To make the driveshafts to the required lengths (How to measure the shafts : https://mearcat.blogspot.com/2019/02/measuring-custom-driveshaft-lengths.html), the Mini and Toyota intermediate shafts were cut with the grinder and machined to length on the lathe. To keep the two pieces aligned when welded, I drilled a 5mm hole in one piece and machined a matching pin in the other piece so that they could be lightly pressed together. Machining the Mini driveshaft steel was a bit slow but the hardened steel in the Starlet shafts was much slower work on the lathe and could only be achieved with a cobalt drill bit (HSS drill bits generally won't do anything to hardened steel) and carbide inserts. Due to the hardness of the steel I could only take between 0.1mm and 0.15mm cuts at a time so it took over 4 hours for this simple machining job!
The two pieces for either side of the car ended up like this :
Pressed together with Toyota shafts on the left and Mini shafts on the right :
I was originally going to give the pieces a welder/boilermaker to have them professionally done but after talking to a welder at a local workshop, he suggested that the job could be done by me if I was confident in my welding - and that's a yes. It was noted that the two driveshaft pieces (Mini, Toyota) are likely dissimilar metal grades (with the Mini section of the shaft a softer steel) and under excessive load, the Mini spline will probably shear before a decent weld gives way. To give it the best chance of success, he suggested preheating the shafts in an oven of at least 250degC prior to welding. Preheating minimizes the temperature difference between the area being welded and the rest of the shaft base material, and will help the entire shaft cool at a similar rate therefore helping to lessen shrinkage stresses that can lead to cracking and distortion. Once the welds were complete, a slow cool would be required - NOT quenching.
So with my pizza oven cranked to the maximum (approx 300degC) and as per advice from the welding workshop, I made some tack welds around the "V" groove and placed them in the oven for about half an hour to pre-heat.
Each pre-heated shaft was clamped in the lathe chuck and and supported with the tailstock. Note : The lathe power cord was disconnected to prevent damage to anything electrical when welding, and the lathe was also covered with lots of sheets/rags to stop any weld spatter getting on the ways. After some more heavy tack welds around the circumference of the V groove, bigger welds (90deg at a time on opposite sides) were done until the area was filled.
Once the welding was complete, each shaft were placed back in the 300degC oven and allowed to slowly cool to room temperature over the course of 4-5 hours by turning the oven down every half an hour. Once cooled, the welds that sat proud of the shaft surface were then machined off :
I then made a custom 3mm thick sleeve to be welded on over the join area and also drilled some holes in the sleeve for plug welds. The reason the sleeve in the photo below is so short is that there is only about 40mm between the inner and outer CV boots, otherwise I'd have made it longer.
I repeated the same preheat, weld, cool-down process for welding the sleeves and used the lathe to clean up the shaft afterward. These sleeves may not be necessary, but it was simply an attempt to provide more strength to the join areas.
Note that I am not a metallurgist nor do I have experience in heat treating steel so this is an experiment to see how reliable the DIY solution can be with some direction from a professional welder.
The last item was to check for was runout in the driveshafts. Some research online revealed that the tolerance for runout on a RWD driveshaft is typically 0.01in (0.25mm). A RWD prop-shaft will rotate at a much higher speed due to the rear diff reduction ratio, whereas a FWD driveshaft will turn at the same speed as the wheels. Because FWD driveshafts rotate slower than a RWD driveshaft and and much shorter, the tolerances aren't as tight and twice as much runout is considered acceptable. In any case, the runout on my shafts varied along the length of the two driveshafts but at worst it was a very acceptable 0.008in (0.21mm).
I don't have the tool to install the CV boot bands so after everything was sanded down and given a coat of black enamel paint, all the pieces (including new Mini outer CVs) were given to a workshop to fill the CVs with the correct grease and assemble.
The only problem I see is that one of the Mini boots (top one in the photo below) has been stretched too far when clamped.
I had the workshop correct the location of the boot and clamp it at the correct position on the shaft
The two pieces for either side of the car ended up like this :
Pressed together with Toyota shafts on the left and Mini shafts on the right :
I was originally going to give the pieces a welder/boilermaker to have them professionally done but after talking to a welder at a local workshop, he suggested that the job could be done by me if I was confident in my welding - and that's a yes. It was noted that the two driveshaft pieces (Mini, Toyota) are likely dissimilar metal grades (with the Mini section of the shaft a softer steel) and under excessive load, the Mini spline will probably shear before a decent weld gives way. To give it the best chance of success, he suggested preheating the shafts in an oven of at least 250degC prior to welding. Preheating minimizes the temperature difference between the area being welded and the rest of the shaft base material, and will help the entire shaft cool at a similar rate therefore helping to lessen shrinkage stresses that can lead to cracking and distortion. Once the welds were complete, a slow cool would be required - NOT quenching.
So with my pizza oven cranked to the maximum (approx 300degC) and as per advice from the welding workshop, I made some tack welds around the "V" groove and placed them in the oven for about half an hour to pre-heat.
Each pre-heated shaft was clamped in the lathe chuck and and supported with the tailstock. Note : The lathe power cord was disconnected to prevent damage to anything electrical when welding, and the lathe was also covered with lots of sheets/rags to stop any weld spatter getting on the ways. After some more heavy tack welds around the circumference of the V groove, bigger welds (90deg at a time on opposite sides) were done until the area was filled.
Once the welding was complete, each shaft were placed back in the 300degC oven and allowed to slowly cool to room temperature over the course of 4-5 hours by turning the oven down every half an hour. Once cooled, the welds that sat proud of the shaft surface were then machined off :
I then made a custom 3mm thick sleeve to be welded on over the join area and also drilled some holes in the sleeve for plug welds. The reason the sleeve in the photo below is so short is that there is only about 40mm between the inner and outer CV boots, otherwise I'd have made it longer.
I repeated the same preheat, weld, cool-down process for welding the sleeves and used the lathe to clean up the shaft afterward. These sleeves may not be necessary, but it was simply an attempt to provide more strength to the join areas.
Note that I am not a metallurgist nor do I have experience in heat treating steel so this is an experiment to see how reliable the DIY solution can be with some direction from a professional welder.
The last item was to check for was runout in the driveshafts. Some research online revealed that the tolerance for runout on a RWD driveshaft is typically 0.01in (0.25mm). A RWD prop-shaft will rotate at a much higher speed due to the rear diff reduction ratio, whereas a FWD driveshaft will turn at the same speed as the wheels. Because FWD driveshafts rotate slower than a RWD driveshaft and and much shorter, the tolerances aren't as tight and twice as much runout is considered acceptable. In any case, the runout on my shafts varied along the length of the two driveshafts but at worst it was a very acceptable 0.008in (0.21mm).
I don't have the tool to install the CV boot bands so after everything was sanded down and given a coat of black enamel paint, all the pieces (including new Mini outer CVs) were given to a workshop to fill the CVs with the correct grease and assemble.
The only problem I see is that one of the Mini boots (top one in the photo below) has been stretched too far when clamped.
I had the workshop correct the location of the boot and clamp it at the correct position on the shaft
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