Work started with the building of the uprights, first the holes was marked out for the hub carrier and drilled, assembling the complete hub carrier with bearings and rotor. Then we proceeded to mark out the holes for the caliper. After drilling I assembled everything again to make sure all was a good fit and to measure the spacers I needed to make on the lathe for the spacing of the caliper to the rotor. It came down to 10mm thick and 20mm wide, a very nice sturdy size. I must admit the easiest disc brake conversion I have ever done. It probably helps when you are starting with new metal and do not have to work around someone else’s work. The inner wishbone tubes was used in conjunction with a 12mm piece of ready bar and washers to get the spacing between the lower wishbone mounts correct. These was tacked in place and clearances checked and then welded permanently. We decided to make the inner mounts from angle to add strength and the outers from 6mm lazercut sheet metal, the inner mounts is boxed and the outers are able to bend in when tightened, to ease wishbone removal and installation. The same principal were applied to the top wishbone mounting point, a single piece of angle and a 6mm lazercut unit on the rear, with this configuration the angle is in front to fight the most amount of forces applied on it. Afterwords a gaset was welded on the front side of the upright to add rigidity to the unit.
One of the things that wasted more time than necessary was the mounting of the differential to the lower sub frame, from time to time you encounter a problem that the answer is just so damn easy you try and over complicate things and waste time, well this was one of those situations, we almost spend about 2-3 hours getting the differential mounted to the frame, to make it worst was the fact that only about 1 and a 30 hours was needed to get it done, the rest was wasted on measuring and scratching head and over complicate the whole scenario. After all this measuring and going nowhere, we realized that the drive shafts is the deciding factor, the one is 40mm longer than the other one. This means the differential should be mounted 40mm off center on the sub frame if the sub frame is mounted center in the car, as easy as that. After the whole ordeal, it was a matter of measuring the offset, tack some angle in the rear, fasten some other in the front, measure the angles, cut and weld some rectangular tubing.
We rounded the day of by manufacturing the lower wishbone adjustable brackets, the reason for these units being adjustable is to adjust the toe on rear wheels, it would have been allot easier to simple just weld these in place and mount the wishbones, but from time to time you need to look in the future and do your planning good, thus vehicle being build to be a race car, this small amount of work will in the future be well worth it. Another added benefit to these is the fact that all the 1mm here and there that crept in as error would be able to be adjusted away. Adjustment will be done in the form of different thickness shims. The same techniques as the uprights was applied to them with the angle and the 6mm lazercut ears.
Sunday, the one day over the weekend that should be handled with care, thus meaning no loud noise etc. Well in my case this is normally the day I use to apply sealer, paint and do planning. Sealer was on the menu for the morning, basically finished all the seams on the inside of the car and those in the front wheel arches. Got quickly bored of this and decided a little noise would be in order and started the re drilling of the hubs and rotors to a PCD of 4/100. My father joined in on the fun after lunch and he continued the drilling. Here and there I helped him to hold a part that would not fit in the drill press. I moved on the continue the sealing of the seams as this is just one of those tasks that I absolutely hate, but it had to be done. Finished in conjunction with my father with the seams in the boot, he just finished tapping the M12 x 1.5 thread in the hubs. Our plan is to use normal 40mm long Allen Caps for wheel studs, screw in from the back. For those that do not know, the hardness level on a standard bolt is 4.8, a HT (High Tensile) bolt is 8.8, the average Allen Cap bolt ranges between 10.8 and 11.8, I have even seen some at 12.8. This makes for one very strong wheel stud without spending a fortune on wheel studs. We continued until 7 o’clock and called it a day.
Monday morning, the thought went through my mind, what the hell am I doing on the farm building a car, aha, thank you government for a public holiday, quickly I realized I had the Tuesday also off, nice, I will be able to get a decent amount of work done. After the duo finished a quick planning session, we agreed that today will be the day that we finish the lower wishbones, we had allot of work ahead. He again started re measuring every square mm of the parts already build and the exact same on the car. Something he seems to enjoy immensely and I do to a point I think is necessary, but working with my father on this car has thought me one very important lesson, rather plan for a day, and then spend a few hours getting the work done 100% correct first time than wasting time in re doing work. While he was busy with his arsenal of measuring equipment, I started to assemble the Uprights to take a final measurement on the spacer needed between the upright and the caliper. Whenever I got a chance between helping my father I machined the spacers, drill and tapped the holes to keep the rotor in place on the hub. I’m very pleased with the outcome of the Uprights, the caliper and rotor sits beautiful, the whole feel if it is just correct.
We started with the wishbones, first of all we had to make a jig to work from, I purchased a piece of 6mm metal sheet only for this purpose. Some angle was cut into pieces and welded in place to keep the pipe in the correct position after everything was marked out on the sheet metal. Once this was done the dreaded, grinding of the pipes and making the templates for the different joints started. I must just state, working with pipe looks very need at the end of the day if done correctly, but what a time consuming job. By this I do not mean just hammer the end flat and weld it in place. the majority of the afternoon was spend to grind the joints and make the templates on paper for future use. Once the assembling of the pipes and bushes started, I was jumping up and down like a kid on Christmas morning, we started with the straight beams, welding each side, turned on their side and welded, grinded and cleaned them, the same with the angled beams. Proceeded by placing them back into the jig and welding the outer support into place. Once we were satisfied we added the side support, the same was applied to the second one. Cleaned them and admired our work at 9 o’clock the evening, a straight shift from 8 o’clock the morning to 9 in the evening only taking a food break and a few coffee breaks. We have finished them, exact units that will be used on the right and left hand side for the lower wishbones.
Work started to out with getting the size of the inner side of the wishbone correct, it pulled about 2mm – 3mm from the intense welding of the support pipes in a small area. We used gas to heat it up, take a measurement and bend it to the correct length. I assembled the wishbones to the sub frame and the uprights to get an overall view of what would need to be mounted to the car. it took me awhile to realize that I indeed was apart of building what was lying in front of me.
I started prepping the inner Lobro joints for re drilling. The standard Lobro’s have the same PCD layout as the BMW LSD, the only difference is the diameter of the holes being 10mm on the BMW side and 8mm on the Sapphire parts. I taped them up with some masking tape to keep the biggest amount of drilling burrs out of the inner part. Drilling these units was not just a matter of drilling, these units is case hardened and like to eat up drill bits. I used a 5% Cobalt drill bit with some Rocol RTD Liquid to ease the drilling.
All our focus was then shifted back to mounting the rear suspension, first we placed the suspension on a trolley and moved it beneath the car, added some make shift upper control arms to get the uprights level. Took a few measurements of possible mounting points for the sub frame and the upper wishbone. We moved back to our suspension simulator we build, drilled a few more holes according to our new measurements and simulated the dynamic camber we would get. We figured that a upper wishbone with a width of +- 200mm and length of 250mm will provide us with the desired effect. Designed the adjusters that will need to be machined for the upper wishbones to adjust camber. We realized that we need to get the sub frame higher, only problem was that we need to cut more away from the car, didn’t take us long to make short work of the metal in our way and moved the frame higher and the car to the desired height.
We quickly found the correct mounting place for the sub frame, only problem was that it was part of the car that had very thin metal and would not be ideal for suspension mountings. A pair of angles was bend from 3mm sheet metal and mounted to the car, some parts I could replace with Aluminium once everything is proven. It was decided that we would use tubing to build the upper frame from, we only managed to weld the front mountings onto the tubing before we ran out of time.
The work we were capable in doing the last few days placed me more or less on schedule to have the car ready for next year’s season. Maybe not 100% done, but at least the mechanical stuff more or less sorted, the interior I will sort out in the next year.
More Pictures – 7 August 2010 – Rear Suspension – Phase III
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