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Old 12-07-2020, 08:21 PM
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Originally Posted by eschaider View Post
The simple answer to your question is in bold about midway down this post. The why and wherefore stuff is what is in front of and behind the answer.

For transmissions, strength is not a horsepower metric it is a torque metric. Most enthusiasts loose site fo this and fall back onto the romantic notion of who has more horsepower going through their transmission as an indicator of strength. Transmissions are torque multipliers and as such their measure of strength is their capacity to transmit torque.

There are three metrics that in large part determine a transmission's torque capacity (strength);

The first is the center to center distance between the mainshaft and the countershaft. The greater the distance the greater the torque capacity — all other considerations being equal. Larger center to center distances provide larger levers if you will.

Think of the distance from the gear tooth's optimum tooth contact point to the center of the gear as a lever. Just like when you use a pry bar to open a box, the longer the pry lever the greater your leverage. In the transmission it is similar but we rely on the gear ratio for the leverage. The center distance is a measure of how much gear mass that leverage (torque multiplication) is spread across. Not surprisingly more is stronger less is weaker.

Now expand the single gear image in your mind to two meshing large diameter / large center to center spaced gears vs two smaller diameter, smaller center to center gears. You don't need the math to get the right answer. The bid stuff wins every time!

The second metric is gear face width. This one is comparably straight forward. Wider faced gears are stronger than narrower faced gears. It's not rocket science. Once again in this situation more is better.

The challenge the design engineer has with large diameter, wide tooth faced gears is inertia. When you change gears, it is the synchronizer's job to match gear speeds on the gear change so you have a smooth (hopefully fast) gear change possible. The large diameter wide tooth faced gears have huge inertia.

That is one of the reasons the TKO shifts so poorly. It literally uses 1960's Top Loader synchronizers to attempt to synchronize much larger heavier gears than they were ever designed to handle. When Trmec did the T-56 they initially used double cone synchronizers because the gears were so huge. Later for selected OEM customers they began to supply (without a lot of fan fare) triple cone synchronization which later found its way into the T-56 Magnum.

The third and final (for this discussion) metric is the steel and it corresponding heat treat that the gears are made out of. We all have heard the common 4000 series molybdenum steel designations like, 4130, 4140, 4340 etc. There ar other steels up in the 8000 series that are used is some ring an pinions and a few specialty steels like the high nickel 9310 steel that is useed by Rockland Gear in their T-56 Tranzilla six speeds.

The overall strength of a given sized gear can be enhanced through the selection and use of specialty steels heatreated to a particular strength and hardness. Generally harder, tougher (hard to get both together) and higher tensile produce more desirable gears but each comes with it own set of idiosyncrasies the need to be catered to for a successful implementation.

Tremec uses a proprietary steel that has served them well (for the most part) in daily driver type applications. Rockland uses a particular 9310 alloy and heat treatment for the strongest T-56 six speed derivative available any where today. The Rockland T-56 style Tranzilla has a torque rating in excess of 1000 ft/lbs of flywheel torque. Liberty uses yet a different alloy for their Prostock clutches transmissions. Each alloy / transmission design is optimized for the target market the manufacturer was aiming at.

Now to your original question about the 1⅜ inch Top Loader input shaft.

By increasing the diameter of the input shaft you increase its strength only. It will have no impact on the strength of the gears internal to the transmission only the input shaft.


This becomes apparent with the original Tremec T-56 offerings for the Mustangs. Originally, they used a standard Ford input spline configuration. In service behind the supercharged 03/04 Cobra's these shafts began to shear off. The Tremec fix was to offer a larger diameter 26 spline input shaft based off a GM spline spec. It wasn't the spline count that saved the day (although it didn't hurt) it was the larger diameter input shaft. The input shaft change in diameter had no effect on the torque capacity of the transmission's internals, they remained the same.

You will see transmission manufacturers from time to time rate a transmission they offer at a particular torque spec. If you ask them how the transmission's torque capacity was determined (and you are persistent enough to pursue the answer) you will find that they have no real torque rating capacity available to them or that they want to use. Tremec does and for the most part their recommendations are pretty much the way it really is.

The aftermarket manufacturer that is blowing smoke up your behind will couch his torque rating representation with words like, "but not in a heavy vehicle" or in cars below XXXX lbs. This is someone who is trying to sell you a transmission and doesn't want the diminished torque capacity of the design to kill his sale. you should put as much distance as you can between those businesses, their transmission and your car as you can.

If a transmission is capable of XXX ft/lbs of torque transmission then it can do that in a light car or a heavier car. XXX ft/lbs is the same in either situation. What is not the same is the impact the gear teeth see at the time the clutch is released.

The shock loading on the gear tooth face from an aggressive clutch goes up considerably as vehicle weight increases. FWIW aggressive clutches that shock the drive train do nt perform as well in a race environment as a smooth engaging clutch that does not shock the driveline.


Ed
Install "X" transmission in your car and get "Y" results.
Oh Jesus effing Christ man... blow it out your ass! Seriously, ban me from this site but dude you can't please everyone, especially your sorry ass. Do you work for Tremec??? No seriously, you must work for Tremec with as much horse**** as you spew here! I'm tired of this ****, another prima donna spewing hore**** here. Tremec is the ONLY transmission??? Give me an effing break!!! Obviously you have never raced ANYTHING. Please, enlighten us with your racing experience!!! Oh, I'd love to hear that!!! Go karts, slot cars... what else??? Oh, hold on...let me pull that up from XYZ's website and give you a bull**** answer!!! Again, these internet commandos have ALL the answers!!!! Please, adhere to all their recommendations and ask what NHRA team they work for...

Last edited by jetblue69; 12-07-2020 at 08:27 PM..
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