Rear chassis crossmember strengthening

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Rear chassis crossmember strengthening

Postby sloglow » Thu Dec 21, 2017 6:18 pm

I'm trying to find details of how to strengthen/reinforce an Imp rear crossmember for competition purposes. The images of this mod that were previously on the forum within various posts are no longer accessible due to the changes in photobucket licensing. I'm rebuilding a G15 which was used in competition and have found the crossmember cracked vertically at one of the inner trailing arm mountings.
Any images or details of how the crossmember is strengthened would be most appreciated.
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Re: Rear chassis crossmember strengthening

Postby moose » Fri Dec 22, 2017 9:13 am

https://photos.app.goo.gl/BPnZ0jTLWBI1ueQr1

only one photo at the moment of the crossmember the album is work in progress. I put gussets to support the sides of the mounting points for rear arms and extra holes vertically between the mounts for rear arms and add spacers to the top, drill the shell and add captive nuts in shell this holds the crossmember in 3 planes if you need any help get in touch cheers mike
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Re: Rear chassis crossmember strengthening

Postby colimp66 » Fri Dec 22, 2017 12:02 pm

I strengthened my crossmember at each of the wishbone mounts by doubling up the outside of the vertical plates as well as triangular pieces welded in at the top of the wishbone mounts to prevent flexing.
Unfortunately I didn't take photos of it once I had finished it. It is on the car now but will try and crawl underneath it for you to get a photo or two of what I have done.
A sport crossmember has more bolts holding it to the car if I remember correctly so could be worth checking if you have one of those.

Cheers
Col.
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Re: Rear chassis crossmember strengthening

Postby sloglow » Fri Dec 22, 2017 9:17 pm

Mike and Colin

Thank you both very much for that info, it's very helpful. Some good and well thought out work in that album Mike.

Unfortunately I don't think I can use bolts at the top of the crossmember as the glassfibre body of the G15 sits above it and I doubt if the body is sufficiently strong to add any strength. I've attached an image of the crack, I don't know the full extent of the cracking until I remove the body in the next week or so. If you have any photos of the diagonal bracing/gussets they would be very helpful.

Thanks again for your help

David
Attachments
Rear crossmember crack 1.JPG
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Re: Rear chassis crossmember strengthening

Postby bks974c » Fri Dec 22, 2017 9:23 pm

Not sure on this but does the G15 not use the Imp crossmember as part of its chassis :? rather than a removable item.

Scott
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Re: Rear chassis crossmember strengthening

Postby sloglow » Fri Dec 22, 2017 9:40 pm

Scott, yes it does. The rest of the chassis is square tubing, the crossmember is welded in. Problem is that it's not possible to fully inspect the crossmember and repair it without removing the body.

David
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Re: Rear chassis crossmember strengthening

Postby bks974c » Fri Dec 22, 2017 10:03 pm

Yes that's what I thought, so some of the usual modifying won't work eg additional bolts etc. a bespoke solution to stop it twisting would be more suitable but I'm sure other G15 owners will have found solutions. Once the body is off you will have a chance to check the rest of the chassis, I believe the area most likely to cause problems is where it kicks up at the rear suspension and spring and shocks mount.

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Re: Rear chassis crossmember strengthening

Postby benwick3 » Sat Dec 23, 2017 10:08 am

It's right the the crossmember forms part of the chassis for the G15. As has been said none of the normal methods of adding strength are appropriate. Also, it's necessary to remove the body to check out the integrity of the complete chassis, particularly the welds. On two occasions I found that not all of the chassis members had been welded fully to the adjacent members. With your problem I think the only answer is to clean and weld the crack to form a repair.

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Re: Rear chassis crossmember strengthening

Postby Darkspeed » Sun Dec 24, 2017 12:01 pm

Strengthening a G15 chassis is a great deal of work to do correctly and to brace the rear crossmember it is body off - repair chassis and then brace which also involves modifying the body to clear the work.
They crack in different places on the cross member depending on what series the chassis is.
Last edited by Darkspeed on Tue Feb 13, 2018 8:56 pm, edited 1 time in total.
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Re: Rear chassis crossmember strengthening

Postby sloglow » Tue Feb 13, 2018 10:53 am

Just to tidy up this thread.

My thanks to everyone who responded.

I removed the body and welded the cracks in the x-member. Both sides had cracked, the r.h. worse than the l.h. There is about a 5mm gap between the body and the top of the x-member on my car so I was also able to weld a plate across each crack. I checked the rest of the chassis for continuous welding and damage as Pete advises and it does not show any other cracks. I think I had all the seams rewelded back in the 90's when I first rebuilt it which seems to have paid off. Pete's advice is sound as the other G15 I have has welds that are not continuous.

Thanks to all

David
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