Diff cage

Since this has proven to be more involved and complicated than I had first thought, it gets it's own update.

Once the diff was given a quick clean and a wire brush, it was time to start modifying the casings to better suit my needs. As standard the diff has five mounting points. Four that are hard bolted at the front and one large rubber mount on a wing on the rear cover.

Whilst all five mounts are obviously used in the BMW, the rear wing gets in the way for what I want and I've no where to mount it anyway. So the rear cover was taken off, partly so I could clean the diff out and partly so I could cut the cover down without damaging the diff at all.

The inside of the diff looks largely as you would expect, but with one minor difference. BMW use the diff to mount the speedo trigger, and as such it has a fan on one side to trigger the sensor. I'm not sure yet if I'll keep this or not, as I may use something on the prop or maybe a front wheel. The diff is easiest as BMW have already done all the R&D for me and the sensor is reliable. The prop gives a better indication of rear wheel speed, as it measures total wheel spin better but will require me to mount a suitable sensor. The front wheels give a better idea of road speed as they don't react to wheel spin, but are easily the hardest to make work.

So now to cutting the rear cover down. This was done in a few steps to ensure I didn't over do it or bugger it up! The first step was to clean the cover up and make a new gasket for it and then cut the meat of the wing off.

And then the remaining metal was cut down and the two bolt mounts cut back and sanded flat. I did later sand the edge of the cover flat too just to make it more complete.

So now the diff was cut back I could get on with the cradle. The first thing to do was to make the diff side of the frame. This would then allow me to accurately measure up for the tubes to the transmission tunnel mounts. This is a story best told in pictures.

So with the diff side of the cage completed, the diff was positioned against the shell to sort the lower legs.

The next problem was how to match a piece of 1.5" tube against a mount that was about 1.5" wide. My solution was to make the mount wider, but in a way that allowed the extra width to not get in the way.

 

And that is as far as I've got with it. Due to all the heat from welding, the lower leg mounts have skewed upwards by 4-5mm, so I'll need to cut the lower mounts off and re-do them. But that means I can also make them a touch bigger and stronger, so that's no bad thing.

August and Septemeber updates!

I'm really not doing well with keeping this blog up to date! Which is going to make this update a bit full.

But first things first. The heater tray was fully welded in, cleaned up and then etch primed. The lower flanges were spot welded from within the foot wells and then cleaned back to hide the welds. The top plate will will be done when I'm ready to get that far. But I'm happy with how this all looks for now and it still allows the engine to fit easily. Or as easily as a 2.5l V6 will in a Sprite!

The next step was to get cracking with the rear suspension and get more done on the back end before moving on to the front. So the first thing to do was to actually finish the transmission tunnel off and get the plates fitted to the rear bulkhead face to help strengthen the diff mounts.

I've not got a photo showing all four plates welded as yet, as the bits over the top of the upper mounts hasn't been done. I tried doing one of them, but the very restricted access makes it virtually impossible to see what I'm doing, so those bits can wait until I next roll the shell over.

But with the plates as in as they can be for now, I had a look at the suspension itself and the brakes. This first meant getting the coil overs hanging in place so that the linkages would all hang under their own weight. So I made a set of top brackets for the coil overs and got them bolted in place, only to realise that the lower mounts on the coil overs, which I hadn't really looked at before, take a 10mm bolt whilst the De-Dion tube takes a 1/2" bolt. But as a temporary fix, I've removed the misalignment washers so I can at least clamp a 1/2" bolt in place for now. The thread lengths are different on the top mounts so I can fit them more easily as I have to do it with one hand feeding the coil over in from below whilst trying to put a washer and nut on from above. This was I can locate them one thread at a time.

With that done, the rear suspension was now intact at last, and I could get the hubs in place.Only it very quickly became apparent that the disc brake drive shafts and hubs that I have don't fit the De-Dion ears that I got hold of! Arse. I know this isn't a problem with the ears, as the design of them hasn't changed. So following yet more research, it turns out that I should have used the smaller drum brake hubs and drive shafts. So back to Ebay it was!

And once I found a set of shafts and hubs, I could actually get the hubs bolted in place and the callipers on the ears too. Only to find that the brake discs I had been planning on using are too big. Thankfully, this isn't a big problem as the right discs are only £25 or so each, even from Caterham! I can still use the discs I have to measure up for where the wheels fit and what not as they still move the wheel outwards by the same amount.

This photo shows the difference between the two types of set ups. The main difference is the width of the CV joint. The drum brake tripod joint is much slimmer. This also means it's lighter, which is a good thing.

And whilst I know they won't fit, as the tyres are too wide for the arches, I couldn't resist trying a wheel on for size. I quite like the way it looks! Just need to see how much surgery is required to make a square wheel arch shell accept a 185 section tyre.

So following the sense of achievement that seeing a wheel on the car for the first time if four and a half years gave me, I had to spend far more time than I wanted to carefully measuring clearances so I could make a start on fitting the diff. But as that's quite involved, I'll put that into it's own update.