I now know the front diff is unhappy and knowing the Chinese build quality I am sure the rear diff is likely to self destruct as well. Replacement diffs are not easily available and they are an odd ratio (5.2:1). In this current setup it is also a little too low geared. The obvious answer is to replace the diffs. Ford Sierra diffs are a bit bigger but they are virtually indestructible. Even better, the Sierra 4x4 was fitted with viscous limited slip diffs. That would solve my cross-axling problems. As the car is virtually flat underneath it will paddle itself along even if it is bellied out in mud, as long as I can maintain some traction.Of course I can't just drop in Sierra diffs. They are wider than the original diffs and the drive shafts would end up too short. As I am now using narrow wheels I can afford to lengthen the wishbones and recover some of the lost driveshaft length. The CVs are also pretty puny and I doubt if they are likely to last long. Looks like I am going to be replacing all of the suspension!The current plan is a little complicated. I hope to enlarge the Sierra diff flanges to fit Porsche 930 CVs. These are renowned for being very tough even at extreme angles. The driveshafts will be VW Passat ones as they will fit 930 CVs at one end and Honda Civic outboard CVs at the other. Honda Civic CVs will fit Rover 25 front uprights with a small amount of modification. With this increased track I have room for a peugeot 306 power steering rack which solves my steering issues. To keep things simple I'll also use Rover uprights on the rear. That of course leads to the possibility of rear wheel steering. Are you confused yet? Watch this space to find out if it all works!

The project has been on hold for a while as I accumulated parts. Now most of the bits have arrived so I can start work. First the uprights need modifying. A mount had to be made for the top ball joint. The lower ball joint taper needed to be opened up and the track rod end joint had to be mounted on the other side of the steering arm. To move the track rod I had to machine the taper over size then make a sleeve to reduce it back to the correct size. As you can see some of the setups on the mill were quite complicated to get the correct angles.

The finished parts. The uprights are from two different models of Rover 25. Earlier Rovers used cast steel and the strut mounts are a convenient shape to just bore a taper. Later ones are cast iron and need a taper mount to be made up. I am not sure which I prefer. The cast steel version looks better and is easier to machine but the top and bottom ball joints end up a bit closer together than I would like

It turns out that some of the 2WD Ford Granadas used a slightly larger limited slip diff than the Sierra. Even better, some have larger diff flanges that will accept Porsche flanges. Unfortunately they are quite rare. I did eventually locate two but the courier managed to lose one. How do you lose a diff?? I wouldn't recommend Parcel2Go for transport. They may be cheap but if something goes wrong you have to really fight for compensation. In the end I got a diff with the smaller flanges and converted them.

To prevent heat from damaging the splines or sealing surfaces the flanges were welded in a bowl with the important surfaces submerged under water. This was the first real job for my shiny new 280A Portamig welder. It was expensive but it welds much better than my old Miller 150

The final result. Looks good to me!

The original diffs next to the Sierra diff. From left to right in the first pic, old front, old rear, Sierra 7". The 7.5" diff is slightly bigger again.

The wishbones are a little complicated so I CNC machined some fixtures to ensure that they come out exactly as designed. This is the bottom wishbone. The top one is a bit simpler.

This shows the spacers I used to ensure the wishbone mounts came out with the correct spacing.

These wishbones allow about 14" of travel which quite closely agrees with my CAD model. I managed to optimise the mounting points to give about 20" of clearance under the chassis at full droop which is pretty impressive. By the way, those wooden blocks are just for checking ground clearance. When I am working on the car I use proper axle stands!

Unfortunately the nudge bar needs to be redesigned to allow for the extra travel and larger wheels. This beast started out with 25" diameter tyres and now it is going to get 32" diameter tyres. That is a pretty big difference

There is exactly 16" from the centre line of the axle to the chassis on full compression. 7.50-16 tyres are a smidgeon under 16" radius so they should just fit

The diff is now tacked in place. I had to tip the nose of the diff down as far as possible to allow clearance for the steering ram. There is very little clearance in this area. In fact I will have to machine off most of the lower diff mounting point. Luckily these diffs have lots of mounting points.

930 CVs are used a lot in sand rails and the general consensus is that 22 degrees is safe and 24 degrees is pushing your luck. I went for a maximum of 23 degrees as there should be very little load on the transmission if the suspension is at full droop. I also don't have the sudden shock loadings that you get in sand rails. At more than 21 degrees you can feel the joint tightening up as you rotate it. From previous experience with my trials car the joints will loosen up with use.
I mis-calculated the driveshaft lengths very slightly. The wishbones could do with being about 6mm shorter. Considering the number of variables and the difficulty of measuring some of these parts I thought that was not bad. The CVs are still operating well within their safe travel range so this isn't a problem. The rear track may end up 12mm narrower than the front as I now know the correct dimensions!

I am not sure just how hard I can push the outer CVs. This is at full lock and full droop. It looks frighteningly close to the limit to me. Unlike the 930 CVs they are cheap so I can afford to carry a spare.

Progress has slowed a bit recently but I am still slowly getting it done. See page 5 for the ongoing story.

Comments

Do you like what I am doing? Am I doing it all wrong? If you have any questions or suggestions, do let me know by posting a comment.

Note: Spammers and trolls will be shot!

Leave a comment

Home page