|
Progress on the 140 diff. I have completed the evaluation on the 140 large case diff for modification into LSD. I have concluded it is possible but there are several challenges.
1) I have to make up ~ 7mm of clutch space, meaning I have 9mm to do what was done in 16mm. This can be accomplished in 2 ways. I can machine out the case to open the stack clearance up to maybe 11mm. In doing this I will be reducing axle shaft bearing area. I can also use thinner disks and steels. The stock steels are 1.1mm ~ 0.042". I can cut that down to 0.025 steel. Cutting the steel thickness in half essentially means the steel will run a 2 times the temperature and have half the strength, ouch. I can combat the temp and strength problem with the use of a super alloy Inconel 718. It has about 3 times the strength of mild steel and is used in rocket nozzles. The only problem with Inconel is the 2 sheets I need 12" x 24 of 0.025" and 12" x 12" of 0.060" cost $400 total. Hopefully I will find something in between the $30.00 of mild steel and the $400.00 for the super alloy. So the bottom line is its hard and expensive but it is doable.
2) Making and fitting the clutch drum as shown in the original post. With 0.025" almost knife edge steel tangs and double the HP of the stock 560SL, I believe this should be made of a good alloy steel like 4340 pre-hardened. Not impossible but difficult for me to machine. The Carrier will also have to be machined out to accept this clutch drum, requiring specially hand made tooling and a milling machine with a rotary table. I do not have the rotary table I need to make this at the moment. Nothing $600.00 or so wont fix.
3) The axles on the 126/107 carrier are designed to float axially with the spider gear in that there is no bearing in the side covers. The 140 carrier has ball bearings pressed onto the axles and into the side covers. In order for the limited slip feature to work the side gear cannot be restrained axially. I cannot count on the side gear spline to allow for this movement under load. therefore the bearing has to be made a slip fit which means the side covers will need to be modified with liners. The axial motion only needs to accommodate 0.020" or so but it needs to be there. I'm hoping I can get away with opening up the bore and going with some spray on treatment like a process called DLC - Diamond Like Coating or something maybe cheaper.
So in any case I have come to the conclusion that this LSD diff is going to cost in the neighborhood of $2000 between tooling and material. But I haven't given up yet. I just ordered a used 1995 SL500 diff with the same carrier and ASR sensors. I am putting my diff back together so I can have a running car while I experiment. Due to the cost I expect this to be a year long project. I will probably start out by purchasing a rotary table and fabricating and fitting 2 clutch drums probably out of plastic first. If that all works out I will see about the bearing linings and finally purchase the Inconel backed clutches and steels.
|