rear suspension: suggestions?

trev · Posted: Sat Oct 13, 2007 9:06 am Post subject: rear suspension: suggestions?

since the dust has settled after a hectic year, I'm now getting back into working on my subaru bug project (link in signature, below: with a progress update from last week).

way back when I started modifying the chassis to fit the 915 box and subaru engine, I just lashed straight in and cut the centre out of the rear torsion tube to make room for the front end of the gearbox. It's far enough forward that the original Subaru engine mounts line up with the stock (not even reversed) beetle gearbox mounts at the end of the frame horns. This has allowed the engine to fit under the stock decklid with NO cutouts visible from outside. Once the decklid is closed it looks like stock bodywork, which was what I wanted all along.

Now that I've had a couple of years Eeeek

tp think about it, I'm no longer happy about cutting out the centre of the torsion tube, I feel that I've lost a lot of strength in the rear of the chassis and I'm considering reinstating the torsion tube, either by welding back in the centre or replacing the whole tube. I've got a donor swing axle chassis I could cut up to get the tube from. Alternatively, I could switch the 1303 frame head onto the swing axle chassis and weld in IRS trailing arm mounts. Replacement 1303 chassis's aren't exactly common around here, which would be the obvious solution.

I've also got a rear suspension subframe from a late squareback which I am also considering welding the whole thing onto the back of the 1303 chassis to fix my mistake. The only problem is there's no frame horns on that and I'd have to "suspend" the engine and gearbox assembly from a custom made cross-member like in a bay window van and then work out some sort of rear engine support bar.

It is still my goal to have all the trickery concealed beneath stock body panels (except for widened wings) so I would really appreciate any input you guys could give.

this is where the gearbox is at present, right through where the tube was:

and the centre of the torsion tube ( I think I had to clearance even more after this pic was taken):

the chassis as it is at the moment:

ricola · Posted: Sat Oct 13, 2007 3:09 pm Post subject:

Trev,
If you put the torsion housing back in you will have to lower your engine a lot from where it is now. I think you even have to lower it from the stock position with a 915 and that's using bugat's shortened nosecone.

I'd just make some structural framework around the nose of the trans to get the strength back in. Have you seen pics of Steve's bug recently with his G50 in Oz?

Rich
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trev · Posted: Sun Oct 14, 2007 4:46 pm Post subject:

I haven't Rich, is it on aussieveedubbers?

ricola · Posted: Mon Oct 15, 2007 7:56 am Post subject:

http://www.clubvw.org.au/steve_carter.htm

Or dig out your old Volksworlds to see how Mark Thurston got the strength back in to his Oval's chassis after fitting his G50 (some pics also on www.lbc2.com)

Rich
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chuggaboom · Posted: Mon Oct 15, 2007 12:06 pm Post subject:

thats the pic your after

trev · Posted: Mon Oct 15, 2007 9:19 pm Post subject:

thanks for the input guys, this kind of thing looks like it might do the job for me.

trev · Posted: Tue Nov 06, 2007 12:16 am Post subject:

my version of the brace above:

still have to put a connection between the underside of the frame horns in line with the torsion tube but have to make the front gearbox mount first.

more on www.veewrx.com

ricola · Posted: Tue Nov 06, 2007 9:19 am Post subject:

that'll do the job nicely Wink

I plan to do something similar but as low profile as possible to fit under a stock or maybe modified rear seat
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rjes · Posted: Sun Nov 11, 2007 5:38 pm Post subject:

Mark's oval was very neat in thet he minimised the body mods needed, and retained torsion bar rear suspension by using short bars in 1303 spring plates, allowing the inner splines to be welded back in with a gap between them for the gearbox.
Rich - I guess you'll create a 'floor'over the G50, creating a shape to fit rear seats around similar to a 911. Maybe you could make a rear seat which retains the stock shape, but is only very thin in the middle, and makes the springing below into two seperate seats? That'd be pretty neat, and subtle, especially as the rear seat will be more visible in a cabrio!
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ricola · Posted: Mon Nov 12, 2007 11:28 am Post subject:

I'm hoping I can hide it completely under the back seat. I'll have to incorporate the seat belt mounts into the bridging piece too. I think I'll probably make it all as slim as feasable without compromising strength and adapt the rear seat to suit...

Mark used coilovers as well as torsion bars which is what I plan to do too. I had a long chat with him a while back and he said that when you cut the centre out, you can then cut this section in half and as they are tapered, push them inside the remains of the torsion housing before welding them back in place to suit early short torsion bars. Will be time to get the 9" angle grinder out soon! Grin

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