Transfer case/Dyno question

[Ordieh]

Anyone have an idea why 6 hp more on dyno with front drive shaft removed in 4hi lock vs 4hi , shaft in and just strapped down (both obviously with tc off)? My tech has an explanation. I'm just curious if there might be another theory.

 

[4speedfunk]

Of course. You're not driving the front axle.

 

[JPaul]

It seems counter-intuitive, but it really does add some powerloss when you're powering the front axle in addition to the rear. My Jeep Liberty had a center axle disconnect where the front driveshaft was disconnected inside the transfer case, but it and the front axles still spun while moving since they don't have freewheeling hubs. You'd still get better gas mileage that way then with all four tires being driven by the engine.

 

[Ordieh]

In 4hi and shaft in, nothing in the front drive is turning.......it is just sitting there strapped down and spinning the heck out of the differential in the transfer case. I noticed that the case gets pretty warm (not enough to burn your hand) with just one pull! Next time I put Homer on the dyno, I'm going to check the temperature and then switch the Dex VI out for Royal Purple and see if there is a temperature drop on a subsequent pull. Any additional insight into experiences with H3's on a dyno will be much appreciated.
P.S. Homer has a brand new 4494 so there shouldn't be anything abnormal going on inside the case.

 

[4speedfunk]

H3s should always be ran on a 4-wheel dyno. Ain't preachin...just what I've heard. Probably cooking the sun & planetary gears by running for any length of time like that.
I would recommend pulling the front shaft and doing your dyno runs in 4hi-lock, with the rear wheels only. This way you aren't slipping the t-case so much. I think there may be some safety reasons as well.


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[atvspeed4]

You should NEVER take driveshaft out and run transfercase in AWD!! That is absolutely cooking your transfercase. If you are going to pull front drive shaft, do what was said above and put in 4hi lock before removing shaft and running on dyno. That is like pulling an axle shaft on a rear limited slip and flooring it...

I am surprised that on a dyno the traction control was not freaking out that the front tires were not moving but the rear were spinning.

 

[4speedfunk]

Yup. I agree.

Actually the truck won't even move with the driveshaft out and t-case in 4HI-Street. It will send all of the power to the front output flange and the truck will sit still and spin the front output. Rear axle gets nothing.

You are essentially doing the same thing to the rear axle, when you strap it to a dyno and leave the front wheels on the ground and the t-case in 4HI-Street. Front axle gets nothing.

It does this because in 4HI-Street mode...the t-case will always send the power to the end that is spinning (i.e. raised, broken, or disconnected). His is why we must use 4HI-lock to get anywhere with a broken axle or removed driveshaft. Like ATV says...spinning only one axle in 4HI-Street means the torque-sensing (sun & planetary) gears are working overtime.

Use a four wheel dyno. Or pull the front shaft, put it in 4HI-Locked, and do a rear-only pull on a two-wheel dyno.

 

[Ordieh]

Hey atvspeed4,
Attempting to do a pull in AWD (4hi) with the front shaft removed would be kinda dumb..............nothing happens but spinning the front output on the t'case........... Why would anyone do that? The TRACTION CONTROL button works......try it!
I think that 4speedfunk is right on target but I still plan to do the temperature thing one time. I know a guy that has 143K (he says) on the original chain in his '07 4493. He said that he went with Royal Purple on the first fluid change and has changed about every 20K since. Of course the 3.7 doesn't have the torque of the 5.3 but that is still pretty darn good. I personally sold a '07 that had a little over 100k on the original 4494 and the chain was getting pretty sloppy (Dexron VI).
I'm in the process of changing Homer's cam again and will be visiting the dyno next week if I can get scheduled.

 

[4speedfunk]

It not just bad for the t-case...it's dangerous. If for whatever reason, the front wheels decide to go...game over! Search "dyno fails" on YouTube...awesome stuff.


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[08H3]

No one has asked the obvious question. Why did you even make a run like that? Only thing I see to gain is TC damage.

 

[Ordieh]

To end an argument , collect on a sizable bet and do some experimenting! I agree that there is more than normal risk.......always some level of risk around one of these things. A buddy had a rear u joint let go......scary and did a bunch of damage. Good reason to have a [no spectators allowed] policy.

 

[scoreh3]

In 4hi and shaft in, nothing in the front drive is turning.......it is just sitting there strapped down and spinning the heck out of the differential in the transfer case. I noticed that the case gets pretty warm (not enough to burn your hand) with just one pull! Next time I put Homer on the dyno, I'm going to check the temperature and then switch the Dex VI out for Royal Purple and see if there is a temperature drop on a subsequent pull. Any additional insight into experiences with H3's on a dyno will be much appreciated.
P.S. Homer has a brand new 4494 so there shouldn't be anything abnormal going on inside the case.

When did RP start making a Dex VI ?? Be very careful and make sure it's a Dex VI . The the last time I talked to a RP rep , he said the trans fluid they sell marked GM is NOT made for a Dex VI trans.

 

[Ordieh]

RP doesn't make a DEXRON VI. A RP rep told me that MAX ATF was never licensed but can be best described as an UPGRADE. I don't know for sure but I have a lot of experience involving lubricants and have found the RP products to be superb. I have decided to mount a permanent temp gauge in Homer's 4494 and record enough readings to establish a baseline using DEX VI and then switch to MAX ATF? I will follow up with results (pro or con).

 

[scoreh3]

I like RP and use it in everything but my trans . Please let us know how it works in your trans .

 

[5gn-h3t]

I will preach. DO NOT RUN AN H3 ON A RWD DYNO WITH THE FRONT DRIVESHAFT IN!!! I used to be an ATV/MC/sled dyno operator. I saw a 4x4 ATV go from 2wd to 4wd at full output. It had A LOT of straps on it and still jumped a couple feet up in the air. I can't even imagine an automobile doing that. The ATV had about 35hp.

 

[Ordieh]

It is possible with a H3 but not likely..........this isn't a ATV, MC or SLED........ Try switching your H3 x'fer case at full throttle.........won't work!

 

[4speedfunk]

Its got nothing to do with switching modes. You're already in the correct mode for a disaster. All you need is some sort of sudden load change in the rear axle, the t-case, or the dyno itself...and HI-Street mode will send all the power to the front output. It will essentially neutral drop the front axle. "Houston, we have lift-off!"

Ever seen a single-track muscle car doing a burnout? The rear tires will spin individually, at times suddenly alternating back & forth from left to right, as the load on the tires increases and decreases. We used to physically "bounce" cars while burning-out, just to get them to switch sides and sometimes get the diff to spin both tires at the same time! This cycling of left to right is a byproduct of the spider gears inside the diff, and the H3 t-case (in 4HI-Street) does this same thing with the front & rear outputs. Its moves the power back & forth, always sending the juice to the spinning axle (the one with the least resistance)...just like that muscle car. All you need is a tiny deviation in load at the rear axle, and KA-BLAM!..the front axle suddenly awakens from a deep slumber. All it takes is a jerking motion or the slightest rotation in the front axle, to initiate the shift of power. This is what makes it dangerous. Its not electronic. Its entirely a mechanical device, so don't think you can fake it out.

BTW...we're not arguing here...just concerned with safety. Hate to see someone get hurt or destroy their H3. Its only eight bolts to remove the front shaft.

 

[5gn-h3t]

It definitely isn't an ATV. It's a lot more dangerous. If the rear end was to unload for some reason, all that power would be sent right to the front. The ATV was in 2WD mode too. I'm done...