Driveline Noise - Please Help

7

79ihfanatic

Member
I have a 79 Scout with a 345 727 and d20. I have d44s and 4.11 gears and recently I have developed a driveline noise that sounds like a gear rattle or as if something is rattling around in the transfer case. The strange part is that it only happens when im moving 45mph or higher. The faster you go the louder and faster it gets. The noise is louder the more you get on the gas as well. If you lighly hold the gas just enough to keep speed its very quiet. I thought maybe it was the transfer case so I rebuilt that. Still had the exact same issue. All brand new u joints front and rear with a cv axle in the rear. I am at a loss for what this is. I pulled the rear driveshaft and allowed it to run up in gear sitting still til the rpms maxed and nothing made a sound. Does anyone know what else it could be or what I can try next? Also the faster you go the truck vibrates which I think May be a unbalances ds in the rear thanks for any help
 
79ihfanatic said:
no I havnt done that yet bc I was not sure if it was safe to run the truck up to 50 front wheel drive
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Remove the rear driveshaft complete from the rear output yoke back. Do not remove the yoke. Then engage four-high. You can drive around on the front axle only (after engaging the lockout hubs of course) just like you would in 2h only at any speed. At slow speeds in a sharp turn, you will experience some "wheel kick" but that does not cause any problem.

I'm currently driving a rig like that continuously until I can have a fresh rear drive line built.

This allows you to isolate the issue in a more effective manner.

In "front wheel drive" only, you will most likely hear a "whirring" sound due to only the front output of the d20 transfer case being loaded, that sound will disappear when you back off the throttle and "unload" the front output. That kind of noise is normal.
 
79ihfanatic said:
no I havnt done that yet bc I was not sure if it was safe to run the truck up to 50 front wheel drive
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Front wheel drive cars do it all the time so in general it's safe.

Often on old 4x4's the front drive shaft doesn't get balanced so you May experience vibration from it. Ease into it.

The key is does the problem you're describing continue when there is no rear shaft?
 
Ok so I pulled the rear shaft and got none of the previous noise. So im guessing it has to be something with the rear shaft or the rear end. When I replaced one on the u joints onto the h coupler on the cv shaft I did notice that you can spin the caps of the joint by hand in the coupler. Could that be causing this noise? The joint doesnt have enough room to shake as if its the wrong joint just the caps spin. This noise also sounds more like gears chattering. Anyone have any ideas?
 
Hard to tell -- too many variables

u-joint cups should not "spin" in the yoke --- wrong u-joint; wrong yoke; worn-out yoke...

Who built the drive shaft? Is the cv joint good? Was the driveshaft balanced? Picture of the rear differential / driveshaft May help knowledgeable people.

Differential -- if limited slip and no ls supplement, the rear will chatter, but it usually only happens during turns...

Pull the diff cover and see if you have any little metal pieces laying about...
 
I had the diff cover off not too long ago and had no metal bits or shavings. There is a limited slip supplement added to the diff as well. The noise very clearly comes through the floor at the shifter/transfer case area. Not sure if the rear end gears making noise would travel to there and sound so isolated. I meant that the u joint cups were able to spin in the cv joint itself. I think its worn on that side bc the other identical u joint in the cv fits just fine. The driveshaft is going to be balanced tomorrow and I am going to see if they can replace or do something about the worn cv. I am not sure who built the driveshaft as it was on there from the p.o. I will post a pic of it tomorrow but it is identical to the cv shaft sold on anything Scout

thanks for the help ill update after the shaft is balanced
 
Ok so at the grand total of $300 I had the driveshaft completely rebuilt and balanced. New slip yoke, slip spline, tube shaft, and cv joint and a new spicer u joint. Only problem is my strange noise continues. The truck rides alot smoother now though so I guess thats a plus. I also changed the fluid in the rear diff and I didnt see any new chips or anything in the ring an pinion. I did notice that my trans mount is shot. Can a bad trans mount cause the gears in the d-20 to not mesh properly and could that be the noise im hearing?
 
That could be allowing some unwanted movement and vibration. Being a married unit, the d20 is totally reliant on the trans crossmember, indirectly via the transmission for support.
 
So now disco the front driveline and drive it around with just the rear. Also be certain the front hubs have released so they don't spin the front diff and associated junk. Also make sure the t/c is filled with oil. This should exclude a couple more suspects.
 
Ive made sure the front is not spinning at all and the tc is full of fluid. I use 15w 40 synthetic in it now but it made the same noise before o rebuilt it and when it had gear oil in it. Transmission is also recently rebuilt
 
Couple things. You don't want multi-vis oil in the t-case. It's way too thin. You also don't want gear lube in there. What you want is straight 50wt motor oil aka "racing oil". 40wt is also acceptable for colder climes. This May not have any bearing - pardon the pun - on your issue, but it is something that requires attention.
 
Another thing to check is the front hubs. Just because they say "free" means nothing without a physical check. Lose the front shaft completely and verify the hubs are not locked so the front diff is still (not moving) during a road test. If the noise is still there, then things are pointing towards the t/c.

As far as proper oil, I have never run motor oil in my t/c. I'd like to hear more on that.
 
The service manual calls for gl1 mineral oil in the t-case and manual gearboxes. Gear oil is for the diffs. Mineral oil is sometimes difficult to source these days in some locales, but the racing oil can be found on the shelves of most auto parts stores. It has to do with the gl rating of the oil. While 90wt gear oil is the proper viscosity for the gears in the t-case, the soft metals don't like the gl 3, 4, 5 ratings of gear lube. It causes premature deterioration of soft metals like brass. Not overnight. You can get away with it for awhile, just not long term.

**edit** and for the sake of this discussion, this info applies to original IH app gear boxes. More modern components swapped in from other brands obviously May have different lubrication requirements.
 
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Kind of drifting off here but...
Uhhh, so by "over time" you mean like 30 years or so right? I was under the impression that the brass and other yellow metals wanted the gl-4/5 additives. Oops...
So, for all you guys out there filling their d-20s with gear lube, know that I have been doing this for over 25 years and haven't had a failure. Doesn't mean I was right. Just means you're probably okay.
Now I know what to do with that case of kendall 50wt on the shelf...
And yes, the nps I was talking about earlier are designed to use atf.
Thanks scoutboy for the tip.
 
dealbreaker74 said:
another thing to check is the front hubs. Just because they say "free" means nothing without a physical check. Lose the front shaft completely and verify the hubs are not locked so the front diff is still (not moving) during a road test. If the noise is still there, then things are pointing towards the t/c.

As far as proper oil, I have never run motor oil in my t/c. I'd like to hear more on that.
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Here is the write up from bp discussing the oil

gear oil - binder planet forums
 
A manual transmission has brass or zinc components in the synchro assemblies, thus the warning to avoid any lubricant product that contains sulphur or similar additives. And this chemical incompatibility is not something that can/will affect the synchros quickly, they will wear out (thus the need for a occasional transmission overhaul). And this is not something that is unique to only IH transmissions, it is something that affects all manual old skool transmissions no matter who the root manufacturer is.

But, an "all gear/no chain" transfer case with no center differential (again old skool stuff, not so-called modern/shift-on-the-fly or all wheel drive) case has no synchro components, nor are any brass alloy or zinc used internally.

A 50weight motor oil is the same viscosity as 90weight gear oil, just two different viscosity designations are used.

Thus 50w motor oil (or the older "mineral oil") simply works in both the t18/t19/t90/t98 transmissions and in any non-chain drive Dana/spicer transfer case,...one product both applications.

Axle/differential gears are a totally different animal, they need a "hypoid" type gear lubricant, the non-syn stuff is heavily doped with sulphur which is being phased out and replaced with other forms of extreme pressure additives that simply cost more.

I run the cheepest plain old 50weight motor oil I can find in all my IH transfer cases and manual transmissions. With that stuff installed, I can shift both a d18/20 and a np 205 on the fly (within reason) if ya do it carefully and that involves no vacuum/electricity or throwaway "shift motors"!
 
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