much use now I know but when I did this job I made a steel jig and bolted it in place before chopping out the old crossmember.
Maybe the measurements posted by marjon will help. Hopefully its something simple. Good luck

The mistake you made was in the first line of your post, you removed the tub. Before fitting the new member.

tottot said:

The mistake you made was in the first line of your post, you removed the tub. Before fitting the new member.

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Yer I agree I wouldnt have removed the tub before tacking the new one in place.

potus said:

Not much use now I know but when I did this job I made a steel jig and bolted it in place before chopping out the old crossmember.
Maybe the measurements posted by marjon will help. Hopefully its something simple. Good luck

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Similar...but in timber





Can you get another crossmember with longer arms?

My steel effort..

potus said:

My steel effort..
View attachment 275813

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Thanks all, just to be clear it's the A frame crossmember I replaced not the rear, the rear was done some time ago. I realise the A frame cross member does not play a part is supporting the Tub (belt anchor brackets through the front excepted) so as Marjon said and I suspect it is the repairs to the chassis beneath it that have caused the problem. I wish I had used a steel jig / plate or similar to prevent movement but hindsight is a wonderful thing and I guess I did not consider it would move. You live and learn I am loathe to start messing around with the six tub mounting support brackets on the chassis as these are all level relative to each other and it's not really these that are at fault, so it seems I need to try to correct the height of the rear of the chassis by undoing the movement. The repaired chassis beneath the new A frame crossmember (now removed) would seem the place to do this. Anyone got any thoughts / advice on the best way to proceed? Cut from above through the new repair or from below. Cut all the way through or just part? I've attached a couple of pics but as I untacked and removed the cross member last night and the tub is off I don't think they help much. I'm thinking along the lines of supporting the rear crosssmember in a way that I can control its downward movement. Supporting the chassis forward of the A frame crossmember, removing the rear springs as these will act to shove it upwards at the rear, drop the tub on, cut the chassis (through where?) and then lower the rear crossmember until the tub aligns with doors again, brace the chassis acrosss the cut point - repair the cut point. Views / input all welcome.
Cheers

Sounds like welding distortion pulling the back of the chassis up. Without seeing in the flesh it’s hard to say exactly.

I’d do like your saying and slit through the chassis, I’d go for the top down on the repair then when it’s realigned and welded up over plate the cut/weld.

As above, then test fit tub. If good support chassis in several places from the ground [ no axle weight or weight on axle] When welding in new crossmember do small sections at a time, keep a tape measure handy and check distances from ground and diagonals within the chassis as you weld.