And it kept me awake until nearly dawn thinking about getting an overdrive for the T-10 by swapping in an OD for 3rd and changing the shifter to allow it to be the new 4th.
In doing my research for this I discovered that the OE 3rd gear is already a slight OD as the ratio between the input and cluster shafts is 1.28:1, while the output from 3rd is 1.23:1, which means the ratio of the gears on the 3rd position of the transmission is already an OD just not very much of an OD, 0.96, probably just a tooth larger on the cluster than the main shaft. It’s looking like I will have to order a custom cluster with a custom gear for the main shaft that is as small as will fit. This is not an inexpensive alternative.
And it’s not like I could amortize the costs by selling duplicates at a profit until the tooling costs are covered. This application is very niche, not many people are in the market for this combination of light weight and OD top gear, and can live with only 4 speeds. Also I have been looking at the ratios in use on the transmission and most of them are not actually useful in making 3rd OD. Swapping the gear for 2nd gives an OD that is not even enough to make the output OD, the gears are 1.25:1 as they are before swapping which is less than the 1.28:1 of the input gears. So basically I’m looking at finding the smallest gear that will fit the output shaft and designing a gear to machine into the 3rd position on the cluster and hoping the resulting ratio is enough to be more overdrive than the underdrive ratio of the input shaft to the cluster. Also most of the different ratios available are just from changing the ratio of the input to the cluster, the 2.43 S cluster, and the 2.64 W cluster are the same ratios except for the input/cluster gear. In fact checking the spares list shows that most of the ratios are shared with common 2nd ratios for the S, W, CC, and Z clusters, common 3rd for S and W, and common 3rd for X, CC, and Y. So yeah, I will have to order a special cluster and gear for the main shaft if I want to hang an OD 3rd on my transmission.
And I have been going back and forth between the PDF of the spares list, the calculator app, and this post for like 4 hours, it’s time to put this one to bed.
And yes that is an actual number, it’s google to the google power, an impossibly large number I’m using for humorous effect. If you are wondering exactly how impossibly large, that is a 1 followed by google zeros.
But I have already gotten on a tangent (SQUIRREL!) in only one paragraph. That’s not a good sign for the rest of the post, but I’ll be good and make it make sense. What I have been contemplating is weight reduction in the powertrain.
This takes us back to the engineering maxim of choice: Light, Strong, and Cheap; pick two. I absolutely need light, and I need to balance strong and cheap. The idea here is start with the Super T-10 aluminum case and make or modify the cluster and counter shafts to get 1st and 2nd underdrive, 3rd direct, and over drive in 4th by putting the overdrive in the 3rd position on the cluster and modifying the shifter to swap 3rd and 4th on the pattern. The effect will be a manual version of the gearing in the 4l80, except way lighter and more expensive but still lighter and maybe cheaper than the 5 or 6 speed manuals.
I’m still not sure of the best way to do it because I’m not a transmission engineer, I’m just a shlub that has lots of time doing systems. My initial take is copy the gears from 1st, and put them on the 3rd spot on the cluster, except swap them between the cluster and the main shaft so that it overdrives instead of underdrive. This compensates for the underdrive between the input shaft and the cluster, and gets me a decent amount of overdrive, without having to spend a bunch of money, hopefully.
There will have to be some money spent obviously, but I’m hoping this will reduce how much money that is. The plan is taking the 2.43 1st cluster and machining 3rd gear to the outside diameter of the main shaft, welding the main shaft gear for 1st where 3rd was, and machining the cluster gear for 1st from another cluster to install on the main shaft, or machining the profile of the gear onto a main shaft gear. The modified cluster will need to get heat-treated again because of the loss of strength from welding the new gear on it. And I won’t get a 0.403 overdrive because of the reduction between the input shaft and the cluster, I’ll get 0.403/(whatever the reduction from the input shaft to the cluster)2 because the initial ratio is reduced by the input shaft reduction and then again as an overdrive because the installed gear is driven by the reduction still.
And it’s late for me (0400) and I need to get some sleep, so I’mma pack this one to bed and me right after.