Question and some advice about a Tucker 1342 "transfer" case

[Wrench9]

I had severe wear on my from a previous owner running it dry of oil. I switched both the top and bottom gear to run on the other side and the center gear doesn’t matter at it gets contact on both sides. I did this until I found a new set of gears to put in. It ran great on the opposite side and it is just a heli cut gear they should be able to be run on either side only thing would be that they probably have worn into each other in their original position

 

[Blackfoot Tucker]

I hate to bother the group again. I got everthing back together and installed the tcase without the front and rear driveshafts, just to tranny to tcase shaft. Mainly to see if it was leaking oil. I was surprised how much noise it made when it was turning. During normal operation it may not be noticeable with all the additional noise from the differentials and the tracks turning. I was happy with the build, it was silky smooth to turn by hand and the freeplay on the new bearings was set to .002 as recommended. The gears had no wear or pitting on the contact faces. Question: Is it normal for these cases to be somewhat noisy?


One thing that bothered me when installing the gear set was if they were matched to run in a certain orientation. The center and lower gears are symmetric and can be installed with either end shaft facing forward. I did not see any obvious markings indicating the correct orientation. At the time I convinced myself they were symmetric and didn't matter. I hope it does not have to come out again. It is a PITA. Can anyone shed some light on the situation? I hope this is clear, if it isn't please send me a PM. I can include some sketches or something.

Tacoman,

One of my very best friends is basically a gear cutting genius. His business has different dimensions, but he reverse engineers gear systems, he sometimes manufactures gears from raw steel, he cuts gears for other companies on blanks or parts they provide, he manufactures parts for old gear shapers, and he also services gear cutting machines; both gear shapers and gear hobbers. He knows a helluva lot about gear design, as well as manufacturing gears, and I reached out to him….

He explained gears in a transfer case can be either spur gears or helical gears. Spur gears are also called straight gears, and they are inherently noisy. The noise is a function of the amount of tooth contact between mating gears. The greater the amount of teeth in contact, the quieter the gears. Helical gears by definition have greater contact amounts than spur gears, and are thus quieter. Spur gears are less expensive to manufacture than helical gears, and I’m quite sure Tucker uses spur gears in their transfer cases. (However, to be fair to Tucker, it may not just be due to cost. Helical gears have strong axial forces and that requires more robust cases or housings. The Tucker proprietary transfer case is basically two aluminum castings bolted together and I’m not sure that’s robust enough for a helical gear design.)

My friend explained the amount of gear to gear contact is expressed as contact ratio. By definition, the minimum possible contact ratio is 1.0. A contact ratio of 1.3 is significant because below that number there is more gear noise, and above 1.3 gear noise is appreciably less. He said that in some transmissions in newer cars the contact ratio is 2.0 and they are very quiet and he also said those gears are made to very close tolerances. An automatic transmission typically uses planetary gear sets and they are very quiet. Over the years gear train noise has become associated with either (or both) poor design and lower quality gears.

To illustrate spur vs helical gear noise, my friend explained the manual transmissions installed in American cars and pickups in the sixties and seventies used helical gears for the forward gears and reverse gear is a spur gear. That’s why when you are in reverse, and especially if you go faster than a crawl, you hear a gear whine noise.

I hope this explains the transfer case noise.

Note: My friend sent me a link to a trade publication discussing gear noise and gear design methodology to reduce noise. I think one would have to be either an engineer with an advanced degree, or a serious gear nerd to understand all the formulas and design elements presented. Put differently; way over my head….

 

[Tacoman]

The gears in a the t-case are helical cut, so I thought they would be pretty quiet. They had no apparent wear or pitting. All the bearings were replaced and bearing preload was set for .002" of freeplay.

 

[Wrench9]

My new gears do still whine a little but not even close to what is was with the old gears. We are basically inside an aluminum can without a lot of sound deadening so we will hear some noise. I run a synthetic 80w-140 oil or a number very close to that I don’t have the bottle in front of me now. The t case can get hot as it doesn’t have a lot of capacity in the older machines. That is why I use the 140 synthetic oil. If everything is spinning freely and all bearings and clearance were correct I think I would give it a try

 

[Tacoman]

I am running 80w90 but not synthetic. I will try that if there is still noise. I am a little leary about going to 80w140.
I rechecked the bearings and they are set correctly. Can't measure any in/out play on the shafts when it is installed on the machine. It was bench set at .002in clearance.
There is a little turning freeplay between the input shaft and the output shafts but there is nothing to adjust there, it is what it is. I'm thinking that the noise will not be so apparent when the brake and drive shafts are installed, the machine is moving and the case is under load. That will be my next step. Hopefully it will be ready for November snow.
This all started because the case was leaking bad and I got carried away replacing stuff once I had it apart. I learned a lot AND IT DOESN'T LEAK. On to the next issues, mostly cleanups.

 

[Blackfoot Tucker]

Tacoman,

We use Amsoil Severe Gear 75W-90 full synthetic oil in Thundercat and that's also in CHUGSzilla. It's kinda spendy, but we think it's the best.

I forwarded your reply to my friend, and I mentioned what we use for oil in the transfer case. This was his response:

"Depending on tooth counts, pitch, helix angle and pressure angle I can easily calculate contact ratio. If approaching 1, noise will be an issue.
How worn are these gears? Any galling or distinguishing wear between drive and coast flanks? Is there a market for precision, replacement gears. Good gears are quiet gears."

 

[Tacoman]

Question: Why synthetic? Do you really get a performance or durability benefit?

 

[Tacoman]

Question: Why synthetic? Do you really get a performance or durability benefit?

If it still makes noise under load or while coasting, synthetic will be my next step. Maybe 90w140 before I take it apart again. I am thinking (hoping) it may be the lower end gears "rattling" while not under load. I have never spun up a transmission or t-case while it is not under load.

 

[Blackfoot Tucker]

Question: Why synthetic? Do you really get a performance or durability benefit?

In general terms, I prefer synthetic oil to mineral oil. I use full synthetic oil in the engines in my vehicles, and even with 200,000 plus miles on them, the engine internals look great. Synthetic oils have better temperature tolerance, and I believe lower coefficients of friction.

On their new machines Tucker uses a different transfer case than those used on the snowcats I own. I don’t even know if parts for the old ones are available, and I don’t want to even think about what Tucker would charge for replacement gears. Both Thundercat and CHUGSzilla have engines that produce significantly more power than the Chrysler Industrial engines they replaced, and that extra power translates to more forces on the gear train. Bottom Line: I want to use the best lubricant I can for these applications.

Is it significantly better? I honestly don’t know. It’s definitely significantly more expensive.

 

[Wrench9]

I am running 80w90 but not synthetic. I will try that if there is still noise. I am a little leary about going to 80w140.
I rechecked the bearings and they are set correctly. Can't measure any in/out play on the shafts when it is installed on the machine. It was bench set at .002in clearance.
There is a little turning freeplay between the input shaft and the output shafts but there is nothing to adjust there, it is what it is. I'm thinking that the noise will not be so apparent when the brake and drive shafts are installed, the machine is moving and the case is under load. That will be my next step. Hopefully it will be ready for November snow.
This all started because the case was leaking bad and I got carried away replacing stuff once I had it apart. I learned a lot AND IT DOESN'T LEAK. On to the next issues, mostly cleanups.

Dont worry about the thicker oil especially the synthetic (Lucus) is what I run The cases get prettty warm when they are in use and there isnt a large quantity of oil in them i little play is normal and they arent new gears so that will add to the play. I would use it and drain it or at least some or it to check it after a few hours of operation. If you did flip the middle gear around and are now running it on both sides with a different gear as input and output gear ride on opposite sides you may see a little contamination in your oil when you check it and the gears are not mated anymore due to the flipping of the center gear. keep an eye on your oil and change it. I had to change mine once when I installed the new gears as they were basically breaking in to wach other now the oil is staying perfect