Transmission Ratings..???????

[only90s]

What is the deal with Transmission Power Ratings...?


Seems like stock T5s can handle much more than the 300 horse rating (or about) they are rated at. Bob and I have both been throwing over 500 flywheel horse at ours for about 3-4 years and now Bob is putting over 600 flywheel horse through his and they dont break...?


Also I believe the T-56 behind the Terminators is only rated at 440 ft/lb of Torque and we all know with a few mods they are well over that and they live.

I realize if racing and slicks were involved things would be different.

But in the real world what is the deal...why do these trans live with so much more power..?



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I ask because I decided some time next year I need to rid myself of the Ridiculous .79 Road Race 5th Gear in my Fox and get a new trans. I am torn between spending about $2500 for a G Force rated at 600 horse or a Super Alloy T5 (rated at 450 horse) from Astro or ProMotion for about $1100.

Common sense tells me to step up to the G Force with the 26 spline clutch and be done with it-even when I build my next motor I should be good...>BUT my cheapness tells me I dont need that much trans and spend less.....

[Mustang5L5]

I've got some good technical answers for this but unfortunately it wil have to wait til tonight

[only90s]

Cool...no hurry at all.

[Mustang5L5]

basically the torque ratings of the trans are "guesses". Yeah i know that's not really a good answer but it's kinda true. They are really calculations based on the tooth contact area vs estimated torque applicable in terms of shear strenght of material used...with a safety factor built in. Yeah, that sounds complicated. Basically some smart engineer figures out the specs of the steel used, the estimated force on the tooth contact area and the torque multiplication and calculates out the rated load with some safety factor in it. A bunch of mumbo jumbo i know.

The 3 main factors in trans torque rating are:

#1 Gear material
#2 gear "spreading"
#3 gear ratios

For example. AN 85-89 T-5 is rated at 280 ft-lbs. That's 20 ft-lbs less than what the engine is rated for from the factory. Of course, there is some safety factor. Who knows what it is? could be 1.5X or 2X meaning the teeth will shear at 450 ft-lbs or so. Who knows. But in 1990, Borg warner upgraded the material used in the gears and the rating increased to 300 ft-lbs. This increase is due to #1... factor of stronger resistance of the teeth shearing.

The biggest weakness of the t-5 is the fact that under load, the teeth of the gears want to push each other apart. This is #2 on the list above. The bad part of this is that the farther apart they are, the less material is in contact. So the faster the gearset spins, the more force tries to spread them apart. 3rd gear always breaks because this gear is the furthest from any sort of structural support, so the mainshaft flexes more here. Since it can flex more, the gears spread and the teeth shear (back to #1). It's one of the most common, if not the most common cause of t-5 failure.

Ford revised the bearing design between the input and mainshaft in 1993 to reduce the deflection of the mainshaft. They implimented this on the 93-95 cobras, and as a result, the gear spread was lessened and the torque rating was now 310 ft-lbs.

For the Z-spec trans, ford changed material, and the gear ratios. The ratios are slightly lower, which allows more torque rating due to less torque multiplication...so now you have a 330 ft-lbs rating with the Z-spec due to #3. The 4-banger t-5 is rated for 240 ft-lbs. Why? gear material is the same. Gear spreading is the same because it uses the same mainshaft and case. It's because the 4-banger gear ratios are shorter allowing for more torque multiplication through the gears. For that reason, the torque rating must be dropped. If you could drop the ratios far enough, you might be able to blow a t-5 with a 4-banger engine too!

Why do they hold more power though? To be honest? Luck. SOme trans are built tighter than others, some have better materials, and some have BETTER DRIVERS! Depending on how you drive, your style might play a huge role in how the trans lives. If you don't powershift, and don't shock the trans too much, you can make them live behind 400HP. But other guys break them behind stock 5.0's. There is also the luck of getting a good, well-built t-5 with good gear material and built tightly to reduce the spread of the gears.

So how do the aftermarket T-5's increase strenght? Well, depending on what options you get, there are a few ways. #1 is different, stronger gear material. #2 is altering the way the teeth are cut. helical gears are quiet..but weak since a smaller gear area is in contact at a time. Aftermarket gearsets use straighter cut teeth...or perfectly straight teeth. These give more contact area, so they resist shear more. Downside is they are noisy. Why do you think reverse is so loud? It's a straight cut gear. So don't get straight cuts unless you can live with that noise in all 5 forward gears. They also provide a stronger mainshaft which doesn't deflect as much as the stocker. Finally the case can be revised so it's also stronger and resists allowing the internals to flex away from each other.

I don't really know if i answered your question, but hopefully i gave you enough info you can formulate your own answer from it. I myself am pondering the same question. I want to stay with the t-5 since it's light and shifts like butter and easy as hell to rebuild. I have a t5 here i am rebuilding and was thinking of either a Z-spec t-5 gearset or an astro gearset. I'd do the build myself. I only want about 350-400HP and think it would be fine for my needs.

I've rebuilt five t-5's so far. As far as i know, all 5 are alive and kicking still. 3 were sold. One is in my car, one is a friends car and i currently am working on #6 which will be my primary t-5 (and my current t-5 will be my backup)

[TorchRedSVT]

good read mike...thanks for posting

[only90s]

Great read....Thanks for the info...

[PROTREE]

they dont last under load , you can put 1,000 hp to it but if it does get loaded it cant break ........

[JB's 90 LX]

My car is nothing radical but I have never had an issue with my T-5. It has held up extremely well even on ET Streets on a mid-12 second car cutting 1.6x short times. This off season, I finally decided to go with an Astro A-5 as i'm now running a mild supercharged application and figured better safe than sorry!
I just ordered the gear set yesterday. Haven't decided if I'm going to have a go at rebuilding my trans myself or have it done. I'll post another thread on this subject so I don't hijack yours.

Good luck with whatever path you take.