http://www.aam.com/technology/tech_p...frontaxle.html

i have always thought the front diferentials in these trucks were prety weak. i am not positive but i think the 1500 trucks have the 7.25 front. that unit is rated at 3165 Nm, that converts to 2334 ft-lb's

if you take the 2.5 1st gear that the 4l80e has that would calculate out to 933ft-lb's at the motor. seems like they are prety strong to me. i have been waiting for it to break but it apears that breaking is not gaurented like i thought.

then there is the fact that the tq is split between the axles so only part of the tq made by the motor is geting to the front diferetnial. it seems to me avoiding any wheel hop and impact loading is the key. if there is no wheel hop it apears the front end can survive a lot of power. as odd as it sounds i think dead hooking to avoid wheel hop will help survival of the front diferential.

 

hey, just found at http://www.drivetrainsuperstores.com...fo.asp?axle=77 they say we have the 8.25" front. that is rated at 3583ft-lbs or about 1400 motor ft-lbs.

that is just nuts, i wonder if i am going something wrong? i think they might just be that strong because of the low range of the t case.

 

Did you take into effect the actual gear ratio as well? 3.73 plus your trans gear of 2.5

 

What about the torque converter torque multiplication?

 

I usually unload my bars to help keep the front end from springing up and keep the front wheels from toe-out. We still get some hop if you try to leave with too much boost.....but sometimes it's hard to resist. The other problem we have...with the HDs that is....the tie rods are less than sub par. Go over to the DieselPlace.com and llok for a guy that posts as SuperDiesel. He has made a few sets of stainless steel sleeves that go over the tie-rods and help support them....not sure if the regular trucks are the same size or not....but it's worth looking into. A bent tie rod or broken one for that matter....is quite embarassing at the track.

edit..I realize this was not the topic of the post, but when he was talking about front end hop, it crossed my mind.

 

i dont think the gear ratio of the diferential has an effect of the input tq rating but the TQ multipication of the converter does. i think using 2.2 for a STR would be a fair guess. so 3583/2.56/2.2= 636 ft-lbs. that still seems like a **** load of tq.

it is after the tranny and after the tcase so they eat up some tq and then the tq is split between the front and rear. not sure at all how much goes each direction. then remember the STR only is in effect for a short period of time.

i have been suprized that the front end in my truck has lasted this long but after seeing the numbers it kind of makes sence. i still think if i can avoid wheel hop it might take me into the 9's.

 

I'll bet with a smooth launch that axle would take you a long way further than a wild wheel hop launch. The tq would really spike when a spinning wheel slams into stationary pavement.

How are your launches now? It looked like the 10.91 launch was really smooth. It's hard to tell from a video though.

 

Do you remember the tq ratings for the 1/2 ton autotrac and your transfercases?

 

yes, the autotrack was something like 2500ft-lbs and the hd case is over 5000ft-lb's. since that is after the tranny you have to divide by 2.5 and that is over 2000ft/lbs at the motor(not taking converter STR into acount).

i have pushed it harder out of the hole and got wheel hop and ended up backing off on the nitrous for a smooth launch. there was prety much no wheel spin on my 10.91 run. that was with a 75shot. both times i tried a 100shot i got a lot of wheel spin.

i can't find any posi for the front but that AAM site almost looks like one might be avaliable.

 

Have you even tried turning the bars down...unloading the front end. I know I only have a few posts here, but trust me it works. 1.80 60 ft in a 7k Diesel....without unloading the bars...high 1.9 and 2.0 and it pulls back and forth. It's worth the 5 minutes under the truck to give it a try.