I’ve started to mock up the front 4×4 system.
In CAD everything looked extremely tight. I spent ages moving components back and forth to get everything to fit.
So far, in the mock up. There looks like bags of room. When I say ‘bags’ I mean a good 6-7mm! In the above shot, you can see how close the front of the diff is to the chassis and how well the rear clears the upright tube for the front arms.
Considering there were several evenings spent thinking that I was going to have to extend the chassis further or use a wider nosecone, it’s strange how things turned out so well. I’m using a totally standard ‘original’ shape nosecone.
The front prop-shaft was a top tip from another 4×4 Haynes Roadster builder (Liam). But it has taken me over a year to get my hands on one. It is the prop-shaft from a classic Volvo Amazon 120/121/122/130/220 (1956 – 1970). It is 2 piece with a sliding central joint. I was extremely lucky with the rear half. I found a BNIB (brand new in box) item for sale on Fleabay for £10. It came with all the genuine Volvo stickers and had been sitting on a shelf for 40+ years. The front half took 15 more months to find. A prop-shaft came up that looked right, but it was advertised as ‘Old Volvo Prop-shaft’. It looked right and it was cheap. I took a chance that worked out perfectly. It had some light surface rust but was actually in very good condition. I’ll get it rebuilt anyway – just in case.
The rear section; despite being brand new; will need shortening, with the rear yoke replaced with the splined shaft necessary to fit the MT75 gearbox. I have a tubular prop-shaft (not the cast XR4x4 item) from a Escort Cosworth. I’ll get a local prop-shaft company to join the two. They’ve made several oddball prop-shafts for me in the past and they cost a fraction of some of those that advertise in the magazines.
The prop-shaft sits neatly above the chassis rail. It sits as close to the Rover V8s’ engine block as I could get it. The reasons for this are, if it was any further out the front section would foul the standard P38 tubular exhaust manifolds and the rear section would encroach on the drivers’ foot-well. The foot-wells are already a bit narrower than standard due to the MT75 sitting a little further back than normal. This chassis is 100mm wider than the standard chassis at the bulkhead but it is standard width at the front to fit a standard nosecone. The tray that the battery often sits on has been modified with a central recess. This is so the Rover V8 clears the front Sierra differential.
The prop-shafts’ central bearing section mounts on sliding joints. I’ve urethane mounted this bearing to keep a little bit of the vibration out of the chassis. The mounts don’t rotate, they slide and are there for shock absorption. The central bearing is free to slide forwards and backwards on the stainless inserts. There are stainless bars attached to the brackets that pass through the middle of these inserts. I’ve made them a close tolerance fit. I’ll make the mounting bracket removable so that I can grease this joint as and when needed. If they squeak or wear then I’ll replace them with brass. I made them with what was in the spare metal heap.
Once the prop-shaft and front differentials’ brackets have been completed; with everything securely mounted, I’ll finish making all the boxing tubes for the engine bay.
The rear half of the car has a lot more triangulation than the standard Haynes Roadster. That doesn’t mean I’ve just added tubes everywhere, as the weight is probably close to that of a standard car. Analysis showed that adding some shear panels and angling a few tubes, increased rear stiffness nearly 120% (Over twice as strong as standard). However, as at the time I never knew what engine and gearbox I was going to use, the analysis was never done on the front end of the chassis. My FEA (Finite Element Analysis) Guru has taken an overseas contract, so I’m going to have to make up the triangulation on what I have learned from tweaking the rear. I doubt if it will be twice as strong, but it will definitely be a lot stronger than standard.
As you can see in the above shot, the front of the chassis currently has very little. If left un-triangulated the chassis would form a weak point hinge at the bulkhead.