LandyManLuke Posted June 5, 2009 Share Posted June 5, 2009 Having read plenty about replacement rear crossmembers, and horror stories of fitting. I decided a long time ago that when the time came, I would build my own, that time came with an MOT failure, when I had just moved house and was still getting the workshop set up. The state of the crossmember at the MOT was pretty dire, it became evident how much worse the corrosion really was as I removed what was left of the crossmember. The crossmember was cut from the chassis 25mm in front of the tow bar brace brackets. The accuracy of the cut gave me a solid datum to use for designing the new crossmember. The component parts of the crossmember where all drawn up in solidworks, and combined to produce the final article. The drawings produced from the CAD model were used extensively in the workshop for measuring out and cutting parts, so much so that I could have done with a folder to keep them all in. the chassis side sections were printed 1:1 on A3 so that they could be used to trace the profile on to the steel. The old crossmember was used a lot for taking measurements, ideally, I would have measured a few other crossmembers as the corrosion on mine was pretty severe. Old crossmember supported on the bench for measurements to be taken. Crossmember component parts in solid works. It took a few weekends to cut out all of the component parts for the crossmember, it would have been quicker and easier to get them CNC cut, but I couldn't afford to go for that option. Instead, it was quite a lot of time spent with a 1mm cutting disc in the grinder. The main body of the crossmember is 160x80x5 box. This size is very close to the original crossmember dimensions. The following photo shows the main section of box, with the initial cuts for the angled ends, which are set up in to the body to allow for the radius'd edge which is part of the infill plate. As you can see, the old crossmember was in very poor condition. The main body was drilled for the Mantec and tow bracket holes, which were fitted with seamless anti crush tubes. Then the angled end pieces were prepped with a relatively large V & gap, welded in and flushed off completely smooth. The tub brackets where fabricated from plate, The slots were drilled at each end then cut out with an air hack saw and filed smooth. The chassis extensions and spreader plates were designed to positively locate on to the main box section to make alignment easier, hence the thin tail on the bottom edge. this made jigging and welding much easier. The four extensions wer tacked on and test fitted against the chassis, I ended up adjusting and re-tacking them, after the initial dry fit. The four extensions were welded inside and out. Before welding the rest of the chassis extensions, they were jigged up using some scrap flat and the length of tube that would become the JATE ring holes. This kept the whole thing relatively true whilst the top and bottom plates and spreaders were welded in. Here, you can also see the holes cut in the extensions for the plug welds at the join to the chassis. The tub floor supports were then bent up and welded on, with gussets, with heavy use of the CAD drawings to get alignment and positioning right. I ended up calling my own bluff and tacking them on and dry fitting the whole crossmember, which at this point was heavy enough to be a pita. I had already welded in the internal braces into the chassis legs so at least it was relatively easy to slide the new crossmember on. the long piece of jate ring tube was actually incredibly useful for supporting and aligning the crossmember at this stage. I left it in until the crossmember was welded in, then cut it out. I'm afraid to say that's where the photos run out for now. I was too busy racing for an MOT that i didn't take any more. The crossmember was dry fitted for the final time and then given a coat of primer and 3 coats of black paint. The crossmember was butt welded on all four sides to the chassis, and plug welded through the holes shown to internal bracing plates that extended 100-150mm or so into both the old and new sections. I pulled the wiring loom out to the rear as much as possible and protected it with spiral wiring wrap before pulling it up in to the chassis away from the welding heat. The end of the spiral wrap slightly melted in a few spots but the loom was fine. The exhaust hanger bracket (only one, I don't have a back box) was mounted in-situ as it wasn't so crucial to get spot on, and the old crossmember's bracket was a repair made in a similar way about 3 years ago, so wasn't worth measuring anyway. I'll try and remember to take some pictures of the crossmember on the 90. It's been on there for about 8 weeks now and I'm quite chuffed with it. Quote Link to comment Share on other sites More sharing options...
ThreeSheds Posted June 6, 2009 Share Posted June 6, 2009 The quality of workmanship shown by members of this forum often shames my efforts.. As it does here - lovely job LandyManLuke Looking forward to pics of the finished article. Quote Link to comment Share on other sites More sharing options...
tommeke Posted June 8, 2009 Share Posted June 8, 2009 Very nice fabrication work!!! Quote Link to comment Share on other sites More sharing options...
RichardAllen Posted June 10, 2009 Share Posted June 10, 2009 Luke, Can you post the solidworks files in the CAD archive ? Regards Richard Quote Link to comment Share on other sites More sharing options...
Les Henson Posted June 10, 2009 Share Posted June 10, 2009 Very tidy job, Luke Les. Quote Link to comment Share on other sites More sharing options...
RichardAllen Posted June 10, 2009 Share Posted June 10, 2009 Luke, What arrangement have you used for fixing the mudflaps (I have a particular hatred of the tendency of rivnuts to corrode, seize and then be a b****r to get out) ? Regards Richard Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted June 10, 2009 Author Share Posted June 10, 2009 Erm, mudflaps? what are they?! - I don't have any fitted. I can post the solidworks parts, but there are rather a lit of them, and i'm no SW expert - self taught - so they're probably not that good. Also, they would definitely require adjusting to fit, indeed i made some adjustments as i went along and haven't updated the models yet. Quote Link to comment Share on other sites More sharing options...
bluespanner Posted June 24, 2009 Share Posted June 24, 2009 Nice work. I just welded a monster lump of box on the end of the chassis... Quote Link to comment Share on other sites More sharing options...
dieselweasel Posted November 24, 2009 Share Posted November 24, 2009 Great job but I'd have been tempted to deviate from th' norm... Quote Link to comment Share on other sites More sharing options...
LandyManLuke Posted April 25, 2010 Author Share Posted April 25, 2010 Well, about a year on, here are a few photos, taken this evening whilst the 90 is in the garage for yet more MOT welding. Galvanised chassis can't be far off Quote Link to comment Share on other sites More sharing options...
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