Differential fitment
Differential fitment
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Non-fitting limited slip differential fitted into another model
Non-fitting limited slip differential fitted into another model
I had to rebuild the transmission on my car due to a noisy bearing, and I figured I could do some upgrades while I was at it. I was going into my Sophmore year of college. At the time I thought that a Limited Slip Differential (LSD) could be worthwhile because:
I had to rebuild the transmission on my car due to a noisy bearing, and I figured I could do some upgrades while I was at it. I was going into my Sophmore year of college. At the time I thought that a Limited Slip Differential (LSD) could be worthwhile because:
More power could be used while turning. My car is front wheel drive and underpowered; the limited slip differential would have allowed for a greater torque differential between the unloaded inside front tire, allowing for more acceleration while cornering. With the 76 hp from factory my car has, this seemed good for curved on-ramps in addition to the basic handling benefits.
It could help in the snow since there is more friction between the left and right wheels compared to an open differential so a slipping wheel would not make the other wheel 'useless'
There were no differentials that were readily available on the market for my car, but after measuring the factory differential of my car I found out a unit made for another model had the same ring gear location, bearing spacing, and bearings. After getting the differential, I found that I had to drill holes in the ring gear for fixing it, which I hoped would not compromise its structural integrity from the bolt clamping force.
There were no differentials that were readily available on the market for my car, but after measuring the factory differential of my car I found out a unit made for another model had the same ring gear location, bearing spacing, and bearings. After getting the differential, I found that I had to drill holes in the ring gear for fixing it, which I hoped would not compromise its structural integrity from the bolt clamping force.
A spacer ring was also needed between the differential and the gear, which I had made to a tight tolerance to make sure the gear fits tightly to maintain good runout specification and attempt to keep forces in compression on the gear's flange. This was also in hopes of reducing the chance for the extra holes to cause more stress by constraining how much the flange could move.
A spacer ring was also needed between the differential and the gear, which I had made to a tight tolerance to make sure the gear fits tightly to maintain good runout specification and attempt to keep forces in compression on the gear's flange. This was also in hopes of reducing the chance for the extra holes to cause more stress by constraining how much the flange could move.
I drilled the pilot holes for the ring gear on mills at school with my own carbide drill bits (the gear was case hardened to ~62 HRC), being able to finish about 3 hole. The rest were finished using a drill press at home and carbide tipped drill bits.
I drilled the pilot holes for the ring gear on mills at school with my own carbide drill bits (the gear was case hardened to ~62 HRC), being able to finish about 3 hole. The rest were finished using a drill press at home and carbide tipped drill bits.
The spacer was manufactured by Brazos Valley Drivelines. The price was high due to my tolerances, but I wanted to play it safe since the differential gear failing could be catastrophic because the wheels always turns with the differential even in neutral.
The spacer was manufactured by Brazos Valley Drivelines. The price was high due to my tolerances, but I wanted to play it safe since the differential gear failing could be catastrophic because the wheels always turns with the differential even in neutral.
The speedometer gear was designed by me using the original as a reference in SolidWorks. It was printed through JawsTec in PA12 using a Multi Jet Fusion process. PA12 was selected since it has good chemical resistance toward oils, which it is bathed in since it is installed in the transmission. The glass transition temperature is quite low but its heat deflection temperature was quite high so at the time I thought it was adequate for the application of spinning the speedometer cable drive gear which is quite low load.
The speedometer gear was designed by me using the original as a reference in SolidWorks. It was printed through JawsTec in PA12 using a Multi Jet Fusion process. PA12 was selected since it has good chemical resistance toward oils, which it is bathed in since it is installed in the transmission. The glass transition temperature is quite low but its heat deflection temperature was quite high so at the time I thought it was adequate for the application of spinning the speedometer cable drive gear which is quite low load.
Much of this project was quite rushed since I did not want to occupy my parents' garage for too long, but ended up being pushed back several times due to school. Next time, knowing what I know now as a Senior, I would attempt to calculate the fatigue life for the speedometer gear to get an idea for its expected life and see the effect of the extra holes on the stresses on the differential ring gear using FEA due to the complex geometry in that area, including the fact the new holes intersect with a large chamfer. It was fixed onto the transmission using rubber gasket maker since it is chemical resistant and has enough adhesion for this relatively low force application, while having plenty of surface area for bonding.
Much of this project was quite rushed since I did not want to occupy my parents' garage for too long, but ended up being pushed back several times due to school. Next time, knowing what I know now as a Senior, I would attempt to calculate the fatigue life for the speedometer gear to get an idea for its expected life and see the effect of the extra holes on the stresses on the differential ring gear using FEA due to the complex geometry in that area, including the fact the new holes intersect with a large chamfer. It was fixed onto the transmission using rubber gasket maker since it is chemical resistant and has enough adhesion for this relatively low force application, while having plenty of surface area for bonding.
The car has been regularly driven with the differential installed since June 2022. As of September 2023, approximately 8000 miles has been put on this setup, with 3000 of those miles consisting of 1000 mile road trips between Colorado and Texas.
The car has been regularly driven with the differential installed since June 2022. As of September 2023, approximately 8000 miles has been put on this setup, with 3000 of those miles consisting of 1000 mile road trips between Colorado and Texas.
The only major failure so far is a differential seal popping out in August 2023, since it cannot be fully seated or it will not properly sit on the oil seal boss on the axle. Currently, a wider seal or installing the seal with rubber gasket are being considered since the transmission would need to be structurally different otherwise.
The only major failure so far is a differential seal popping out in August 2023, since it cannot be fully seated or it will not properly sit on the oil seal boss on the axle. Currently, a wider seal or installing the seal with rubber gasket are being considered since the transmission would need to be structurally different otherwise.
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