... I am in the reseach phase of a project. All hush hush ya know.

I am trying to find out about any High HP explosions of T-18's or SM420's or the SM465 particularly the input shaft.

Second part are the input shafts on the SM's 10 spline like the T-18's?

lets say the clutch won't slip..........

I take it that means no.....??.........and or that no one has had that issue..


Basically I am looking for a real world scenario on whether or not. doubling the torque applied to the input shaft has shown to have drastic results.

taking your semi-standard 300 hp motor and doubling the torque applied to the input shaft via massive hp upgrades or diesel engines???

We all know a T-90 won't take a V8, but what is the torque limit to a Heavy duty truck transmission?

Are they strong enough, that we realistically can't exceed that limit. I think not. but what is the upper end.

I have seen many HP explosions of car trannys. Muncies and Saginaws Most of these were in cars with 400 hp plus, and normally the cluster gear let go.

Call me stupid,,, Flame Me,,,,, but if you have any information it would be appreciated.:confused:

trannies are rated on torque, not HP.
T18's and SM465's lived happily in Diesel dump trucks with 500 ft-lbs of torque. I'd check with Novak convertions as the the actual torque limit of the trannies.

If you feel it's a big deal, you can get a replacement input shaft for an sm420 that is 1.5" and I think 10 spline. Shaft and input retainer are larger, everything thing else is std. These were used in large diesel busses. Dump trucks had the standard input shaft and I haven't heard of it being a problem. pm me if you need the hd input, and I'll give the contact info for where they are.

A T-18 input shaft is 1-1/8" in diameter. About the same size as a D44 30-spline axleshaft. So people break axleshafts with (for the sake of argument) 350 lb/ft from a stock engine and a crawl ratio (again for the sake of argument) of say 50:1 - feel free to substitute some other numbers here. This hypothetical combo is putting 17500 lb/ft to the axleshaft. So if your engine will be delivering in excess of 10k lb/ft to the transmisison input shaft you might have reason to worry some about twisting it off. I really think that something else (behind the transmission) will fail first.

T18's and SM's you mentioned are very strong pieces. IMHO the NV5600 is not as strong and it lives behind Cummins that people push past 1000 lb/ft rear-wheel. I've seen T18's behind BB Fords and SM465's behind BB Chevys that had to be making comparable amounts of torque live long and happy lives with no issues. Right now in the parking lot here at work is an orange GMC that has a 6-71 blower on a hot 427; he can twist off axleshafts at will, but the transmission has never been an issue. (Owner uses it to tow his 9-sec. camaro).

I wanna know what you think you'll build that'll out-pull THAT one... even without the nitrous.

This hypothetical combo is putting 17500 lb/ft to the axleshaft. So if your engine will be delivering in excess of 10k lb/ft to the transmisison input shaft you might have reason to worry some about twisting it off.

this has been brought up before and it is not a realisitic way to look at things. your tires will NEVER (EVER) generate 17500 ft-lbs of torque. there is a finite traction limit dictated by the weight of the vehicle placed upon the tires, and the ability of the tire to generate friction on the ground. even if you jam a tire hard into a rock, you would first break an axle shaft or drive shaft u-joint before anything in the drivetrain. or flip over, since 17,500 ft-lbs of torque would put you right on your head.:flipoff2:

Seems like Moser thinks is certainly possible to put 12k lb/ft per axle. http://www.moserengineering.com/moser_interior/axletech.htm

if you're going to have 3000hp top fuel dragster with 24" wide superglue tires and wheelie bars, you MIGHT have a chance of generating mad torque, but you, as a 4 wheeler, will never see it.

If your truck is 4,000 pounds, and has a 10 foot wheelbase, and the center of mass is around the midpoint of the truck, you have a lever of 5 feet applied to that. So that 17,500 foot pounds would be applied against 20,000 of leverage. So now we can see how hard it is to pop a wheelie. Of course, as we start climbing a steep wall, the lever effectively shortens, and we see rigs topple backward occasionally.

Don't nitpick these numbers. specifics don't matter, the important thing is the principle.:D

Guy with that orange truck I mentioned has been through FOUR SETS of Warn axles for his D44 front. How much torque does it take to twist off a 4340 30-spline axle? Not all ujoint failures either. So take 4340 which may have a yield near 180 ksi depending on how it's heat treated, it's 1.31" diameter, and you tell me what it takes to twist that fucker in two.

Thanks 82FB.

Good info here..

And is what I have already been reading.. I have not heard of any massive failures of truck transmissions under applied torque.

I have read about many that had other problems, that caused failures.

Thanks Folks

Guy with that orange truck I mentioned has been through FOUR SETS of Warn axles for his D44 front

he's got a detriot, doesn't he?

If your truck is 4,000 pounds, and has a 10 foot wheelbase, and the center of mass is around the midpoint of the truck, you have a lever of 5 feet applied to that. So that 17,500 foot pounds would be applied against 20,000 of leverage. So now we can see how hard it is to pop a wheelie. Of course, as we start climbing a steep wall, the lever effectively shortens, and we see rigs topple backward occasionally.

Don't nitpick these numbers. specifics don't matter, the important thing is the principle.


I don't have to nit pick, the 20k torque is split between the two axle shafts, cutting it in half. :D and you'll never see that much traction on dirt or mud. maybe slickrock on a hot day, but that's all I can think of.

IMO this thread may have gone off at a bit of a tangent. There are a lot more issues in a transmission than just input shaft strength; tooth design, pitch, contact patch, side thrust, case flex, shaft deflection etc and how all these interact are all concerns that relate to your obsevation that cluster gears often go first. I still maintian that the transmissions you mentioned have been known to withstand regular doses of over 1000 lb/ft without issue.

Back to the tangent of shaft strength. Not a detroit in front, an ARB. By "sets" of axles I mean full sets; two inners and two outers; a total of 16 destroyed Warn shafts. If one shaft was only twisted off, it was replaced solo. Obviously in some ujoint failures both shafts have been destroyed and pieces of knuckle launched into a low earth orbit.

BTW that 180 is a fairly conservative number. And in this illustration, you do NOT get to divide by two. :D

You guys are lookin into this a bit much. Anything can break. I broke my NP435 three times. There is no way to calculate axle loads very close in a trail situation.

Originally posted by KYODER
[BThere is no way to calculate axle loads very close in a trail situation. [/B]

Bingo. But ARB tests their locker designs by putting them in a fixture, installing a Warn shaft, and applying torque until something breaks. This is all very controlled and easily measured, and the answer to the question I posed above is MEASURED at over 20k lb/ft. Per shaft. And I can walk across the lot to the machine shop and fetch a man who has a big pile of broken parts to demonstrate that these stresses can be regularly achieved in a 4x4.

FWIW, there are some guys on the TDR site that have blow the input shafts on NV4500s behind Cummins. However, all the cases I remember reading of were in severly abusive situations (ie sled pulls), with tweaked motors, and nasty clutches (like the dual-disk, solid-hub Mcloeds (sp)).

Pete

I broke the output shaft between the Atlas and the NP435. The Jeep has seen much abuse! Did I mention the Big Block Chevy. I did not expect it to break where it did. Anything breaks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!

Originally posted by KYODER
Anything breaks!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!

Everything except T18 imput shafts. :flipoff2:

Originally posted by KYODER
.... Anything breaks!!

No argument here. Nor will I argue with Pete about what he said. For factory applications that put out >1000 lb/ft there is a Spicer 5-speed transmission I've worked on that has an input shaft about the size of my forearm. These will put up with a 12V110 Detroit or a KTA600 Cummins, or a UD24 International....

Given the dimensions of a single part, the mechanical properties of the material, and the stress applied to it, the probability of failure is given by the Weibull modulus. This is a straightforward (but algebraically involved) calculation.

Sounds great, I will now see if I can break one.