IFS SURVIVAL: PRETTY BASIC REALLY!
Is IFS as strong as a comparable straight axle in overall axle torque rating?
Yes. The biggest reason for IFS failure is lift kit manufacturer insufficiencies in testing and trail use before the
lift kits are released to the public! Many Manufacturers drop the front diff inappropriately creating increased
CV angles at their claimed lift gain, leaving the cv's at their greatest operating angle with the wheels straight. If
the steering is turned a little, the outer cv's are beyond their operating angle, and disaster is at the next turn!
Can IFS handle more high speed abuse and jumping than a straight axle?
Yes. This is common knowledge in the off road world that when it comes to speed and suspension abuse IFS is
king! It's pretty straight forward when you think about your suspension moving over bumps! On an IFS truck the
largest amount of weight changing direction is your front tires. On a straight axle, most of the weight cycling up
and down is the entire front axle, so this weight moving rapidly under the vehicle creates extreme harshness
making the vehicle uncontrollable at higher speeds. In many cases a 1 ton front axle with large tires may weigh
more than the frame and chassis, so you know who's gonna win the smoothness battle here!! Not the Chassis,
but the front axle!! This will take a toll on electrical wiring, radiators, hoses etc. Lets say this is an example of
50/50 weight ratio. Most IFS weight Ratios are more like 95/5. Pretty easy to see why IFS rules here! It also
goes to reason that if you put a 1 ton straight axle under a small vehicle it is alot more dangerous at speed!
Do Some IFS lift kit manufacturers, cheat by not lowering the front diff. Adequately?
Absolutely! Don't want to mention any names, but many lift kits that claim 6" of lift only lower the front diff
3.75"s! This increases your CV angle 2.25"s. Basically the only safe amount of lift would be ~ 4"s on these
particular kits. When a truck is lifted, normally larger tires are going under it, so not lowering the front diff to
OEM specs is a ticking time bomb for the CV's and front diff!
Is the 1/2 ton GM/AAM 8.25 diff just to weak to be a contender with SAS (Dana 44)?
Yes, we have found this to be true!! For whatever reason the AAM 8.25" by weight and size ratio is very
insufficient when compared to the AAM 7.25" that is under the S-10's, or the 9.25" under the 8 lug 2500-3500
trucks! We have found that the 8.25" is only capable of handling only 7% more axle torque than the AAM
7.25", and can handle only 63% of the axle torque that the AAM 9.25" can!! (Realift testing) Maybe gas
mileage and efficiency won when it came to the 1/2 tons! If you have a 1/2 ton get the 9.25" in it or be
careful!! Without a locker available we performed all testing on the 8.25" with it spooled. We found that the
cases surprisingly survived much better when locked than with open diffs. The side pinion gears acted like a
wedge's stretching/spreading the 3rd members making the aluminum case more prone to breakage! Aluminum
cases do not hold up well to the shock loads of an open diff or unlocked 3rd member when severe
differentiating occurs! We would recommend to always have the differential locked when putting extreme loads
on the AAM Series ICA's
Is the AAM 9.25 diff as strong as a 99-08 3500 1 ton Dodge truck in terms of axle torque?
Yes, with a good lift kit that is installed correctly this statement has been proven! As it turns out they are
basically the same axle, 1 is an I.C.A. (Independent Carrier assembly) and 1 is SAS (Solid axle suspension)
These axle's both share most of the same 33 spline axle parts.
Is it's OK to crank up the torsion bars to get fender clearance to prevent tire rub?
Never, this is the silliest thing that an individual can do to their truck. Here's why!! When you crank the torsion
bars you didn't just raise the truck you weakened your CV strength and steering strength. The reason it is
harder on the cv's and the steering isn't just from the extra angle, but more from the increased load on
your tire at any given angle of the suspension cycle, which means more traction and load at the more
dangerous angle. At the oem operating angles the suspension supports the entire weight at this given angle,
and the cv's and steering system can handle tons of abuse because the load on the cv and steering
decreases as the wheel extends. For Example: If the wheels are all the way drooped/extended in OEM form,
there may only be 250-300 lbs of load on the tire so it's nearly impossible to put a tremendous amount of strain
on the cv's or steering because the suspension loading is too soft. Crank the torsion bars up and now you may
have up to 1,000 lbs of load on the tire with the wheel drooped/extended. Potentially 4 times more force with
the cv's and steering angles at there most vulnerable point.
What about the Red sled in Peterson's? What happened here?
The red sled for starters used the weakest 9.25" front diff of all G.M. trucks the 88-96! The 97-08 are much
better. Lots of extra reinforcement has been added to the aluminum cases and better axle heat treating
processes. The red sled was obviously an example of many things stated above! The front diff was not
centered, this is terrible, because the cv's will both work incorrectly. 1 side bottoming in the tripod joint and the
other trying to pop out of the tripod joint. This is hard on everything. You cannot break 2-3 cv shafts and
expect not to do some damage to the (ICA), which ultimately happened. I have never broken or seen any 9.25"
cases break the way the red sled case broke. (1) I have a feeling that the drivers side case half had worn
bushings therefore making the passenger side half handle most of the torque. (2) The drivers side cv shafts
bottoming on the tripod joint put to much side force on the right hand case, and (3) I also think the 3rd member
support bearings may have been to tight also. (4) When the case broke the front locker was not engaged,
which would make it more prone to break a case.
It may not make sense to an old time SAS guy, but it's true! So basically they proved all of our historical facts
in just a few articles and a few issues, just not how to fix them! I think it's sad that they stopped prematurely on
the sled. 1-2 more article's and they may have really turned some heads!
Would the installation of a front locker just destroy IFS front cv axles?
No, on an IFS setup the locker actually helps it survive, mostly because the wheel with the most traction
happens to be the wheel with the better cv and steering angles. It also reduces the force at the extended wheel
dramatically since the wheel with the most traction is the one most apt to do it's job. Normally with an open diff
the wheel that is extended or drooped takes all the axle torque which is exactly what you don't want.
I hope this has alleviated a lot of the war on IFS/SAS.
If your truck is set-up correctly breakage should only occur on the cv axle shaft or tripod joint, although these
failures can ultimately destroy a case half. We have broken alot of stuff over the last 7yrs. During the first 3
years of this testing we destroyed countless #'s of cv axles, cases, driven axles and steering components with
just minor to moderate wheeling! Since we have learned all of the things stated above this is what we have
broken in 4 more years of Severe Rock Crawling:
7.25" with 35" tires (3 S-10 cv axle shafts, 1 Tripod joint, 1 Aluminum Case while reversing)
8.25" with 35" tires (7 1/2 ton cv axle shafts, 2 LH stub shafts, 2 Cases broken from tripod joint interferences
and broken stub shaft interferences)
9.25" with 37" tires (Nothing after our most severe testing yet) Just for the heck of it we delivered full throttle
power to just 1 front axle the drivers side then the passenger side with a 1993 200 HP 4.3 litre in low range in
1st gear equipped with 4.88 gears and no breakage occurred! The 7.25 failure occurs at about .25 throttle the
8.25" Failed just under 1/2 throttle!
THE LEADER IN NON-DROP TORSION BAR RELOCATION!